Weight transfer?

[dpex]

I had a couple of 'interesting' experiences today. Came around a sweeping RHer and cut in. Grandpa's head ws over the centre-line and a cage was coming through the same corner, albeit from the other direction. Oops!

Now I'm in the shit. Halfway through the corner (badly set up) and now needing to keep my head on my shoulders. Panicked, just a bit, and went stiff armed, which just set up a left/right oscillation (speed wobble). Ooops! Ooops!

Anyway. I survived the event but pulled over to have a wonder at what happened. Never done cornering speed wobbles before.

Turned around, went back past the corner and came at it again; albeit sitting quite upright and going a bit slower, just to see if I could notice what might have gone wrong.

Two things came out of this 'test'. 1) I noticed my arms were rigid (elbow locked) and realised that cvost me some control. 2) This was the biggie (I think). I noticed I laid the bike down to the right but moved my weight to the left.

So I stopped to consider these issues and consider a possible solution. Stiff arms and weight-shifting the wrong way.

"Maybe I need to get down on the tank?" Don't know enough about bike dynamics to reason it through, but somehow the idea seemed to have merit.

So back up the road I went and came back at the corner with arms very bent and weight hard down on the tank. At first if felt very uncomfortable till I realised two things (albeit in the parts of a second one gets to notice 'stuff' in a corner. 1) Bent arms meant I couldn't force the counter-steer, it just seemed to happen. 2) Being down on the tank my body was locked with the bike's angle.

So I went back and did it again. This time with a bit less worry on account of the first time actually felt both good but unnatrual...if you see what I mean.

Second shot, much better. So I did it again. This time with a lot more speed..and in a lower gear (3rd at entry speed of 100Kph..and a small bit more). Same result. Comfortable, in control. But still felt a bit unnatural. I think the unnatural bit was that my weight/position had to go with the bike.

Thought about that for a while, then went back and did it again. Felt really good. I realised I'd got into this stiff armed, opposite weight-shifting habit without realising.

Every serious corner from there to the rest of the ride it was chest on the tank, soft elbows, and to my great pleasure a sense that I had much greater control.

Your comments on the whys and hows of this would be welcomed.

[dpex]

As I nearly always do having been confronted with an issue I don't understand, I went off to sundry to ask their expert opinion.

One thing which came from this was learning about 'trail-breaking'. Gavin, from Henderson Yamaha, a dedicated racer, mentioned this.

He asserts that "an" amount of rear brake pressure causes the arse-end to hunker down a bit and thus provide greater traction. I kind've understood the dynamics...kind've.

Notwithstanding, I have also learned, much to my heart's terror, that hard rear breaking in a corner is a recipe for bad shit happening.

But then later I asked Jason Godsmark (another dedicated racer) about it. He asserted the concept was good but hard to get right.

Anyone got any opinions on this issue?

[Hitcher]

Sigh. I feel another "countersteering" thread coming on...

[Mom]

This time with a lot more speed..and in a lower gear (3rd at entry speed of 100Kph..and a small bit more). Same result. Comfortable, in control. But still felt a bit unnatural. I think the unnatural bit was that my weight/position had to go with the bike.

Here is my favourite thing about cornering, chose the right gear to go in makes life a whole heap easier. My advice is to actually slow down and think about what gear you need to be able to enter the corner safely and exit on power without hanging your head over the line. Your line into the apex of the corner is vital to where you head ends up. So, slow down, select a line, select a gear, and take that corner.

[FJRider]

On both issues, life is a learning curve, if it works for you... who are we to say differently.
an "amount" of acceleration in a corner, also adds traction...

"Concepts" in motorcycling are not uncommon...(hence the RE5...) you choose what is good for you.

[MSTRS]

There is no need to 'hunker down' on the tank.
For road riding, leave your bum where it is on the seat, maybe shift your shoulders a little to the inside of the corner, Do your slowing as you approach that corner and change down a gear or two (that should provide enough engine braking without touching the brakes), move to the outside of the approaching arc, countersteer or lean to tip in, you will 'feel' the apex, now throttle on a bit, exit corner. Rinse and repeat.
It can help to tense your leg and push down on the outside peg too.

[dpex]

Sigh. I feel another "countersteering" thread coming on...

Aw, come on Hitcher, this isn't just about counter-steering. It's a whole dynamic I don't yet understand. I will, after I have questioned a whole lot more folk. But it would be good to get some opinions here.

[slofox]

If you use rear brake in a corner, it is important to keep the throttle on as well. This stops loss of traction but allows some speed to be bled off safely. Better not to overcook your entry into the corner in the first place of course.....but if you are confronted with the unexpected, you can indeed use the rear brake - just DON'T throttle off....a delicate touch is good....

I always hunker down on the tank if I am out highway riding, especially on the sweepers or twisties. My weight is lower so COG is as well = better cornering. Besides which, it just feels right to me. I try to be part of the machine - let it do the work - all I do is direct it and that is mostly with body weight. I don't climb all over the bike either - I stay tight to the tank with knees and elbows in and just go with it...That way, I can relax .....one of the things I really like about riding a bike....it's like flying two feet above the ground.

[MSTRS]

If you use rear brake in a corner, it is important to keep the throttle on as well. This stops loss of traction but allows some speed to be bled off safely. Better not to overcook your entry into the corner in the first place of course.....but if you are confronted with the unexpected, you can indeed use the rear brake - just DON'T throttle off....a delicate touch is good....Good stuff



I always hunker down on the tank if I am out highway riding, especially on the sweepers or twisties. My weight is lower so COG is as well = better cornering. Besides which, it just feels right to me.
Can't see the COG thing being lower by 'hunkering down'. Your weight is carried by the bike and is concentrated on the contact points...pegs and seat, and too a lesser degree the bars. By moving the bod about you are redistributing weight, certainly, but you are not lowering it.

[jrandom]

Yo dpex, do the trackday on Friday, then read A Twist of the Wrist I and II, then do the next trackday, and all will become clear.

I have PDFs of the books if you want a copy, just PM me with your email address.

:niceone:

[R6_kid]

You should sign up for "Ride Right Ride Safe" - you're exactly the kind of person that will benefit from it.

[jrandom]

I find a 2D visualisation the easiest way to start thinking about finding the center of mass (I think 'center of gravity' is an odd term).

Imagine a set of points on a plane. Say, a bunch of particles grouped together to form a solid body, although conceptually it doesn't matter whether they touch or form a 'cloud'.

The COM is the single point on that plane that has the lowest average distance to each of those points.

It should be intuitively clear (please don't make me prove it rigorously) that as you take your particles and stretch some of them out in one direction, that COM point will shift.

Extend that into three dimensions, and it then becomes clear that standing up on the footpegs and therefore moving your body mass further away from the existing 3D COM point will shift the 3D COM point upwards.

Therefore, moving your body around, regardless of the 'contact points' involved, can indeed change the COM of the bike-rider system, and the way it tips from side to side.

QED.

[beyond]

Watch the rear braking thing in corners. Yeah it can work well but it's so easy to screw up and then you end up backing your bike into a corner which is good if that's what you want. Normally though, that's unexpected and causes people to shut off the throttle, the bike regrips and you get a nice highside with the resultant bonk on your block.

