Bike dynamics

[dpex]

I realise bike dynamics is a massive subject, but as a result of reading the "Pace" article submitted by 2wheeldrider (good articel, BTW) I have a couple of Q's one or more of you more expert-types may be able to answer. The Q's are specific to my experience on my bike: (600YZF...64Kks new rear tyre, front's okay)

Did a trip along the Coromandel Peninsula. Very windy road. Great ride.

On one 'memorable' corner...memorable because it was a right-hander and had about 3 metres to the left before one got airborne and landed on the rocks 10 metres below.... I made a lousy choice of line-in and entry-speed. Too wide. Too fast. Freaked a bit (read...I freaked a lot). Hit the front brake, too hard, and the bike stood up; making the issue nearly worse than worse.

Other elements. I was pushing way hard into counter-steer. Stepping heavily on the inside peg. Pressing my knee hard into the outer-side of the tank. Yet the bike stood up.

I needed to change my pull-ups after that incident.

I'd appreciate someone explaining the dynamics/physcis of what happened. Notwithstanding, I realise I braked too hard, but why did the bike stand up?

The other issue I'm battling with his where I should be when traversing the exact centre of a curve. In a RHer I go wide left, then try to take the straightest line, then come out wide left again.

But what I did notice on this very light traffic ride to Coromandel was, a lot of me was over the centre-line during man RHers, but not the bike.

But every diagram I have seen asserts picking the straightest line through a curve.

God knows. I've wapped a few over-hanging tree-leaves through left-handers, but tree-leaves ain't vehicles.

So, perhaps someone could explain a bit more about the line-in/line out game.

Thanks.

[mowgli]

Read "Twist of the Wrist" by Keith Code. It will explain the standing up tendency under brakes in detail.

Regarding crossing the centre line I expect you're turning in too early and simply cutting the corner. Do a search on "delayed apex" and give that a shot. Much safer IMHO.

[discotex]

I'd appreciate someone explaining the dynamics/physcis of what happened. Notwithstanding, I realise I braked too hard, but why did the bike stand up?


That's what bikes do when you use the front brake in corners. Physics and momentum and shit like that.



God knows. I've wapped a few over-hanging tree-leaves through left-handers, but tree-leaves ain't vehicles.


Could be a parked car around the corner. Or a letterbox at head height.....

And I think you answered your own question re right handers. Keep your head on the left side of the road (unless you can see right the way through the corner).

[James Deuce]

It's a combination of factors that make the bike stand up, but the main reason is conservation of angular momentum.

Effectively if you brake upright the weight transfers to the front of the bike in a direct line along the vertical centre of mass. The forks and front tyre "get busy" and a great deal of braking force can be generated, slightly more than 1G by the good guys.

If you brake leaned over, the bars are turned and the bike tries to pivot around the steering head. This makes the bike want to steer out of the corner, so it stands up. If you are turning right, braking can add in a force equivalent to a good push on the left bar.

The effect is pronounced at low speed. Things like inertia and gyroscopic precession tend to keep things under control to a point at higher speeds.

Factor in a change of steering geometry as you load the front more, the rider freezing in panic, and the rider looking directly at where they are going to crash instead of where they need to be and it all goes wrong,

[Movistar]

I'd appreciate someone explaining the dynamics/physcis of what happened.

You ferked up...

Seriously though, at least you had the balls to come on here and relay what happened!

There are a zillion different theories and sound reasoning for 'Bike Dynamics' and what happens when you ferk it up (or get it right for that matter).

Search on here, google it, whichever path you choose you will find many different and many same answers.

Entry speed is the key.

What is the correct entry speed?

Search on here, google it, whichever path you choose you will find many different and many same answers.

What is the correct cornering line?

Search on here, google it, whichever path you choose you will find many different and many same answers.

I know I'm not being much help, and I'm not trying to be a smart arse.

This is the essence of what makes motorcycling such fun!:
Getting it wrong, figuring out why, applying the solution, getting it right!

If you can 100% always just do the last step please, tell me how!

