Front to Rear Brake Pad Friction Balance

I am trying to figure out which brake pads to run for this season and I want to hear if anyone has any experience running a higher friction pad out back.  I will explain my reasoning below.

THE CAR:
07 350z
Full Aero, 400 lb df front, 660 lb df rear, @130 mph
Brakes:  Front and rear calipers off of a Porsche Cayenne Turbo S truck.  6 pot monoblocks front, 4 pot monoblocks rear.  350mm front rotor, 325 mm rear rotor.  The front has cooling.  The rear does not.  The rear rotor's inlet is on the outside of the rotor, not the inside.  

I have been running Pagid RSL29 both front and rear.  These are great pads.  They are quiet on the street, they are great on the track.  Except.....once the rear pad gets to about half its life it starts to overheat.  The rears runs hotter than the front.  Likely due to no cooling and I do not see a way to fix that.  I could slam air into the inside of the rotor but as the cooling vane inlet is on the outside I will likely be doing nothing.  This is the nature of heat exchangers.  A rotor is just a round heat exchanger.

The brakes on my car were made for a very front heavy truck.  The balance of my Z is now nearly 51/49 F/R.  I have moved a lot of stuff to the back of the car.  

In order to get a higher temperature handling pad for the rear I really must go up in Mu (coefficicent of friction).  For one year I ran the car with only the front 6 pots and kept the crappy 2 pot OEM Nissan Brembos.  That season sucked.  The car just dove.  Once the 4 pots went to the rear it felt great.  Sometimes I feel like I could run even bigger brakes in the rear.  

I know this is not normal but I have always run the same Mu pad front to rear.  I have a driving style that I would call "ass end in".  I use the back of the car to rotate the car around turns.  I try to rely the least amount on the steering wheel as, for me, this always has been the style that leads to the lowest lap times.

I will post up the 3 Mu charts of the pads I am considering.  RSL29 in front, RS14 or RST3 in the rear.  I am also open to another rear pad if someone knows of one that is a better fit.  

 

I've run RSL29 and RST3 on the front of my ND -- and also the RSL1.

If you can get it in your shape, the RSL1 compound is an endurance compound like the 29, with a similar initial bite but more overall friction.

RST3 is a sprint pad, with similar mu to the RSL1 but a bit more initial bite.  It will take more heat, but wears quicker.  That's the GMX5 Cup spec front pad.

I am running higher friction material on the back of my Datsun. I like a lot of rear brake as it helps rotate the car aggressively (we have similar driving styles).

The Datsun has disc/drum brakes. The car weighs 1652lbs but has 280ZX discs up front and 240Z drums on the rear.  The brakes are such overkill that I can run cheap street pad and shoes if I want.

To achieve the brake balance I wanted I went with Porterfield racing shoes I the back and the street pads in the front.  This has been a very nice improvement. 

The real solution in my case would be to fabricate a brake balance bat like my formula car had but that's a lot of work. In you case you have a brake cooling issue so your only solutions are ducting are a pad that tolerates higher heat.

In reply to Andy Hollis :

I can get the RSL1.  It has significantly more friction that the RSL29.  Around 25-30% more.

Tom1200 said:

I am running higher friction material on the back of my Datsun. I like a lot of rear brake as it helps rotate the car aggressively (we have similar driving styles).

The Datsun has disc/drum brakes. The car weighs 1652lbs but has 280ZX discs up front and 240Z drums on the rear.  The brakes are such overkill that I can run cheap street pad and shoes if I want.

To achieve the brake balance I wanted I went with Porterfield racing shoes I the back and the street pads in the front.  This has been a very nice improvement. 

The real solution in my case would be to fabricate a brake balance bat like my formula car had but that's a lot of work. In you case you have a brake cooling issue so your only solutions are ducting are a pad that tolerates higher heat.

 

Interesting that we run a similar breed of car and have a similar driving style.  I might just try this out with the RSL29 up front and the RSL1 in the rear then.  The way I burn through pads I guess I won't have to live with it too long if I hate it.

Do you have an adjustable prop in the rear circuit? If so, I'd run the RS14 and dial out a little bit of rear pressure if the car gets Squirrely as things heat up.

AngryCorvair (Forum Supporter) said:

Do you have an adjustable prop in the rear circuit? If so, I'd run the RS14 and dial out a little bit of rear pressure if the car gets Squirrely as things heat up.

I currently do not.  I have considered running one, but it requires removing the factory bias block, running new lines, and a quite costly two line variance valve

I would rather manage my brake bias with mechanical means than pad compounds, as that way you're less likely to get changing balance as the two ends of the car deal differently with heat.

Keith Tanner said:

I would rather manage my brake bias with mechanical means than pad compounds, as that way you're less likely to get changing balance as the two ends of the car deal differently with heat.

You're not wrong.

