- 1 Do I Need Bigger Brakes?
- 2 97+ OEM Brakes
- 3 Performance Friction
- 4 StopTech
- 5 Brembo - "Lotus" caliper
- 6 Comptech - Brembo
- 7 Dali Racing
- 8 Mov'It Porsche / Brembo Package Adapted To NSX
- 9 RM Racing Rotors & Pads
- 10 RM Racing / AP Brake Kit
- 11 Brake Pads
- 12 Drilled vs. Slotted vs. Normal Rotors
- 13 Miscellaneous
Do I Need Bigger Brakes?
97+ OEM Brakes
Owners of earlier model years can gain a small benefit by upgrading to the '97 brakes. This is not an earth-shatting difference, but should give a little more stopping power. The '97 pads are a drop-in replacement. By just replacing the rotors and the mounting bracket you could go to the larger '97 rotors.
Upgrading the calipers would be a bit more involved. The changes for 1997 were:
Front calipers pistons 40/34 mm (91-96: 40/36 mm) Rear calipers piston 48 mm (91-96: 42 mm)
Front rotors 298x28 mm (91-96: 282x28 mm) Rear rotors 303x23 mm (91-96: 282x21 mm)
Mounting bracket for calipers (10 mm longer) Brake pads (harder Japan pads, more noise, more wear on rotors, part.no. ends with -J02)
Master brake Cyl (probably for different size pistons in calipers ABS Modulator. (same as above)
The brake balance was been moved to the rear (more increased rotors in the rear (R 303 versus F 298), bigger piston in the rear, slightly smaller in the front).
[FG] I just installed the 97 pads on my 95. Have had 300 miles on them and have just started to probe their limits. Here are a few observations...
The initial "bite" is not as sharp as the RM pads. However, the pads are more progressive.
The brake grab is very linear depending on pressure. More so than the 95 pads where the ultimate pad friction is not as high.
Less effort is required on the 97 pads for the same amount of stopping power. I have been quite amazed at how little pedal pressure is required to slow down from 100 MPH compared to the 95 pads.
Overall, the pedal feel is improved and in a way I prefer them to the RM pads that give most of their grab initially and then are less progressive later. The 97 pads have more finesse (if there is such a concept for brakes) and should make trail braking easier and more controllable.
[WME] In my '96 I had shudder and extreme fade after only some miles downhill the mountains here.
With the 97+ models it's far better - you'll have the fading only on certain tracks (e. g. the short version of Hockenheim) where you have to brake very often and there is no long straight to cool things down. At the F-1-track in Spa-Francorchamps (6, 8 km, 2 long straights) I had nearly no fading.
[MJK] I upgraded my 94 brakes to 97. I changed all 4 calipers, splash guards, rotors and the spare tire. I rebuilt all 4 calipers and installed speedbleeders at the same time. I did NOT change brake lines, spare tire holder or the master cylinder. All works perfectly and gives a modest street feel difference. A change from the OEM pads to street track aftermarket pads gives a much more dramatic difference in initial bite by comparison - in my case to Carbotech Bobcats. This is not a hard DIY. The toughest part is getting all the air out of the rebuilt calipers - get plenty of fluid. In retrospect, this does not give much difference in street feel but may be worth more to someone who spends more time on the track. The upgraded brakes WILL NOT work with 15/16 91-93 wheels or the orange 91-96 spare tire. All pads are interchangeable.
Performance Friction, the world-renown brake pad and brake system manufacturer is one of the most successful brake companies in the world that no one has heard about (outside of the Motorsports Industry) has made a street application for the NSX. Without question, this brake system is the best on the market and that conclusion comes from years of racing domination, not the marketing desk.
Also, unlike other brands whose street kits have only the nametag in common with their top level racing components, these PFC parts are the real deal that win Championships across the board of top-level professional series JGTC (Used on the EPSON NSX), Champ Car, ALMS, Rolex, World Challenge, Grand-Am CTSCC, WTCC, Australian V8 Supercars, etc.
Working with U.S. Time Attack record holding team FXMD, Performance Friction (PFC) has taken the data from tire size, vehicle weight distribution, vehicle weight, center of gravity, brake rotor size and thickness, pad swept area, calculated brake forces, from a stock NSX, the testing of the FX750 Unlimited Time Attack car, and the JGTC/Super-GT NSX to come up with an engineered brake system with the best balance for the NSX. This is not just a "Big Brake Kit". PFC went through all of the steps designing this system for the NSX just like they would for a JGTC, ALMS, Daytona Prototype, Australian V8 Supercar, IndyCar, Atlantic, NASCAR, Formula 3 Car, or any other type of racing vehicle they design brake systems for.
THAT's the difference. PFC dosn't use off-the shelf parts slapped together and call it a "BBK" but rather engineer a proper brake system for optimum performance.
-The 4-piston Z31 caliper used in the NSX kit is a Forged Monobloc design -FEA-created design that optimizes weight while keeping the caliper rigid. -This unique caliper uses four pads per caliper - one per piston for an incredible bite and the ability to mix pad selection for mixed-use cars.
Piston Size Front: 36.50/41.00
Piston Size Rear: 32.00/32.00
-PFC's newest V2 Direct Drive Rotors. -Made from a precision casting -All external surfaces are machined to tolerances of 0.004", including the OD of the vein area that most manufacturers leave rough-cast. -**This is the only rotor that are mechanically, thermally, and dynamically balanced - meaning you will never warp them because they are balanced in all situations, all temperatures.
Rotor Size Front: 14" (355mm x 32mm) -largest and widest rotor used in an NSX system.
Rotor Size Rear: 14" (355mm x 32mm) - largest and widest rotor used in an NSX system.
Brake Bias: 60% front / 40% rear
MSRP: ~$8,000 System sold as a complete package. Front & Rear. Less E-brake.
[BJ]JGTC NSX technology for your NSX. The largest rotor and most advanced and stiffest caliper on the market for your NSX. Will not fit many wheel sizes but will provide the ultimate stopping power for your NSX. A must-have for JGTC NSX fans, Track, FI, or wide-body cars. Used on the FX Motorsports Development to many track records and overall wins[/BJ]
The StopTech Big Brake System is the only other option besides Performance Friction that is designed with proper piston sizes maintaining the NSX's proper brake bias. StopTech is actively involved in top level motorsports -ranging from Speed World Challenge to Grand Am CTSCC.
ST40 Calipers *(and the new TROPHY caliper is now available)
13" (328/28mm) Rotors.
Trophy STR lightweight forged calipers are based on StopTech's ST-40 caliper. STR calipers are engineered to be 20% lighter without sacrificing caliper stiffness or performance due to the same metallurgy and design featuring durable hard anodized caliper bodies and rotor hats.
The Trophy brake systems feature durable hard anodized caliper bodies and rotor hats.
~Front $2,095 / Rear $3,295 (with E-brake) Trophy Caliper upgrade $750 per axle.
~$5,390 -Full system Front/Rear/E-brake
[BJ]Probably the most popular system on the market. The only commonly-used brake system for the NSX that has an engineered brake bias specifically for the NSX (the other being PFC). Front system works well with OEM rear caliper (like the Brembo) and delivers one of the best bang/buck on the market. From a bias standpoint, this and PFC are the only good options out there without digging into brake bias knobs, and spending a lot of time testing to get the bias back in order.[/B]
Brembo - "Lotus" caliper
13" (328x28mm) Rotor
Originally used on the Lotus Esprit.
~$2,795 front, $2,795 rear, $1,000 e-brake
~$6,590 - Full system Front/Rear/E-brake
[BJ] Tried and true, you can pretty much never go wrong with Brembo. Fits many wheels and the front system with the OEM rear has been proven to be very reliable and up to the challenge of heavy track use. While increasing the front size alone adversely affects the brake bias, it is minimal and non consequential for 99% of buyers. Even advanced drivers. Upgrading the rear system too will make an even WORSE imbalance of brake bias by having the same caliper piston size and rotor size front and rear. A brake bias adjuster will most likely be needed. For a complete front and rear system, StopTech is probably a better option. For a front only, and for the name and reliability of Brembo, you can't go wrong with Brembo.[/BJ]
Comptech - Brembo
**Possibly not available anymore**
Comptech offers a couple brake kits.
Comptech/Brembo Brake Package - (Mid-Level/Front Only) is the newest brake package designed in conjunction with Brembo.
Features 13" Cross-drilled/Ventilated Rotor
DOT-Approved 4-Piston Cast Aluminum Caliper w/36 & 40mm pistons
DOT-Approved Stainless Brake Lines (for all 4 corners)
2024 aerospace Billet Aluminum mounting hardware (more expensive/much stronger than 6061 aluminum!).
Calipers are directional for rotation to correct for pad taper by having differential pressure across the pad. No "off brake" disc drag (= better mpg, longer pad and rotor life).
Pads are 2 x 64 square centimeters.
Will work with most 17" wheels.
Same Kit, but with 12.3" rotor (to fit 16" wheel), Price: $2,295.00. (Possibly not available anymore)
[BSD] Hey, guys, hope you had a good weekend. I did because part of it was spent (with Bruce McPherson) at the track with the NSX.
I was using a recent brake package from Dali Racing. It is the one with Brembo made cross-drilled vented rotors (in original size) with a set of stock size pads. I do not know who made the pads but Mark sent them to me with the rotors as a kit.
The rotors arrived in a typical box, except it said "Brembo" on it which is always a good thing when it comes to brakes. And, inside, the rotors were in plastic bags. Rotors can rust but you don't want them to before they are on your car. Brembo does an above average job in this department.
The rotors were also gold/brass looking. That is a little unusual as most rotors are a typtical shiney silver almost stainless steel look. Hey, brass looking rotors... doesn't matter to me.
One thing about pads... they come in different thicknesses. Actually, pads are shaped to fit the backing plate for the particular application, and then made to the right depth for the particular car they go on. Sometimes, pads are cast a certain size, then cut or grinded down to be just the right size. In this case, it appears that the pads were actually cast to be just the right size for this application as opposed to being cast for some other application, then cut down. This is a sign of quality as it appears the manufacturer didn't just chuck some parts together.
Assembly was normal and I'm sure the FAQ has great descriptions of replacing rotors and pads.
That screw (or 2) that hold your rotor to the car... is for assembly purposes only. You can destroy, or otherwise, waste those things cause they can be a huge pain in the arse to get off.
Anyway, I've had these brakes on for a while, probably several months. On the street they act just like any other set of stock brakes. No nosies, no vibrations, just plain old brakes with atleast normal grip.
The brass look to the rotors... just another rust prohibitor. The first time you hit the brakes, a bunch of it will wear off leaving the expected steel look. (Duh, Brian says to himself.)
At the track, I was not sure what to expect. I just hoped no shudder. The first session, the pads had to "outgas" or go through the process of "green fade". This is where the bonding material in the pads melts, then boils. The gas created from this reduces the friction of the brake pads to the rotors and makes for a greatly reduced braking performance. The green fade seemed to last much longer than normal and was still going after my first session.
The second session I went out and took it fairly easily until I could feel good about the brake pedal and the fade. I had a passenger, too, so double reason to be careful. Not too many laps later, the fade was mostly gone and I could then feel confident in braking.
I ended up with a passenger again my next session and the brakes were good. As things got really hot and bedded in, the brakes started to make a noise. The noise was a low frequency groaning, almost a hum. I kept going and the hum would come and go, but mostly was there. Braking was not affected by the noise.
Back in the paddock, I think I figured out what the sound was. That is, the brake pad material was getting worn into the rotors. This is common with your basic level carbon-metallic brake pads. The stock NSX pads will do this to some extent, but when they get that hot, they also wear down really fast. Even Porterfield R4S pads, when they get this hot, have a super fast wear rate and I have disintegrated 2 sets of those front pads. These pads, however, did not disintegrate. The bonding of the pad to the rotor is a design feature of modern brake pad material I think. You end up getting brake pad (in rotor) to brake pad wear which is good for both pads and rotors as far as wear and grip goes. But, there can be two side effects of this. One is the hum and the other is some kick back through the brake pedal. In fact with Performance Friction "HP" or "black" compound (may be called 'Z' now) the buildup on the rotor is so bad that it makes it feel like the rotors are warped. Most brake pads that do this are also hard enough to then wear off the pad buildup on the rotor during normal street use. The R4S did this well while the PF black pads took a really long time and a lot of street driving to get it worn off. These pads seemed to wear it off really quickly, even during the cool down lap, so I did not feel any roughness in the pedal or any sound as soon as the hot laps ended. This is very desirable for street/track performance. Real race pads are so hard they grind the rotor a little and keep the buildup down. It is really a street/track thing, as far as I know, to get a lot of pad buildup on the rotors.
I think I did a total of 5 sessions this weekend and the track is pretty hard on the brakes. It is a bunch of straights connected by several turns. There was no shudder or signs of warping, and no bad behaviors. Even when hot, the pads gripped consistently, and I don't baby the brakes.
These pads rate right up there with the best I have used. They are good on the street, even better than the Porterfield R4S pads which can grind a little in street use, but seemed up to the task for all out track use. There is another track in our area that is harder on brakes, but this is a pretty hard track for brakes. Nothing like Second Creek or Hallett, but way harder than something like TWS.
I don't know how far to rate them as race pads since, like I said, only this one track. But, I would recommend them over the Porterfield R4 (race pads) for combination strett/track because they seem good enough for track but don't have the negatives that many real race pads have.
The rotors were also good - and the big thing. Pads are easy to change and wear out quickly, while rotors are harder to change and it really bites to have warped rotors. These did not warp and seem to be made with quality and as far as I can tell are a big improvement over stock rotors. I'm definitely keeping this combo on my car for the long haul with only a set of R4 pads in my spare box (just in case) for my next trip to Hallett.
Mov'It Porsche / Brembo Package Adapted To NSX
**Out-dated, possibly not available anymore**
[Guido Frensmeyer, mov?it - 98/11/24] Of course Porsche does not manufacture them, Brembo does. But these calipers have nothing in common with a Brembo caliper. The Brembo calipers are made for race cars. That means that they have to be as light as possible to keep the unsprung weight as little as possible.
Since race cars are light you do not need a extremely stiff calipers to achieve a firm pedal and a good braking force [BJ]-WRONG. You need the stiffest caliper possible. Theirs a reason why monoblock calipers are better than 2-pc). Also a race caliper like Brembo, Alcon, Ap, Willwood are inspected after each race and are not meant to last years without replacing seals, pistons ... [/BJ]
The bi-turbo caliper was designed to stop a heavy production car in any weather. Without replacing anything for years. They are extremely stiff, equipped with the biggest pistons and dust shield to protect them. The pad area is bigger than on any other caliper ( 75,5cm? ) . That means you not only have the biggest braking force but this force is generated on a bigger area. The disc therefore is forced more equally and the heat is transferred to a bigger area. This area can take more heat of course than a smaller area.
To ensure good braking even in rainy weather the discs has holes.-WTF? On all other discs the holes are drilled after casting and tend so to crack. The holes on the bi-turbo disc are cast-in 4 mm and therefore do not crack. [BJ]they can and have[/BJ] The first row is cast 12 mm inside the outer edge of the discs. This will never crack. -BS. We have tested all different calipers in former time to stop our heavy cars like Corvette ZR1, BMW M5, BMW 850 csi, Audi V8, Ferraris ... None did a satisfying job. Always replacing pistons, seals, discs, pads, everything was very expensive. Since the new bi-turbo brake was released in `93 we only use this setup. No problems so far.
[CMI - 99/4/15] You have read Doug Hayashi's comments on how he uses the Comptech Brembos to brake later in the corners to make passes. There is no doubt about that package allowing you to do that. I had a few concerns going that route though. First, there was no way that I was going to spend $9000.00 on brakes (although this would be a better investment for those who track their car then the supercharger would be IMO). Second, going that route would mean purchasing two sets of wheels (street & track). Third, buying those larger wheels to clear the brake caliper would mean I could no longer haul my race rubber to the track IN MY CAR.
When I first heard about the Porsche/Brembo package that was modified for our cars and talking to Wolfgang Messer about their performance on his NSX I called Steve at The Ultimate Garage and decided to take the plunge (isn't the Internet wonderful:)?). When I installed them, they didn't exactly clear the stock 16" front wheel. Steve said it was all right to cut a little meat off the caliper as they are very substantial. After messing up that pretty red powder coat, (not visible with the wheel on) I was able to mount the wheel. (Modified brackets are being worked on as we speak) I should mention here for this to work, you have to install custom hub centric spacers (24 mm). I also ordered these from Steve. I know the downside of spacers but the upside is now the stock wheels look great on the car from a fitment perspective. Since they fill out the wheel opening, it makes them look larger then 16/17".
You are probably wondering how they work. Well, with the stock Yoko rubber, you can overpower the tire but I did not find that to be a problem as you can still modulate the brake. This combination of the huge front brake with the small stock rear brake proved to be no problem on the street. I also had the opportunity to run this setup on the track, in the rain, and also had no problems with bias. As a matter of fact, after coming into turn one at Gingerman too fast in the rain, wondering if I should drive straight off the track, I stepped a little harder on the brakes and the ABS kicked in and I was able to steer around the corner. I have ordered the rear brake setup from RM's new brake package but after this weekend, feel it will be more for a balanced look rather than function.
Everything I tried this weekend with the Porsche/Brembo fronts and the stock rears, worked fine. I guess that's why everyone that I know with the Comptech Brembo package had to add proportioning valves and dial the rears to practically nothing. I like my new brakes!
[BJ]Because the Brembo Lotus/Lotus or Comptech "Indy"/"Indy (motorsport/motorsport) have the same piston sizes front and rear, the brake bias becomes heavily biased to the rear and adversely affects braking performance. This is why proportioning valves are often needed in these setups, to reduce the line pressure to the rear caliper and thus reduce rear bias.[/BJ]
[CMI - 99/5/20] I later added RM's new rear brake package to balance the look of the rotors. BTW, as always, Randy's rear brake package fit perfectly.
[WME - 99/8/11] I'm no techie, but I have my experiences with OEM-brakes/tires and bigger brakes/racing slicks. Yes, tires are the limiting factor, yes, bigger brakes don't make shorter stoppings, But: Only if they are still able to brake after some hot laps - we all know the tests with cold and hot OEM-brakes, how that can affect the distance (also with ABS). After the 10th braking 100 km/h to 0 most cars have much longer distances (and up to 600 degrees Celsius or more at the rotors).
The stickier the tire, the more work for the brakes, the more fading with OEM-brakes. Other way round: The better the brake, the more work for the tires on the long run.
Try Hockenheim (short circuit) with street-tires and OEM-brakes und you'll pit after 10 laps because tires *and* brakes feel mushy and unsafe. Try with Yoko-slicks and OEM-brakes and you'll pit after - let's say - 7 laps because brake-pedal goes to the floor. Try with OEM-tires and my Porsche-brakes and you'll pit after 8 laps, because tires feel like marshmallows. Try with slicks and Porsche-brakes, make 20 laps and see others pitting. Now you can work with the real potential of your car. Been there, done all that.
Conclusion: Bigger brakes *and* stickier track-tires make shorter stopping on the long run.
RM Racing Rotors & Pads
[RM] In talking to list members I found several of them were confused about my brake set- up for the NSX. The race/street pads that have been the topic of several posts are the product of over a years worth of testing diferent compounds. These pads are built solely for RM Racing and are available ony through RM Racing. Several list members have these pads now and have converted from the use of other manufactures such as Porterfield, Performance Friction, Stillen Ect. Please try to contact these owners by posting if you would like their opinion. I have sold other manufactures pads in the past just as every other vendor does, we are not brake pad manufactures. Due to my own frustration I sought out a company with no NSX experience to develop, with my help, these pads. We built 50 sets and are 3/4 of the way through the order. As always, I stand behind the parts I sell. So far we have had great response from every owner who has tried the pads.
As for the new slotted rotor, this was a result of conversations with list owners for an alternative to cross drilled rotors. (Eric Kerub was very persistent ). After talking with several brake manufacturers this seemed like a great opportunity to make a better product than what is now avaliable for o.e. size replacement. The rotors are being manufactured due to my request and constant conversation about look and finish. Again, we are not brake manufacturers and we do use subs for this type of work.
[KS] I am now using RM Racing's pads on the NSX and I love them. On the street, they have an extra bite, an extra grabbiness that makes you say "Oooh, yes!" On the track, they're there and they work. No over dusting, either. My current favorites.
[AW] I've been using RM's slotted rotors and pads for several months now, including one track event at Willow Springs. No problems, no cracks, no fade, and much lower pedal pressure for any given rate of deceleration (what others are calling "stopping power" although technically I don't think that's really what they mean).
When cold they do take a fraction of a second to warm up (i.e. pedal pressure is initially higher), but you get used to that. And the pad dust is either produced in greater volume or is more visible than with the stock pads, so the wheels require more frequent cleaning to "look nice." Whether these are significant problems is, in my opinion, a matter of taste.
I measured the thickness of both front rotors this morning as 1.091". Stock new thickness is 1.100" according to the shop manual, and the unworn (outer) portion of the RM rotor measures 1.104". The extra 4 thousandths may be the plating that RM puts on the rotors, rust buildup, extra free material from RM, measurement error (although my 1" micrometer, my digital caliper and my 1" measurement standard all agree to within half a thousandth), or it may be some combination of the above.
In any event, in about 6,000 miles of driving and one track event I've worn off about 9 thousandths (based on the stock thickness). The factory service limit of 1.020" means that I'm allowed to wear off 80 thousandths. In other words, at this rate I'll get nearly 54,000 miles out of my RM rotors before I hit the service limit. I consider this to be an entirely satisfactory wear rate.
[EBK] They are great! I am the only one (Randy tells me) that orders the race-only pads. You hear what people are saying about his street pads... well multiply that by 5 and you can imagine what the race ones do. My 4 point belts stop me from flying through the windshield.
As far as the rotors are concerned, it was me that harassed Randy to get them. Last year I sent him back a set of cross-drilled rotors with every hole having 5 or 6 cracks in them. One crack went to the top of the rotor (could have been a real situation). I always have used slotted on my Bimmer and since there were no slotted available on the NSX until now I had no choice. Go with slotted!
[NM] RM Brake Pads (approx. $300): Stop reading this and call RM Racing and get a set of these. They stuck like glue (rain or shine) vs. stock. I was screaming down the back straight at 125-130ish and would wait until at the white cone at Mid Ohio to threshold brake into that sweeping right hander. The braking was consistently FANTASTIC and if I had wanted to move in a couple of inches at a time - I felt there was more stopping power left. Furthermore, they do not dust or squeak much more then stock. I believe the ATE SuperBlue and these pads made a great combination!
[CA] I have had the RM rotors and pads for about 4 days now, the install was very very easy, the rotors cam with a light silver coating, I am noit sure why, however the quality of these slotted rotors is very high as well as the pads.
I called Randy, and he told me how to break the rotors and pads in, after a day or two of normal (read civilized) wear, I decided it was time to *really* break them in, Randy suggested a few runs from 80mph to 0, (not that he would ever suggest exceeding posted speed limits!), I figured an off ramp would be perfect, so off I went, the first few stops were not impressive, the felt like my stock rotors and pads, after the 5th go around, I could feel the difference, these babies stopped quick!
I think my tires were surprised at the command these rotors / pads had...as if to say (stop NOW!) on heavy braking, you can hear the tires voice their displeaure, although ABS did not kick on like many members had complained, I was damn close to it, the brakes hauled the NSX down to civilized speeds very quickly.
I did do one run from 130meters per hour to 10mph, and I have never experienced the controlled braking in the NSX as with these rotors and pads, although I didnt try the RM pads with stock rotors (anyone else?).
So here is how they rate on the Anders scale (***** 5 stars max)
INSTALL **** 4 stars, the 2 phillips retaining bolts can be a pain, but otherwise a cake walk. AFFORDABILITY *** 3 stars, $800-900 is still a chunk of change for rotors and pads. PERFORMANCE **** 4 stars, not Brembo or AP racing rotors, but make the stock setup very effective AESTHETICS ***** 5 stars! these babies look awesome, they ROCK! OVERALL **** 4stars! good Job Randy, Highly recommended.
[DNG] As far as the RM pads goes, if you don't resurface the rotors, then you'll get some initial squeaking as the pads has to 'mate' to the irregular surface of the rotors. Drive around town for about 100 miles or so for the pads to match the groves of the rotors. The squeaking will go away. I had the same problems with my RM pads initially, but went away after breaking in.
[DG] I recommend them. MUCH grabbier than the stock pads, and less fade in track use. The penalty is that they DO dust more than stock -- about as much as the typically-German ones on the M3.
[CMI - 98/7/25] Last September I installed RM's Brake kit. Since most of us feel the stopping power is awesome, I won't elaborate on that. I have four track event on these pads and they are down to 1/8" and I could still lock the brakes before ABS would kick at the end of the straights of Road America. Now the point I want to make: Other pads with good stopping power, such as Porterfield or Hawk Blue, seem either to break up toward the end of their useful track life or chew the hell out of the rotors during the normal life of the pad. The RM pad did neither. FWIW, I may not be the hardest on brakes at track event, but I can abuse them with the best of them.
