sean_w_smith

OK I will revisit my experiences with pads I have used on my M5. bot going to talk about pads from my M3 and other cars than I have not tried on my M5.....

Stock - Joke. I can totally fade the brakes within 1 lap.

R4S - still a joke. Killed an entire set in less than 2 hours of track time at CMP. bite and fade resistance slightly better than stock but these don't work as a track pad on this car. on the m3 these work ok for up to intermediate drivers.

Panther XP8 : Much bettter. but still fade after 3-4 or laps. They never went completely but I got the some hot the front brakes caught fire after a couple of hard laps on VIR Full. Approaching 150 Mph into the VIR Back straight braking zone.... My current choice for a track pad. These are wearing very well.

Bobcat - my current street pad choice. similar in most ways to R4S. Less squeal though. Good price.... not a REAL track pad. maybe for novices....

Skill level has a lot to do with it. I have had students who have run 4 track events on stock pads or mild track pads without killing them or having significant fade. reason, there are novices/intermediates and don't drive too fast....

Hawk Blue and PF97, 00, 01 etc will destroy your wheels. Especially with any moisture. I destroyed a set of BBS RK's last summer at Road Atlanta with PF 01s. Conditions were dry. I get of my car, and then go riding with my student and then the rain starts. Come back an hour later and dust is cemented to wheels. Any ferro carbon compound will suffer from this type of problem. Carbon Kevlar is much friendlier on wheels and rotos...

XP8's seem to be rotor friendly and have used them for street use but the bite cold is not good for street. Bobcats and R4S's work better hear....

I considered R4 but the temp range is too low. Given how hot I can get the brakes something like an XP8 etc is going to be only real choice. good luck....

Overall from trying many pads I like Porterfield and carbotechs because 1. they work, 2. they are fairly inexpensive compared to other pad options. 3. They are rotor friendly compared to Hawlk and PF. The dust won't destroy your wheels in record time like Hawk Blues and any PF race pad I have ever tried...

From experiences on the M3 the PF01 is the best track pad I have ever tried but its not that much better than pads like R4 and Xp8 which don't destroy your wheels or rotors. So I used Carbotech and Porterfield even on the dedicated track car...

Honestly if you plan on tracking the car regularly I would get a BBK for the front. Again, I am not a BBK fan in general. I have run 60+ events on my m3 with stock brakes, stock rotors (not euro floating), ducts and race pads and NEVER EVER warped a single rotor....

Have Fun...

Sean Smith
Raleigh, NC

00 M5 - Daily Driver
95 M3 - Track Car
93 MX-6 - Beater and Backup Track Car
04 WRX Wagon - Winter/Snowboarding Vehicle

Lscman

Sean,

Great info....thanks! Your track experience and feedback is real helpful.

A BBK is a nice option, but hey, you're talking to a guy who logged 30K track miles (over a 10 year period) running a 3800 lb Lincoln Mark VII with stock 10.9" front rotors. I was able to run B group totally stock with non-R rubber and $40 PFC-Z street pads. In addition, I run significant SCCA Solo and I (still) prefer to remain in stock class.

I'm not out there to tear up the track. Everything is relative & I do prefer the underdog role. When a B group Viper or M3 driver I passed examines my Lincoln for modifications (that don't exist) while I'm at the concession stand getting a hot dog, it makes for good dinner discussion. This offers a feeling of accomplishment that can not be matched with hardware upgrades or by driving superior vehicles. I've been on both sides of the fence. With respect to track, I feel...the more peelin' paint and rust, the better. While my 540i may not eclipse the performance of my Vette, I expect to do a little better in this car than in my previous family commuter vehicles (lol).

Lscman

I appreciate your post, but this flies in the face of E39 pad mfr recommendations. The E39 brake systems are sized to provide balanced front-to-rear rotor temps under moderate duty. This is done so OEM street pads will offer good bias & braking performance under typical use. Under severe track duty, weight transfer issues take over & the braking systems on these cars do not behave like a race setup. The temps of the front rotors go sky high and the rears don't. Race pads do not exhibit a linear coefficient of friction, so if you run the same race pad front and rear, the hot front brakes will bite hard and the cooler rear pads will not bite well. This will, in fact, overheat the front brakes even worse and cause the overworked front tires to take even more abuse. This can contribute to understeer as the tires become hot & greasy.

This is why on E39 the Hawk HT10 is matched to Ultimate...and why Pagid Yellow is matched to a Pagid street pad..and why XP8 is matched to Bobcat...and why XP9 front is matched to XP8 rear.

To dissect this further, let's look at the Dave Z sample package. The HT10 front pad will offer a similar friction coefficient at 1100 degrees compared to the Ultimate pad operating at 800 degrees on the rear. This is exactly what you want for the M5.

I got these recommendations straight from the pad manufacturers, not retailers (like Dave). They mirror recommendations I've seen for Corvette and other cars with STOCK rotors and calipers. Since these mfrs produce matching race pads for the rear of the E39, there is no reason for them to mislead customers. The goal is to balance the coefficient or friction between the front and rear at the actual temps experienced on-track.

If you're running StopTech front brakes with the stock rear brakes, the same pad compound front and rear may be optimal. This is because the front-to-rear temperatures will be better-balanced under severe duty use. A stock Porsche will behave differently than a stock BMW M5 under severe duty braking, and your note will indeed apply. Weight transfer and brake sizing on various on sedans and sports cars will vary & this will impact pad recommendations.

sean_w_smith

I love it when people bring unique track cars to track days and auto-x's. We auto-x'd the F350 TD last year....