Cornering: relax your grip on the bars, keep your arms relaxed and drop the inside shoulder into the corner and everything else others have sai :)

[Hitcher]

Imagine a set of points on a plane.

Cool. Is the type of plane important? I'm really into P38 Lightnings at the moment.

[jrandom]

Cool. Is the type of plane important?

If it could be an Ilyushin IL-2, that would make me very happy.

[BMWST?]

all valid points....but your reaction to the particular problem you had was the only thing you could have done...lifting your body/head away from the car has to be compensated for leaning the bike in more...if you relax while you do this you shouldnt have any undesireable effects...on a rh it can also help with your sight line round say a bank on the rh side of the corner...

[Grub]

Going back to the original post, I think you've pretty much nailed the issues, now just practice and perfect.


2) This was the biggie (I think). I noticed I laid the bike down to the right but moved my weight to the left.

Exactly and then you went on to experiment and find that body down low or even better on the inside (in this case the right) of the bike stabilised and controlled it. This is great stuff because you kept trying things and was able to feel the difference.

There was a youtude clip of a Superbike racer explaingin his cornering and he mimiced what you describe. Be leans forward with 'soft' elbows and then moves his head and shoulders in towards the apex of the corner. He ends up as MSTRS describes with his shoulders (not his arse and knee) low and to the inside of the bike.

The ideas of stiffening a leg or applying pressure to a foot peg are good. It doesn't really matter how you get there, but you can feel that you have right when your weight is on the inside arse cheek ... in this case it would have been the right cheek carrying your weight.

[dpex]

You should sign up for "Ride Right Ride Safe" - you're exactly the kind of person that will benefit from it.

I have done that. But, for various reasons I haven't managed to connect with them.

[dpex]

You two, Hitcher and Jrandom, should try flying something simple, like a racing glider filled with 200KGs of water, around the Lindis Pass area when, suddenly, the ridge lift turns into down-draught and the only thing under your arse is shale cliffs, and there's apparently no place to go.

The diff, of course, between this and biking is, when you screw up in a glider you get a lot of time to look into the face of pain. But hell's teeth, just being up there, as free as a bird, is worth it.

[dipshit]

There was a youtude clip of a Superbike racer explaingin his cornering and he mimiced what you describe. Be leans forward with 'soft' elbows and then moves his head and shoulders in towards the apex of the corner. He ends up as MSTRS describes with his shoulders (not his arse and knee) low and to the inside of the bike.


This one?
http://www.youtube.com/watch?v=sxb5nRufuZ8

[Hitcher]

Hmmm. Plane...

http://www.kiwibiker.co.nz/forums/album.php?albumid=209&pictureid=9819

[Grub]

This one?
http://www.youtube.com/watch?v=sxb5nRufuZ8

You da man! It's long but a great watch!

[slofox]

I find a 2D visualisation the easiest way to start thinking about finding the center of mass (I think 'center of gravity' is an odd term).

Imagine a set of points on a plane. Say, a bunch of particles grouped together to form a solid body, although conceptually it doesn't matter whether they touch or form a 'cloud'.

The COM is the single point on that plane that has the lowest average distance to each of those points.

It should be intuitively clear (please don't make me prove it rigorously) that as you take your particles and stretch some of them out in one direction, that COM point will shift.

Extend that into three dimensions, and it then becomes clear that standing up on the footpegs and therefore moving your body mass further away from the existing 3D COM point will shift the 3D COM point upwards.

Therefore, moving your body around, regardless of the 'contact points' involved, can indeed change the COM of the bike-rider system, and the way it tips from side to side.

QED.


Jeez JR - you said that way more impressively than I was gonna try to do......+1 from me dude....!!

You are right of course - and heads are heavy - the higher up they are the more the COM (better?) moves up - just like you said....I think.....

[swbarnett]

Can't see the COG thing being lower by 'hunkering down'. Your weight is carried by the bike and is concentrated on the contact points...pegs and seat, and too a lesser degree the bars. By moving the bod about you are redistributing weight, certainly, but you are not lowering it.
C.O.G is the point at which it can be said that gravity acts on a body as a coherent unit and is determined by the distribution of mass within the unit. A bike and rider can be considered one coherent unit. When you sit tall in the saddle your body mass is set high, this brings the C.O.G up because the mass distribution of the unit (bike and rider) is higher. Similarly, if you hunker down your body mass is set lower so the G.O.G is consequently lower.

How the two components are attached is largely irrelevant, it's the distribution of mass in the unit that matters.

[dpex]

You da man! It's long but a great watch!

That was a great vid. Thanks for that. I will go out today and start practicing that. I think the hardest part of learning a new skill is over-riding an existing bad habit.

[jrandom]

By the way, yous fullas who I'm emailing ATotW I & II to, be aware that the email's about 20MB worth, so prepare your pipes and mailboxes accordingly.

(I'd post it here, but the copyright implications would make Hitcher's head explode. And that would leave a big mess.)

[enigma51]

Watch the rear braking thing in corners. Yeah it can work well but it's so easy to screw up and then you end up backing your bike into a corner which is good if that's what you want. Normally though, that's unexpected and causes people to shut off the throttle, the bike regrips and you get a nice highside with the resultant bonk on your block.

Cornering: relax your grip on the bars, keep your arms relaxed and drop the inside shoulder into the corner and everything else others have sai :)

Trail braking is for when you wanna look cool! :whistle:

[jrandom]

Trail braking is for when you wanna look cool! :whistle:

And/or go straight into the gravel at Turn 1 eh?

:eek:

[enigma51]

And/or go straight into the gravel at Turn 1 eh?

:eek:

steady on there i had at least 2 cm to go still :banana:

[MSTRS]

COG...COM...whatever you call it, I know what I was trying to say (even if I wasn't right). Obviously it depends on the style of bike, but think about this...
Ultimately the entirety of bike/rider weight is carried by the tyres, but...You are sitting on the seat. Your weight is mostly being borne by the shock, just behind the swingarm pivot point, therefore letting the rear tyre carry a greater share of the total weight. Now bear down on the pegs. You have transferred your body weight, in relation to the 'carry point', lower and forward, in addition to taking some weight off the rear tyre and increasing that amount to the front. When that weight to peg is applied to the outside peg, the bike becomes more stable when cranked over. Add too much weight further forward (by using the front brake, say) and the equation becomes unbalanced, causing the bike to resist leaning and to try and stand up.
So, when you are setting up to tip in, you need to move some of the weight forward, but not too much, and conversely when exiting the corner you need to move that weight backwards (by putting your weight back on the seat and accelerating).
Have I made any sense?

[ital916]

while everyone is debating COGs, I find it funny that buell have led the way in bike COG technology, innovating such ideas as mass centralisation. It could just be me but hasn't that always been the aim of bike manufacturers......mass centralisation. They do have some cool tricks though, fuel in frame, which is still am mulling about as to whether it is a good or bad idea.

Anyway dpex, sounds like you had a close call, take it easy. Don't think too hard about it though, can't waste precious riding time.

[Max Preload]

How the two components are attached is largely irrelevant, it's the distribution of mass in the unit that matters.

