Variable ABS

I was watching a rally and noted that the driver was able to turn a knob on the dash and change how agressively the antilock braking system would act. Apparently the driver could adjust it from no ABS intervention to where it was active almost every time he used the brakes. Does anyone know how the race teams get the ABS to be adjustable? Do they use a special controller, or are they just manipulating the input signal? Is the technology to have adjustable ABS available on the open market or is it strictly proprietary? I've seen some ECU's that allow for the type of variable traction control I've also seen in rally racing, but that is a different topic...

I didn't know they were usieng ABS in rally cars, are you sure it wasn't the centre Diff, or just brake bias?

Well ABS basically works by sensing wheel lock up and cutting braking momentarily to restore proper wheel rotation and repeating the process. Given that, I'm not quite sure how you can really have much more than an on or off setting for ABS. If you were seeing him change the ABS settings, the driver could merely "turn a knob" telling the computer at what point of lock up or braking force the ABS is allowed to be activated.

I didn't know they were usieng ABS in rally cars, are you sure it wasn't the centre Diff, or just brake bias?

My money is on the brake bias. Rally drivers would hate ABS.

I was thinking about it at school, and I think that since ABS works by sensing the wheel speed differences and cycling the abs module at a predetermined speed difference. I've heard that a 993 porsche system will start working at 4% difference, so maybe the knob just changed the control map to allow for larger or small differences.

Its no hard to change the setting on the ABS, all you need is access to what ever chip or software controls the modulation.
With the right software and controller interface you could adjust any number of different variables.

However, I still doubt it was something you saw fitted to a Rally car.

some rallies occur on pavement in places.
could be he was adjusting for known dirt conditions, or pavement.
on pavement, it would be beneficial to have abs.
on really hard clay, a little abs might help.
on loose gravel or dusty pavement, abs is a big NO-NO.
could he maybe have been adjusting TCS or braking bias?
this seems more likely, but if u say abs...

some rallies occur on pavement in places.
could be he was adjusting for known dirt conditions, or pavement.
on pavement, it would be beneficial to have abs.
on really hard clay, a little abs might help.
on loose gravel or dusty pavement, abs is a big NO-NO.
could he maybe have been adjusting TCS or braking bias?
this seems more likely, but if u say abs...

ABS is so people who panic can still steer while they brake.
It has no place in motorsport, let alone a rally car.

on pavement, it would be beneficial to have abs.


Most rally racers use drifting in corners, whether its asphalt or dirt. ABS wouldn't work too well while attempting to drift a car around corners.

correct, but if there was abs on a rally car, most likely it would be used on pavement.
not saying i'd put abs on a rally car, but it was there, and he asked why, i gave my opinion.
and thankyou but i understand the purpose of abs.

i still think it was a brake bias controller.
makes more sense

correct, but if there was abs on a rally car, most likely it would be used on pavement.
not saying i'd put abs on a rally car, but it was there, and he asked why, i gave my opinion.
and thankyou but i understand the purpose of abs.

i still think it was a brake bias controller.
makes more sense

In motorsport ABS = Absolute Bull Sh*t.

Actualy ABS was banned from F1 because it generated dangerously high G forces under brakes. There was concern the drives could black out, or suffer eye damage (high negative G forces do bad things to the blood flow in your skull).


I would be prepared to say, that on a sealed surface any modern ABS system can out brake even the worlds best drivers. Quite simply a computer can monitor and controll wheel speeds far more accuratly than the human brain can.

Of course on a loose gravel surface being able to lock the brakes is very important, as it lets the tyre dig down through the loose material on top, into the harder packed base underneath. In not yet aware of any ABS system than can make the sort of judgement needed to know that.


Modern Rally cars are exclusivly AWD or FWD, there is very little powersliding done now day, only the odd bit of hand brake is used on very tight corners.
Fitting them with ABS for the tarmac stages would make them a lot faster, however Rallying to my knowledge has only ever benifited from Launch control and active centre diffs as computer controlled performance aids.
The rest is left very much up to the Human element of Motorsport.

how about we look at this question from the point of view that we KNOW that rally cars often have fitted, a variable diff or brake bias control?
:dunno: