# Need Help w/ The Physics of A Wheelie

1. Jun 24, 2012

### NJD21

So the attachment has my FBD of a bike.

What I'm trying to understand is how exactly a bike does a wheelie while accelerating (in the x-direction) by applying equations involving torque/moment.

For equations involving torque/moment:

So if I take the sum of the moments at the axle, I assumed the torque from the static friction should overcome the torque from the weight so that the bike rotates about that point in the counter-clockwise direction; however when applying principles involving "kinetic moment", (mass x acceleration) provides a negative moment about that point (clockwise rotation). And because of this negative moment, I'm not sure how the bike would be rotating about the rear axle.

Any help is appreciated. Thanks.

#### Attached Files:

• ###### Wheelie.jpg
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2. Jun 25, 2012

### haruspex

Can you explain that part more?
In your diagram, you correctly have the friction forwards on the back wheel at contact with the road, so this provides an anticlockwise moment. If that exceeds the clockwise moment from the weight, the front wheel will lift. What else is there to consider?