6 piston Brembos really worth it?

[Whiskey11]

So the area that is hitting is this area around the bolt that goes through what I'd call the "bridge" area. Not sure if that's right or not. The Bolt itself is fine but there are two reliefs on either side of it that are causing the issues with rubbing. The rest of the caliper just clears the barrel of the 18x9 ET45 PF01's:



Inside of the wheel where it is rubbing:


Close up: Ignore the closest scratch, that's from installing the wheel, the furthest away is the one I'm talking about.


Clearences baby!:


I'm hoping those 3mm spacers show up so I can see just how close we really are. Push comes to shove and I'll run the 5mm spacer. I'm getting 7 turns of the lug nuts which is what I'm getting using the stock lugs with the stock wheels with the 5mm spacer and I haven't had issues yet with that setup while autocrossing.

I would be shocked if the same area would hit on the 18x10.5" wheels but without one here to test fit I can't say for certain. Worst case, run longer studs and a small spacer. The S550's front studs are kind of short compared to the S197 studs... or at least they seem that way anyways.

 

[oldVOR]

That area isn't a critical portion of the caliper and can be filed down to provide the necessary clearance. The pad pin itself is still very close and can rotate a bit (minimal at best) to the full shoulder area and contact the wheels inner barrel. The outer most shoulder of the pin could also be filed to provide additional clearance.

 

[Norm Peterson]

Would such filing/grinding be considered class-legal?


Norm

 

[2Fass240us]

I did 11 track days in just over a year, all on the little 12.4" front brakes. While I did heat-check one set of fronts, I've got 6 days on the rotors I replaced them with (4 days running as an intermediate, 2 with the advanced guys).

I assume by "heat-checking" you mean you noticed the existence of small heat cracks? I've seen this a lot with the 2011+ GT rotor (13.2") and Wilwood Superlite setup I ran on my 2007. I'm moving to 14" rotors and Superlites for my 2013, so we'll see how that goes.

Have you gotten uneven pad wear from caliper spread? That was the catalyst (and toasted plastic pistons) for ditching the OE sliding calipers.

Not that I'm recommending anybody stay with brakes that small, only that 14" represents a pretty solid upgrade for a car that only has a little more than 300 HP at the crank.

Agreed. It's enough of a diameter and mass increase that it should handle everything except endurance racing for 95% of us, with proper cooling.

 

[ArizonaGT]

Whiskey, thanks for the pics. That is close indeed. I think the spacer will get you the clearance you need. I'd suggest switching to the FRPP hubs w/ ARP studs, however--way more thread engagement plus get some fresh hubs on the car from what I assume is many autocrossing seasons. I replace my hubs every 12-18 months (preventive).

 

[Norm Peterson]

I assume by "heat-checking" you mean you noticed the existence of small heat cracks?

Yes. And if you can catch a fingernail in any of them it's time to toss both rotors on that axle.

Have you gotten uneven pad wear from caliper spread? That was the catalyst (and toasted plastic pistons) for ditching the OE sliding calipers.

Not particularly. A little front to rear taper, yes. Don't know this for sure, but I suspect that higher temperature rated track pads do a slightly better job of insulating the calipers and their pistons.


Norm

 

[2Fass240us]

Have you gotten uneven pad wear from caliper spread? That was the catalyst (and toasted plastic pistons) for ditching the OE sliding calipers.

Not particularly. A little front to rear taper, yes. Don't know this for sure, but I suspect that higher temperature rated track pads do a slightly better job of insulating the calipers and their pistons.

My uneven wear (presumably due to spread as it got worse over time) happened after using DTC-70s for 2-3 events. Between that and my OE pistons crumbling, I'd argue the opposite of your theory is true.

 

[Whiskey11]

Whiskey, thanks for the pics. That is close indeed. I think the spacer will get you the clearance you need. I'd suggest switching to the FRPP hubs w/ ARP studs, however--way more thread engagement plus get some fresh hubs on the car from what I assume is many autocrossing seasons. I replace my hubs every 12-18 months (preventive).

The picture with the wheel on is with the 5mm spacer. It's pretty tight in there but it all fits otherwise.

As for the hub replacements. My hubs were still tight and not making any noise, but I went ahead and upgraded them anyway:



Problem solved for a while! Hence the 15" rotors and 6 piston brakes!

 

[ArizonaGT]

My uneven wear (presumably due to spread as it got worse over time) happened after using DTC-70s for 2-3 events. Between that and my OE pistons crumbling, I'd argue the opposite of your theory is true.

We nuked the phenolic pistons on our Crown Vic LeMons car in similar fashion.

 

[DiMora]

Does anybody even make a 18" wheel that clears the 15" rotor ?
Has anybody used 6 pot / 14" rotor's ? Do they buy you anything over the 4 pot /14" rotor?

Roush.

They used them on every TrakPak car:

 

[DiMora]

Does anybody even make a 18" wheel that clears the 15" rotor ?
Has anybody used 6 pot / 14" rotor's ? Do they buy you anything over the 4 pot /14" rotor?

Roush.

They used them on every TrakPak car. 18" forged rims and Roush-Branded Stop-Tech 6 piston calipers.

 

[Norm Peterson]

My uneven wear (presumably due to spread as it got worse over time) happened after using DTC-70s for 2-3 events. Between that and my OE pistons crumbling, I'd argue the opposite of your theory is true.

I do think that your symptoms are related.

The only way I can envision caliper spreading happening is from a combination of high caliper temperatures in the 'bridge' region and "excessive" caliper piston forces. High caliper forces are what you end up with if you're operating out there on the down-slope of pad mu vs temperature - IOW some fade is already present. Basically, you're stomping on the pedal harder to make up for lost mu.

