Originally Posted by
zzyzx_xyzzy
Lifting the rear wheel lifts the CG and moves it forward, making the system more prone to flip forward at even less deceleration. Hence, you see trick riders (like the pic you posted) riding on the front wheel at the balance point where they are on barely feathering the front brake. NOT maxmimally decelerating.
Maximum braking is achieved when the rear wheel has no weight on it, but does NOT lift off the ground. Since at this maximum deceleration limit there is no weight on the rear wheel, there is also no braking that can be done by the rear wheel. So maximum deceleration also implies 100% front brake usage.
The nose wheelie picture I showed was to illustrate an extreme of what no weight on the rear wheel looks like. In practice, the rear wheel would be lifted only slightly off the pavement.
Maximum braking can be
calculated by assuming no weight on the rear wheel. It is not the
only way that maximum braking can be achieved. The maximum deceleration is still only 0.5g for a wheel on dry payment. If you load the rear wheel
and use the rear brake, you can get up to that maximum out of both brakes. The rear wheel only contributes about 0.1g of deceleration but that is still 20% of the total.
Originally Posted by
zzyzx_xyzzy
On dry pavement maximum deceleration is strictly limited by the CG location (which you should remember from that very same passage of Bicycling Science, since their 0.5g figure is derived from a typical CG location with respect to the front wheel contact patch in the first place); if you are looking at the effect of CG shifting on max. deceleration you should calculate max. deceleration from CG location and not "assume" max deceleration.
Which is to say, shifting weight down and back INCREASES the 0.5g max.decel. figure .... but that maximum deceleration for any given CG location is still only achieved when using 100% front brake.
The only exception is if the surface you are riding has limited traction, in wet or off road conditions. (very specifically: if the coefficient of friction between tire and pavement is less than the ratio of CG setback from front wheel divided by CG height off ground). In that case if you are not shifting weight you will do best by mixing front and rear brake. but if you do the physics you will still find something surprising: that even more stopping power can be had by shifting weight FORWARD (so that CG setback/ CG height = coefficient of friction) and front braking only.
It's been a little while since I've looked at Bicycle Science but I'm fairly certain that the value of maximum deceleration he uses is 0.5g even with body shift. The body shift only loads the rear wheel so you can squeeze some braking power out of the rear wheel.
As for a shift of weight forward giving you better stopping power, this is just wrong. Slide forward on any bike while braking and you'll skid the rear tire. If you want long skids, you do exactly that. Any 10 year old knows this.