[Ixion]

Most bikes will stand up under front brake in a corner . There are exceptions. Dunno why, I always just accepted it as one of the ThingsThatBe, laid down before the beginings of Time by the High Biker Gods. They do that. Conversely, a bit of rear brake will help tighten the corner. Again, depends on the bike. I trail brake a lot m'self, but I know others (doubtless better and faster riders) who never do it. Your choice.

As to the corner line thing, y'need to remember that there are track lines and road lines. A lot of the stuff you see written about "lines" is fine for the track , but it can get you killed on the road. BTW don't assume that left handers are safe as regards hanging over. Twice in recent years I've collected a leaning outward roadside marker post with my shoulder on a left hander. Hurts like hell. Glad it wasn't my head. Always keep ALL of you well to the left of the centre line on a right hander unless you can see right through it. And don't assume that other traffic will obey the same rule. Sooner or later you'll meet Harry Huriup in his SUV midcorner. Harry always specifies self centering steering on his vehicles, and that's exactly how he drives - right down the centre line. So you better be ready to change line real fast when you meet him, because he doesn't give way to bikes. It's HIS road, he paid for it, and he's going to use ALL of it. Sucks to be you.

[puddytat]

Most bikes will stand up under front brake in a corner .

As to the corner line thing, y'need to remember that there are track lines and road lines. A lot of the stuff you see written about "lines" is fine for the track , but it can get you killed on the road.

I agree with that.
Exploding mirrors give you a hell of a fright.......keep your head in your lane as its so easy to fall into the habit of riding the centre line:Oops:

[CookMySock]

Most bikes will stand up under front brake in a corner . There are exceptions. Which bikes are notably exceptions ?

I have spent more than a few hours (days??) studying steering geometry, which makes me a noob to the science, but I would like to follow it up.

thanks
Steve

[The Stranger]

Hit the front brake, too hard, and the bike stood up; making the issue nearly worse than worse.

I'd appreciate someone explaining the dynamics/physcis of what happened. Notwithstanding, I realise I braked too hard, but why did the bike stand up?



I too have never bothered to rationalise this one. It just does stand up.
Almost without a doubt the best response in this situation was to add a little throttle.
If in doubt gas it out.



The other issue I'm battling with his where I should be when traversing the exact centre of a curve. In a RHer I go wide left, then try to take the straightest line, then come out wide left again.


Stay wide until you can see the exit. On some bends that may be the racing line, but on many you wont apex until well through the curve.

Why exit wide?
what happens if the next corner happens to be a left hander?
You have potentially buggered your entry to the next corner.
Stay wide until you see the exit (and thus possibly the next corner) then select your best exit for the following corner entry. If the next corner is a left hander you may want to exit tight to give a better entry line, if it's another right hander you may want to get harder on the gas to push wide and set up for that.



But what I did notice on this very light traffic ride to Coromandel was, a lot of me was over the centre-line during man RHers, but not the bike.


Where were you looking?
The bike tends to go where you look.
Were you looking across the centre line?



But every diagram I have seen asserts picking the straightest line through a curve.


Many diagrams do show late apexing, NOT picking the straightest line.
As noted there is a difference between a road and a race line.

[RiderInBlack]

Never out corner ya-self on the open road, especially where ya can't see through the corner. Riding hard is fun, but ya should be able ta change ya line in a hurry if ya have to. I've had to change my line too many times ta mention. Road kill/pot holes/Pea-metal/gravel/tractor mud/cow shit etc just where ya don't want it.
I prefer ta late apex on all corners I can't see through. Right handers especially. I've seen too many milk tankers swinging out wide over the white line ta get their trailers around a corner, to risk putting my head over the white line on blind right handers. Bikers have lost the heads that way.
Have ridden a heavy bike, I have found riding (NOT LOCKING) the back brake helped it corner. The new bike doesn't seam ta need this as long as I use the right gear (lighter/more engine braking/different set-up, who knows). Even before bikes, I was taught to do all my braking before the corner, glide through and power out. Even in a cage it is not a good idea ta try braking in the middle of a corner. Although ya front brake is the stronger brake, it is not one ya want to do too hard in a corner. Ya more likely ta loose the front ta way.
But hey what do I know. Best lesson ta Stranger (He teaches Ride Right Ride Safe).

