What braking instability actually is
Under braking, weight piles onto the front and lifts off the rear. If too much brake sits at the rear, or the coast diff barely locks, or the rear is too stiff to keep its tyres loaded, the rear axle loses grip exactly when you need it planted. Add trail braking — carrying the brake into the turn — and a marginal rear becomes a spin.
When the wriggle becomes a sudden bite — see snap oversteer.
How the engineers diagnose it
Instability on entry has a short list of causes — the engineers work them in order of size:
- Brake bias — rear lock-ups or a rear that walks under straight-line braking is bias too far rearward. Move it forward and re-test; the lock-up trace shows which axle gives first.
- Coast differential — instability that appears only when you trail the brake into the corner is the coast side of the diff: too open lets the inside rear spin up, too locked drags the rear straight and unsettles it.
- Rear platform — a rear too stiff (springs, rear ARB) or too low can’t keep both tyres loaded over bumps under braking. Soften the rear or raise it a touch and the axle settles.
Stability on entry is the foundation of a fast lap — you can’t brake late into a corner you don’t trust. One change, three laps, corner by corner. See the glossary and the setup guide.
The levers that cure braking instability
Biggest lever first — the brakes and diff, then the rear platform: