Factory brake pad friction coefficient?

[spuggy]

Anyone know the friction coefficient for the factory brake pads, either Textar or Mintex?

Trying to work out the "real" front/rear torque ratios for braking force (as opposed to simply the hydraulic ratio), and almost all the manufacturers except EBC seem to be pretty coy about providing hard numbers for street pads....

[petevb]

As long as you're using the same pads front and rear are you sure you care? Only if you're also modeling the effect of the proportioning valve I'd assume.

The tough part is the c/f isn't a number, it's a curve- temperature, drilled rotors, etc move the actual values around slightly. Pagid used to quote actual c/f numbers for their pads, but now they just quote relative figures.

If I had to guess I'd put stock pads around .45, but that's only a guess.

[spuggy]

Originally Posted by petevb

As long as you're using the same pads front and rear are you sure you care?

Yup, absolutely positive

I'm trying to determine to what extent I can offset the front bias of the 996 or 996TT caliper set by using (e.g.) EBC Yellowstuff pads in the rear and something less grabbier in the front.

I can actually tolerate quite a lot of rear bias (lowered, stiff springs, 40/65 LSD, fat rear tires), so I'd prefer to get more work out of the rear brakes.

Objective is a good balance.

Only if you're also modeling the effect of the proportioning valve I'd assume.

Don't have one of those.

The tough part is the c/f isn't a number, it's a curve- temperature, drilled rotors, etc move the actual values around slightly. Pagid used to quote actual c/f numbers for their pads, but now they just quote relative figures.

Yeh, EBC quote their figures at temperature gradients, which helps a lot.

Some (most) manufacturers aren't even quoting an average figure for street pads...

If I had to guess I'd put stock pads around .45, but that's only a guess.

Yeh, trying to keep the actual guessing to a minimum...

[petevb]

Originally Posted by spuggy

Yup, absolutely positive

I'm trying to determine to what extent I can offset the front bias of the 996 or 996TT caliper set by using (e.g.) EBC Yellowstuff pads in the rear and something less grabbier in the front.

Got it.

I've mixed pads before to increase rear bias, in my case using Pagid blacks in the rear and yellows up front. This insured that both pads had similar temperature performance, and thus the brake balance stayed consistent at the brakes warmed up.

In my experience certain race pads can lack "bite" from dead cold, despite what the friction graphs say, and they obviously increase friction as they get warmer. A street pad will stay more stable and then fall off earlier when it gets hot. Thus mixing a race pad in back with a street pad in front could result in rear-lockup as the brakes heat. Thus while your theory is sound and clearly works I'd suggest you ideally look into pads of higher and lower friction from a single manufacturer, which is likely to insure the testing is consistent and performance is well matched.

[KTL]

Porterfield provides torque curves for their pads. R4-S is a good street pad

http://porterfield-brakes.com/images/portrace2008_11_06_02_41_04.pdf

Call 'em up and they'll give you all the tech info you need.

[moneymanager]

Resurrecting an old thread.
If I want to experiment with different pads front and rear for track use, would i start with a grippier pad at the front or at the rear? Or perhaps I should ask what result I might reasonably expect to get from trying the grippier pad at the front vs the rear?

[KTL]

You can end up with too much front brake if you use higher friction fronts. That is, assuming your brake bias is fairly good to begin with. Too much front makes for a sucky handling racecar in my experience. Doesn't let you aggressively brake like you need to, in order to make good time.

As an aside, I moved my bias rearward by installing larger piston-ed rear calipers and it made a fantastic difference. I had 993/S4 fronts and 930 rears. 245 front tires, 275 rear tires. Forward bias was very detectable and found it made me much to tentative on the brakes to avoid lockup (front). Installed the larger 993 rear calipers and what a difference the slight increase in piston size made by shifting the bias rearward a bit.

That said, you could experiment with higher friction rears to shift some bias rearward. Just have to be careful to not go to far or else evil tail-swapping can arise when the rears lock before the fronts. Only way to know is to do some testing in a safe enviro.

[moneymanager]

Thanks Kevin. I am trying Raybestos race pads at the front this weekend with Ferodo 2500's (a good weekend DE pad) at the rear. I think I probably need to swap the rears for something with a bit more bite but we'll see. I have not previously run with pads that could lock up the fronts so this will be a learning experience.

[wwest]

Given the dynamics of this issue/question it might be a simpler effort to just add ABS capability to only the front (or rear only)...???

On the other hand our 2000 Chrysler T&C F/awd minvan had a unique solution. A set of valves, one for each rear wheel, that allowed FULL hydraulic braking pressure up to a point, and then modulated/limited the pressure rise level/slope once that point was reached.

Might be a rather easy retrofit.

[KTL]

With my former 993 front, 930 rear setup I experimented with pads to help reduce the front bias. I had Hawk HT10 on the front and Performance Friction PF97 on the rear. Seemed to help a bit as the car was able to be driven more aggressively. Still, I was not happy with the balance. Always seemed to be tentative on the brakes to avoid lockup, compared to my street car where I could really lay into the brakes on the track.

Once I made the switch to the 993 rears, it was a considerable difference. I could brake much more aggressively w/out locking up the fronts.

I think the Raybestos front (ST43?) and DS2500 Ferodo rear combo will take you in the front bias direction. Plus i've found that the DS2500 really wears out fast when temperatures rise. Their graphs indicate the 2500 is a light duty track pad



Sure the Ferodo pad will be doing less work since the front compound has the higher friction level. So the Ferodo shouldn't necessarily wear out from excessive heat. But I think it will be doing less than its fair share of work and the front bias will not give you good results.

[moneymanager]

Interesting about the 2500's. I've raced them many times although Ferodo advises against it. In early days I had M calipers all around. THe rears would last for 30-40 events; the fronts were toast after 8-9. I then added wide A calipers at the front. Front wear dropped 50%. Bigger pad area contributed, but I think main benefit came from wider 24mm rotors. Heat is a huge deal.
My experience all along is that my rear pads are doing very little of the work. So I think your conclusion that my ST-43 fronts will be too much for these rears is probably spot on.
(An hour later, after staring at all this for a while, I've decided what I've been thinking of doing is stupid. I need to move first to the ST43's at the rear and the front. That will at least ensure that the front/rear bias will be about what the factory intended. After I get comfortable with that set up I can begin to think about whether a bit more bite from the rear pads would be advisable. ST 43's on order.)

[KTL]

Yep heat is indeed huge with respect to pad wear. On his '87 3.2 a friend installed some modestly larger rotors & small Brembo calipers up front (VCI 964 kit like this 911 Brake Upgrades using 964/944T calipers) and left the stock rears in place.

Previously he'd burn through a set of pads front & rear in about 8-10 track days. When he changed to the bigger fronts, and also got some air to them via bumper ports (IROC bumper) and hoses to the rotor backing plates, his pad wear was reduced significantly. Pads now last last at least three times longer now and no worries with flushing brake fluid before each event. The rears hardly wear at all now.