On crumbling . . . with a high enough ▲T across the friction material, sustained for a big enough portion of the time, even a material with low thermal conductivity will let heat through it. Once it does get through the pad material and the low-thermal-resistance steel backing into these particular pistons, there's a lot of resistance to it flowing any further (air gaps between the pistons and their bores won't transfer much heat). I would certainly expect a pretty large, nonlinear ▲T within the pistons themselves between the pad contact surface and the fluid surface - probably intentional for the brakes of most street-intended cars even though it puts the pistons themselves at risk under extreme braking events that are repeated at short time intervals. Before I got downsized out and eventually took retirement, thermal transient and 2-D heat transfer analyses was part of my day job, and I don't think I've forgotten all of the concepts quite yet.

I'll risk a guess that with pads of more or less similar composition but lower temperature rating you'd be fading the pads.


Norm

 

[2Fass240us]

The only way I can envision caliper spreading happening is from a combination of high caliper temperatures in the 'bridge' region and "excessive" caliper piston forces. High caliper forces are what you end up with if you're operating out there on the down-slope of pad mu vs temperature - IOW some fade is already present. Basically, you're stomping on the pedal harder to make up for lost mu.

It's interesting that you mention pad downslope...are you operating off a graph or assumptions? To my knowledge Wilwood is the only pad manufacturer willing to provide that information.

Getting back to the topic at hand though, most of their racing pads have little in the way of downslope, save the Poly As:

The BP-10s I run on the street definitely do though:

Point being if I've ever been (or will be) on the downslope, I'm unlikely to feel it in the pedal given the focus on getting the car slowed on track and resultant inability to detect small fade.

Before I got downsized out and eventually took retirement, thermal transient and 2-D heat transfer analyses was part of my day job, and I don't think I've forgotten all of the concepts quite yet.

Not cool about downsizing, but cool about heat transfer analyses. I took a class on it in school but that's as far as I took it. I've also run a few calcs on rotor thermal expansion to determine sufficient caliper:rotor Clarence but admit to being Rusty.

I'll risk a guess that with pads of more or less similar composition but lower temperature rating you'd be fading the pads.

I'd say that's a distinct possibility. Carolina Motorsports Park is very hard on brakes and I'd hesitate to go with a lesser pad than the DTC-60s. I may move to the 70s or try Carbotechs for next season as I'm in the market for a new set anyways.

 

[Norm Peterson]

I was using Hawk's own temperature-mu chart. DTC's look OK until you get out there past 1300° - 1450°.

Years ago, I faded some mass-market OE replacement pads so badly that there was serious question about them being able to lock up summer tires on ice. No matter how much force I could muster at the pedal.


Norm

 

[2Fass240us]

I was using Hawk's own temperature-mu chart. DTC's look OK until you get out there past 1300° - 1450°.

I'm glad you posted that; I've seen it before but wasn't able to locate it. It looks like they even start to fall off slightly at 1250°F, with the big drop at the 1450°F as you mentioned. While I would be able (I hope!) to detect the 1450°F fall-off, I'm not sure I would at 1250°F.

End of the day the best way to make decisions is to invest in a way to measure temperatures. This only goes to 1239°F; you can get these pens up to 1800°F though. The latter suffer from the same challenge as the IR gun though: it's difficult to gather real-time info since you have to pit to get a reading.

 

[Powered by Ford]

Does anybody even make a 18" wheel that clears the 15" rotor ?
Has anybody used 6 pot / 14" rotor's ? Do they buy you anything over the 4 pot /14" rotor?

Yep. I have Baer 6P 14" 2-pc rotors brake kit. Uses corvette pads and clears my 18x9.5 Forgestars

 

[ArizonaGT]

The DTC70s also seem to crumble apart past their MOT range, not to mention they eat rotors. Switch to a PFC01 compound and get range 1600-2000*F that's much easier on rotors...

 

[2Fass240us]

Has anybody used 6 pot / 14" rotor's ? Do they buy you anything over the 4 pot /14" rotor?

Powered by Ford's post made me realize I missed this the first time around.

The only real difference between the 6-piston and 4-piston calipers is that you can get better pad wear from the 6-piston ones through staggered* piston sizes and the force being applied across 3 pistons instead of 2 (per side).

In the Wilwood flavor, the 6-piston Superlite is only offered in one flavor: 1.62"/1.12"/1.12", for total piston area of 4.04". The 4-pistons on my 2007 were 1.88"/1.62" for a total piston area of 4.84", but you can get them in multiple piston combinations. So there's actually a bit of a disadvantage with the 6-piston in terms of selection.

*Technically my 4-piston Superlites were staggered as well.

 

[2Fass240us]

The DTC70s also seem to crumble apart past their MOT range, not to mention they eat rotors. Switch to a PFC01 compound and get range 1600-2000*F that's much easier on rotors...

That might explain why I had some crumbling on my DTC-60s from earlier this year. Looks like another manufacturer is in my future.

 

[CobraRed]

Roush.

They used them on every TrakPak car. 18" forged rims and Roush-Branded Stop-Tech 6 piston calipers.

http://themustangsource.com/forums/attachments/f686/49105d1192118655-2008-roush-427r-trak-pak-mustang-photos-2008-005.jpg/IMG][/quote]

I had those wheels on my SN95, nice forged wheels.

[IMG]http://i.imgur.com/u19qcwd.jpg

Then when I was in a crash, one of the wheels was messed up and I sent it out to be repaired because it had walk, which is hard to fix. 2 years later and the money to fix the job + $ to strip the chrome and they still wouldn't finish it for me. Never got the wheel back.

So I sold the two rear wheels and still have a front wheel in my cellar to this day. It's a sad story, but will make a great end table.

Would have been cool track wheels for my 2011, but they are not light.