[KG - 2000/2/16] RM's high performance pads are a whole lot better then the OEM items. In fact the brake performance is now stunning compared to what it was before and I've not changed the fluid or the brake lines yet. I don't track the car, but this is my experience on the road so I'm well pleased.
RM Racing / AP Brake Kit
[KM - 99/5/21] I have been through several iterations of the NSX brakes because of Road Atlanta here. It is especially tough on brakes in three spots of the course, the hardest being the back straight where 135 mph to 50 mph is around the NSX limit. So, for the past 18 months, I have experimented with the following:
Stock brakes, Stock pads - fade and shudder after two laps at speed Stock brakes, RM Carbon Kevlar pads - shudder after three laps, less fade RM slotted rotors, RM CK pads - less shudder after 6 laps, some fade RM Slotted rotors, Hawk pads - worked well when hot, no shudder, no fade, bad brake dust/noise, bad for street driving
I just switched to the RM AP Racing setup before NSXPO and Laguna Seca and had no fade and shudder running in the A group. On the last run of the day Sunday, since only six cars were on the track, I was able to let loose a little more and really push the brakes - again no fade, no shudder after about 10 laps.
Yesterday, I had the opportunity to do some 0-100-0 runs and did about six of these on a flat road. The car stayed stable and tracked flawlessly and I did not notice any biasing problems at all. There was no shudder, no fade and no smell. I think Randy has researched this out relatively thoroughly and has brought a good product to market. I did not try the Porsche/Movit kit because I just didn't want to have the offset issue, and have to grind down the hats. The Mirenda's and Wolfgang Messer have had a good deal of success with these and you do get to keep your stock 16/17 wheels, but these brakes were simply not designed for the NSX. The disadvantage of the RM AP Racing setup is that you do have to also buy bigger wheels, but thats the price of having 13" rotors all around.
I have also driven NSXs with the Comptech/Brembo package and the RM AP Racing setup is very close, if not just as good. There is a significant price differential involved.
My opinion would be that unless you are tracking the car as a mainstream hobby, RM's slotted rotors and pads will do nicely for aggressive street/track driving. If you do about 8-10 events a year (my average) and you get into a brake-heavy track, it would probably make sense to change over to a more solid setup. My main reasons were to do it for more confidence in the car (shudder at decelerating high speeds is never a confidence boosting thing) and better braking ability. I made my decision to go with this setup after nearly running into a few P-cars that could brake much, much deeper than I could with the previous setup. More pistons and clamping pressure are nice, but the element of balance has to be maintained and the RM AP Racing setup does that very well.
[LE - 99/7/14] The Mugen-Dome race cars use AP Racing calipers, 6 piston front and 4 piston rear. Some other JGTC cars use Brembo. I'm not sure what rotors they're using.
[BJ] JGTC/Super GT cars use everything from Performance Friction, Alcon, AP, Brembo, Endless, etc..
01 - World-renown motorsports (track) pad.
08 - Similar characteristics to 01 but greatly increased life
[KS - 99/7/1] I've tried a number of different brake pads on my car, which I use primarily for track events. I like the RM Racing street/track pads a LOT, and consider them the benchmark against which to test other pads. I generally average three track weekends (500 track miles) to a set of front pads, four weekends for the rear pads.
Recently I put a set of Ferodo pads on my car (all four corners). I got these from Guus Toth; the Europeans use them in their competition events. I was surprised at two things about these pads (on the front, anyway): rapid wear and questionable ability to stand up to heat. I drove only about 10 miles on them at a track event a couple of months ago, and then this past weekend I drove maybe 100 to 150 miles on them at GingerMan Raceway. I found that they were already worn down to 2 to 4 mm pad material thickness, so they were ready for replacement. Furthermore, while they performed nicely on the track most of the time, towards the end of the event (when they were getting thin) they were hardly working at all, even on the street. When I replaced them after the event, I found that the surface had small pits all over it - not as though the pad material was crumbling and falling apart, but it wasn't a solid smooth surface like I'm accustomed to.
When I replaced the Ferodo pads with new RM pads, the brakes were emitting a horrible grinding sensation (sound and pedal feel) - not a wobbly vibration like warped rotors, more like the feel when brake pads that don't have squeakers are getting down to bare metal. We theorized that the Ferodo pads left deposits of pad material on the surface of the front rotors. We had them turned and the sensation disappeared.
[DS] I would warn AGAINST using the R4 pads. I tried them last year. Not only did the pads wear just as fast as the R4S, but they took the rotors with them.
I use the R4S pads (and Motul 600) very successfully and I am hard on them. I'll be trying a different circuit for the first time in the NSX this weekend. This circuit is harder on brakes than the other one I use, so if this opinion changes I'll let you know.
[ABM - 99/6/17] My experience is that the R4S is a great street pad that can withstand occasional track use. It offers better grip than stock and is not too dusty (though more so than stock).
The R4S is not a good track pad for those with a lot of track experience / very heavy brake users. They wore down to almost nothing in a single weekend at TWS.
When I called Porterfield, they said the R4 would actually last longer because of superior ability to manage heat. So, I ordered a set. They were right. The pads are maybe 20% worn after a weekend at the track (the R4S pads were 80% gone after one weekend).
So, I now keep a set of the R4 pad for track duty(fronts only since they do almost all the braking, and besides, the rears are a pain). I simply swap out the front pads when I put on the track tires. I have driven with them on the street and they feel good. Quite dusty, but no "track pad" issues such as noise or cold braking loss. Note that the R4 requires you to remove the metal brackets in the front pad area in the caliper. Also, the pad itself on the R4 is larger. That is, the backing plate is the same, but a larger percentage of it is covered in pad material.
Drilled vs. Slotted vs. Normal Rotors
[KS] I've run my slotted rotors for eight track events this year, and previously ran another forty or so track events on my NSX with OEM and cross-drilled rotors. I keep meticulous records of total miles and track miles. And there is no difference in pad wear since switching to the slotted rotors.
[MCA] Not all cross-drilled rotors are the same. There are two main types:
Drilling and chamfering the holes (additional finishing, etc.) Casting the holes in (i.e., not really "drilled") -- this is what MOVIT does on the P911TT brakes, I think AP does on the Diablo SV, etc. Am not sure what process Brembo uses.
[DB] Standard Brembos have a couple of small slots and that's all. You won't see drilled rotors on a race car. It's a cool-looking style which is mechanically disadvantageous and has no net thermal benefit. Even the slots are perhaps unnecessary because all modern brake pads are outgassed during manufacturing, or use low gas generation materials.
The desired mechanical characteristics of rotors are: high heat capacity to allow the lowest possible temperature rise for a given energy input in a short time (like slowing from 100 to zero in a few seconds;) good mechanical stability over the required temperature range, meaning it mustn't distort from ideal shape and must maintain its mechanical strength over the required temperature range; and good thermal conductivity and dissipation to get rid of the energy to atmosphere as quickly as possible.
Drilled holes create severe mechanical stress risers unless they are correctly finished, which most of them aren't. If they're correctly finished holes, they make moderate mechanical stress risers. The holes slightly improve dissipation and decrease heat capacity, for no net thermal gain to the task presented to them.
Bottom line: money for style, not performance. From most sources (not all,) a mechanical disaster.
DIY Slotted Rotors
[MJ] I have a buddy that just slotted my OEM rotors, and he would be happy to do yours as well. He does Pcar rotors by the hundreds, so I think he knows what he is doing. 1 pair - $35, all 4 - $60. You pay the freight back and forth, 1 week turnaround.
He recommends that you turn the rotors and inspect them for cracks, useful life left etc. before you send them over. OEM rotors for '92 over at CUSH were $460 a set of 4 last time I checked, and I don't mind picking up a set FOC (ie, you pay just the cost of the rotors + slotting, no markup) and getting them slotted for you if you want to "order" a new replacement set..
Please contact him directly for slotting:
Wayne c/o Alta Designs 4990 MT Bigalow Drive San Diego, CA. 92111 619-292-2363 - o 619-292-0942 - f [email protected]
=have someone cut slots in your rotor? -EEEK
[KS] They don't necessarily reduce ground clearance. I have two-inch diameter hoses running from the front air dam to the brakes. They squeeze between the lower corners of the radiator and the air conditioning condenser housings in the wheel wells. They don't go any lower than the radiator.
What Brake Fluid Should I Use?
[BSD - 99/7/27] Brian's plan for picking a brake fluid: Start with something cheap. Ford HD comes to mind. If, and only if, you boil it, think about ways to fix the problem. You might then add brake ducts. You might try upgrading fluids. Try one with better measurements, like Motul or whatever. If that doesn't work, then add more brake ducts and/or try a more expensive fluid. -I disagree, ATE Superblue is cheap and works extremely well, don't start off with cheap Valvoline Dot 4 crap, start with a inexpensive higher quality racing fluid. Brake ducts are not necessary for most applications, proper fluid and pads are the main culprit.
[AWN] The manual says to use DOT3 and DOT4 fluid. DOT5 is not recommended. Ideally you should change your brake fluid at least once a year. You can do this by bleeding the brake system, which is also a good thing to do before (and possibly during) any track event. Stay away from silicon-based fluids (Castrol SRF is silicon-based). Silicon-based fluids are fine, you just don't want to mix silicon with non silicon based.
What Fluids Have People Tried?
[RM, MS, AWN, A/H] The following brake fluids have been used in the NSX with good results: Factory specified Honda brake fluid, Motul 300, Motul 600, Castrol SRF (expensive), Ford Heavy Duty Brake Fluid (racers secret - cheap with a higher-than-normal boiling point, works extremely well). ATE Superblue.
[CMI] If you want the best, go with Castrol SRF. It has a WET BOILING POINT of 518 degrees and a dry boiling point of 590 degrees. It saves the trouble of changing for every track event. One word of caution, hold onto something when you pay the bill. 1 liter can is $74.95. BTW, I believe it is worth it.
[KS] You can use any brand of brake fluid. The wet and dry boiling points are the best way to judge how good a fluid is - the higher both boiling points, the more protection you have against the fluid boiling. (Fresh fluid boils at the dry boiling point temperature. Fluid can absorb moisture over time, which lowers its boiling point. When it has absorbed as much moisture as it can, it boils at the lower, wet boiling point temperature.)
The owner's manual recommends only DOT 3 or DOT 4 brake fluid. This can be any brand of brake fluid as long as it's DOT 3 or DOT 4.
DOT 5 is silicone-based brake fluid, and while boiling temperatures are higher with DOT 5 (thus the higher performance), there are some other disadvantages of DOT 5, such as the inability to mix it with DOT 3 or DOT 4. However, there are some DOT 3 and DOT 4 brake fluids that actually meet the higher temperature standards of DOT 5 (see below). Technically, these higher-temperature brake fluids could qualify for status as DOT 5.1, which is for NON-silicone-based brake fluid, but they are usually sold as DOT 4 anyway. You can read the Federal regulations regarding brake fluids (TITLE 49, PART 571, Subpart B, Sec. 571.116, Standard No. 116; Motor vehicle brake fluids) at the DOT website at [www.access.gpo.gov/nara/cfr/cfr-table-search.html http://www.access.gpo.gov/nara/cfr/cfr-table-search.html]
The major characteristic of high-performance brake fluid is its resistance to boiling. This is measured by its boiling points, which are usually provided on the container as dry boiling point (for fresh brake fluid) and wet boiling point (over time, brake fluid will absorb moisture, lowering its boiling point; wet boiling point is when it has absorbed all the moisture it can).
I use Motul 600. Motul 600 is a DOT 4 fluid with a dry boiling point of 585 degrees F, and a wet boiling point of 421 degrees F. This is higher (better) than the Ford fluid, which is rated at 550 degrees F dry. Motul sells for $8-12 per half liter (pint) bottle. I'm pretty sure you'll find that the boiling points on Motul are higher than any other brake fluid except that Castrol stuff that Phil uses (don't look for it in the stores, it's special order Castrol only). Boiling point on the Castrol stuff is about the same as Motul dry, much higher wet, which means it will make a big difference only if you don't plan on flushing your brake fluid every once in a while. Oh, and the Castrol stuff costs $75 per pint. So Motul is not only a great brake fluid, but a bargain as well.
ATE Super Blue has a dry boiling point of 513 degrees Fahrenheit, wet boiling point at 388 degrees. I prefer Motul Racing Brake Fluid 600. You can buy Motul for around $12 a bottle from a number of sources, including RM Racing. Thus it has much higher boiling points than the ATE Super Blue but it doesn't cost a huge amount. I've been using it for six years in my NSX with excellent results.
