Understanding Brake Bias – BoxThisLap.org

Braking and braking is one of the most important elements and actions in the car. Calibrating it and looking for balance is a major task for engineers and racers. All racing games and simulations have implemented this feature and knowing how to use it is a great asset to understand how the cars work and how to make them faster. Let’s see what iRacing Wikidot has to say about this.

This is an adjustment of the relative amount of hydraulic pressure applied to the front brake calipers and pads compared to the rear brake calipers. This is required to optimize braking performance when a car slows down, load transfers to the front tires, which generally improves their grip while reducing grip at the rear of the car. In addition, the size of front and rear brake discs, pads and piston area are often different, requiring different amounts of pressure for the same braking performance. The goal is to adjust the ratio of braking forces between front and rear (brake preload) to maximize overall braking efficiency. If the brakes are still applied when the car turns into the corner, adjusting the brake preload will also affect the car’s turn-in balance.


Brake Preload – Expressed as a percentage. This indicates the relative amount of brake pressure being applied to the front brakes by the master cylinder(s). For example, 52% would mean that the front brakes would receive 52% of the brake pressure and the rear brakes would receive 48%.

tuning tips

Maximum braking performance occurs just before the brake locks up because a skidding tire has less grip than a rolling tire. Therefore, tuning brake balance is all about controlling how the brakes lock up. Since maximum performance obviously occurs when all 4 tires (and associated brakes) are doing their maximum work, an ideal brake bias is one that locks the front and rear brakes at the same time. However, in practice, locking the rear tires typically results in a fast spin, and locking all 4 wheels results in a slower spin, especially when the car is coasting braking. For this reason some ‘extra’ front bias is usually used as the car remains stable when the front brakes lock up (but you lose the ability to steer the car – it just goes straight) and this gives the driver time to brake detect override and reduce brake pressure to regain maximum braking power and control. To tune brake bias, pay special attention to what happens during braking and corner entry. Sudden spin in this range often indicates a rear brake lockup, while a bad bump can indicate a front brake lockup. Video recording or data acquisition systems can be helpful in identifying this, but remember that the inner (unloaded) tire locks up first.

increasing the preload: Displayed as a larger number, increasing forward brake bias puts more braking power into the front tires. This stabilizes the car in braking zones and increases understeer on corner entry. The trade-off is that if the preload is too high, the rear tires will not be fully utilized and the overall braking effect will suffer. This can also lead to rapid wear of the front tire due to the front tire locking up, especially the inner tire that locks up first.

Reducing the preload: As a result, the rear tires are braked more, which improves the braking effect to a certain extent. However, excessive rear brake preload affects performance in two ways. First, it reduces the overall braking effect. More seriously, too much rear brake preload, especially if the driver isn’t braking in a straight line or has weak footwork when downshifting, can cause the rear tires to lock, leaving the car in a dynamically unstable state that can easily do so can result in loss of vehicle control. Note that with moderate rear brake preload, the car will tend to spin (oversteer) on corner entry when the brake is released.


Brake bias settings do not affect other garage settings. However, they affect tire wear (due to brake lock-up) as well as stability and vehicle balance during braking.

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