Can't say I haven't fallen off anymore...

[Lucy]

Always before I've 'dropped it', usually while stopped, but today I fell off properly, whilst riding, had my foot stuck under the bike and everything. Didn't hurt and the bike is fine too, I was going really really slowly.

Things I have learnt today:
It's easier to ride up steep rutted rocky gravel roads, than to ride down them.
Riding sandy rocky gravelly roads (Tukino skifield access road) on a BMW R80 with a near bald front tyre is a really dumb idea. Well, it's ok going up, but coming down is quite tricky.
When nice soldiers from the Singapore army try to help you down a steep bit, they too will drop it...

Thick soft sand makes the gravel bits seem really easy.

Things I remembered to do today:
Stand on pegs to put COG lower (yay didn't fall off in the sandy bits, although it wobbled and skidded heaps)
Look where you want to go.

Things I remembered AFTER falling off about five times:

USE THE BACK BRAKE. Doh. What a ning nong. When I started using the back brake coming down it was a whole lot better and I only fell off once or twice after that.

[Taz]

USE THE BACK BRAKE. Doh. What a ning nong. When I started using the back brake coming down it was a whole lot better and I only fell off once or twice after that.

Use both brakes gently. Even on gravel with road tyres the front will still give the majority of the braking force.

[Lucy]

Use both brakes gently. Even on gravel with road tyres the front will still give the majority of the braking force.

True, but I probably didn't actually need to brake, just needed to grow some balls. It was really slippery, as soon as I touched the front brake the wheel locked and slid out.

[xwhatsit]

just needed to grow some balls.
Ah. You might have trouble there.

Nice! Looks like you had a blast! At least with an airhead twin the bike can't fall too far :D

[jrandom]

Stand on pegs to put COG lower

Gah. Thud.

A few minutes of thinking should make it plain that standing on the pegs does nothing of the sort. It raises the bulk of your body's mass up into the air, thereby making the center of mass of the bike-rider system higher, not lower.

But it does allow your knees to act as suspension and stop your body getting bounced around, which is kinda necessary when riding offroad.

However. The 'stand on pegs to lower COG' myth is just that; a myth.

By all means, stand up offroad to help with absorbing the bumps and jumps, but in many situations, particularly on smooth surfaces, your bike will handle better with a lower center of mass. That means moving your torso closer to the ground, not further away from it.

[Motu]

You wouldn't have dropped it if you had a sidecar attached.

Do you still have it by the way??...??

Handle bars have a lot to do with it on surfaces like that - standard BMW bars are low and narrow,put's your weight too far forward,standing on the pegs will make it worse.Weight to the rear and more rear brake on down hills....sounds like you got it in the end.

[xwhatsit]

By all means, stand up offroad to help with absorbing the bumps and jumps, but in many situations, particularly on smooth surfaces, your bike will handle better with a lower center of mass. That means moving your torso closer to the ground, not further away from it.
All very valid, but don't forget the wrong-way-up broomstick-in-the-palm-of-your-hand trick -- with the bulk of the mass up top, everything happens slowly and predictably and you can catch it when it starts to topple. Move the broomstick brush-side-down, and it'll fall over in a flash before you can balance it.

[Ixion]

Gah. Thud.

A few minutes of thinking should make it plain that standing on the pegs does nothing of the sort. It raises the bulk of your body's mass up into the air, thereby making the center of mass of the bike-rider system higher, not lower.

But it does allow your knees to act as suspension and stop your body getting bounced around, which is kinda necessary when riding offroad.

However. The 'stand on pegs to lower COG' myth is just that; a myth.

By all means, stand up offroad to help with absorbing the bumps and jumps, but in many situations, particularly on smooth surfaces, your bike will handle better with a lower center of mass. That means moving your torso closer to the ground, not further away from it.

It is more complex than that. You are thinking only of sprotsbikes.

When descending a steep badly surfaced slope, what is needed, as Mr Motu said, is weight BACK

Now, sitting down it is hard to move your weight back. And when the front hits a bump and the suspension compresses, weight moves even futher forward.

Standing, it is easier to move back . Sitting , all you can do is push your upper body backwards, and even that is akward. Standing, you can move your whole body back - and most of us carry the majority of weight in our arse (no offence ladies).

And when the front compresses, one can lean further back easily.

You will not be leaning, so the increased pendulum effect of the higher CoM is of no matter.

You can't do it at all on a sprotsbike of course. All that happens is you end up crouched over the steering head like a dwarf about to give birth.

[Motu]

Yes - you need to stand up to balance...yourself and the bike.You need to be able to stand on the pegs not touching the bars....all you weight on your feet,then you will be able to have no weight on your hands.Can't do that with low narrow bars.

[jrandom]

When descending a steep badly surfaced slope, what is needed, as Mr Motu said, is weight BACK

I have ridden a mountainbike down an bumpy incline or two in my time, y'know.

I find the simple incorrectness of the 'lower COG' comment vaguely annoying, y'see. So I point out that it is incorrect.

Standing up on the pegs is, of course, necessary for riding offroad, and very good advice in many circumstances. But doing so does not 'lower' any 'center of gravity'. In fact, it raises it.

Sorry to butt in like this; I'm probably more obsessed than I should be with trying to stop people making themselves sound like idiots.

:pinch:

[Lucy]

You wouldn't have dropped it if you had a sidecar attached.

Do you still have it by the way??...??

Handle bars have a lot to do with it on surfaces like that - standard BMW bars are low and narrow,put's your weight too far forward,standing on the pegs will make it worse.Weight to the rear and more rear brake on down hills....sounds like you got it in the end.

Hiya, yes I do have the sidecar. It's been on for a while but I haven't been riding as much as I hate cornering with it on, so I took it off this morning so I could go on a decent ride.

I am itching to have a go offroad and do the Raetihi ripper and other trail rides around the place, but can't afford another bike at the moment, so thought I'd give it a go anyway, but yeah, going up was all good...

Not sure why I stood up in the loose sand and little river crossing, it just seemed like the right thing to do, I would have done it on my pushbike, so I guess that's why. I guess I just said COG cos I wanted to sound grownup. Apparently it made me sound like an idiot anyway. Oh well.

Can't wait to go up there again when I've got a TTR or something. I'm sure my GN would have been good too, not that I can complain about the BMW, it coped well with being dropped multiple times on both sides. Nothing broke as far as I can tell, and it kept on going.

[gijoe1313]

Well, sounds like a learning experience and as Ixion is wont to say, all part of life's rich tapestry when the patina of time clouds over your riding years, you can look back and say "I damn well bloody did it!"

Good on you for doing things a little more differently every day! A great adventure and all! :niceone:

So how is the ride? Tough little thing that ticks along!

[jrandom]

I guess I just said COG cos I wanted to sound grownup. Apparently it made me sound like an idiot anyway. Oh well.

See, now I feel all bad and stuff!

But at least you, too, can hold forth with authority now whenever someone repeats the 'stand on pegs to lower COG' myth, and point out that raising your body up in the air doesn't make the center of mass lower, it makes it higher.

Good on ya for getting out there and riding those trails, sounds like you're having a great time.

:niceone:

[buggsubique]

that's a great ride up the Tukino rd. Are those Singaporeans up there? ha, They would have wondered what the f*ck was going on! Great stuff!

[cave weta]

can I throw in another worm?

I was told that standing up, while raising the Cof G does lower the polar moment which is the point at which the mass changes direction. The seat is higher than the pegs so the point of Effect is lowerered increasing manoverability
anyway ...
thats what I think...
or thats what I think I think..
or thats what I think he thinks ..or something!

Lucy-you will fall off.. thats how you tell that you are having fun!

[MSTRS]

...grow some balls. ...


... you got it in the end.

Which is logical....:whistle:

[jrandom]

I was told that standing up, while raising the Cof G does lower the polar moment which is the point at which the mass changes direction. The seat is higher than the pegs so the point of Effect is lowerered increasing manoverability

Jesus motherfucking Christ, my head asplode.

Have a read of this http://en.wikipedia.org/wiki/Moment_of_inertia, and meditate upon the examples given of divers and skaters pulling their limbs in or sticking them out to spin faster or slower.

Long story short: moving mass closer to the axis of rotation decreases the resistance of an object to a change in its rate of rotation.

So, when a bike tips over to go around a corner, if your body is up in the air, there's a bunch of mass that's further away from the axis of rotation, and the bike will tip in slower.

If your body's lying down over the tank, its mass is closer to the axis of rotation, and the bike will tip in faster.

Standing up on the pegs therefore decreases maneuverability, in the sense that the bike will respond more slowly to steering inputs. Of course, sometimes that's a good thing.

The same effect is noticeable when you balance a pole with a weight on one end in your hand. If the weight is up at the top, the pole will tip over more slowly. If the weight is at the bottom, in your hand, right on the axis of rotation when it tips, the pole will tip over more quickly.

[jrandom]

I think I will now go back to being depressed at the fact that the Average Motorcyclist (tm) was obviously doing something other than paying attention to their physics teacher in high school.

:doobey:

[Lucy]

See, now I feel all bad and stuff!

.

:

Good, now bend over... yeah but nah, I was confused by the wording at first, but appreciate how having more weight on the pegs makes sense sometimes. When I say 'standing up', a fly would have trouble fitting between my arse and the seat, but I had moved more weight down lower. And on further reflection, on the flat sandy bits I was definitely sitting.

I saw the mountain bikers on tv last night racing and crashing down Coronet peak, and couldn't help thinking how exposed their legs were, and what pussies they were only having to pick up a mountain bike, not a 400kg motorbike with a full tank of petrol.

[jrandom]

I had moved more weight down lower.

Ah um hmm, no; if you lifted your arse and torso, you moved weight higher, not lower.

I don't understand why people have difficulty grasping that the essential point is where the mass of the bike-rider system sits in space, not whether the rider is touching the bike via the seat or via the pegs.

The advantage of putting your weight on the pegs is that it allows you to use your knees as suspension, and move your body mass around with far more agility than when your bum is plopped on the seat.