I find Chuck's info on the Castrol SRF to be very interesting. You'll note that its dry boiling point is almost identical to the Motul, but the wet boiling point is much higher. Thus if you flush your brake fluid fairly often (which you should if you take your car to the track a lot), the Castrol SRF might not make much difference vs the Motul, but if you plan to leave your brake fluid in your car for a while, the Castrol SRF will provide better protection against boiling after the fluid has been around a while and absorbed a lot of moisture.
OTOH, if you use Motul, you can take the savings on the brake fluid over the Castrol SRF and spend part of it on getting your fluid flushed more often, and still have virtually the same protection against boiling.
[EBK] There is a little bit of "voodoo" regarding this boiling point rating in my opinion. I tried every brake fluid out there until I finally found one that didn't cook on me. I've boiled Motul 600 on 2 different occasions (diff track event/atmospeheric temp/elevation etc..) I have never boiled the ATE Super Blue fluid. The Porsche guys here have boiled the Motul as well, and they are the ones who refered me to the ATE 2 years ago. I have also boiled the Honda fluid, the Ford fluid (recommended by Comptech) and a number of others.
[MJ] I use ATE super blue and it is great, especially @ $10/quart.
[DS] If you don't want fade, get some Motul 600 brake fluid.
[PM - 99/7/27] The best brake fluid available is Castrol SRF at $75.00/litre. I've run SRF exclusively since spring of 1996. No problems of any sort either on the street or on the track.
[DS] I get Motul 600 from Porterfield. 1-800-537-6842. They charge $8.95/0.5L or $89.00 for a case of 12 plus s&h. I usually order by the case as you can never have brake fluid in your system that's too fresh. I change it about once every 2 months.
[DH - 99/7/27] I use the Ford Heavy Duty in my Comptech Brembo setup, and it works great. Never boiled, never fades, even in two hour long enduros on hard braking tracks. It is kinda hard to believe when the Ford stuff costs so little, something like 4 or 5 bucks a can (maybe even less). I bleed them prior to a track weekend.
Ford Heavy Duty Brake Fluid is also known as Ford High Performance DOT 3 Motor Vehicle brake fluid.
[EBK] I went through a lifetime of nightmares figuring the right setup for the track. I have finally found the ULTIMATE package (without going the $11K Comptech/Brembo route). First of all fluid is key. Use ATE Super Blue Racing. I have boiled the infamous Motul 600 but never the ATE. Secondly, a set of stainless steel braided lines can't hurt. Rotors.... This will vary among different drivers, car set-up's, track conditions, and how hard you are on them. I am very hard on the brakes and for me, I'm convinced the only way to go now is slotted. In second place would be stock configuration (perhaps a better cast, like Bendix but nothing done to it). And in last place would be cross-drilled.
Finally, all this is irrelevant if you do not have the right pads on the car. Before I say what I have to say, I want to assure you all that I have no shares in RM racing, and I do not get any kick backs for pad sales :). Now...I bought a set of "race-only" pads of Randy at the beginning of the season, and at the time, nobody had tried them yet, but I never got to try them because my car was in pieces throughout the first half of the season. Just over a month ago, I tried these pads for the first time....WOW!!!!! Unfricken believable! I did a 3 day track event (fri/sat/sun) on the same pads with absolutely NO brake fade and the power of the pads were no less than if I had thrown an anchor out of the rear end every time I broke. I LOVE THOSE PADS....Best I've ever used! Just in case you are wondering what kind of pads I have used to make this comparison, I've pretty much tried all pads (not just on my NSX though, I track a BMW as well) from the worst I've ever had - Stillen Metal Matrix, to very good Cool Carbon, and Hawk Blue. But none of them were as good as the RM race pads.
At Mt. Tremblant, my "home track' and an ex-Formula 1 track, I pretty much know it by hart. At the back straight Before my TT's I was hitting about 125 mph before hitting the brakes at the same spot to enter the right turn at about 60 mph. Now..... This time I had the TT's. My speed down the back straight hit about 145 mph!!! and, When I broke at the same zone I always brake at (but this time carrying WAY more speed) I almost STOPPED the car before the entrance. I was so shocked I messed up the rest of that lap. As the day progressed I found myself braking deeper than ever thought possible while basically standing on the brakes with no fade whatsoever the entire weekend! Well done Randy! and thank you.
I know of three people who tried some type of carbon metallic, and all three, (including myself), were dissatisfied customers. The R4S might stop a wee bit better than the stock pads, but your wheels will always been black from the dust. They seem to wear faster than the stock pads. I tried the following combos: Stock Pads, metallic Pads, R4S pads, all with drilled rotors. Metallic Pads, Drilled Rotors - didn't stop very good. Pads trashed in a weekend or so at ButtonWillow.
Drilled Rotors, R4s pads, stopped pretty darn good. Pads lasted about 2 months. Also suffered crack rotor. Thus a DNF(did not finish) in the time trial event. This really sucked..... Drilled Rotors, Stocks Pads, stopped pretty darn good. Pads lasted 2 months(with a couple of track events)
Went back to stock rotors, stock pads. Pads will probably last me a year. Stopping power is a tiny bit less, but I am not spending $250+ for Pads and labor every two months, plus the irritation/headaches of going to the dealer all the time. Plus the wheels are always clean. Yes the rotors were chamfered, or whatever you call it. I call it a cheese grater, at the rate it ate my pads. But I have to admit, the drilled rotors do look really cool on the car.
One thing to keep in mind is that I am really hard on brakes. Really hard. When driving on the street, if the intersection is clear andsafe, and no one is behind me,I always try to brake at the last possible moment and savor the G forces of the car stopping and my body hurling against the five point harness right on the mark from 60-0 in what feels like 20 feet.
The "dust and squeal" complaints are from people using Porterfield's carbon-kevlar pads. Both carbon-metallic and carbon-kevlar pads work well when cold, and both continue to work well when very hot. Carbon-metallic pads eat rotors. That's their one disadvantage over carbon-kevlar.
[DH] I went to Laguna Seca with stock rotors and R4S pads. The brakes were awesome. I am switching to the R4S pads as my daily use pads.
1. Comptech/Brembo brakes use Brembo iron rotors and Brembo calipers. The price is $10K including the required new wheels (Forgeline).
2. Cooltech brakes use their own aluminum-ceramic (also called MMC for metal matrix) composite rotors with Brembo calipers, 8 piston front, 4 piston rear. The price is $15K including the required new wheels (Speedline). The rotors are not the major reason why they're so expensive.