[Motu]

Which bikes are notably exceptions ?


There are more front suspensions than the standard teles...each has different characteristics,there are different steering geometries,weight distributions etc,etc.Try a few more and get back to us.

I very seldom have a bike stand up under braking - I preempt that by picking the bike up myself,braking,then laying it down again and tightening the line.It means I fucked up,simple as that.

I was riding an unfamiliar bike down a familiar road the other day - and it was not a pretty sight.....I can sympathies with a newish rider on a country road.I was getting the corner speeds wrong,wrong gears,overshooting,hitting road kill and gravel.All the stuff I have a hard time believing other people can do...it was just plain bad riding.But it was not a bad rider (quiet in the back!),not a bad bike,and not a bad road - but combine hazardous road conditions and a bike that needed totally different inputs than I am used to....and you have a recipe for disaster.We can all get it wrong sometimes,no matter how experienced - the important thing is to learn from it.

But by 140km I had it sussed.

[Ixion]

Hm. OK, thinking about this, just rambling thru m'arsehole so to speak.

In a corner the front wheel must try to describe a greater radius arc than the rear wheel. And therefore must go faster. Which is why trail braking works - can't speed up the front wheel to turn more tightly, so slow down the rear.

Slowing down the front, conversely, will make the front wheel arc attempt to be less than the rear wheel arc. And the only way the bike can respond to that is to straighten up. In essence, the back wheel starts trying to overtake the front wheel, it can't because of the tyre grip on the road, so the resultant force forces the bike upright. Similar logic to the bike flicking upright in a high side.

But, this effect will be countered by the other result of applying the front brake , the diving of the forks. That reduces the trail, and thus makes for a steeper turn in, countering , or partially countering the stand up effect.

Logically therefore, one might expect the stand up effect to be least noticeable in a chookchaser. Short wheel base, and long soft forks. Lots of dive under braking. Hence maybe Mr Motu's comment. And conversely , most noticeable on a bike with a long wheel base and stiff front suspension and lots of compression damping.Maybe a crusier?

I've never noticed if girder fork bikes tend to stand up. And probably their front brakes would be too ineffectual to produce the effect.

[beyond]

Hiya,

The brakings been covered.
Lines?
I'm not saying I know it all and some will think I'm blowing my own trumpet here. I'm not. I learnt my road lines from a guy I would easily put in the top 5% of riders in this country.

I have a few vids on youtube that are rear facing and some forward facing that will help you with the correct lines.
You may or may not want to check them out. Your call.

http://www.youtube.com/watch?v=44cfxcvi9IU

http://www.youtube.com/watch?v=AxB4Q1SiNhI

http://www.youtube.com/watch?v=VbaMhjZ_nIQ

http://www.youtube.com/watch?v=l8bomS17y1I

[Motu]

Worst bike to brake in corners with is a leading link - they don't just stand up,they sit up,the front wheel locks up,then they start hopping off the road into the ditch.They definitely need to be left alone to go their own way around a corner.They could be used as a learning device....

[CookMySock]

[...] so the resultant force forces the bike upright. an interesting read. Thanks.


I've never noticed if girder fork bikes tend to stand up.I have read a lot about girder forks - in particular one persons opinion why they are <a href="http://64.172.168.34/neatstuff/girder-1.htm">superior.</a>


Worst bike to brake in corners with is a leading link - they don't just stand up,they sit up,the front wheel locks up,then they start hopping off the road into the ditch.They definitely need to be left alone to go their own way around a corner.They could be used as a learning device....Sounds to me like they need to be used as a boat anchoring device.

Steve

[Ixion]

an interesting read. Thanks.

I have read a lot about girder forks - in particular one persons opinion why they are superior. (http://64.172.168.34/neatstuff/girder-1.htm)

Sounds to me like they need to be used as a boat anchoring device.

