View Full Version : Rear brakes for maniacs only

07-29-2008, 06:49 PM
Well, not brakes but brake pads.

Some may remember that I went to Laguna Seca (http://www.lxforums.com/board/showthread.php?t=116179) again on May 31. Among other things, right in the middle of my sweetest run where I consistently ran my best times like three laps in a row... I cooked the rear brakes and got meatballed. After a cooldown all was well, but I can't be having my track sessions abbreviated due to smoking or flaming brakes.

ToddTCE and I discussed my options today, which aren't so many. His original idea was to maybe use the Polymatrix E pad compound to keep the BP-20 pad from... well, turning to charcoal. The trick to this is biasing. Too much bite in the back versus the front and bad things start to happen.

After kicking things around for awhile Todd suggested I check out an alternative he's had some good experience with in other areas: Porterfield's R-4 carbon kevlar pads. He told me what to look for and off I went to talk to them.

Sure enough they have the pad config needed for the Wilwood calipers I have on the back. The R-4 pad is supposed to be dead on the numbers that Todd told me to look out for: about a 0.50 friction coefficient all the way up to 1200-1300 degrees. Porterfield is supposed to be sending me a performance graph so I can compare the R-4's performance to the BP-20's I cooked. I'll post it up when I get it.

Its an experiment. It could pay off big or it could suck. We'll just have to wait and see. I have another set of BP-20's I can throw on trackside if I have to.

07-29-2008, 06:53 PM
You let us know how it turns out............................................... ........O-tay?? :mrgreen:

07-29-2008, 06:56 PM
You let us know how it turns out............................................... ........O-tay?? :mrgreen:

07-29-2008, 07:19 PM

07-29-2008, 08:24 PM
Sounds good keep us posted!

07-29-2008, 10:38 PM
May I ask how they managed to know your rears were cooked ? Were you throwing black clouds and flames or something ?


07-29-2008, 10:59 PM
holy crap. I was just starting to recognize dyno curves... now Matt has brake pad graphs with metrics like temperature and friction coefficients.

Matt my friend you are WAY out there blazing another trail. cool, er I should say hot...

07-29-2008, 11:12 PM
Ain't it great?!

08-09-2008, 10:55 PM
lSorry guys, somehow I missed the responses in here until now.

May I ask how they managed to know your rears were cooked ? Were you throwing black clouds and flames or something ?
Actually, they throw out white clouds of smoke, not black. And yes I found this out the hard way. I got meatballed off the track when I was pouring smoke off the back wheels.

holy crap. I was just starting to recognize dyno curves... now Matt has brake pad graphs with metrics like temperature and friction coefficients.
I've actually been checking them out for awhile, and yeah its a whole other woild. :D

This graph describes the performance for most of the Wilwood line that normal humans use.


The stock Wilwood kits come with BP-10 pads on the front and T pads on the back. You choose 'lesser' pads for the rear to 'bias' your braking performance to the front so bad things don't happen when you slam on the brakes and turn hard in a corner at the same time. Race systems often have a 'proportioning valve (http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml)' that adjusts brake performance front to rear, but you can also do it with different pads.

The next step up in performance is to use BP-20's on the front and BP-10's in the rear. This is either an aggressive street performance duo, or maybe something for a big autocross course. Note how the BP-20's live longer as the heat climbs, and give a higher friction coefficient.. And remember that on the track I was seeing temps over 1200 degrees on my front rotors (before I put in my powered uber ducts). So you need a track pad. Here are the Wilwood track pads:


Compare this graph to the street pad graph and you see higher friction coefficients and flatter curves... ending at higher temp points. In fact they don't end... I bet the rotors go around that point. As an aside, you want to ask your brake pad mfr what their curves look like. Chances are you will have a hell of a time even getting a coefficient out of them let alone a graph showing coefficient as temp climbs. By way of comparison, EBC Yellow Stuff gets a lot of kudos for being a good track pad... and they advertise that the Yellow Stuff pad gets "up to 0.50". Kind of puts their performance in perspective when you see the graph above, where PolyMatrix H is at 0.64, and even the 'B' pads beat the EBC's hands down when they are still cold.

A good track combo is a B pad in the front and a BP-20 in the rear, or better still, an H pad in the front for the terminally serious, coupled to a BP-20. You can't go higher than a BP-20 in the rear without getting some serious worry about brake bias screwing up your life. The pads in the rear that would be a step up would be literally too good.

So what do you do when you're me and you have gotten phenomenal performance off the fronts and cooked the rears? You literally know you have to have something better, but you need a sweet spot of around 0.50?

Enter the Porterfield R-4:

I am encouraged by this graph because of that nice flat curve that goes to a high temp number that I know I see on the track. On paper this thing stays at around 0.49-0.51 throughout the whole usable spectrum. I need just a little more temperature tolerance and this pad seems to offer that, along with some better performance.

I put the pads on today and I must say, for street performance they are impressive, in that there is no sign that I have a race pad on back there. No noticeable rotor wear, no noticeable dust. No noticeable performance degradation from using a pad outside its temp range. Since I will do very little driving around off the track that works for me as if I can keep these things on the car it will be one less thing I have to do in prep for a track day.

We'll see. Experiments ongoing.

08-09-2008, 11:09 PM
what I want is a bracket setup to run a R/T rear brake on the back of my car to run 15-16" wheels

Todd TCE
08-10-2008, 05:44 PM
If you were willing to get rid of the parking brake drum I could whip up an 11.75 that will fit inside a 15" wheel. Keeping the drum in there however means the rotor size must be larger thus the outer radius of the caliper over the top of it is even greater....and won't clear the smaller wheels.

08-10-2008, 05:57 PM
todd isn't the parking brake drum the same in the r/t ,sxt and SRT?Meaning a smaller SXT rotor could fit the SRT rear?The it's just a matter of fitting the caliper?

08-10-2008, 06:38 PM
but the SXT isnt a vented rotor, there in lies the rub. E shoes seem to be the same size across the board, but id prefer to have a fat rotor out back as well.

Todd TCE
08-10-2008, 08:29 PM
I think that's right but if you factor the drum size and rotor size you may still have a problem with caliper clearance to the inner wheel. Just brain stormin' here. No firm info on how you could pull this off with oem parts. I don't think any of the oem rotors are going to be small enough to do this inside a 15.

I'm assuming your speaking of a need for smaller wheels for drag racing. The loss of both rotor OD and width would be something I'd look at for the open track use but for drags and street use the width be much of a loss. The OD loss will have some impact on the overall brake balance of things. That's why I'd move to the two piece set up where you could have not only the vented part but also an adjustment to piston size.