Glossary
Brake Bias Explained: Front/Rear Percentage, Adjustment & Tuning
Brake bias is the proportion of total braking force applied to the front axle, expressed as a percentage. Because braking transfers load forward, the front tyres can take far more brake than the rear, so the bias is always further forward than the static weight distribution. Circuit cars typically run 55–65% front, adjusted with a balance bar between twin master cylinders or an adjustable proportioning valve.
| Car type | Static front weight | Typical brake bias | Notes |
|---|---|---|---|
| Formula car | 42–46% | 54–60% front | Low CG keeps transfer modest |
| GT3 | 45–50% | 58–64% front | High braking g, ABS on many modern cars |
| Touring car (FWD) | 60–64% | 68–75% front | Very front-heavy under braking |
| Speedway sedan | 50–55% | Often rear-biased or LR-biased | Brakes used to steer the car on entry |
Finding the right bias
Start a few percent forward of the calculated dynamic split, then brake hard in a straight line and listen for which axle locks first. If the fronts lock, move bias rearward one notch at a time until the rear locks or the driver reports instability, then come back forward one notch. The best bias is just forward of the point where the rear would lock.
Why bias changes during a race
Fuel burn-off usually lightens the rear, pad and disc temperatures differ front to rear, and front tyre wear reduces front grip. All of these shift the optimum. A cockpit-adjustable balance bar lets the driver trim bias lap by lap; a note of the setting at the start and end of each run is valuable setup data.
Frequently asked questions
What does one turn of the balance bar change?
Depends on the pedal geometry and master cylinder sizes, but typically 1–2% per full turn. Record the number of turns from a known reference point.
Does changing master cylinder size change bias?
Yes. A smaller master cylinder produces more line pressure for the same pedal force, so a smaller front cylinder moves bias forward.
Can brake bias fix corner-entry handling?
To a degree. More rear bias helps the car rotate under trail braking; more front bias stabilises it. It is a common driver adjustment for entry oversteer or understeer.
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