Indeed. Contact points are only relevant for stress at those points, not CoG.

[sharky]

Applying the brakes as you head into a corner loads up the front wheel. For max traction and control after braking you need to redistribute or even out the weight. You need to apply throttle as you tip in to achieve this not rear brake. All braking forces load the front, acceleration loads the rear. Picture stoppies and wheelstands.

[vifferman]

while everyone is debating COGs, I find it funny that buell have led the way in bike COG technology, innovating such ideas as mass centralisation. It could just be me but hasn't that always been the aim of bike manufacturers......mass centralisation.
Yes.
No.
There was a point (recentlyish) when bike manufacturers realised that the trend towards getting the mass low in the bike was OK to a point, then it actually made the handling worse (transitions slower). So, this evolved into mass centralisation instead, which is about getting the weight on each wheel close to 50%, and getting the position of the rider close to the COM as well. It's not just Buell doing this - there are quite a few bikes now that have the fuel cell under the seat (which also allows the airbox to be bigger, and for a smaller change of COM with changing fuel load), 'stacked' gearboxes, which makes the engine more compact and shifts the mass forward, and various other seemingly minor redesigns to lighten components that aren't close to the COM.

[Mikkel]

I find a 2D visualisation the easiest way to start thinking about finding the center of mass (I think 'center of gravity' is an odd term).

...

Therefore, moving your body around, regardless of the 'contact points' involved, can indeed change the COM of the bike-rider system, and the way it tips from side to side.

QED.

+1 on the COM vs. COG (our most dominant COG would be at the centre of the planet I'd say).

I took the liberty of reattaching some pictures I drew in MS paint (1337 skills I know... :rolleyes:) for another discussion a while back.


My experiences so far with regards to cornering suggests that:

-It is important to have the bike settled while cornering. Setting up cornering speed early and coming in smoothly is preferable to braking hard since you don't have to allow the bike to settle before tipping in. Maintain enough drive through the corner to keep the speed constant and the weight distribution even.

-Whatever you do, don't scare yourself - it's the fastest way to running off the road, locking up or in any way stuffing up something crucial.

Just my observations.

EDIT: Forgot the images.

[pritch]

and conversely when exiting the corner you need to move that weight backwards (by putting your weight back on the seat and accelerating).
Have I made any sense?

Not sure. I'da thunk you keep the weight forward to hold the front end down while accalerating? Horses for courses though...

[swbarnett]

...the center of mass (I think 'center of gravity' is an odd term).
I believe that 'centre of gravity' is just another term for 'centre of mass' that is used when the mass is under the influence of a gravitational field. I think you're right that 'centre of mass' is the more correct term.

[dpex]

Far be for me to expostulate in any expert sense, but the UTube vid posted by Grub paints some interesting pictures.

One of the instructors is quite clear that he keeps most of his weight on the pegs throughout each circuit, thus significantly lowering the COG. Ergo, if I follow this, my 100Kgs would be mostly on the pegs, not the seat, meaning 100Kgs is now nearly 600mm lower than it would be if I were sitting with little weight on the pegs.

I presume transfering my weight to such a lower position would make the bike inherently more stable.

I also note one of the instructors does not support lateral butt-shifting and makes a good case for his opinion.

Interesting stuff. Sadly, today, the rain stopped me testing out what I learned from that vid.

[Max Preload]

One of the instructors is quite clear that he keeps most of his weight on the pegs throughout each circuit, thus significantly lowering the COG. Ergo, if I follow this, my 100Kgs would be mostly on the pegs, not the seat, meaning 100Kgs is now nearly 600mm lower than it would be if I were sitting with little weight on the pegs.

That's perhaps what he *thinks* is happening, but the reality of the physics is quite different. If his body position doesn't change, the CoG doesn't change regardless of whether he's sitting on the seat or distributing his mass equally between the pegs - I say equally because I don't want to get into moments from the position of the rider relative to the CoG of the bike.

The rider's weight being supported by the pegs rather than the seat will have no difference in the CoG of the combination of bike & rider any more than say having a frame bolted under the chassis of a car (instead of a roofrack) loaded with a pallet of 200-series blocks lowers the CoG of that combination. All other things being equal the car will still tip over at the same speed whether the pallet is strapped to the roof or to the frame connected directly to the chassis because the CoG is the same.

Slinging yourself off the side of the seat and getting lower to the ground however DOES make a difference because you're actually changing the CoG of the unit.

[jrandom]

One of the instructors is quite clear that he keeps most of his weight on the pegs throughout each circuit, thus significantly lowering the COG.

Weighting the pegs is good, because it allows you to use dem leg muscles to push the outside of the bike down when you corner and stop it from skating out.

At least, that's the mental image I use.

The idea that floating your bum above the seat and putting all your weight on the pegs somehow lowers the bike's center of mass, however, is an old chestnut that bikers like to spout (HI MSTRS! :D) without ever having actually thought about the physics of it.

Just sorting out those copies of ATotW right now, please stand by...

[MSTRS]

The rider's weight being supported by the pegs rather than the seat will have no difference in the CoG of the combination of bike & rider any more than say having a frame bolted under the chassis of a car (instead of a roofrack) loaded with a pallet of 200-series blocks lowers the CoG of that combination. All other things being equal the car will still tip over at the same speed whether the pallet is strapped to the roof or to the frame connected directly to the chassis because the CoG is the same.


Ah, I beg to differ. Any unit with a given wheelbase that has a heavy weight added up high will be much less stable than with that same weight dropped to under the chassis. The inertia that weight exerts on the tyres in a change of direction will be magnified by the distance between that weight and the tyres. The contact point of the tyres on the road is essentially a fulcrum, and the weight is the lever acting on it. We all know what happens with a longer lever.

[Max Preload]

Ah, I beg to differ. Any unit with a given wheelbase that has a heavy weight added up high will be much less stable than with that same weight dropped to under the chassis. The inertia that weight exerts on the tyres in a change of direction will be magnified by the distance between that weight and the tyres. The contact point of the tyres on the road is essentially a fulcrum, and the weight is the lever acting on it. We all know what happens with a longer lever.

Want to put some money on it? (Shall I tell him the weight is the same distance from the fulcrum regardless of where it's attached?)

[Max Preload]

Perhaps my post wasn't particularly clear. The pallet of blocks is still above the roof - it's just attached to a frame that goes around the side of the car with no contact and connects to the chassis instead of being strapped to a roofrack.

However I do still offer my monetary incentive...

[varminter]

So, not one of those tools for shaving bits off lumps of wood then?

[dipshit]

I also note one of the instructors does not support lateral butt-shifting and makes a good case for his opinion.

Many top-level instructors emphasises moving the upper body in more and only moving your butt a small amount if any.

Note the difference between your typical kiwi amateur racing style...
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=63871&d=1182044060

...and the body position of top-level riders...
http://www.webbikeworld.com/Motorcycle-racing/motogp/2007/catalunya.htm

The reason is because your CoG is around about in the middle of your chest. That is the important bit to get inside the centreline of your bike in a corner. Posers that like to get there butts way off almost end up moving their CoG in the wrong direction back across the centreline.

