Shake when spinning rear wheel off the ground

[Offroader]

I just built a new wheel with a new MXUS 3000 turbo motor and new tire. With the bike upside down and giving full throttle the rear tire spun with almost no shake at all.

I've never felt such smoothness with my other cromotor builds and I've built a couple of them and used new tires also.

I am going to think it was just luck that the wheel may have been in balance, but could it also be the motor?

What could be the reasons why this build was so smooth while my other motor builds had a bit of shake to them. Enough shake to wobble the whole bike while the bike is upside down on its seat.

Can anything be done to smooth out a shaking wheel or it this something that you would never feel while riding so not worth doing anything about it.

 

[amberwolf]

I've had regular bike wheels that when pedals used(bike upside down) to crank it up to full speed would shake the bike enough to make it fall over...but couldn't feel that when riding cuz I never approached those RPMs, even up to 30-40MPH+ downhill on "smooth" roads.

That said, usually what causes the out of balance on my wheels is the valve stem, and/or reflectors. Sometimes it's problems with tube or tire thickness being inconsistent around the circumference.

Motor wheels have been worse in some; one of the 9C cover sets I have is out of round; I think the center hole is drilled a mm or more off-center. Never had that with bike hubs. So if the wheel other than motor is balanced and true / round, perhaps the MXUS is simply more precisely machined than previous motors and so the wheel is more balanced when true.

 

[Punx0r]

The out of balance results in a force acting in the direction of the wobble proportional to the rotational velocity. This is thrust acting on the bike. When the bike is upside down the speed is high (motor unloaded), so the thrust is greatest and because the bike is balanced upside down with no rider, it's both lightweight and easily upset, so the thrust has maximum effect in shaking/wobbling/making it fall over. It's also more likely to hit resonance, which will really make it jump about.

When riding it the mass of your body dampens the effect.