3. Stillen less expensive stuff is not as good. Maybe not as good as stock.
4. Carbon rotors: don't ask, and not suitable at this time.
The Brembos are known excellent. The advantage of the Cooltech kit is the rotors are 40% the weight of iron and have five times the thermal conductivity, and last very long indeed. Disadvantage is price, but the rotors themselves are only about $500-600 each, so that's *not* the big difference. It's the other stuff, especially wheels.
It is perfectly possible to get different rotors which fit the stock calipers, but both Comptech and Cooltech decline to do this due to their belief the stock calipers are inadequate. Stillen doesn't care. In addition, it would cost Cooltech $20K in tooling for custom rotor molds to fit stock wheels, even if the calipers were good enough. They can't see recovering their costs, and the calipers would still be inadequate. The Speedline magnesium wheels via Cooltech are $5k a set including tires. The Forgeline aluminum wheels via Comptech are $2K per set without tires, and that is quite cheap.
So, you ask, why are new wheels required? Answer: because the axial thickness of the new calipers, be they AP or Brembo or whoever, will not fit between the rotors and the wheels in the *axial* direction. The stock NSX calipers are thinner than anything else on the market in the axial direction, and the wheel inner axial clearance to the rotors will not allow anything else. Understand this: diameter is not the problem, it's the other direction that won't fit.
Since good wheels are expensive, this drastically increases the cost.
Is there hope? Cooltech is working on a custom wheel deal and less expensive other components to cut the cost of an NSX MMC kit by half. I told them if they succeed, I'd be a customer. Comptech has given up trying to go downscale at this time; they just can't find the right combination of parts for it, and they're not willing to sink serious design time into it.
Carbon rotors suitable for the street are in the research labs of one or two companies, but they may never make it to you or me. Racing carbon rotors on a street car are not advisable because they don't work well when cold.
Doesn't this show dramatically why brakes/wheels really are a system, and when you change one thing, sometimes other things will also have to change? But more cooling air to the rotors is always helpful.
[BDV] Just got back from a weekend at Road Atlanta. The previous time I was there, I ran Castrol LMA and RM pads. The track had just been changed and now calls for braking from 145mph to about 45 mph, on the back straight, with most of the braking zone downhill.
I lost my brakes on the 5th lap. The LMA boiled, and the RM pads glazed. I bled the fluid, but the pads were still glazed, and the car didn't stop worth a damn.
Tossed the RM pads (thought they were good street pads though) and changed to Hawk Blue. Tossed the LMA, and changed to Motul 600. Now breaking is unreal. The rotors did NOT get chewed up, and fade/boiling/etc. never happened.
The Hawk Pads are real race pads, good for 1400 degrees F. I was told they are bad on the street, but this is not true. The street bite is as good as the RM pads, but no high temp fade. Cost is about $220 for both axles. Not sure about wear because I have not checked yet.
Only one down side. Initially, brake dust was huge. But after a few sessions, it is now normal. Also, not recommeded for drilled or slotted rotors. I used my stock rotors with zero problems.
I am told that the Hawk pads are used on 3000lb stock cars, and other cars of similar weight. Brake system now considered optimzed. Whew. Was able to finally outbrake the Porsches. Not sure everyone needs this much braking, but if you do, this is the way to go.
[KS] Doug and Brian both recommended the Porterfield R4S pads, which they enjoy for track use. I have used the R4S in my NSX on the track and I liked them. I also currently use the R4S in my Integra GS-R primarily on the street (but occasionally on the track), where Alex's description of the MetalMasters sounds exactly like the R4S; when they're warmed up they're fine, but when you just start out they aren't there at all. The other thing I found is that to break them in properly you have to REALLY heat them up, either with a whole bunch of panic stops 70-0 or a few laps on the track. They'll totally fade and then you need to let them cool down. Do this a few times and they're broken in. All in all, I'm not sure they're best for street use only.
[KK] I purchased Friction tech kevlar from Brake Warehouse. These are for street use, not racing. They are supposed to be easier on rotors than stock and perform slightly better. They are supposed to be broken in for about 400 miles of easy braking which I have done and have about 600 miles on them. They have no squeal, NO brake dust and stop extremely well, however, they seem to take slightly more INITIAL pedal pressure. I think they are excellent pads for street use and cost about $100 total for all four wheels.
What Is Brake Bias?
[BSD] The following assumes ABS has been defeated. As it says in the user manual, ABS is a steering aid when braking, not a shortest distance stopping device.
The brake system, when set up properly, will apply pressure to the pads (front and rear) such that maximum braking is possible. To explain, the pads will grip the rotors according to the coefficient of friction (Cf) of the pads times the force from the pistons/calipers. As force is added, braking force is also added.
As the car brakes, weight will transfer to the front wheels. This increases the amount of traction the front wheels have and decreases the traction in the rear. This is why the front pads and calipers do more work than the rears (and are a different size). The stock proportioning system allows for a certain ratio of the brake pedal force (after booster) to be sent to the fronts and a certain pressure to the rears. I am assuming there is a stock non-adjustable brake bias (proportioning) system on an NSX.
Even when weight shifts to the front of the car, the front tires can only grip so much (according to the tires' Cf with the road and the weight on the tires). At that point, the rear brakes should also be gripping the rear rotors at the maximum they can without causing the rear tires to lock up. Both ends should max out the tires at the same time. The proportioning system is how you accomplish this.
Assuming the stock system is set up perfectly for the stock pads and stock tires means that the stock system (non-adjustable) is _not_ set up correctly for different tires or different pads.
Let's say we put on R1 race tires front and rear which have more grip than the stock tires. Now, as the car brakes, weight shifts to the front and the tires grip the road and slow the car. However, the front tires at the previous maximum braking level are not doing as much braking as they _could_ do. If you continue to press the brake pedal, both ends will do more and more braking and more weight will shift to the front of the car. This gives the front even more grip and the rear even less. Now, the rear brakes will be doing too much for the tire grip and the rear tires will lock up first. When you put on stickier tires, you want more brake bias towards the front. =Not necessarily true and a wrong statement to generalize.
The same argument, in reverse, works for running in the rain or on other more slippery surfaces. When braking in the rain, the fronts just can't get enough grip to brake the car as hard as it can in the dry. This means less weight shifts forward (less grip up front) and more weight is left in the rear (more grip in the rear). In this case, the fronts lock up first. That means more brake bias to the rear is appropriate.
Hope this makes sense.