Reply to "Locating bits and pieces"

M!ke H.

I was going to write something like the following but found this. Vehicle dynamics are very complex with many variables. Low-speed, mid-speed and high-speed brake dynamics are all different. Spring rates, wheel rates, shocks, tire sizes and other things affect braking. Changing any of these things can affect how brake bias affects the overall braking. Please, if you don't understand this stuff (most people don't) ask a professional to help. When it comes to brakes there is no middle ground. Stock in good condition or consult an expert.

Below, not my words....
......Maximum braking performance occurs just before brake lockup, as a sliding tire has less grip than a rolling tire, thus tuning brake balance is all about controlling when the brakes lockup. As max performance obviously will occur when all 4 tires (& associated brakes) are doing the maximum work, an ideal brake bias is one that locks the front and rear brakes at the same time. In practice however, locking the rear tires typically result in a rapid spin, and locking all 4 wheels results in a slower spin, especially if the car is trail braking. For this reason, some “extra” front bias is normally used, because when the front brakes lockup the car remains stable (but you lose the ability to steer the car – it just goes straight) and this allows the driver time to recognize the brake lockup and reduce brake pressure to regain max braking performance and control. To tune the brake bias, pay particular attention to what happens during the braking phase and corner entry. Sudden spins in this zone often indicate rear brake lockup, while a bad push may indicate front brake lockup. Video replays or data acquisition systems can be useful in identifying this, but remember the inner (unloaded) tire will be the first to lock.

Increasing Front bias: Shown as a larger number, increasing brake bias to the front will put more braking force into the front tires. This will stabilize the car in braking zones and increase understeer at corner entry. The compromise is that with too much front bias the rear tires are being under‐utilized and overall braking efficiency will suffer. This can also cause rapid front tire wear due to front tire lockup, especially of the inside tire which is the first to lock up.

Reducing Front bias: This puts more braking on the rear tires, which, within limits, improves braking efficiency. Too much rear brake bias, though, hurts performance in two ways. First, it reduces overall braking efficiency. More seriously, too much rear brake bias, particularly if the driver is not braking in a straight line or has weak footwork on downshifts, can cause the rear tires to lock up, which puts the car in a dynamically unstable condition that can easily result in loss of vehicle control. Note that with a moderate amount of rear‐brake bias, the car will have a tendency to rotate (OVERsteer) at corner entry upon brake release......

Mike