# Mechanics: Motorcycle propulsion

1. Mar 17, 2010

### jrenman

1. The problem statement, all variables and given/known data

You must find the time it takes to accelerate (at constant applied torque) a motorcycle from 0 to 100 km/hr,

given:
Rider mass: 75 kg
Bike total mass: 190 kg
Torque at crankshaft of motor: 105 Nm
Front and rear wheel masses (10 kg and 17 kg respectively)
Radius of wheels: 0.25 m (includes tire)
Radius of wheel hubs: 0.075 m

Wheel composed of 4 straight, uniform spokes. 1/3 of the wheel mass is in the hub, 1/3 in the spokes, and 1/3 in the rim (includes tire).
Ratio of transmission primary drive gear to crankshaft gear radii: 2.5. Ratio of rear sprocket to front sprocket radii: 2.5.

Once you find an equation for the acceleration (and therefore the time), compare the increased performance that would result from the following two modifications to the bike:

a) Lowering the non-rotating mass by 5 kg, and increasing the torque by 5 Nm [this is what you would get by changing the exhaust system).

b) Reducing the front and rear wheel masses by 2 kg and 5 kg respectively, and their moments of inertia by 50% each (this is what you would get by changing the wheels).

2. Relevant equations
N_ext = mR_(centre of mass) x a_com + I_com$$\alpha$$
??

3. The attempt at a solution
I think I am supposed to find the time from 0->100km/hr, then calculate an equation in terms of masses and moments of inertia(?) of wheels and then...
I'm not sure where to start really or what steps to take to get in the right direction.

Any help and advice would be wonderful.