Brakes fade under track usage

[Joe Ricard]

OK not just another brake upgrade thing.

the Red Neck Racer had it's 1st track day Friday.

each session was 7 laps give or take. ended up with 60 total laps for the day. some times there was less than 15 minutes between sessions.

Stock 17mm MC Stock front and rear calipers and good fluid Pagid black pads.

Really a great Autocross set up. Easily modulated and serious stopping power cold.

So get things warmed up, or should I say smokin hot. rotors are now Blue and there is ash like deposits around the pads.

Contibuting factors which I never seen coming (sometimes I am such a rookie) Front cow catcher air dam blocked air to brakes, not the best pad choice. Regular supplier of Castrol LMA was out. so I got Valvoline synthetic brake fluid. (NOT worth a damn).


Plan to fix before next track event goes like this:
make cooling ducts for front. Get better brake fluid, and what are the best pads for track use. 1900 pounds of car capable of serious speed on R3SO4 Hoosiers 225/45-15. Might even have Slicks for next DE.

[lapuwali]

I'd certainly start with pads and fluid. You might pick up some heat-indicating paint and place some on the edges of the rotors to see how effective your ducting is, when you get there. Put some on the rear rotors, too. It would be interesting to see the temp difference between the front/rear rotors.

The next escalation step I'd try would be slotting (not drilling) the rotors. The benefits may be marginal, but it's pretty cheap to do.

After that, the next step I'd try would be vented front rotors, using a pair of Mueller's hubs. Talk to Eric Shea about widening spacers for your stock front calipers to use with the vented rotors. I personally think this is the best low-buck solution, since it involves changing the fewest parts, and as you note, the stock 17mm MC and stock calipers with good pads provide plenty of stopping power. You just need to find a way to shed the extra heat generated by track abuse.

[jhadler]

Hey Joe,

Told ya your brakes would take a beatin'.

Good pads, good fluid are important. But brake ducts are KEY. It doesn't matter if you're running Full blown super pads and racing fluid, if you can't get air to the brakes, they WILL get too hot.

Get some air to those brakes. Even dryer hose from Home depot wrapped on there with zip ties will make a huge difference.

I like Porterfield R4 or R4s pads, and Ate Super Blue fluid. Motul 600 is pretty good fluid too.

-Josh2

[Grantsfo]

Originally posted by jhadler



I like Porterfield R4 or R4s pads, and Ate Super Blue fluid. Motul 600 is pretty good fluid too.

-Josh2

Thats what I used when I had 4 lug too with great results.

[URY914]

Do the things you listed and you won't have a problem.

Well, I mean you'll still have problems but not with your brakes

[Joe Ricard]

Josh my contact pyrometer showed 550 degree rotors after running half a lap staying off the brakes being easy on the car and then tooling around the parking lot @ 25 MPH for 10 minutes. Rears were 300 ish.

Made sure NOT to engage parking brake. Just parked in gear.

Going to get some ducting going soon. Thanks

[jhadler]

Yeah, those temps would be expected. You should try and get someone to shoot a couple high speed photographs from the side while you're under heavy braking. I'll -bet- good money that your rotors are incandescant. And if they aren't then you're not braking hard enough. Yes, your brakes will get that hot. 1400 degrees is not uncommon for rotors while under load. That's why _air_ is critical in keeping temps under control. Even the best brake pads in the world won't survive without cooling.

A good primer for brakes in on our SCCA Time Trials website. Great shot of glowing brakes on an Integra.

http://www.sccatimetrials.org/requirements/brakes.html

-Josh2

[jhadler]

I will add that I have _punnished_ the Porterfield R4 pads and still had the ability to slow the car. Smoke pouring from the wheel wells, quite literally, and still had brakes. Not to say they didn't fade, they did. But they didn't go away either.

Yes, it was deliberate.

And I've run high performance street pads on the track (with no ducting) and they went AWAY after one or two laps. yes, they were GONE.

I won't ever do that again... Not fun...

-Josh2

[jhadler]

Joe, nice pic of the car by the way. Very good action shot.

[Acox914]

joe, mueller hubs and m calipers....



you could always ziptie an elbow onto the a arm.. ala trekkor

[Brando]

Keep in mind that your front rotors also house your front wheel bearings. Different metals, grease in there... More to think about when saying "cooling is key".

[Scrappy]

Iffin your rotors are bluuoooooo from heat, check 'em for cracking too!

[Eric_Shea]

If you're going to do more of these track days then you need to move up to M-Calipers and Vented Rotors.

You are a text book study in what we see with 914 calipers. They are awesome for even the most agressive autocross but... get agressive on a track and you'll experience fade.

Also... brake less

[lapuwali]

So, Eric, why new calipers? Spaced stock calipers should work great with vented rotors, and you don't mess up the brake balance by fitting front calipers with larger pucks.

Are you not still working on adding spacers to the stock calipers?

[jhadler]

If properly setup , meaning good pads, fluid and **COOLING**, stock 914 brakes can work reasonably well, even under track conditions. Not STELLAR, but pretty good.

