Originally Posted by
zzyzx_xyzzy
One of the points that Jobst makes is that the friction circle is really a circle and the braking and cornering forces are at right angles to each other. So if you can brake or corner at 1g, then you can combination brake and corner not just at (0.5g, 0.5g), but at (0.71g, 0.71g) -- the brake force and the cornering force make a right triangle with the hypoteneuse at 1g. Or if you want to just bleed off a little speed it hardly affects the cornering limit -- braking at 0.1 g reduces the cornering limit to 0.994g. (caveat: weight shift might affect the friction budget differently for front and rear wheels)
Motorcycles with their wide tires do tend to torque steer if you brake while leaned over, which is another thing to get used to.
Yeah, they tend to stand up when you apply the brakes, making you carve a wider curve. Always a teeth-gnashing experience to force it back down as you're jamming on the brakes.
Yes, you're correct that we have to use vector-addition to find the resultant combined vector of two forces on the friction-circle. The thing is, at the limit, you have to give a large enough buffer for +/- effects of going under or over the limit. If you're at 1g of cornering, most of the corrections will be with the throttle or rear-brake. The front would really only be used in an emergency scenario. In which case, a moderate 0.5g of braking would require backing off to 0.87g of cornering to relieve enough grip.
However, that's not enough because you have to account for the what-ifs of going over the limit. Humans aren't perfect and they tend to go over as well as under the limits. Once a tyre starts sliding, the fiction-coef. goes down tremendously from 1g to 0.7g:
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So in the case of cornering at the limit of 1g, you have to back off enough to ensure that you're not over 0.7g total just in case the braking is too much to overwhelm the friction-limit. In which case, if you want to safely brake at 0.5g in a corner, you have to back off the 1g of cornering to .0.49g in order to accommodate the braking safely.