I think a deep dive into parts books might be required here, to look for a traditionally vented rear rotor that fits the existing packaging.

In the meantime, ducting to the rear brakes can still be helpful even with the outboard venting. Sub-optimal, but helpful.

Keith Tanner said:

I would rather manage my brake bias with mechanical means than pad compounds, as that way you're less likely to get changing balance as the two ends of the car deal differently with heat.

This really is the proper way to do things but when you trying to add more rear brake the only alternative is a brake balance bar which will likely require some level of fabrication.

In reply to Tom1200 :

A combination proportioning valve (like the common Wilwood model) could also do the job.

Bmsluite said:

Brakes:  Front and rear calipers off of a Porsche Cayenne Turbo S truck.  6 pot monoblocks front, 4 pot monoblocks rear.  350mm front rotor, 325 mm rear rotor.  The front has cooling.  The rear does not.  The rear rotor's inlet is on the outside of the rotor, not the inside. 
 

Interesting, so the vanes are curved to suck air in from the outer circumference and eject it into the inside of the disc?

GameboyRMH said:

In reply to Tom1200 :

A combination proportioning valve (like the common Wilwood model) could also do the job.

The issue there is you can only take out rear brake. 

In reply to Tom1200 :

The combination proportioning valve connects to both brake circuits and lets you run more rearward brake bias than stock.

I don't know if it's relevant but it's commonly seen with autocross miatas.

Typical setup for an NB miata in street class autocross would be to run a street pad in front and more aggressive pad in the rear. It is a way to manage the fact that they are heavily front biased, and lock up the fronts easily. My last miata came with part store pads on the front and Hawk HPS on the rear. I changed the fronts to OEM Mazda pads.

GameboyRMH said:

In reply to Tom1200 :

The combination proportioning valve connects to both brake circuits and lets you run more rearward brake bias than stock.

The only ones I've ever seen reduced the rear. Got a link to one?

GameboyRMH said:

Bmsluite said:

The rear does not.  The rear rotor's inlet is on the outside of the rotor, not the inside. 
 

Interesting, so the vanes are curved to suck air in from the outer circumference and eject it into the inside of the disc?

No, he means the venting is outboard (ie the wheel side) vs inboard (ie the suspension side) of the rotor. 

Tom1200 said:

GameboyRMH said:

In reply to Tom1200 :

The combination proportioning valve connects to both brake circuits and lets you run more rearward brake bias than stock.

The only ones I've ever seen reduced the rear. Got a link to one?

"Run more rearward brake bias" means "delay the point at which reduction of rear pressure begins".

ie the stock proportioning might begin at 350 psi, but the adjustable valve allows you to set that point anywhere from 200 to 1000 psi.

I believe that in order to use a prop valve correctly, you need enough brake torque available in the rear to lock them first. Piston sizes and rotor diameter are the best choices there.  Autocross Miatas in stock classes have artificial rule limitations - and the NB2 does not actually run a prop valve. It does all proportioning via the ABS system. 

In reply to AngryCorvair (Forum Supporter) :

In the case of my Datsun the rear brakes simply didn't have enough power / bite so no amount of pressure would have helped.

It's an econobox with brakes intended for a car with 155SR12 tires and a top speed of 88mph.

The much larger front brakes, which while decreasing the stopping distance, screwed up the brake balance.  I went to larger rear wheel cylinders, which helped but it needed a bit more. Hence the race shoes in the rear; this is still a compromise. 

Tom1200 said:

GameboyRMH said:

In reply to Tom1200 :

The combination proportioning valve connects to both brake circuits and lets you run more rearward brake bias than stock.

The only ones I've ever seen reduced the rear. Got a link to one?

This unit here: https://www.summitracing.com/parts/wil-260-11179

In reply to AngryCorvair (Forum Supporter) :

Ah, like these:

I think the only way to get air into that would be with a custom ducting piece that takes air from a hose behind the disc, moves it into a flattened section to squeeze around the outside diameter of the disc, and then blows into the side of the hat. If there's enough room between the disc and the wheel, a folded aluminum piece might be a good option.

In reply to GameboyRMH :

Yes.  They are this way on the 370z with the akebino package.  The rotors came from nissan/akebono and the calipers from porsche/BREMBO.  She's a proud Frankenstein car 

In reply to GameboyRMH :

Yes sort of like that like.  That one specifically is a actually a floating one piece.  Pretty standard on the high performance audio and BMW cars now.  It's cast as one but the ring can actually move away from the hub like a floating rotor

Anyways, yeah I would have to draw air in from the outside.  I could try a 3d printed duct that I connect to the lower control arm bucket.  I guess it's time to bust out the 3d scanner.... 

In reply to Bmsluite :

The issue with drawing air in from the outside is that it will increase the air pressure in a typical wheel well and produce lift. You could mitigate it by adding lots of ventilation to the rear of the wheel well.