Different Pads On Front & Rear

[HyperGSX]

Is it bad to run a different rotor/pad combo on the front and rear brakes? I have some cheapy Autozone pads and rotors on the rear and I am upgrading to Powerslots and MetalMasters on the front. Is this not recommended or is it okay?

 

[3literpwr]

Is it bad to run a different rotor/pad combo on the front and rear brakes? I have some cheapy Autozone pads and rotors on the rear and I am upgrading to Powerslots and MetalMasters on the front. Is this not recommended or is it okay?

Its fine.... Lots of road and rally racers do it all the time to get the setup that they want...

larry
#622 scca club rally

 

[doodie]

rear brakes don't do much anyways. You'll be fine.

 

[HyperGSX]

thanks for the advice guys

 

[jtmcinder]

Its fine.... Lots of road and rally racers do it all the time to get the setup that they want...

Yeah, but on a lowered and stiffened car, they are usually moving bias to the rear. If the original poster has a stock suspension, then he'll be about breaking even ... more front bias, but better front brakes. If he has a lowered and/or stiffened suspension, then he's doing the exact opposite of what he should.

Aren't MetalMaster rears about $45? Com'on. We're talking about the things that keep your car from smashing into things.

- Jtoby

 

[Defiant]

Yeah, but on a lowered and stiffened car, they are usually moving bias to the rear. If the original poster has a stock suspension, then he'll be about breaking even ... more front bias, but better front brakes. If he has a lowered and/or stiffened suspension, then he's doing the exact opposite of what he should.

WHAT? Lowering and stiffening are going to displace the godawful boat anchor at the front of the chassis and cause all Physics to enter Bizarro World?

I doubt you could do much to a DSM to get rear braking into the picture for as much as 20%, short of racing in reverse all the time.

Meanwhile, the stewards at LeMans may not allow different brake pads front-to-rear, but even then it'll be more an issue with your sponsor than the car.

You'll be fine on the street.

 

[ACM]

Defiant,
pick up a copy of Carrol Smiths' "Tune To Win"It explains the physics of weight transfer very well.

Part of the weight transfer formula is the height of the CG above the ground. The lower the CG the less weight transfer - that applies fore, aft, and laterally.

If I can find my copy I'll post the formula.

Charles

P.S I routinely get my 95's vented rears too hot to touch when I'm autocrossing. Not as hot as the fronts though

 

[jtmcinder]

Oh, com'on, Chuckles, you don't need no stinking book. Take the CG height and divide it by the wheelbase and multiply by acceleration (in gs) and mass. It's the same as lateral transfer (CG height divided by track times gs times mass).

Defiant: when less weight transfers, you have relatively more rear grip when braking, at least compared to before. So, to keep all four tires at their limit when braking, you need to move some braking bias (as measured in torque, for you purists) to the rear. So, on a lowered DSM, you want to either soften the decompression ratio, up the mu of the rear pads, or increase the rear rotor diameter.

Take a look at some recent magazine tests of braking systems. I recall one case where upgrading the fronts INCREASED braking distance. Fortunately, the writer knew why and said so: the car was now so front-biased that the rears where no longer helping to stop the car.

This is why working with someone like Todd at TCE is so important when planning a brake upgrade. Todd knows how to keep the bias correct and - if you ask - he can help you to shift the bias around. (No, I don't work with Todd - in fact, we argue a lot on the web - but I still can recognize someone smarter than I when I read what he writes.)

However, there is one other complicating point that often gets ignored. You actually do not have to do anything crazy like change the prop valve in order to shift some bias to the rear. If you merely up the pads' mu (i.e., front AND rear - for you NABR-types, the placement of that apostrophe was on purpose), then you will shift some bias to the rear. What? you say. How is that possible? Answer: you will now be spending more time below the cut-off point in the prop valve. (The cut-off point is where the prop valve stops letting the rears get the same pressure as the fronts and begins to apply the decompression ratio.) So the rears will be getting more line pressure relative to the front, which shifts some bias to the rear.

In short, if you are not cooking your fronts road racing, there is really no need to upgrade your brakes (assuming 2G AWD big brakes to start with). Just up the pads with Metal Masters (for non-LFBers) or R4-Ss (for the serious) and your lowered DSM will brake as well as you need it to. (See, I obviously don't work for Todd.)

- Jtoby

 

[ACM]

Quoting Carroll Smith simply precludes any discussion on the accuracy or validity

Charles

 

[Defiant]

Bah, math. Voodoo hooey. Come back when they figure out Pi.



What's going on in an AWD DSM with its viscous torque distribution during braking? If one end locks, will it lock them all?

 

[jtmcinder]

Sorry for the slow reply. I just found this thread when doing a search.

Yes, a VC is a two-way limited-slip device, so it also steps in when one wheel locks up (just as it steps in when a wheel spins under power). This is one of the reasons why people with center-diff controllers (e.g., the DCCD on an STi) often put the car in full lock for rallycrossing. They want to use the center diff as a back-up to the anti-lock system.

- Jtoby