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

[MSTRS:Me]

...grow some balls. ...

... you got it in the end.

Which is logical....

[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.

[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.

[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.

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.