Steve

Girder forks have a lot of advantages. When telescopics came out a lot of people were not impressed. Which led to 'orrible things like the Girdraulic . Not to mention the Dowty Pneumatic (I won't mention it , in case VeloFellow is listening).

And while leading links may have had some issues they ahd some advantages too. Especially if we include the earles fork, of BMW and Douglas fame as a leading link (which it is). Many people still swear that the Earles fork was the best design ever made. And the latest BMW forks are technically leading links.

[dpex]

Whoever was the driver in vid three, he/she needs to be grounded. Overtaking on double-yellow lines, blind hills, then overtaking a car overtaking.

You think this is good riding? If you do then you're a complete arsehole. And come your funeral I'll come to piss on your coffin.

[RiderInBlack]

Whoever was the driver in vid three, he/she needs to be grounded. Overtaking on double-yellow lines, blind hills, then overtaking a car overtaking.

You think this is good riding? If you do then you're a complete arsehole. And come your funeral I'll come to piss on your coffin.Think ya need ta rewatch the vid and pull ya head in.

Firstly take in account that the cam was probably mounted lower than the rider's helmet, therefore the rider's view was better than the cams. the "Blind" hill wasn't blind for the rider.
First "overtaking" car the rider overtook had already finished overtaking and was moving back into it's lane at the time the rider passed with plenty of safe space. The last "Overtaking" car had slighty moved right to give more room for a parked car. The rider still had a safe passing space it that case too.
Where the rider passed on the "Yellow lines" he had clear view of the road ahead and the lines were ether just starting or just finishing.
By the way I have not ridden with that rider or am him.

[CookMySock]

You think this is good riding? If you do then you're a complete arsehole. And come your funeral I'll come to piss on your coffin.Don't be nasty dpex. We all don't ride "good" all the time. Sometimes we play up, just like you do, and if you want to go do something dumb on a bike you should just go do it and have fun. If people are gunna get themselves killed doing crazy shit, then they MIGHT want to consider those who care about them, but thats their business, not ours.

Steve

[Crisis management]

I realise bike dynamics is a massive subject......
Stepping heavily on the inside peg.
Yet the bike stood up.


Mostly what others have said here but don't overlook the effect your peg weighting will have....loading the inside peg makes the bike stand up.

The lighter the bike the more effect you will have but you need to learn the basics of bike control.

My standard answer is read "Twist of the wrist 2", I know thats already been suggested but take this as another hint.

Try riding slowly and experimenting with the effects of different control inputs, thats what I do for days when I get a new bike.

Have fun.

[pritch]

Try riding slowly and experimenting with the effects of different control inputs, thats what I do for days when I get a new bike.


Good suggestion, it's a good idea after a layoff as well, like a couple of weeks ago when we had the first fine weekend in ages.

Also while riding around East cape last time a near miss involving a local plumber and his Xtra wide trailer suggested that instead of using the usual line I should use an imaginary line running parallel with the centre line but a metre toward my side.

In his book Pridmore suggests staying nearer the middle of the lane and that's hard to argue with...

[James Deuce]

Blimey. No one's picked up on "conservation of angular momentum" thing, have they.

More simply, the steering head acts as a pivot when you brake while leaned over.

You crank the bike over and you are describing the arc of a circle with your bike. You apply the brakes and one of the forces balancing the bike suddenly changes its vector from keeping you describing that arc to wanting to fly off at a tangent to that arc.

Thing is you are steering the bike, so rather than spearing off at a tangent all the mass behind the steering head (if you are turning right) tries to go left, while you continue to hold the bike down to the right. Thing is the mass heading to the left translates into a steering input to the left and et voila, bike stands up. Let the brake off and it will suddenly flop down to the right because you are (usually) trying to subconciously counter this force (if you aren't target fixated). Often letting the brake off is all you need to do to fix the problem you just created by braking.

Bear in mind that while all this is going on you are reducing the available amount of front end traction tremendously. The further over you are leaned, the less braking force you have available. If you need to brake hard in a corner, stand the bike up first.

I suggest going to a big wide open carpark and practicing that though, because it feels counter intuitive on the road.

Bring a trailer.