Threshold braking
Threshold braking is braking at the very edge of the tires’ grip, just short of locking the wheels or triggering heavy ABS intervention. A tire stops the car hardest when it is still rolling with a small amount of slip, not when it is skidding. The skill is reaching that peak quickly, holding it, and easing off smoothly before you turn in.
- Peak braking happens with the tire still rolling, slightly slower than the road. A locked tire stops you less well and can’t steer.
- Squeeze the pedal on firmly and fast, but don’t stab it. The car needs a moment to settle its weight onto the front tires.
- ABS protects you from lock-ups; it doesn’t find the threshold for you. Lean on it constantly and you lose feel and time.
- Keep your braking point fixed while you learn. Brake harder first, later second.
Why the limit is just short of locking
A braking tire turns slightly slower than the road passes under it. That difference is called slip. Grip rises as slip increases, peaks at a fairly small amount (often somewhere around 10–20% on typical tires), and then falls away. At 100% slip the wheel is locked and skidding.
A locked tire has two problems. It gives less stopping force than a tire at peak, and it can’t steer, because a skidding tire goes wherever the car’s momentum takes it. It can also flat-spot the tread in a single stop.
Threshold braking is driving right at that peak. On good street tires that’s often around 1 g of deceleration (about 22 mph lost every second, or roughly 35 km/h); on track tires it can be more.
Each tire can only make so much force. Brake hard and there's little left for turning. Blend one into the other (trail braking) and you stay near the edge of the circle the whole time.
Building pressure: the shape of a good stop
When you hit the brakes, load moves forward onto the front tires. That takes a fraction of a second. If you stab the pedal, you ask for full braking before the front tires have the load to deliver it, and they lock or the ABS chatters.
So the first part of a good stop is a firm, fast squeeze: from nothing to near-peak in a quick but progressive motion. Then hold steady pressure while the car slows. Near the end, ease off gradually so the front doesn’t spring up suddenly at turn-in. That release is also where trail braking begins, later on.
In a car with a lot of downforce, available grip falls as speed falls, so the pressure has to come down through the stop. Most track-day cars make little downforce, so for them the hold is close to flat with a smooth release at the end.
1,400 kg car, 0.5 m centre of gravity, 2.6 m wheelbase, 1.55 m track width. More load means more grip, but not proportionally, so pairs of tires lose total grip as load shifts.
With ABS and without it
ABS watches wheel speed and releases brake pressure on any wheel that’s about to lock, many times a second. On a modern system that keeps you near peak and lets you steer. But ABS reacts to a problem rather than preventing it. If it’s working hard on every stop, you’re over the threshold and relying on it, and on some older or road-focused systems that costs distance and heats the brakes.
A good target with ABS is to brake right up to the point where you feel it just begin to work, and back off a touch. You’ll feel it as a buzz or pulse through the pedal.
Without ABS, the warning is a lock-up: the steering goes light, you may hear a squeal or see smoke from a front tire. Ease the pedal pressure slightly (don’t jump off it) until the tire rolls again, then hold. Lock-ups usually start at the front because that’s where the load and most of the brake force are.
How to practise it
Brakes get hot fast. Bed your pads before the event, take a cool-down lap after hard sessions, and if the pedal goes long or soft, back off and come in.
- 1Ask your organizer or instructor where it’s allowed. Many HPDEs and car-control clinics run a braking exercise in a paved area with cones. Never practise on public roads.
- 2Start at a moderate speed with a fixed braking cone. Brake firmly and note where you stop.
- 3Repeat, squeezing to the same peak slightly faster each time. Feel for the edge: the first hint of ABS or a tire starting to squeal.
- 4On track, keep your usual braking marker for a few sessions and work only on pressure. If you stop short of the turn-in point, you have room to brake later.
- 5Only then move the braking point, a car length at a time.
FAQ
Is threshold braking the same as an emergency stop?
The physics is the same, but on track you also release smoothly and set up the corner. In a real emergency on the road, with ABS you simply brake as hard as you can and steer around the hazard.
Should I brake with my left foot?
Most HPDE programs teach right-foot braking first. Left-foot braking is a separate skill; ask your instructor before trying it on track.
Why does my car stop worse later in the session?
Usually brake fade from heat, or tires going off. A longer, softer pedal suggests boiling fluid. Brake earlier, cool the brakes and have them checked before going out again.
How do I know I’m at the threshold?
With ABS, it just starts to intervene. Without it, a front tire is on the edge of squealing. If you never feel either, you probably have more to give, and your instructor can help you find it.
- The racing lineThe racing line is the path that lets you carry the most speed through a corner and out onto the next straight. How turn-in, apex and track-out fit together.
- Trail brakingTrail braking means easing off the brake progressively as you turn in, instead of finishing braking in a straight line. Why it works, when to learn it and how to practise.
- Oversteer vs understeerUndersteer is when the front tires lose grip and the car runs wide; oversteer is when the rear lets go and the car rotates too much. Here’s how to tell and react.