Quote:
Originally Posted by dfox
So a rule of thumb?
What your quoting is a generic statement. The reality is that every bike is different, and what holds true for a cbr600rr won't hold true for the ninjette.............
|
Todays' motorcycle tires allow lean angles of 45 degree.
Well, that means that these tires can support 1 g at that angle.
Tires used in GP can withstand higher g's, almost up to 2.
What all this g business means?
These tires generate a gripping force that can equal (g=1) or surpass (g>1) the value of the weight that they support.
If that is true, then a front tire commanded to stop rolling by strong enough calipers, can generate a decelerating (gripping) force equal to the weight (vertical force) that it supports during braking (hence, the more loaded the tire becomes the better).
Once the rear wheel is floating, all the weight of bike and rider is supported solely by that braking front wheel.
Let's say the Ninjette and the rider weight 500 lb, then you can achieve a decelerating force of 500 lb (which is equivalent to the free fall of my previous calculation).
Up to this point we have only considered achievable friction force, which applies to any bike (hence, the book is correct).
As you have correctly explained, the geometry and location of the CG of the bike-rider will determine if the bike flips much (performing a stoppie) or none.
A cruiser is long and much heavier than the rider; hence, the combined CG is low. Even if it can brake at 1 g of deceleration, the moment that tends to keep the rear wheel planted wins over the flipping moment. In this case the rear wheel does not float and still carries some of the total weight; therefore, it has some braking power to be used.
A sport bike is short and not much heavier than the rider; hence, the combined CG is high (about half the distance between tire patches). Anything above 1 g of deceleration will make the flipping moment grow above the moment created by the weight applied to the CG, inducing a stoppie.