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TOPIC: Some Brake Questions

Some Brake Questions 2 months ago #83194

  • DavidNJ
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There is some info in the threads, but many are quite old.

My questions:

1) Do all Spec E30s run brake cooling ducts to the front brakes? I've seen several links to kits for that.

2) What brake pads are commonly used? I've seen some references the Hawk HT-10, but can't imagine anyone would be using those now; Hawke has several pads that supersede them. There are also great pads from PFC and others.

3) Are the same pad compound used front and rear? For example, in Spec Miata often DTC60s are used in front and DTC30s with a lower coefficient of friction are used in the rear to create more front brake bias.

4) There are two different brands of brake caliper used in E30s. Is the Girling or ATE used in Spec E30s or does it even matter?

5) Do all Spec E30s use ABS? Is there a difference in the different model years? Does the ABS ever cause a problem by preventing the driver to lock the wheels in a spin?

Thanks,

David

Re: Some Brake Questions 2 months ago #83195

  • Ranger
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Most, but not all cars have brake cooling set up. Most years I had brake cooling set up, but I'm not convinced it was useful. Our itty bitty brakes cool pretty fast.

Few use HT10's. Those are kinda old school. IMO most of us use Hawk or PFC. #3 is prob Carbotech. Hawk and PFC make good pads for us and have nice contingencies. See Bimmerworld for PFC pads. Hawk DCT60/70 and PFC 01/06/08.

Most of us use the same pad all around. I'm an oddball and put higher bite pads in the rear. Our rear brakes don't do a helova lot because the slave piston is small and then there's the bias valve. I certainly wouldn't suggest creating even more front bias.

Most of us use ABS. Those that don't use ABS don't take long to recognize that they need to get it fixed. Otherwise you'll flatspot a lot of tires. SCCA types wiil try to tell us about the charms of no ABS braking, but once they get into our class, they too get ABS working. There is no ABS difference in model years. Yes, it changes how the car moves if you've lost control and lock up the brakes.
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Re: Some Brake Questions 2 months ago #83203

PFC doesn't make the 01 compound anymore I don't believe. It's been replaced by the 11 compound.

I also like to run a bit more pad in the rear. In my case PFC-08's up front and 01/11 in the rear. I don't think it's all that uncommon.

You'll see both Girlings and ATE calipers in use. They both have their charms. ATEs can benefit from adding brass bushings.

The Girlings are super easy to change pads by just taking out the bottom bolt and rotating the caliper upwards. (Great for endurance racing.)

I have cooling ducts. I'm not sure that they're necessary. If it's a cool day, I'll tape them off.

Re: Some Brake Questions 2 months ago #83204

  • bedmonds
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Brake ducts are a must. 125-150 degrees cooler than the rears coming off track so they are working on track.
Brian Edmonds
#28 BPE Motorsport Spec E30
Mid South Region Lightning Series Director

Re: Some Brake Questions 2 months ago #83205

  • Ranger
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Oops, I forgot about the brake caliper question. ATE fronts are better then Girling fronts as long as you buy the aftermarket steel caliper pins for the ATE's. If you don't buy the pins then you have a trade-off between the soft OEM pins in the ATE design, and the weaker Girling caliper design. In the latter case, I don't know which would be more desirable.

All rears are ATE.
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Re: Some Brake Questions 2 months ago #83209

  • DavidNJ
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Does the front have so much bias from the factory that it needs to have its bias adjusted down? Is that the result of the increased negative camber which can adversely affect front braking traction?

Also, wouldn't the PFC11's have better modulation than the PFC08s which are sold as endurance pads?

Re: Some Brake Questions 2 months ago #83210

Bias is fine from the factory, and using the same compound front to back is fine. Using the 11s in the back with the 08s up front makes the car easier to rotate under trailbraking... something you may either love or hate.

Re: Some Brake Questions 2 months ago #83211

  • Ranger
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OP, as you probably know, there's no consensus about anything in this hobby. So I'll take the contrary view to Julian. My theory is that our cars are so rear biased that the rear brakes don't do much of anything. Putting higher bite pads on the rear won't overcome enough of this bias to be detectable.

Back in 08 or 09 I spent a bunch of time testing brake pads. One of the lessons learned is that the difference in braking g's between limp rear pads and vy high bite rear pads is so small that it's indistinguishable from noise.

Yes, I put high bite pads in the rear, but this isn't really because that idea was obviously better. The data supported the idea, but the difference was so small that with some more rigorous testing, we might find that I got over excited by not enough proof. I use high bite pads in the rear because the idea ought to work better. I can't honestly say that the data made it a slam dunk tho.

Our rear piston is a 1/3rd smaller then front so that gives us a ~60/40 bias. Then our bias valve kicks in at ~300psi, depending on who you talk do, and that adds another 60/40 so now it's about 70/30 forward biased.

As an experiment a couple years ago, and with my high bite pads in the rear, I bypassed my brake bias valve. I expected the car to suddenly become a handful under hard braking. To my surprise, bypassing the brake bias valve didn't seem to make any difference. The relative size of the pistons seem to dominate the situation.

One last thought. One thing that did make a difference is tires. If one front tire is less grippy, for whatever reason, braking g's go way down. Sure, this is intuitive, but the affect is more significant then I'd figured. The one front tire slips and then ABS kicks in. With fresh front tires, one can do some serious braking g's. But if one of those front tires is hot/cold/worn, or just hits a patch of asphalt with a little less grip, stopping distances are long.

That's front tires mind you. Since the rear brakes don't do much, the rear tires don't matter much (to braking distances). I feel strongly that everyone that has ever reported that their rear tires locked up, is wrong. That is unless their tire was airborne because the car was bounding, or the rear tire slid across something very slick. Rear ABS engages "ice mode" which is, in a breaking zone, quite exciting.

Caveat. There's certainly folks that are better able to feel what the car is telling them than me. I'm mostly here for comedic relief.
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Last Edit: 2 months ago by Ranger.

Re: Some Brake Questions 2 months ago #83212

  • Ranger
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DavidNJ wrote:
Does the front have so much bias from the factory that it needs to have its bias adjusted down? Is that the result of the increased negative camber which can adversely affect front braking traction?

Also, wouldn't the PFC11's have better modulation than the PFC08s which are sold as endurance pads?


Not allowed to adjust bias.

Every marketing dept says that their pad is easy to modulate. It's like religion. Every racer is sure that their pads are best.
"Tower, this is Ranger requesting a flyby.
"Negative Ranger the pattern is full."

Re: Some Brake Questions 2 months ago #83213

  • DavidNJ
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They all say it, but some really are. Between the 08 and 11, it is PFC making the distinction.

These pads are used in many levels of competition, with many top racers who do extensive testing. I believe PFC is the most popular pad in top level NASCAR racing.

It is similar to shocks. There are lots of brands out there. In top level competition, it is largely Penske and Ohlins. JRi is from ex-Penske people. Sachs has some high-level competition shocks. The question to ask: how many pistons do they make and how do they vary? How linear are their adjustments, especially low-speed rebound? Do they have features like base valves and through shafts?

This is PFC's latest guide to compounds. For Spec E30 it is simpler, only the 08 and 11 are available.

pfc.parts/motorsports/pfc-compounds/


PFCSE30Compunds.png
Last Edit: 2 months ago by DavidNJ.
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