Brake bias vs. Downforce

[knobosaurus]

This has been racking my brain for a while now guys. Can someone give me some insight?

My understanding is as follows:

Increasing brake bias means the front brakes get more braking force from the master cylinder than the rear. By ramping up the brake bias too far, the rear will lose a lot of its traction as the weight transition during braking will predominantly sit at the front. Decreasing rear contact patch and weight and Hence decreasing the overall braking efficiency. My understanding tells me we want an even and consistent braking experience to reduce wear on both the front and rear so by throwing on front and rear wings, we can increase the downforce on the rear and front to help maintain relatively even weight distros. By having too high of a downforce, we become limited on the straightaway so we would want to minimize that while also having as much as we can in the corners to maintain contact amd traction.

I know that the setup will depend on drivetrain so let's say we have an s2000. Can we decrease front downforce to help achieve speed but ramp up the brake bias to help cornering entry. Or will this just result in more understeer? I know things like this can be hard to predict on track so what are we looking at theoretically?

[ChargeR]

You're heading in the right direction but I think you have some misconceptions.

Brake bias is a scale that goes both ways. In general brake bias would be defined as the difference in braking torque applied to each end of the car when you step on the pedal. You could also talk about hydraulic brake bias, as in the difference in hydraulic pressure between the front and rear brake circuits (disregarding the bias effect of the caliper piston size and disc size), but that isn't important here. You can have the bias more frontward ie. more braking torque at the front, or the opposite, with more at the rear. The overwhelming majority of cars have brakes biased toward the front.

You're right that incorrect bias will decrease the overall braking efficiency, as with incorrect bias one end of the car will lock tyres before the maximum deceleration limited by the tyres has been reached. Changing the bias in no way changes the maximum possible deceleration, which is limited by the tyres and the vertical force applied to them.

So in your example S2000, lowering the front downforce would make braking performance worse. Less braking torque could be applied at the front before the tyres would lock, because there is less vertical load on the tyre (car static weight + aerodynamic downforce + load transfer due to braking) compared to if the front end of the car had an equal amount of downforce as the rear. Increasing vertical load on a tyre increases it's maximum grip. No matter what you do, adjusting the brake bias will not make it possible for the car with less front downforce to match or exceed the performance of the car with even front/rear downforce. The latter car simply has more grip available as there is more total vertical load on the tyres.

Then once the driver tried to turn the car into the corner, the car would understeer unless other handling corrections have been made for the lack of front downforce.

I can draw some diagrams if it would make the situation clearer.

What I think you are trying to get at is that you correctly think that a vehicle with even front to rear load on the tyres (5F0/50R) under brakes will have better braking performance than an unbalanced car (eg. 70F/30R). However the only way to achieve this is to have a rear bias static, ie. an NSX or a rear engined Porsche.

[knobosaurus]

Logical response. Makes sense to me. Thanks for explaining it in easy to understand terms. I say a 50:50 setup is the setup I'll most likely pursue based on your advice.

Cheers.

[ChargeR]

Yep you're right, the tyres will always develop the most grip when they're evenly loaded which is why the 50/50 weight balance is ideally best for cornering (not braking though). When you add downforce though, the general rule is to match your downforce distribution with your static weight distribution ie. a 60/40 FWD car would want 60% of the total downforce on the front axle, 40% on the rear. This gives the most consistent handling as speed increases, but generally in a FWD car the downforce is biased toward the rear because 1) these cars tend to be set up mostly oversteery at low speed 2) other tyre and suspension effects tend to make all cars more oversteery at high speed.

[sleepingperformance]

In regards to weight distribution, too my understanding, it was always better to have a slightly front heavy car (55/45) as when you accelerate in a corner and weight shifts to the rear, this would cause the car to become neutral (50/50) where as if it was 50/50 from factory and you start to accelerate mid corner, it would become 45/55. Please correct me if I am wrong, but this is my understanding of dynamic balance

[munkaii]

In your situation Josh, a front heavy car is OK for corner exit as the F/R weight transfer on exit will become neutral. It however, will be less effective under braking. There's always a compromise.