Physics of a Wheelie

[steven c]

Interesting.....
https://www.revzilla.com/common-tread/understanding-why-motorcycles-wheelie?utm_source=facebook&utm_medium=social&utm_campaign=boosted-posts%7Ctpfn-content-organic&utm_content=common-tread-learn-organic&utm_term=understanding-why-motorcycles-wheelie-090722-%7Ctpfn-content-organic&fbclid=IwAR3y-a_VGjXVPQTR0AY9poaQnKKT5OzGJPA8EjBwdrnUEL63XHf6hCfEoDk

[Moparnut72]

This is quite a bit different from what we have been told for years. Things from the chain pulling on the top of the sprocket to the angle of the swingarm. I think is is a combination of multiple factors,  but what do I know.
kk

[nc43bsa]

I remember my Ducati 900SS wouldn't wheelie under any circumstances.

I found out later it was mostly because the crankshaft rotated in the opposite direction as the wheels.

[Dukedesmo]

Quote from: nc43bsa on Today at 04:27:54 AM

I remember my Ducati 900SS wouldn't wheelie under any circumstances.

I found out later it was mostly because the crankshaft rotated in the opposite direction as the wheels.

___________________ ___________________ ________

Strange because Ducati V-twins are renowned for their wheelieability. I've got both a 916 and a Monster 900 and both are very easily wheelied, especially the Monster (same powerplant as the SS) also, the crankshaft rotates in the same direction as the wheels - though not sure if that makes any difference? (or were you joking?).

My Guzzi, on the other hand is not really up to it (though doubtless some will say otherwise) due to the fact that it's long, too heavy and lacking the power to get it airborne plus, I'm not sure the clutch is man enough to take the abuse?

To clarify, I'm not into wheelies. I used to do or at least try to do them in my youth but it didn't always go to plan and now I'm too old to be falling off the back plus, I don't want to be breaking my bikes in doing so.

[guzziart]

Good video explaining the physics of a wheelie....even I understood it.

[moto]

This is quite a bit different from what we have been told for years. Things from the chain pulling on the top of the sprocket to the angle of the swingarm. I think is is a combination of multiple factors,  but what do I know.
kk

It is. This is mathematically analyzed in Vittore Cossalter, Motorcycle Dynamics, chapter 6, "Motorcycle Trim," especially section 6.3, "Motorcycle trim in accelerated motion." The tendency to wheelie also depends on rear wheel squat (in the squat ratio, R), which differs with the type (chain, shaft, paralever/CARC) and geometry of the drive.

[Huzo]

I remember my Ducati 900SS wouldn't wheelie under any circumstances.

I found out later it was mostly because the crankshaft rotated in the opposite direction as the wheels.

Nah…Irrelevant.
The torque is still being put into the rear hub, how many times it changes direction on the way down there means nothing.
The mass of the bike does not want to move forward and the resistance of the wheel to turning, imparts an equal and opposite torque the other way.
Imagine viewing a helicopter from above and disconnecting the rear rotor, or even better.
Hold an electric drill with one hand and feel what happens when the drill bit jams or starts to seize. The torque will be imparted back through the system.
The bike wants to rotate around the rear sprocket with exactly the same torque as it’s putting into the wheel, but the CofM has too long an arm and the vertical component is too great.
Imagine you have 800 Nm and gently let the clutch out on level ground, there is little resistance to forward motion, so the wheel can turn and the bike will gently accelerate.
But if you stick a bar in the spokes, it will rotate over backwards irregardless (sic) of the direction of the crank rotation.

Just a thought experiment.
If you laid your SS on it’s side with the frame clear of the ground and clamped the wheel, when you fed the clutch out it would rotate around the wheel.
It would be pulling a wheelie, but on it’s side.
Also, remember the CofM is about 0.5 metres above the road and the tyre contact patch is at road level.
That is also applying a couple that wants to flip over.