Motor bike engines acting as a gyroscope keeping the bike upright

Yoma

Dear All
This is a rather strange question for you one that i can find no conclusive argument to.
when riding a large motorbike i am informed that the engine must be reved at low speeds in order to keep the engine spinning at a sufficient speed to enable it to generate a strong enough gyroscope to keep the rider and the bike upright.
can anyone find any merit in this or is it just all bollocks?
I am interested to know as a friend of mine owns a large Harley Davidson and i want to know if he is simply keeping the bike up or just being bad by reving his engine in car parks.
Many thanks
Yoma

edit:
i also found this:http://www.misconceptionjunction.com...ced-on-a-bike/
suggesting that the wheels of a bike do not actually provide a effective gyroscope.
i am interested in the engine though.

berkeman

Welcome to the PF.

No, you balance a motorcyle pretty much like you ride a bicycle. A bicycle has no engine to rev, right?

Having said that, the gyroscopic action of the spinning engine (and wheels to some degree) does resist tilting the motorcycle. You can use this effect to help you stay balanced when moving very slowly on a motorcycle, like when you are maneuvering tight turns in a parking lot or doing tight U-turns. You hold the engine at a low/medium RPM, slip the clutch, and drag the rear brake. The extra stability is very noticable. But you don't need to do that in normal riding.