What brake bias actually is
Brake bias — also called brake balance — is how the total braking force is split between the front and rear axles. It is written as a percentage forward: a bias of 56% means the front brakes do 56% of the work and the rear axle takes the remaining 44%.
Why always forward of 50%? Because the moment you hit the brakes, weight pitches onto the nose. The loaded front tyres can take far more braking force before they slide, while the lightened rear tyres can take much less. So every road car and race car runs the bias ahead of centre — the question is only how far ahead, and that number is the whole lever.
Forward vs rearward — stability or rotation
This is the trade every driver is really making with the bias knob. Push it forward and the car becomes calm and stoppable in a straight line, but lazy to turn: the front does the work, so it gives up first and the car runs wide on entry. Pull it rearward and the car rotates eagerly into the corner — it points beautifully — but the light rear tyres are doing braking they cannot afford, so the back gets nervous.
- Forward bias → stability, less rotation. The front locks first if anything, so you get understeer on entry — safe, but it dulls the turn-in.
- Rearward bias → rotation, less stability. The rear works harder, locks first, and the car snaps — sharp turn-in, but a knife-edge.
- The sweet spot is the most rearward you can run before the rear starts to step out — maximum rotation without the snap.
Lock-ups: read which end is sliding
A lock-up is when a tyre stops turning while the car is still moving — it stops rolling and starts sliding, so it makes far less grip and flat-spots itself. Which end locks tells you exactly which way the bias is wrong:
- Front lock-up → bias too far forward. The front tyres are overloaded, they slide, and you lose steering — the car pushes straight on just as you try to turn in.
- Rear lock-up → bias too far rearward. The light rear tyres give up, the back steps out and snaps, and the car feels unstable on the brakes.
The move is simple: shift the bias away from the end that is locking. But there is a second half — you also lock up when you ask a tyre for braking and cornering grip at the same time, beyond its limit. That is why how you trail off the brake into the corner matters as much as the bias number, which is the next section.
Trail braking — where bias makes lap time
Trail braking is carrying the brakes past the turn-in point and bleeding the pressure off as you wind in steering. It keeps weight on the nose so the front bites, and it is the phase where the car actually rotates. Brake bias is the lever that governs that rotation.
A more rearward bias keeps the rear light and willing to rotate, so the car turns in keenly as you trail off — great until it is so far back that the rear lets go. A more forward bias plants the rear and stabilises it, so the car is secure but reluctant to point. You tune the bias against how the car rotates on entry, not against straight-line stopping alone — that is where the time is.
Cold discs lie — the brake thermal twist
The bias number you dial in is only the true bias once the brakes are hot. Cold discs and pads bite less, and they bite unevenly, so on an out-lap or the first lap of a stint the effective bias and the lock-up point drift away from what you set — which is exactly why early laps feel inconsistent and easy to lock up.
As the discs climb into their working window, the bias settles to the number you chose. And if one axle's brakes run hotter than the other across a stint, the balance keeps shifting under you. So a bias change judged on a cold lap is a change judged on noise. This is why brake bias and the brake thermal window are the same conversation — you read the temperatures first, then the lock-ups.
Read it first, then move it — one click at a time
A bias move is only right once you know which end locks, in which corner, and at what disc temperature. SimRace.app pulls your full setup and a stand of specialist race engineers logs the telemetry, corner by corner — they catch the lock-ups, see whether the front or rear let go, watch how the car rotates as you trail off, and check it against the brake temperatures before they say a word about the bias knob.
And one rule a good engineer never breaks: never ask a tyre that is already sliding for more. If the rear is locking, you do not chase rotation by going further back — you move forward and find rotation elsewhere. The engineers hand you the move one click at a time, judged over a few hot laps, so you stop guessing the bias and start reading it. See how the engineers work →
FAQ
What is brake bias in a car setup?
Brake bias, also called brake balance, is how the total braking force is split between the front and rear axles, expressed as a percentage forward. A bias of 56% front means the front brakes do 56% of the work and the rear 44%. Because the fronts carry more load under braking they can take more force, so bias always sits forward of 50%. The bias number is the single lever that sets which end of the car locks first and how the car rotates on corner entry.
What does forward versus rearward brake bias do?
Forward brake bias makes the car stable and stoppable in a straight line but lazy to rotate: the front tyres take more load and lock first, giving understeer on entry. Rearward bias rotates the car into the corner and helps it point, but it loads the lightly-laden rear tyres, which lock first and make the car snap and feel nervous. Forward stabilises, rearward rotates — brake bias is the corner-entry rotation lever.
Why does my car lock up under braking?
A lock-up means a tyre stops rotating while the car is still moving, so it slides instead of gripping. If the front locks, the bias is too far forward for the grip available and the front pushes wide on entry. If the rear locks, the bias is too far rearward and the rear snaps. Move the bias away from the end that is locking, and release brake pressure as you turn in so the tyre is never asked for braking and cornering grip beyond its limit at once.
How does brake bias affect trail braking and corner entry?
Trail braking is carrying the brakes past turn-in and bleeding pressure off as you add steering. Brake bias governs that phase: a more rearward bias keeps the rear light and rotating, helping turn-in, while a more forward bias plants the rear and stabilises it but blunts rotation. Tune the bias against how the car rotates on entry, not against straight-line stopping alone, because trail braking is where the balance decides lap time.
Does brake temperature change brake bias?
Yes. Cold discs and pads bite less and unevenly, so the effective bias and the lock-up point drift away from the number you set, which is why out-laps feel inconsistent. As the discs reach their working window the bias settles to what you dialled in, and if one axle runs hotter the balance shifts over a stint. SimRace.app reads disc temperature alongside the lock-ups, so a bias move is judged once the brakes are in their thermal window rather than on a cold lap.
The setup glossary
Brake bias is one lever among several. The rest of the toolkit that decides corner entry and balance, one page at a time: