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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Suspension | Brakes | Chassis > using PF08 in front and PF01 in rear pads to move brake bias to the rear?



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      12-21-2012, 02:33 PM   #1
n55PR
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using PF08 in front and PF01 in rear pads to move brake bias to the rear?

I want to test moving bias to the rear on my 335i for track time (4x20 min sessions). I want the rears to do a little more work. This is on the OEM brakes. Local track has no fast turns, its all hard brake zones into tight turns. The toughest 3 brake zones are 100 -125mph to 40 mphs in a 1min 15 sec loop.

Seems the only way to do this is by playing with brake pad compound selection. I am considering PFC08 Front and PFC01 Rear. Has anyone tried this set up?

Any suggestions on additional combinations? The selection of rear pads is limited Hawk HT-10, Pagid (expensive) and Carbotech is all I could find to fit in the rear.

I have been using Hawk DTC-70 front and HP+ in the rear, and the DTC-70 are almost gone while the HP+ are almost new!
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      12-21-2012, 05:11 PM   #2
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Braking performance ultimately comes down to the tires so I'd probably start adjusting the tire pressure to help maximize grip before swapping pads. As always use judgment.
Regardless I strongly advise against running a more aggressive pad in the rear relative to the front. BMW designed a specific brake bias in these cars to maintain stable braking conditions. It's slightly front biased like all street cars; safe, predictable and stable in other words because the front will lock up before the rear.

What you'd be doing using a more aggressive pad in the rear is making the car less stable under heavy braking because you're increasing the rear bias. I've been there; a squirrelly rear end isn't a desirable feeling. The way BMW designed these cars, the brake system is already providing the maximum safe amount of braking force to the rear axle without locking up the tire (say, enough to get within ~10% of the tire's maximum grip level - this is assuming everything in proportion equal to stock - same tires all around, etc). You'd eat into that margin with a more aggressive pad and may exceed it. Even if you got a rear pad that exactly ate up that front bias safety margin, it probably wouldn't be enough to make much of a difference in overall stopping performance; certainly not worth the risk of making the car unstable. The rears contribute not a whole lot to braking performance anyway so the difference is mitigated further.

For the record I run PFC 08 compound all around on stock brakes. I started with just PFC 08 up front and stock in back, which worked fine. I switched to the PFC 08 in the rear because I went to R-compound tires; they shortened my braking distances, generating too much heat for the stock rear pad to handle without noticeable fade over a session (I totally cooked the stock rears - they were cracked and white around the edges). I didn't notice any adverse effects to bringing the rear pads up to the same aggressiveness as the front.

Edit: good article here, not a ton of specifics but the overall ideas are sound:
http://stoptech.com/technical-suppor...alance-matters
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      12-21-2012, 05:48 PM   #3
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^ Informative post, thx. Are you using oem rotors?
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      12-21-2012, 05:55 PM   #4
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Originally Posted by cvc 22349a View Post
^ Informative post, thx. Are you using oem rotors?
Yes sir - stock rotors. In addition to the pads I did high temp fluid, SS lines and custom cooling for the front brakes (pics). Cooling became necessary after going to R-comps.
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      12-21-2012, 08:30 PM   #5
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Agreed and understand your post 100%, and appreciate your word of caution. However it is exactly that "safety" margin that I want to try tap into, and explore. Squeeze a bit more out of the oem brake system, that is the reason for my post.

Don't know if it is 1% or 15% we can gain, but I am confident the BMW engineers had to give up to the liability lawyers a safety brake bias margin us track guys can play with.....even with stock suspension and street tires and I want to look into it and play with it at the local track.

Have you ever locked the rears? Have you ever felt abs become active in the rear? I haven't in my 335i, when I do I will know the limit. I can get abs active in the front easily at the track with Hankook RS-3 street tires which are decent but not r-compound.

I will probably get PF06 for the front and PF08 for the rear. PF01 have more bite but at rear will probably operate below their rated operating temp.

Has any one tested othe combinations on the 335i?
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      12-21-2012, 10:21 PM   #6
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With the EBD on these cars you won't be able to spin the car with trail braking anyway without being a total jackass about it.

I'd worry a lot more about reducing your consumables budget as much as possible.
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      12-22-2012, 05:42 AM   #7
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Not trying to throw my car around hairpins, although that could be handy at the track we mostly use down here. Fortunately the track time sessions are very relaxed and experimentation would not be an issue to my fellow track time guys.

I will try other forums......the more I am told "don't do it" the more I want to look into it and eventually test it. Seems like some e46 track guys do this on their oem brake systems. We mod engines, suspensions, and just about everything in our cars, why not try to "tune" the EBD on our cars?

If anyone has done some testing in our cars, or has info to share please shime it!

In the meantime I plan to install my Hawk HP+ pads in the rear, keep oem pads in the front and do some brake street testing just to see how the car behaves with a more aggressive rear pad.
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      12-22-2012, 12:25 PM   #8
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My point isn't "don't do it" just that you won't notice much difference. Go ahead and do it and report back.
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