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.Mad Hatter.
11-16-2010, 06:37 AM
I realize there about 7 trillion of these threads floating around, but I have not come across exactly what I need to know (at least not in years and there are far too many threads to search).

So here goes:

Front setup:

Boxster calipers/pads
PureMS brackets/lines
D2 A8 rotors (slotted)

Rear setup:

B5 S4 calipers (buying them used, so the carriers would be included)...

Then I have 2 options:

D2 A8 (269mm x 20mm) rotors with D2 A8 carriers (B5 A4 pads, stock lines)

OR

B7 S4 (300mm x 22mm) rotors and 034 custom carriers (B5 S4 pads, 034 lines)

Does this all seem accurate so far?

Does anyone see ANY reason NOT to go with the B7 S4 rears? The bracket from 034 is very affordable, and I can get rotors at cost so they won't be terribly expensive.

Rundown:

B5 A4 front: 276mm x 25mm
D2 A8 front: 312mm x 25mm

B5 A4 rear: 245mm x 10mm
D2 A8 rear: 269mm x 20mm
B7 S4 rear: 300mm x 22mm

Stock F/R bias= 1.127

D2 A8 F/D2 A8 rear bias= 1.160

D2 A8 F/B7 S4 R bias= 1.04

So, brake gurus...could this cause an imbalance? Am I at risk of having the rear end trail or wearing out the master cylinder?

TIA, and sorry for the redundant post.

[wrench]

hercfe
11-16-2010, 09:44 AM
Stay away from the B7 setup based on the numbers. On paper you will have a gnarly unbalance, which(depending on what you want to do) could really throw out the rear end under hard braking. Or you could just buy an aftermarket brake bias adjuster and install it to correct for the imbalance. The really much better option IMO would be to upgrade to a 330/355 front setup-355 being optimal. Of course, the downside to 355F300R is that your eyeballs will remove themselves from your face during a hard late break. I would also consider upgrading the master cyl. I know not many people do that on here-or any forum for that matter, but it all comes down to how much fluid you can move. Master cyls are matched for the piston size, line size, and line length. If you start really upgrading the surface area inside the system, you lower the pressure and volume of fluid effectively and proportionally. I'm sure someone on here will bash me for this, but IMO the best upgrade to a brake system is better tires, then BIG fronts and stainless lines, then a better master cyl, and finally big rears.

.Mad Hatter.
11-16-2010, 11:45 AM
front setup is remaining what i posted, but i appreciate the input re: the rear.

Kyle H
11-16-2010, 11:55 AM
You probably want to get either stickier pads up front or go with a better ratio. That said, an 8% difference isn't much.... buttttttt you have to remember, the harder you brake, the more weight will transfer to the front.



Personally, I'd go with the 300mm rears.

Kyle H
11-16-2010, 11:58 AM
but it all comes down to how much fluid you can move.

Not really... Most of the time you can cook the tires or the pads before you run out of pedal travel. A larger cylinder would just make the caliper pistons move faster, something with may degrade brake moderation.

.Mad Hatter.
11-16-2010, 12:04 PM
for now the pads up front will be the stock boxster pads, which i assume are decent (pagid maybe?). it actually would be cheaper for me to do the B7 rear, the brackets are like $75 but the A8 carriers are at least the same, if not more, haha. i really do not want to damage the system though, and i have read some issues about the master cylinder.

somebody5788
11-16-2010, 12:11 PM
for now the pads up front will be the stock boxster pads, which i assume are decent (pagid maybe?). it actually would be cheaper for me to do the B7 rear, the brackets are like $75 but the A8 carriers are at least the same, if not more, haha. i really do not want to damage the system though, and i have read some issues about the master cylinder.

I'd just stick to the A8 fronts and B5 S4 rear. Ratio is good and it's not making your stock brake system work any harder!

jm121189
11-16-2010, 05:38 PM
I have the exact same set up you are thinking about, 312x25 up front and 300x22 in the rear and the car stops quick on my summer tires. I had the stock size a4 rears with upgraded fronts for a while and upgrading the rears made a good difference. The balance is better and the car tends to remain more level during hard breaking. I don't have any official numbers or tests to back this up but I can tell you there is a large difference. If anything I would get the bigger rotors just so you have a larger surface to dissipate heat from. I did a track day and was impressed with how long it took before the brakes started to show fade.

.Mad Hatter.
11-16-2010, 06:25 PM
My main concern would be the master cylinder, but I have not heard of anyone really running this setup (excluding you, obviously, lol).

jm121189
11-16-2010, 07:57 PM
I would say go for it, I have not noticed any problems but I also don't know how much a larger master cylinder would help...if any.

somebody5788
11-17-2010, 05:50 AM
My feeling is the master cylinder failures are probably on heavily tracked cars. Running a better brake fluid may help, or maybe it's actually causing pre mature seal failure. I'm just really throwing out some idea's here lol I have no idea but I don't think a daily driver needs to worry about over working the master cylinder.

.Mad Hatter.
11-17-2010, 06:10 AM
That is my thought as well, the car will likely be tracked, if it does, it will be periodic at best.

.Mad Hatter.
11-21-2010, 06:03 AM
Does anyone else have any real world experience with the B7 rear setup? Jim? Bueller?

.Mad Hatter.
11-21-2010, 06:11 AM
I have the exact same set up you are thinking about, 312x25 up front and 300x22 in the rear and the car stops quick on my summer tires. I had the stock size a4 rears with upgraded fronts for a while and upgrading the rears made a good difference. The balance is better and the car tends to remain more level during hard breaking. I don't have any official numbers or tests to back this up but I can tell you there is a large difference. If anything I would get the bigger rotors just so you have a larger surface to dissipate heat from. I did a track day and was impressed with how long it took before the brakes started to show fade.

question; the B7 rotors are 22mm wide, and the B5 rotors (rear) are 20mm wide...i assume this means you used B7 S4 rear pads?

onemoremile
11-22-2010, 01:33 AM
My feeling is the master cylinder failures are probably on heavily tracked cars. Running a better brake fluid may help, or maybe it's actually causing pre mature seal failure. I'm just really throwing out some idea's here lol I have no idea but I don't think a daily driver needs to worry about over working the master cylinder.

My 99.5 Avant has a few thousand track miles and the stock master cylinder is still fine. I'm running stock calipers with Tyrol bushings. I usually run ATE Typ.200 fluid which is arguably the best you can run in these cars.

jm121189
11-22-2010, 07:29 AM
question; the B7 rotors are 22mm wide, and the B5 rotors (rear) are 20mm wide...i assume this means you used B7 S4 rear pads?

I used b5 s4 calipers with b5 s4 rear pads and it works just fine, I assume there is a little wiggle room since the caliper is on a slider and 2mm really isn't much of a difference in this situation. I'm not familiar with the b7 rear calipers but I'm sure they use a totally different pad than the b5 so I doubt you could interchange them.

I would call 034 or jhm if you have any questions since they both sell kits for this set up and should be able to answer all your questions.

.Mad Hatter.
11-22-2010, 09:09 AM
ya thats what i will do, just curious what you ended up using.