Bigger calipers won't do much until you get them wrapped around vented discs. Yes, going to vented discs and calipers can make good gains in brake longevity for track use. But that also adds unsprung weight to the car as well.

Joe, if you're planning on running a lot of track events, then maybe upgrading the brakes might be the way to go. But if it's only the occasional track event, and mostly autox, I'd keep what you've got and just run a separate set of track pads with FRESH fluid for the track. The rears may be a bit of a PITA to swap out (venting clearance setting), but the knowledge that your brakes won't leave you when you need 'em the most is well worth it IMO.

Air is key. After that, fresh high temp fluid and good race pads.

A note about fluids. Generally speaking, the high temp fluids tend to be hydrophilic, meaning they like to absorb water. This is fine, as long as the fluid is fresh. But the high temp stuff will need to be flushed more frequently. The specs on the fluids will list both a dry boiling point, and a wet boiling point. As water creeps into the fluid, the boiling point drops. This is because the water boils at a much lower temperature than the fluid. Once the water boils, it becomes vapor, which is compressible. This mens the brake pedal will hit the floor board at the most innoportune time (like braking for turn 1 at the end of the front straight). Flush before a track event to make sure you've got good, dry fluid in there.

Pads: The better race pads will use ceramic backing plates. This helps keep the heat from going throuhg the pad, through the piston to the fluid. A stainless steel shim between the pad and the piston is not a bad idea either. Stainless steel is a lousy thermal conductor, which is good in this case.

-Josh2

[Eric_Shea]

James, I'm not spacing the fronts. Not enough call for it. Excellent idea though. Mike should engineer some spacers to sell with the Mueller hubs (ooooooooooops, is Brad reading this?). They should be 7mm I believe.

Josh has nailed it from what I can see. If you're going to do more of these then the M-Caliper would be the ticket. The pad size is the same. The only advantage is the vented rotors in my book.

There's a guy here on the PP 911 boards that makes -6 shrouds. He also makes some very nice A-arm ducts. The ARJ kit may be all that's needed (along with the nice pads and fluid). No need to cut the front.

I'd say the bottom line is based upon how many track days vs. autocross days this car will be seeing. Air, pads and fluid will probably get you by for now.

[jhadler]

I'll throw in my comment that I use when someone says they need bigger brakes. I ask them this "Can you lock up your brakes right now?". If the answer is yes, then they have enough brake, and need to work on the modulator instead.

Yes, bigger brakes are worth it for track stuff. The M calipers and vented rotors are a good step. But retaining the same pad size will not make you stop any harder, it'll just keep the brakes a little cooler, which in many cases is enough.

The key with brake upgrades is swept area. Longer, wider pads are the key to more stopping power. That's why the monster brembos are 4 or six pot monsters. So they can apply even pressure on those really long pads. More swept area. And larger diameter brakes mean more braking torque applied by the brakes.

Anyway, just a little more rambling...

Around the cones, tires suffer the abuse. Around the track, it's the brakes that take the beating.

-Josh2

[Dan (almaden)]

M calipers on the front with Billet 4 bolt hubs and vented SC rotors, Porterfield R4SE pads.
Rear:stock 914-4 front calipers on the rear with stock textar or mintex pads
Proportioning valve removed.
Pentosin DOT 4 fluid.

It works great....good modulation, good pedal feel, firm pedal, no fade, stop with the best newer Porsches on the track


None of this set up is guess work....it is on the car and working as advertised.

If you have blue rotors check to see if you have a frozen piston on that caliper. Even under very heavy use it shouldn't be blue.

[jhadler]

I agree with Dan, if your brakes have blued, you might be dragging a pad.

-Josh2

[lapuwali]

Strictly speaking, Joe didn't really say anything about needing "bigger" brakes, just more fade resistance.

As for the swept area comment, I disagree, to a point.

As you say, pad area helps with fade resistance (or can, anyway). By itself, however, pad area does nothing to improve braking torque. Brakes follow the "classic" friction model, in which area of contact is NOT a factor. Only force of contact and the coefficient of friction between the two materials (pad and rotor) matters. If you pressed a pencil point made of brake pad material against a rotor with the same force, you'd get the same amount of braking torque, as you would with a huge pad. The difference is the pencil point would wear very rapidly. I've seen some racers attempting to solve a brake balance problem by milling away some amount of pad material to "reduce the braking". All they end up doing is wearing out those pads faster, and often causing fade by heating up the remaining material too fast. This does end up reducing the braking, but is obviously not the ideal way to do this.

Now, there are also leverage effects at play here. If you apply the force farther from the axis of rotation, you get more braking torque for the same amount of braking force. Look at any recent sportbike front brakes and you see an excellent application of this idea: a thin, annular ring of brake rotor well away from the hub, held there with a spidery "hat". This ring requires a long, thin pad to get adequate (for wear and fade resistance) area, so you need a long, thin multi-piston caliper to squeeze that pad, or you need a thick, rigid (and heavy) backplate for the pad to spread the load for you.

Joe's problem is just one of shedding heat, so there's no need for bigger calipers and/or bigger caliper pistons. Bigger pads would help some, ducting air will likely help a lot, vented rotors would help a great deal.