But the bike-rider system's center of mass and moment of inertia depend entirely upon where in space the mass is.

[jrandom]

not a 400kg motorbike...

I very much doubt that your R80 weighs anything near 400kg. 300, maybe, but probably more like 250 fully wet.

Edit: bikez.com is occasionally unreliable, but says that it's 207kg wet (http://www.bikez.com/motorcycles/bmw_r80_1985.php).

[Lucy]

I very much doubt that your R80 weighs anything near 400kg. 300, maybe, but probably more like 250 fully wet.

yes seems high, but I am just repeating what I read off the frame.

I dropped science after 4th form, so I can't keep discussing this with words.

[jrandom]

yes seems high, but I am just repeating what I read off the frame.

There's a weight on the frame?

That's probably the maximum safe total loaded weight for the machine, not what it weighs itself. 400kg sounds about right in that context, particularly if the machine is in fact 207kg wet as per its bikez.com page.

[Lucy]

There's a weight on the frame?

That's probably the maximum safe total loaded weight for the machine, not what it weighs itself. 400kg sounds about right in that context, particularly if the machine is in fact 207kg wet as per its bikez.com page.

I was just about to edit my post and say that it may be that. Still, I had to pick myself up as well, so those mountain bikers are still pussies.

[Ixion]

I very much doubt that your R80 weighs anything near 400kg. 300, maybe, but probably more like 250 fully wet.

Edit: bikez.com is occasionally unreliable, but says that it's 207kg wet (http://www.bikez.com/motorcycles/bmw_r80_1985.php).

Acch , zer Herrenraden iz built for ze master race , und must be ver stronk. I'm quite sure my BMW weighs at least 500kg once I'm on it. The R80 was the lightweight model, so 400 sounds about right.

An interesting memory is that back in the day, some Briddish iron used to have the pillion pegs mounted directly on the swingarm. So, if you stood on THOSE. you transferred all your weight from sprung to unsprung weight. A useful trick in heavy going.

[jrandom]

An interesting memory is that back in the day, some Briddish iron used to have the pillion pegs mounted directly on the swingarm. So, if you stood on THOSE. you transferred all your weight from sprung to unsprung weight. A useful trick in heavy going.

Really! How interesting. I learn something every day.

I did write a short paragraph at one point in my earlier ramblings in this thread, making an exception to the 'where you rest your weight' for the obvious case of putting it on the unsprung portion of the bike's chassis (I had a mental image of a rod freely rotating within a hollow rear axle and protruding from each side) but then deleted it before posting.

It seemed a safe assumption that what I'd already posted was probably quite unclear enough without further muddying of the waters via purely hypothetical exceptions.

Which now turn out to have been not so hypothetical after all.

Which bikes had their pillion pegs on the swingarm?

[Ixion]

Tis a long traverse through the murky mists of time, but one I remember was the 3TA 5TA series. It wasn't uncommon. Mr Motu may remember others.

EDIT: prompted by a nagging niggle, I just walked outside and took a look at my T500 Titan. Guess where the pillion pegs are located. Duh.

[Ocean1]

An interesting memory is that back in the day, some Briddish iron used to have the pillion pegs mounted directly on the swingarm. So, if you stood on THOSE. you transferred all your weight from sprung to unsprung weight. A useful trick in heavy going.


Which bikes had their pillion pegs on the swingarm?

Quite a few early Japanese trail bikes also.

But actually standing on 'em during semi-violent manoeuvres was a good way to break one’s bits.

[Tony W]

My first new bike, the first Yamaha XT500, (1977 ?) had pegs on the swingarm. I think my DT360 did too.

Mind you, I did not stand on them !

I definitely have better control of my bikes, while seated.
I guess it's a personal thing.

[Motu]

It was pretty freaky being a pillion with swingarm mounted pegs - specially mid corner corugations.The pillion could also weight the pegs to good effect....but you needed to be ''in tune'' with the rider to pull that off without getting an elbow in the ribs.

What seems to be missed in this dribble about standing on pegs and CoG,is the effect of the weight through the pegs - stand on the pegs,then put full weight on each peg in turn.This is how you control a bike standing on the pegs - it's about balance ,not CoG.Weight distribution...and how you control it.

[Ocean1]

But the bike-rider system's center of mass and moment of inertia depend entirely upon where in space the mass is.

Indeed....

[jafar]

An interesting memory is that back in the day, some Briddish iron used to have the pillion pegs mounted directly on the swingarm. So, if you stood on THOSE. you transferred all your weight from sprung to unsprung weight. A useful trick in heavy going.

Harley Davidson still do this even on some of the new ones:whistle:

[xwhatsit]

Even Suzuki A100s have them on the swingarm. Actually not as bad as I thought it would be. Quite a sensible place to mount them, that way you don't need long brackets like rearsets.

[jrandom]

polar moment of inertia

<img src="http://i28.tinypic.com/1s1unt.jpg"/>

[Motu]

I think if you got a little closer to those polars...you would find out quickly they react.Large polar's can be rather savage in their reaction.Large polar reactions bite - 911.....or VW Beetle if you have a lower budget.