# Torque Needed for Start



## Duncan (Dec 8, 2008)

OK - no probs

Think of it as you pushing the car
11.6 inch radius (call it 1ft)
3.89:1 diff
So 100 Lb-ft at the motor = 389Lbft at wheels = 389 Lbs force pushing the car along

1/2 G acceleration on 1800lbs = 900lbs at the tire = 900 lbft torque 

So 900/3.89 = 231 lbsft motor torque

or another way 
1800 lbs - 40% on rear wheels(?) = 720 lbs on rear tires 
For road tires max grip = 80% - 80% of 720 = 576 - maximum force you can put through rear tires
576 lbs at 1 ft = 576 Ft lbs - axle divided by diff ratio - 576/3.89 = 148 Lbft

So the MOST torque you will be able to use is 148 Lbft - then you will spin the tires


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