Originally Posted by High Country Herb
You are right!
A traffic school instructor had all kinds of data he showed us which said it had more to do with how much rubber was on the road than the size of the vehicle, but it turns out he was full of shit. It turns out a Ninja 250 can stop about 10 feet shorter from 60 mph than a Chevy Silverado can.
Of course, a rider will cover more than 10 feet during the reaction time, so it doesn't make a difference in this context, but it does piss me off that traffic school lies to us. Maybe next time I'll pay someone to take the course for me.
He was half right and you are half right.
It's about lbs/sq,in of tire on the road. Most modern vehicles have enough braking power to bring the tires right up to the point of lockup.
All other conditions being the same a vehicle that weighs 4000lbs and has 100 square inches of rubber on the road will be able to stop in the same distance as a 400lbs vehicle with 10 sq in. of rubber on the road because they both have 40lbs of down pressure per 1 sq in.
Many other things play into stopping distance as well, such as type of tire (compound, tred, shape), brake fade, dive, weight shift, road surface, etc.
If you could keep the brakes from heating up, a loaded semi can stop in a shorter distance than an empty one.