[jrandom]

Ah, I beg to differ. Any unit with a given wheelbase that has a heavy weight added up high will be much less stable than with that same weight dropped to under the chassis.

You misread Max Preload's post.

He was stating that if the weight's up high and instead of sitting it directly on the roofrack you keep it where it is and put in some struts reaching around and attaching it to the bottom of the chassis, nothing will change.

It's an analogy to make it clear that resting your weight on the footpegs rather than the seat won't lower the COM of the bike.

Obviously if you take a weight off the top of a car and sling it underneath instead the COM will change, I mean, duh. It's all about where in space the bulk of the mass sits.

[jrandom]

...and the body position of top-level riders...

Way hey hey, maybe you should try riding like that, might be what you need to get those chicken strips off!

:D

[dipshit]

Way hey hey, maybe you should try riding like that, might be what you need to get those chicken strips off! :D

Actually if i was more worried about losing my chicken strips, then i would need to ride more like your typical 'legion in his own lunchtime' kiwi and stick my knee and ass way off into thin air and my upper body back across the bike so i would have to lean the bike over further!

[MSTRS]

Perhaps my post wasn't particularly clear. The pallet of blocks is still above the roof - it's just attached to a frame that goes around the side of the car with no contact and connects to the chassis instead of being strapped to a roofrack.

However I do still offer my monetary incentive...

No, your post definitely wasn't clear on that point. Now that you clarify, all bets are off. Unless you want to bet based on my scenario?

[Hitcher]

When it comes to cornering, technique, rather than physics is what should be going through a rider's mind. Sound instruction and practice will be significantly more useful than esoteric discussions about vectors and centres of mass versus gravity.

[MSTRS]

You misread Max Preload's post.

Obviously if you take a weight off the top of a car and sling it underneath instead the COM will change, I mean, duh. It's all about where in space the bulk of the mass sits.

Yep, glad you agree.
Tell me, though, Why does weighting the peg/s make the bike more stable? And don't give me any of your shit about taking the pressure off the rear shock and allowing the suspension to work unhindered, by taking the weight off the rear sub-frame.:devil2:

[jrandom]

Why does weighting the peg/s make the bike more stable?

Fucked if I know, it just works, I'm happy to let you slow cunts get on with theorising about it.

:msn-wink:

[Max Preload]

Tell me, though, why does weighting the peg/s make the bike more stable?


Fucked if I know, it just works, I'm happy to let you slow cunts get on with theorising about it.

Because then your legs are articulating your body load and acting as a suspension component themselves since they're less rigid than just plonking your fat ass directly on the seat.

[jrandom]

Because then your legs are articulating the load since they're less rigid than just plonking your ass on the seat.

And don't forget, pushing down on the outside peg stops your rear tyre from skating away under power.

:niceone:

[Mikkel]

The reason is because your CoG is around about in the middle of your chest.

That may be - but your center of mass is located centrally in your trunk just above your pelvis (http://hypertextbook.com/facts/2006/centerofmass.shtml). This is very close to the geometric center (http://upload.wikimedia.org/wikipedia/commons/1/17/Vitruvian.jpg) of the human body as well.
Obviously this location will change with changing body positions, but don't underestimate how heavy your legs and bum are.

As for the location of the CoG (http://en.wikipedia.org/wiki/Center_of_gravity_(military)), I really don't know.


When it comes to cornering, technique, rather than physics is what should be going through a rider's mind. Sound instruction and practice will be significantly more useful than esoteric discussions about vectors and centres of mass versus gravity.

How about an esoteric argument about technique then?

[Hitcher]

How about an esoteric argument about technique then?

You would need somebody better qualified than me for that. Unless, of course, you want advice on how to ride like a nana.

[Mikkel]

You would need somebody better qualified than me for that.

Better qualified in technique or mysticism? :scratch:


Unless, of course, you want advice on how to ride like a nana.

Might actually be very useful advice - this being the survival skills forum and all. Probably less likely to get anyone killed than trying to scrape pegs and do rolling stoppies. :yes:

[terbang]

change down a gear or two (that should provide enough engine braking without touching the brakes)

Why not use the brakes? Shifting down on the approach to a corner is so that you can keep the RPM in a suitable range for when you accelerate out. A by product of shifting down is that you will get some engine braking effect that can be used to your advantage, but its not the correct way to slow a motorcycle. Risky stuff in my view telling people to slow by using the rear wheel only (as in shifting down).

[dipshit]

That may be - but your center of mass is located centrally in your trunk just above your pelvis (http://hypertextbook.com/facts/2006/centerofmass.shtml).

It depends on your body shape. A fit strong athlete's will be higher than someone with a big fat stomach and ass.

Now add a helmet into the equation and that the rider's upper body is also in the air stream - the CoG is moved even higher.

[enigma51]

It depends on your body shape. A fit strong athlete's will be higher than someone with a big fat stomach and ass.

Now add a helmet into the equation and that the rider's upper body is also in the air stream - the CoG is moved even higher.

My centre of gravity is the tip of my cock so roughly about knee high



Have you ladies ever thought about just riding not analysing every thing you do? I dont know it might just keep you concetrating on the road and alive!

[Mikkel]

It depends on your body shape. A fit strong athlete's will be higher than someone with a big fat stomach and ass.

You mean like this (http://i301.photobucket.com/albums/nn69/arronsky/2498d1f2.gif)?
Sorry mate, a good athelete will have strong leg muscles as well. A fat stomach and arse won't shift the COM much since they'd be close to it. Unless you all of a gain a lot of weight around your feet or your head you wouldn't see much shifting out of 5 kg difference. (think leverage, it's about the distribution)


Now add a helmet into the equation and that the rider's upper body is also in the air stream - the CoG is moved even higher.

My boots are heavier than my helmet. My leathers are about equally robust all the way along their length. So that wouldn't change it either.

Having your body in the air stream is not going to affect the distribution of your body weight - as such it will not affect the COM. There will be a COP (centre of pressure) and that may move around very significantly depending upon your posture, windscreen, etc.

Just take my word for it - or follow the link in the last post - your COM is not in your chest area, it's at belt level. And if you'd ever done judo, ju-jutsu or aikido you'd know this instinctly.

[dipshit]

Just take my word for it - or follow the link in the last post - your COM is not in your chest area, it's at belt level. And if you'd ever done judo, ju-jutsu or aikido you'd know this instinctly.

Take that Lady lying on the board with the balance point beneath her hips. Now blow a 120kph wind onto her head and shoulders (the exposed bits to the direct airstream when riding a bike) and see what happens..???

Your CoG when riding a bike is about in the middle of your chest.

[Mikkel]

Take that Lady lying on the board with the balance point beneath her hips. Now blow a 120kph wind onto her head and shoulders (the exposed bits to the direct airstream when riding a bike) and see what happens..???

Logic and physical insight are not your strong side are they?

Wind pressure is not going to shift the COM (nor that CoG as you insist on referring to). jrandom went over what the COM is earlier in this thread - and did it quite well I might add - in a way which everyone should be able to understand. If you'd care to familiarise yourself with the definition I'm confident you'd abandon this nonsense about wind pressure changing your bodily weight distribution.