I will comment I have matched the rears with the front race pads with good results as on my E36 and currently run bobcats front/rear street and XP8's front/rear for track with the E39. The bias and balance is fine....

I have on occassion had to throw Stock pads or R4S's on the rear of my E36 with Race Fronts and the difference is not very much. Bottom line IMO rear pad choice doesn't seem to make too big a difference compared to fronts. That said I always change them from stock if for nothing else to get something that dusts less than a BMW pad or for track use wears less than stock.

Sean

Lscman

Sean,

Thanks for replying. It is interesting and encouraging to hear matched pads work for you too. Your opinion about matching race pads obviously echo's 2002M5BGM. That said, it does differ from CarboTech, Performance Friction and Porterfield recommendations.

The use of temperature-sensing paints on rotors is very helpful for determining the best approach here. I have not conducted such testing on my BMW, but I will this season. If anyone has compared front and rear brake temps on an E39, I'd like to hear the results. I suspect on-track the front rotors become heat checked and cracked long before the rears. If these assumptions are wrong, please speak up.

What I've noticed thru the years is:

1) racers with upgraded front cooling ducts and/or oversize front brakes or well-balanced OEM brakes (Porsche) tend to prefer matched pads because front and rear temps are similar. This is the ideal situation that I can only dream about. In addition, folks running street or intermediate pads run matched pads front and rear (no batter how well-balanced the system temps are) because the friction coefficient quite flat with respect to temperature, compared to a full race pad.

2) racers with OEM brakes that see highly elevated front brake temps (when running the same pads) tend to prefer an "unmatched" brake pad combo to keep the respective pads within their operating bandwidth. The key is to find a pad that offers a similar friction coefficient curve at a lower temp.

Conclusion:

It is impossible to "guess" whether matching rear pads on the M5 see enough heat to remain in balance with the fronts. A cooler rear pad may offer a significantly different friction coefficient at a single point in time. My experience has shown this "issue" is not necessarily be detectable by the driver. It took quite a few years for the Corvette C4 and C5 community (running OEM brake systems) to settle upon the use of mismatched front and rear race pads. The use of unmatched pads is "the rule" for those vehicles on-track. The same goes for the GM F-body and Ford Mustang. Those vehicles also overwork the front brakes, so the best setup is a hot pad in the front and a cooler pad in the rear. The M5 community is much smaller & does not run much track time or share information like this, so there is little consensus. It is clear to me that Performance Friction and CarboTech experts strongly recommend mismatched track pads for cars that show significant temp differential between the front and rear.....and they tell me the M5 fits in this group.

Redshift

I disagree with your comments about the C5 "rule" on mis-matched front and rear pads. Some folks believe that is the best setup and some do not. I know a lot of racers who use the same pad, front and rear, and a few who do not. I also use the same pad front and rear and have excellent results.

On the M5, Dave Zeckhausen suggested to me that the Stoptech BBK with PFC01 up front and Axxix Ultimate in the back is the best combo. I went with his suggestion and it felt fine, for the most part, except during one particularly hairy moment during which I felt significant NON-reaction of the brake pedal after the straight at my local track. Rather than fly off into the weeds, I decided to turn in and scrub off some speed -- not doing my front tires any favors of course -- and it turned out okay. That was the only time it happened, and I don't know why....typically the car braked flawlessly.

One thing to keep in mind is that more tire in the front (275mm on OEM rims, for example) will give you greater braking force than stock width tires. The more traction you have up front, the more effective your brakes will be in getting you slowed down, and the less heat and wear they will see for a given style of driving. You seem pretty advanced so I'm sure you already thought of this, but I mention it for the others reading.

I'm by no means an expert or anywhere close to it. I only have on track experience in my own cars to go by, and whatever I read here and on the other forums (forii?).

__________________
Brian - CCA #273611
Tarheel BMW CCA Street Survival Chief Instructor
03 540iT Sapphire Black - 01 M5 LeMans Blue - 02 330Cic Orient Blue - 94 M3 w/S50B32 Imola Red 08 F800ST Blue

*** Parting out entire 03 CB/Imola/Black M5 *** - TONS OF PARTS AVAILABLE

Lscman

I think we both agree the decision to run matched or unmatched pads should be done on a case-by-case basis. I also agree many C5 cars run matching pads front and rear. Many have huge 3" to 4" dia air ducts force-feeding the front brakes with air. These are sold by several mfrs. These cars may work best with matching race pads. Many other C5's have aftermarket BBK's on the front from StopTech and other sources.

In the case of my C4, it's optional ZR1 (ZO7) front rotors were replaced 8 to 10 times for each rear rotor replacement. The front brakes ran much hotter than the rear with PFC-Z street pads on the front and rear. This street compound has suitable cold bite, so on-track braking was balanced. The front pads lasted 2 days and the rears lasted a whole year (approximately 20 to 25 track days). Bias and threshold braking was excellent. The car simply had seriously overworked front brakes. If I had switched to high temp race pads on both the front and rear, I feel sure the rears would struggle to reach min operating temps. The car would have too much front brake bias for the first few laps.

Temperature-sensitive paint will determine the temp differential between the front and rear for each car, driver and severe duty venue. This data will allow the owner to accurately select the appropriate pad compounds front and rear.