Motorcycle horizontal acceleration-front wheel rise

[physics2012]

Motorcycle horizontal acceleration--front wheel rise

The distance between the centers of the wheels of a motorcycle is 171 cm. The center of mass of the motorcycle, including the rider, is 95.0 cm above the ground and halfway between the wheels. Assume the mass of each wheel is small compared to the body of the motorcycle. The engine drives the rear wheel only. What horizontal acceleration of the motorcycle will make the front wheel rise off the ground?

2. Homework Equations

τ=rFsinϕI understand that the solution is when .95ma=1.71/2(mg), so when the torques are set equal to each other. why though? thanks!

 

[PhanthomJay]

All the weight is on the rear wheels. Acceleration of the center of mass is in the forward direction. Is there any rotational acceleration about the center of mass at this point in time?