As for where the COM is located when you are on a bike - that'll depend quite a bit upon what kind of bike and what riding position you're in.

[CookMySock]

like a racing glider filled with 200KGs of water, around the Lindis Pass area when, suddenly, the ridge lift turns into down-draught and the only thing under your arse is shale cliffs, and there's apparently no place to go.You reckon? :whistle: Try it in a paraglider with nothing but a flapping load of washing above you and a pair of jeans below. :eek:

Great thread BTW.

DB

[MSTRS]

Why not use the brakes? Shifting down on the approach to a corner is so that you can keep the RPM in a suitable range for when you accelerate out. A by product of shifting down is that you will get some engine braking effect that can be used to your advantage, but its not the correct way to slow a motorcycle. Risky stuff in my view telling people to slow by using the rear wheel only (as in shifting down).

Fair point. Depends on the road, tightness of corner, how well the rider knows that bit of road. I didn't mean to give the impression that brakes shouldn't be used. But get the pace and the lines right, and brakes are only there as a back up to torque braking.
Still - if you are on a strange bit of road, with tight/unknown quantity corners etc - you'd best be riding slower, anyway.

[OutForADuck]

Dpex, have a read about the following, COG (well discussed here), touch .
points, Getting a Corner set, bump steer transfer and very important, throttle balance.

What you effectively did first time was brace against the handle bars, allowing bump steer that would have been straightened out by the bikes steering trail etc to be transferred to the mainframe through you.. whilst at the same time allowing your body to work against the bike instead of with it (by not usng touch points to make sure you body was anchored with the mainframe - hence laying on tank helped) Guessing you also backed off the throttle and upset any "Corner Set" you had making it all much worse by causing "pogoing"

Pogoing is Weight transfer through the suspension in ways you don't really want - a "Set" is compressing the suspension into a predictable "squash" throughout the corner, touch points are an attempt to not upset this by becoming a single unit with the bike and bent arms allow the steering to react to the road and also not upset it. Thottle balance is all part of getting the "set" right.

Ever seen video footage of a tank slapping bike throw its rider and then stablise???? Perfect example of how we need to make sure we don't stuff up what the bike wants to do naturally :confused:

[dipshit]

Wind pressure is not going to shift the COM (nor that CoG as you insist on referring to).

So the lady lying on the board with the balance point beneath her hips isn't going to need the balance point moved further up if you were blown a direct strong airstream on to her head and shoulders?

The airstream pressure is another force acting on her body just like if she was holding a couple of bricks over her chest. It will move the balance point further up.

[Mikkel]

So the lady lying on the board with the balance point beneath her hips isn't going to need the balance point moved further up if you were blown a direct strong airstream on to her head and shoulders?

The airstream pressure is another force acting on her body just like if she was holding a couple of bricks over her chest. It will move the balance point further up.

I give up - you can keep your flawed understanding, please just don't try and teach anyone mechanics.

[MSTRS]

So the lady lying on the board with the balance point beneath her hips isn't going to need the balance point moved further up if you were blown a direct strong airstream on to her head and shoulders?

The airstream pressure is another force acting on her body just like if she was holding a couple of bricks over her chest. It will move the balance point further up.


I give up - you can keep your flawed understanding, please just don't try and teach anyone mechanics.

Mass translates into a downforce (gravity) regardless of where it's centre lies.
Applying a sideways force won't change the position of that mass's centre.
But shear forces will affect the stability of a mass, and when the mass is moving in an opposing direction to the shear force (wind) then the effect of that shear force is magnified.
Does that explain it?

[dipshit]

I give up - you can keep your flawed understanding,

I take that as an yes, you would need to move the balance point further up.




please just don't try and teach anyone mechanics.

Then please do not get into aircraft design.

[MSTRS]

I had a couple of 'interesting' experiences today. Came around a sweeping RHer and cut in. Grandpa's head ws over the centre-line and a cage was coming through the same corner, albeit from the other direction. Oops!




Then please do not get into aircraft design.

Only on KB...from an O! Shit! moment to aircraft wing/fuselage design.
Fuck me.

[Mikkel]

Mass translates into a downforce (gravity) regardless of where it's centre lies.
Applying a sideways force won't change the position of that mass's centre.
But shear forces will affect the stability of a mass, and when the mass is moving in an opposing direction to the shear force (wind) then the effect of that shear force is magnified.
Does that explain it?

We're not even talking about forces yet. The COM only depends upon the distribution of the mass in a simple or segmented rigid body (as opposed to a fluid). If you have two point weights connected by a weightless rod of some length - if the two weights are equal the COM will be exactly midway between them. If one weight is 4 times as heavy as the other the COM will be located one fifth (1/(1+4)) of the way from the first to the second weight. Doesn't matter weather there's a gust, a gale or even gravity for that matter.

In mechanics knowing the COM for all the objects you consider is rather helpful since it allows you to work with a problem by considering simple point masses with some given rotational inertia. Approximating the problems using simple geometric shapes means that you don't have to perform complicated integrals for each body in order to calculate the exact mass distribution.
In mechanics the COM is what is used for these calculations - the COG is indeed located at the same point as the COM, IF you are in a constant gravitational field. While there is no such thing - for almost any conceivable situation the spatial displacement between COG and COM is infinitesimal. One of the cases where this approximation doesn't hold up are black holes where the gravitational field changes rapidly as you approach the singularity - another is the tidal effect.

I'm not looking for an explanation here - I'm just telling dipshit that no amount of wind is going to affect the location of the COM for a rider (unless it forces the rider in question to readjust their posture - and consequently their weight distribution)... and also suggesting that it would be good to stop referring to the COG instead of the COM. :rolleyes:

[Mikkel]

Then please do not get into aircraft design.

We're not talking fluid mechanics - which I consider a black art, so don't worry.

[discotex]

I think the unnatural bit was that my weight/position had to go with the bike.

While everyone else debates CoG blah blah......

I'm willing to bet you don't keep your head level with the horizon. In other words you keep your neck straight rather than tilting your head to keep the horizon level.

Seems to be the main reason people start leaning out of the corners - because it makes them feel safer. Leaning in while keeping your head in line will make it seem like you've carrying more lean angle than you really have. Apparently more than 20 degrees is what normal people consider as dangerous.

[Max Preload]

I'm willing to bet you don't keep your head level with the horizon. In other words you keep your neck straight rather than tilting your head to keep the horizon level.

I can't even imagine what keeping my neck in it's normal position must be like. I shall give it a try just to see but I imagine it must be pretty psychedelic! :wari:

[AllanB]

While everyone else debates CoG blah blah......

I'm willing to bet you don't keep your head level with the horizon. In other words you keep your neck straight rather than tilting your head to keep the horizon level.

Well F yes - here's some good advise!

Basically you overcooked into the corner and appear to be taking a bad line - ie your line brought your head into the other lane. Your bad, these things happen.

I believe it was the natural reaction to panic and focus on the 'scare' (in this case the car) thus f-ing up the bend.

