Adjustable Brake Bias

[sapix @ RHIT]

I was just wondering what everyones thoughts were on some sort of automated system that would adjust the brake bias of a car depending on the pressure applied to the brake pedel. The controller for this could be thrown onto an ABS controller and I know they already have valves that change the brake bias, and some of these can be adjusted from inside the car, so why not just have a computer do it so it could make it into production? Are there any downsides to this?

[psychic_mechanic]

I don't see any reason on a street car to change brake bias on the fly. Once it is set for your car, tires, and weight distribution, it doesn't need to be cahnged until you change the car. Using the pressure applied to the brake pedal would not be a good way to adjust it either.

I had thought about doing something close to this using the isolation valves in the system to disable the front front brakes temporarily in a FWD rally car. A momentary switch on the shifter could remove your front brakes from the hydraulic circuit, then by pressing the brake pedal you would just be using the rear brakes. I thought this would be easier than trying to shift and work an e-brake with the same hand.

-Vinny

[sapix @ RHIT]

How much of a benefit does an adjustable brake bias offer to a race car? I realize in street usage its not going to be necessary, but wouldn't it allow braking distances to be shortened slightly. It wouldn't be that hard to do if you were making an Anti-Locking Brake System.

Also, why wouldn't using the pressure applied to the brake be a good way to modulate the brake bias. If the pedal is pressed harder there is going to be more weight shifted to the front, therefore the front brakes will need to work harder to maintain the same braking force as the rears (ie using all the available grip).

Not trying to be defensive, just asking for an explaination so I can have a better understanding.

-Thanks

[Q45tech]

When the weight shifts on to the front tires, their grip increases proportional to the weight shift.......as the contact point rubber heats up the the extra gain goes away [depending on ambient temperature and the compounds used-tire type] as the internal and contact point temp goes beyound 160F.

ABS solves all these complex equations. What one needs is a computer program to [count/graph] how many ABS back offs per individual wheel occurs in stops...........the fewer the better.

Setting bias is fun but what about when you have to brake and the car motion [go into a curve] is not straight........the weight load is different.

[psychic_mechanic]

The whole reason to adjust brake bias is too prevent one side of the car from locking up before another.

Once the proportioning valve is set to where all the tires can threshold brake at the same time, there is no need to shift bias to the front as this will only lock up the front brakes (and increase stopping distance in a non - ABS car) prematurely.

Why you might want to adjust a race car more often, is sometimes you race on surfaces with different amounts of grip, or change tires or shift weight in the car before a race. All of these would change the balance requirements, but not by huge amounts.

[Q45tech]

Unfortunately the coefficient of friction on brake pads and the thin film on rotors changes with temperature: 150-200F change is noticeable and the pads vary around the course and as they wear. You cannot assume front and rear or even side to side pads will be linear in their changes. Nor can you assume they will be the same after cooling, the next day.

Why racecars have ****pit adjustable valves.

ABS fixes all this for the street car..........each wheel gets adjustable brake bias automatically..........the early Q with common rear calipers and a ABS sensor on the input to diff [not active or TCS] is an exception, as the worst locking rear side will set the tone for both rear brakes.

[sapix @ RHIT]

Alright, I understand now. Thanks a lot. I guess trying to through all the crap in to adjust brake bias is just wasted effort. I wondered if it would be.

Are there any other cool features that could be implemented with an ABS system?

[Russ3Z]

A number of additional features are already offered on some cars which utilize the ABS system. Examples are traction control, electronic stability control, and artificial limited slip differential.

There are probably many others by now (ABS has really opened a whole new field of electronic driving aids) but its 5 AM here and i'm too tired to think of any more.