Brake bias question

Can someone explain what his happening when I move brake bias back?

Specifically, as bias goes back, braking stability goes away. If you stomp it, you will find the rack wants to pull left or right as the brakes approach lock. Even with dead straight braking, basically.

It doesn’t take much change for this to happen. Just a couple percent change. Is this normal?

What am I looking for behaviorally in the car when I try to adjust bias? Correct not incorrect characteristics.

You’re moving the braking pressure toward the front or rear of the car. Too much front bias and you lose braking power since you’re not using the rear brakes fully, and you also risk locking the fronts when braking hard or trail-braking. Too much rear bias and you lose braking power since you’re not using the front brakes fully, and you risk locking the rears when braking hard or trail-braking.

You want it balanced enough that you’re using all four corners while still being controllable.

Generally, more front bias is going to be easier to drive consistently because it’s easy to see the front tires start to lock and adjust your brake pressure accordingly. It’s harder to run more rear bias because if a rear tire locks, you’re in for a ride pretty quickly. Much harder to catch and save. Plus, it’s easy for the rears to get light on turn-in if you are trail-braking.

iRacing sets most cars up to be a little more front biased so it’s easier to drive, but you can definitely go faster and brake later if you can learn to control the car and master your threshold braking with a little more rear bias. Many of the cars in-game have the ability to control bias on the fly as well. Bind that adjustment to some buttons/keys and go out for a practice session, get the tires up to temp and slowly move the bias rearward until it becomes un-drivable. This can be an important adjustment throughout a run as well, as tires fade and fuel goes down.

In GT4 for example, I’m almost always starting my brake bias at one point more forward and once the tires get hot, I start moving bias backward in 0.5-1% increments until I get it to the limit of what’s drivable.

Thanks. I did play with it and move bias back (I think). Going from 50 to 40 would be to rear, yes?

The kart got very unstable with just 2 percent change. I was surprised at how little change it took.

Majority of setups will have slightly more front bias. When braking your weight transfers towards the front, so having more braking power is beneficial. But it isn’t an exact science. One bias percentage won’t be ideal at every track nor for every driver. Tracks with more flowing corners will benefit from more reward bias. Tracks with big, straight, brake zones will benefit a more forward bias.

On ABS cars brake bias can shift tire temperature to help with handling issues. For example, if you’re wanting to warm up the front tires, shift the bias forward. The ABS will sort out the lock up side of things but it’ll work the fronts more to bring up temperature.

Also, 2% is a pretty big swing. We were testing today at Sebring and we’re making 0.5% bias changes at a time.

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Thanks for that.

What you say makes sense and I think I intuitively understood that. Interestingly, Long Beach has two big braking zones that would really benefit from more fromt bias but also had a number of odd 90’s that seem to rely on downforce rather than braking. People losing back end is very common on many turns, presumably lift off oversteer.

Anyways, I can’t seem to find a braking situation that behaves in the big braking zones while not being a savage in the others.

It’s an interesting challenge.

TJ and Zach alluded to this overall, but I’ll add that I also make some adjustments for individual corners at some tracks - shifting the bias back for heavy straight-line braking corners, and moving it forward for turns with lots of trail braking. For example, the last chicane at Suzuka is a very heavy braking zone that is mostly straight line, but running a bias that works well there can really upset the rear in T1 where there’s a lot of trail braking, so I always shift it forward about .5-1% on the front straight.

I’d make sure to bind some increase/decrease bias controls on your wheel and play with it a bit.

Wait, you guys mean on the fly? That would work, actually. Dial it forward for 1 and the back straight. I am guessing g that might be doable without crashing.

I don’t always make those types of adjustments on a corner by corner basis, but sometimes. Definitely worth a try. Also for longer races I’ll gradually shift it one way or the other as the tires wear/heat up and balance changes. I find that a lot of cars can tend to get more oversteer-y as a long race develops, so I often end up shifting the bias forward a little bit 1 or 2 times over the course of the race. For oval races it’s usually the opposite - those cars push more and more over time, so I’ll gradually move the brake bias back over the course of a run.

That’s a great point about adjusting bias to combat wear related oversteeriness. That’s certainly doable on fly, going down main straight.

Here’s Schumacher making brake bias adjustments in almost every corner at the busiest track in the fastest car.

Don’t forget that the stiffness of the rear axle plays a role in braking.
Because the rotor is on the left side of the kart,so there is a difference in torsion
in the rear axle between left and right.It is not hard to understand that a softer axle has a different torsion than a harder axle and you can notice that in braking.