I'd have to say here that I see little point in arse up knee down riding on public roads - if you have to be doing that to corner the bike well, then you are going wayyyyy toooo fast for a blind corner on a public road.:blink:

[slofox]

if you have to be doing that to corner the bike well, then you are going wayyyyy toooo fast for a blind corner on a public road.:blink:

In principle I would have to agree with that - on the public road you must expect the unexpected...like some stupid cow using the road as a headland to turn her friggin ride on mower round on - on a blind corner on a rural road....who I "met" a couple of weeks ago.......now she did shit herself but I didn't 'cause I'd had the sense to slow up because the corner was blind.....sure made her freak out though...ht. ht. ht..:devil2:

I can only say that if you want to fang it, go on the track.....on the public road, keep some in reserve....like I do....:innocent:...most of the time anyway....

[terbang]

I give up - you can keep your flawed understanding, please just don't try and teach anyone mechanics.

Quite amazing how those who see themselves as so much cleverer than the rest, sound so stupid.

[Hitcher]

Quite amazing how those who see themselves as so much cleverer than the rest, sound so stupid.

Hitcher's Law of the Cornering Thread in action.

[jrandom]

Hitcher's Law of the Cornering Thread in action.

You know that shaft-drives can't wheelie, eh.

[MSTRS]

You know that shaft-drives can't wheelie, eh.

Oh wheally.
But, seriously, Hitcher don't try this at home...

[Hitcher]

You know that shaft-drives can't wheelie, eh.

I have diligently believed you on this matter since you first posted it in the summer of '69, in spite of clear spatial separation between Big Yam's front wheel and the macadam on a couple of occasions. These I put down to "undulations" in the road surface.

[jrandom]

Oh wheally.

Obviously the retrofitted chain drives have been photoshopped out of those pictures.

[MSTRS]

:shit::slap:

[jrandom]

:shit::slap:

Yes, you won't be so gullible again in future, eh?

Can't argue with physics.

[MSTRS]

Yes, you won't be so gullible again in future, eh?

Can't argue with physics.

You do know that the word 'gullible' is not in the dictionary?
And I'll argue with a psychic if I want to...

[dipshit]

Quite amazing how those who see themselves as so much cleverer than the rest, sound so stupid.

Kiwi amateurs...
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=63871&d=1182044060

Top-level riders...
http://www.webbikeworld.com/Motorcycle-racing/motogp/2007/catalunya.htm


And you better tell the F1 guys that aerodynamics doesn't affect weight distribution then.

[jrandom]

Kiwi amateurs...
http://www.kiwibiker.co.nz/forums/at...1&d=1182044060

Top-level riders...
http://www.webbikeworld.com/Motorcyc.../catalunya.htm

Fix your links.

[dipshit]

Fix your links.

Thanks.

Done.

[FROSTY]

All the fancy theories and ideas. FFS
Try this.
Go into ya gargre and get a stick of chalk and a flexible measuring stick.

Take ya bike out to a stretch of road ya know well
Ride the fucken road.
Draw a chalk line from one side of ya tyres to the other
Ride some more --measure how much chalks left -redraw the line
Now shift yer arse over on the seat so your bum cheek is hanging off the side as ya go round corners.
Measure the chalk
Try all the fancy ideas people come up with and see which idea keeps the biggest amount of chalk on the tyre.
The point being-the less tread you use the less the bikes leaned
my point???
GET YER ARSE OUT THERE AND RIDE !!!!!!

[Hitcher]

Is there a particular coloured chalk that works best? I guess black wouldn't be that flash...

[FROSTY]

Is there a particular coloured chalk that works best? I guess black wouldn't be that flash...

hITCH ffs--no no no --LETS NOT GO THERE or we will be argueing the drag ceficient and slip characteristics of differnt chalks instead of riding our bikes

[Mikkel]

Is there a particular coloured chalk that works best? I guess black wouldn't be that flash...

You can get Harleys with white tyres. :rolleyes:

But then again, on a Harley it's easy to measure the lean-angle by looking at the scratch marks on your chrome.

On another note, we all like to ride our bikes. Now, if some of us like to discuss these meaningless things - and don't fool yourselves into thinking we don't realise that it doesn't matter at all out there in the real world - where's the harm in that. How about, instead of getting all annoyed and making arses of yourselves, growing stomach ulcers and whatnot, you leave the discussion to those that might enjoy it and go out and ride your own ride? Just a thought, but hey - I'm just another idiot so don't mind me.

[dipshit]

Indeed. Talking about motorbikes on a motorbike forum... Who would have thought! :eek5:

[The Stranger]

But it would be good to get some opinions here.

Ya recon?
I bet you be more confused than ever by the time all the KB experts are finished.

[swbarnett]

So the lady lying on the board with the balance point beneath her hips isn't going to need the balance point moved further up if you were blown a direct strong airstream on to her head and shoulders?

The airstream pressure is another force acting on her body just like if she was holding a couple of bricks over her chest. It will move the balance point further up.
Yes, the balance point will have to be moved. But not because the CoG has moved. Gravity is still acting through the same centre. It's just that there is now another force acting unevenly about the original pivot point.

There is, however, another possible explanation that means we're both right. The CoM definitely won't move but maybe the CoG does because the force of the air can be seen as equivalent to an added mass.

All this is irrelevant to a rider though. In this case the wind is horizontal. Hence, the resultant force is not helping or counter-acting gravity at all as it's perpendicular to it.

[dipshit]

All this is irrelevant to a rider though. In this case the wind is horizontal. Hence, the resultant force is not helping or counter-acting gravity at all as it's perpendicular to it.

Amateurs...
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=63871&d=1182044060

Pros...
http://www.webbikeworld.com/Motorcycle-racing/motogp/2007/catalunya.htm

One of these is not like the other.

Which lot do you think understand the physics better?

[jrandom]

Which lot do you think understand the physics better?

Based on my experience, they're probably both complete knuckle-draggers.

I also note that your sublime understanding of The Fizziks has not actually enabled you to lean your bike over as far as either of those photographs yet...

:laugh:

[swbarnett]

Amateurs...
http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=63871&d=1182044060

Pros...
http://www.webbikeworld.com/Motorcycle-racing/motogp/2007/catalunya.htm

One of these is not like the other.

Which lot do you think understand the physics better?
Unless one of them is Roger Freeth I doubt any of them has a good grasp of it. You don't need to know the physics to ride well.

How is this relevant to CoG?

[kezzafish]

COM and COG are two different things. They are often thought of as the same because they are in the exact same place until you add the thing that has been missed out in these explanations..... centrifugal force (CF) you have to add CF to the equation of COG, COM and wind resistance. as CF increases so does the amount of effect gravity has on the mass (G force increases) Wind resistance has little to do with cornering compared to COG, COM and CF. Total mass is important and relates directly to how much effect CF has. COM is important because it determines WHERE the CF has the most effect. Also in the equation is enertia or momentum (speed) the greater the speed or mass, the greater the CF. CF is why we have to lean our bikes to corner, we offset the force trying to biff us off by making the force hold us to the ground. our COG does in fact move, the more g force the lower the COG. our mass does not change therefore our COM does not move. but our "weight" increases with g force. This explains why it is better to weight pegs (rather than the seat) because the extra weight we gain with g force is exerted at a lower point.
i'm too fukken tired to try to explain it better and to be honest all this thinking is doing my head in. Interesting thread... time for bed.... blood is red..... my brain is dead. OK seriously i'm going insane. night night

[swbarnett]

just to add to the confusion... you have centrifugal force (CF) to add to the equation of COM and wind resistance. Wind resistance has little to do with cornring compared to COM and CF. Total mass is important and relates directly to how much CF you have. Also in the equation is enertia (speed) the greater the speed or mass, the greater the CF. the lower the COM the lower the leverage of the CF. CF is why we have to lean our bikes to corner, we offset the force trying to biff us off by making the force hold us to the ground. This explains why it is better to weight pegs (rather than the seat). it lowers the point at which this force acts.

i'm too fukken tired to try to explain it better and to be honest all this thinking is doing my head in. Interesting thread... time for bed.... blood is red..... my brain is dead. OK seriously i'm going insane. night night
Just one minor correction - Inertia is a body's ability to resist changes in velocity (speed or direction). This is constant irrespective of what speed is involved (but only if you ignore frictional forces).

Otherwise I agree. Especially the last bit. I'm getting a bit tired of this on-call lark. Paged at 00:30 and can't get back to sleep. Time for another attempt :sleep:

[kezzafish]

Just one minor correction - Inertia is a body's ability to resist changes in velocity (speed or direction). This is constant irrespective of what speed is involved (but only if you ignore frictional forces).

Otherwise I agree. Especially the last bit. I'm getting a bit tired of this on-call lark. Paged at 00:30 and can't get back to sleep. Time for another attempt :sleep:

oh shit, your keeping me up. i've modified my statement to make it a bit more confusing in the hope that no one will prove me to be talking shite. but have stuck with inertia just spelt wrong!

[jrandom]

centrifugal force (CF) you have to add CF to the equation...

<img src="http://imgs.xkcd.com/comics/centrifugal_force.png"/>

[Max Preload]

COM and COG are two different things.

No, they're not. The CoG is the point at which the entire mass of the system can be considered to be concentrated.

[MSTRS]

CF is why we have to lean our bikes to corner, we offset the force trying to biff us off by making the force hold us to the ground. our COG does in fact move, the more g force the lower the COG. our mass does not change therefore our COM does not move. but our "weight" increases with g force. This explains why it is better to weight pegs (rather than the seat) because the extra weight we gain with g force is exerted at a lower point.


Thank you. This is the point I was making a page or three back. What you said, plus the suspension acts in a more balanced way, hence the bike handles better.

[dipshit]

No, they're not. The CoG is the point at which the entire mass of the system can be considered to be concentrated.

That is the COM. The COG can move when other forces are applied. They are two different things.

They may be the same when static sitting on the lab table... but out in the dynamic real world they can be different.

[Mikkel]

Science defies common sense.

There's a lot of common sense here.

If you can not understand, that an object's COM and COG can only be located at the same point in space if the entirety of the object is positioned in a homogenous gravitational field, then you shouldn't pretend to be arguing anything related to physics. Just like well-meaning believers should not be allowed to teach intelligent design or other faith-based sentiments in a science class.

Shut up and go ride your motorcycle. Understanding the underlying mechanics is not going to make you a better rider. And a discussion of the underlying mechanics is only interesting provided that it is based on actual insight into the subject.

Comments like:

That is the COM. The COG can move when other forces are applied. They are two different things.

They may be the same when static sitting on the lab table... but out in the dynamic real world they can be different.

Are as scientific as "everything in this world is fire". It's just hyperbolic bullshit with no foundation in real insight or understanding. If believing otherwise makes you happy, no harm in that - but presenting it as a scientific argument is inappropriate.

[kezzafish]

so are you saying that you agree with the idea that mid corner (with CF) you are not in the same homognous gravitational field as you were on the straight part of the road? i don't quite understand your answer. Except for the "go ride" bit which i agree with however i find physics and discussions on it very interesting and love to shoot the shit with anyone who feels the same

[kezzafish]

maybe we should call COG the point of balance for this discussions sake?

[swbarnett]

From the "Feynman Lectures on Physics" by Richard Feynman*:

"The center of mass is sometimes called the center of gravity, for the reason that, in many cases, gravity may be considered uniform. ...In case the object is so large that the nonparallelism of the gravitational forces is significant, then the center where one must apply the balancing force is not simple to describe, and it departs slightly from the center of mass. That is why one must distinguish between the center of mass and the center of gravity."

I suspect that the CoG will move when a rider is in a corner for two reasons:

1. The Centripetal force acts like artificial gravity and alters the overall gravitational field (Earth's gravity + CF is equivalent to gravity that's not quite vertical)

2. The act of leaning into a corner will lower the overall mass and therefore the CoM.



*A very famous physicist of the last century.

[Mikkel]

From the "Feynman Lectures on Physics" by Richard Feynman*:

"The center of mass is sometimes called the center of gravity, for the reason that, in many cases, gravity may be considered uniform. ...In case the object is so large that the nonparallelism of the gravitational forces is significant, then the center where one must apply the balancing force is not simple to describe, and it departs slightly from the center of mass. That is why one must distinguish between the center of mass and the center of gravity."

I suspect that the CoG will move when a rider is in a corner for two reasons:

1. The Centripetal force acts like artificial gravity and alters the overall gravitational field (Earth's gravity + CF is equivalent to gravity that's not quite vertical)

2. The act of leaning into a corner will lower the overall mass and therefore the CoM.



*A very famous physicist of the last century.

Seriously, how the fuck can you quote Feynman and then dare to start your next sentence with "I suspect..."? ...and then continue to add such nonsense to the mix?

It is needless to say that the quote by Feynman is correct, he does however not mention the other extreme situation where the gravitational field has a large gradient - i.e. close to a black hole.

The difference in the spatial position of the COM compared to the COG is irrelevant in practicaly all and any classical mechanical systems - including riding a motorcycle. The origin of the whole COG versus COM debate is simply that the COM is what is of interest when we are discussing a mechanical system, not the COG (unless we are considering one of the situations mentioned above and consequently their locations differ).

[jrandom]

<img src="http://imgs.xkcd.com/comics/nash.png"/>

[YellowDog]

So the Propellar Heads win it then.

I did a very good slow speed motorcycle skills course a few months ago. It taught me how to use my body weight to counteract physics. At the end of the 3 days I was doing left and right low speed 360 turns on a steep incline. I now find that I crawl all over the bike to keep good balance, which is something I had previously struggled with.

[kezzafish]

Seriously, how the fuck can you quote Feynman and then dare to start your next sentence with "I suspect..."? ...and then continue to add such nonsense to the mix?

It is needless to say that the quote by Feynman is correct, he does however not mention the other extreme situation where the gravitational field has a large gradient - i.e. close to a black hole.

The difference in the spatial position of the COM compared to the COG is irrelevant in practicaly all and any classical mechanical systems - including riding a motorcycle. The origin of the whole COG versus COM debate is simply that the COM is what is of interest when we are discussing a mechanical system, not the COG (unless we are considering one of the situations mentioned above and consequently their locations differ).
if i said that the point of balance changes would you agree? i'd also like to point out that earlier on in the thread you were saying that the COM and COG are the same thing. And to your point about science defying common sense, i would say science defines common sense as common sense is just widely known science? i think your point is correct in a way because as you say, at no point in time does gravity change during cornering but it's effect is magnified. Agreed? i'm not saying i'm right and your wrong because i'm not certain in my belief and am interested in hearing anyone's take. do you agree that weighting the pegs is beneficial? i don't mean to wind you up and know how frustrating it is when you KNOW something as FACT and people don't believe you, but relax man

deleted
aye?

So the Propellar Heads win it then.

I did a very good slow speed motorcycle skills course a few months ago. It taught me how to use my body weight to counteract physics. At the end of the 3 days I was doing left and right low speed 360 turns on a steep incline. I now find that I crawl all over the bike to keep good balance, which is something I had previously struggled with.

does that mean me? (pp heads)

[swbarnett]

Seriously, how the fuck can you quote Feynman and then dare to start your next sentence with "I suspect..."? ...and then continue to add such nonsense to the mix?
Settle down. The quote was to illustrate that CoM and Cog are NOT the same thing but, as you say, for all practical purposes they can be considered as such.


It is needless to say that the quote by Feynman is correct, he does however not mention the other extreme situation where the gravitational field has a large gradient - i.e. close to a black hole.
I think this would be the same as a large object in a weaker field.

[swbarnett]

...use my body weight to counteract physics.
Sorry to be pedantic but you can't counteract physics. All you're doing is learning to work with it.

[swbarnett]

I was talking with my wife last night (Masters degree in Physics and a University lecturer). Her take is that Centripetal Force is not a force at all but an artefact of the cornering body's inertia (when a body is travelling at a finite velocity it will resist any attempt to change it's direction of travel). As such CF cannot alter the CoG.

[YellowDog]

Sorry to be pedantic but you can't counteract physics. All you're doing is learning to work with it.

You're not being pedantic.

Whilst you are correct in stating that you cannot counteract physics; what I am saying is that you can counteract or influence the resulting effect of physics on the bike if there was no change and in so doing change the resulting physics. But yes, it is still physics!

[Mikkel]

Settle down. The quote was to illustrate that CoM and Cog are NOT the same thing but, as you say, for all practical purposes they can be considered as such.

I accept that. But bringing a quote like that to the table kinda evokes certain expectations. Nothing personal at all mate.


I think this would be the same as a large object in a weaker field.

It has nothing to do with neither the magnitude nor the orientation of the gravitational field. Only the gradient in the gravitational field matters.
Anyway, both of the cases are extremities that we need not concern ourselves with. I am merely arguing semantics. :)


I was talking with my wife last night (Masters degree in Physics and a University lecturer). Her take is that Centripetal Force is not a force at all but an artefact of the cornering body's inertia (when a body is travelling at a finite velocity it will resist any attempt to change it's direction of travel). As such CF cannot alter the CoG.

Your wife is right on the money. Observed from outside an object needs to be affected by a centripetal force (a force that is orthogonal to the direction of travel) in order to perform a circular movement. The radius of the movement is proportional to the square of the velocity, proportional to the mass of the obejct in question and inversely proportional to the centripetal force.

If you perform a coordinate transformation and consider the object that performs the circular motion the origin of your coordinate system you will experience an artificial force equal, but anti-parallel, to the centripetal force - the centrifugal force.

And that is what I mean when I say science defies common sense. If it didn't we wouldn't have had to wait for close to 2000 years before a genius arrived that could do away with the common sense approach of aristolethean mechanics. Luckily Newton managed to achieve that, and even developed a language that could express these observations with the outmost of clarity (differential calculus - and yes, it is arguable whether Newton or Leibniz was the first).

[swbarnett]

I accept that. But bringing a quote like that to the table kinda evokes certain expectations. Nothing personal at all mate.
The quote was actually from a Wikipedia article. I thought I had a reasonable handle on the whole thing but it seems my understanding is a little rusty. My wife actually has a hard-bound copy of said lectures in her study.

As to the rest of what you've said, I know enough to see from this that you know what you're talking about (and certainly know more about this than I do). It makes for interesting reading.

[Mikkel]

The quote was actually from a Wikipedia article. I thought I had a reasonable handle on the whole thing but it seems my understanding is a little rusty. My wife actually has a hard-bound copy of said lectures in her study.

She sounds like a keeper mate! :2thumbsup

Working in the field I do, you necessarily develop a huge respect for Feynman. His talk "There's plenty of room at the bottom" is pretty much the manifesto for nano-technology - and that talk was presented in 1959.


As to the rest of what you've said, I know enough to see from this that you know what you're talking about (and certainly know more about this than I do). It makes for interesting reading.

I should hope so, mechanics are a tool in my toolbox. Would be like a mechanic who didn't know how to use an allen key.
Still, it doesn't really matter when it comes to motorcycles - the dynamics of such a complex system are far too hard to analyse without both deep considerations and a multiphysics model. However, the first step to being able to perform a meaningful analysis is to disect the system and understand it on a basic level - mechanically, aerodynamically, etc. When that understanding has been achieved you might be able to couple these different physical models and find an, in most cases approximate, solution for the system given certain exterior perturbations.

Personally, I'd rather go riding :yes:

[jrandom]

I should hope so, mechanics are a tool in my toolbox. Would be like a mechanic who didn't know how to use an allen key.
Still, it doesn't really matter when it comes to motorcycles - the dynamics of such a complex system are far too hard to analyse without both deep considerations and a multiphysics model. However, the first step to being able to perform a meaningful analysis is to disect the system and understand it on a basic level - mechanically, aerodynamically, etc. When that understanding has been achieved you might be able to couple these different physical models and find an, in most cases approximate, solution for the system given certain exterior perturbations.

*cough* pretentious wanker *cough*

Obviously I don't have the title quite sewn up yet...

[kezzafish]

It has nothing to do with neither the magnitude nor the orientation of the gravitational field. Only the gradient in the gravitational field matters.
Anyway, both of the cases are extremities that we need not concern ourselves with. I am merely arguing semantics. :)

Observed from outside an object needs to be affected by a centripetal force (a force that is orthogonal to the direction of travel) in order to perform a circular movement. The radius of the movement is proportional to the square of the velocity, proportional to the mass of the obejct in question and inversely proportional to the centripetal force.

If you perform a coordinate transformation and consider the object that performs the circular motion the origin of your coordinate system you will experience an artificial force equal, but anti-parallel, to the centripetal force - the centrifugal force.

Fuck me, how the fuck am i supposed to know what the fuck THAT means. I believe i once stuck my cock in a girl at an orthogonal angle to the way her piss flaps pointed but i'm not sure?

Gimme a break and please simplify this for me, i left school when i was 15 for a good reason and i'm not interested in going back.

From what you've said and my own assumption: gravity does not change therefore the COG cannot? What happens is: CF is (momentarily) strong enough to defy gravity? is this correct?

[swbarnett]

From what you've said and my own assumption: gravity does not change therefore the COG cannot?
That's the way I understand it. Because CF is not a gravitational force it can't alter the gravitational field. Therefore no change to the CoG.


What happens is: CF is (momentarily) strong enough to defy gravity? is this correct?
In simple terms, yes.