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sam.hollis
03-11-2008, 07:39 PM
Everyone is doing these TT carriers with a8 rotors up front for cheap, what can I do for the rear without spending 1000 dollars on s4 upgrade. Also I have factory 16 inch wheels for the winter will these clear or do I have to go bigger, I'm gonna run 18's in the summer. [confused]

grip_racer
03-11-2008, 07:47 PM
just run more aggressive pads all around, Hawk HPS should be great for a daily driver.

cheapest brake upgrade I know of.

Solaris
03-11-2008, 08:03 PM
You could do A6/B6 rear upgrade. I believe it's a 245 to 255mm upgrade. $200 worth of parts including rotors. Many say it's just not worth it, though. Good pads would be a better investment.

NakedDave8
03-11-2008, 09:11 PM
Pads and cross drilled rotors maybe stainless steel brake lines.

onemoremile
03-11-2008, 09:15 PM
Pads, lines, and fluid. The A6 upgrade won't be visually noticable and may hurt braking performance. Bigger is rarely better. Balance is always better.

Solaris
03-12-2008, 07:11 AM
Pads, lines, and fluid. The A6 upgrade won't be visually noticable and may hurt braking performance. Bigger is rarely better. Balance is always better.

But by putting 312mm rotors up front, aren't you throwing off the bias?

hoganalley
03-12-2008, 07:47 AM
You might be throwing off the bias marginally, but it's not huge. What I'm doing in the next few weeks is putting on 269mm rotors. Mathematically, they're the perfect upgrade to match the 312mm fronts. Only thing I'm not sure about is whether the extra leverage created will trip the rears faster. There's a guy on Audiworld that has done this and he says there's no problem. If you're keeping 16", then A8 brakes is the only thing that will fit.

ModifiedA4
03-12-2008, 09:51 AM
The A6 upgrade won't be visually noticable and may hurt braking performance.

hurt performance? how?

I have the A6/B6 rear upgrade. I did it at the same time as the A8/TT front. The car stops great, and some bias was restored to the rear end.

onemoremile
03-12-2008, 11:16 AM
I said MAY hurt performance. It should help balance out the A8 upgrade but only if the pads match and other basic considerations are in place. People tend to up the fronts with aggressive pads and leave the rears along for the ride.

ModifiedA4
03-12-2008, 01:29 PM
I said MAY hurt performance. It should help balance out the A8 upgrade but only if the pads match and other basic considerations are in place. People tend to up the fronts with aggressive pads and leave the rears along for the ride.

i was only wondering for the particular A6 rear upgrade since i have it, and thought i could be in trouble! [:)]

certainly going too large a rear upgrade can be downright dangerous.

iin10ded
03-12-2008, 02:10 PM
very timely. i got a set of rear s4 calipers for nuthing and wanted to use them. there is a writeup on audiworld [resources / tech articles / suspension] that says:

269mm x 20mm rear A8 upgrade kit will work on the following cars:
A4/S4: AWD, 1.8T + 2.8 + 2.7T (No calipers required for the S4)
A6: AWD, 2.8 + 2.7T
allroad: AWD, 2.7T
Passat B5: AWD, 2.8

Parts required:
Two Audi A8 269mm x 20mm vented rotors: Audi Part# 4D0-615-601-B
Two Audi A8 caliper brackets: Audi Part# 4D0-615-425-B
Audi S4 left caliper: Audi Part# 8D0-615-423-C
Audi S4 right caliper: Audi Part# 8D0-615-424-C
Four 2mm washers: (~$0.05 at a hardware store)

Before the kit can be mounted, the caliper brackets have to be machined to clear the control arm. You need to take off about 0.5mm in a very small area near the control arm. You can do it quickly with an air powered cutoff reel. The bracket has to be spaced from the wheel hub by two 2mm washers.

has anyone done this? thoughts on this with the a8/tt front upgrade? i don't know ho wi would calculate such that the system remains 'balanced'.

tia
jim

ModifiedA4
03-12-2008, 02:37 PM
i don't know ho wi would calculate such that the system remains 'balanced'.



my guess is that you dont want the rears to lock up before the fronts. this is based purely on the piston force/torque relationship to the rotor.

for an approximation,

take the radius of the stock front rotor divided by the radius of the stock rear rotor. whatever the bias is, it works through this rotor size ratio.

hopefully the rotor size ratio of the new setup is close to the original ratio, otherwise a bias shift would occur from stock. now where this gets fuzzy is with the dynamic bias proportioning the ABS is able to do. its possible that with a working ABS unit, all of this worry can go away. confused yet? i am. [:)]

iin10ded
03-12-2008, 02:47 PM
i am! which is maybe why that makes sense. =) i've already got the rotors and calipers, going to order the carriers [$230 ouch!] and see what happens. if i die from my arse end locking up on me i'll be sure to post about it.

onemoremile
03-12-2008, 02:59 PM
The ABS only comes into play after a wheel has locked up. It is on the back end of the event and doesn't regulate pressure to maintain balance. If you are trailbraking into a corner and the bias is too high in the rear then it could put the rears outside their friction circle which would result in a spin.

The A6 rears sound about right with the A8 fronts but the S4 rears sound more in line with the Boxster or Boxster S fronts. The best way to know would be to install them and get up to speed on a skidpad and then hit the brakes. That isn't practical for most of us.

iin10ded
03-12-2008, 03:01 PM
thanks. i'll post up once i get the carriers and do some high speed panic stops. i heart risk. =)

ps that's a great quote in your sig!

onemoremile
03-12-2008, 03:02 PM
Thanks - on both counts!

ModifiedA4
03-12-2008, 03:04 PM
The ABS only comes into play after a wheel has locked up. It is on the back end of the event and doesn't regulate pressure to maintain balance. If you are trailbraking into a corner and the bias is too high in the rear then it could put the rears outside their friction circle which would result in a spin.



this is exactly what I used to think, but now im not so sure. I did some reading on bosch's ABS 5.3, which can dynamically distribute bias if the wheels speed doesnt match what it expects based on pedal position, speed, etc. it did not imply that skidding needs to happen first, aka ABS is activated and pumping the pedal. like i said, im confused on how this works, even after reading about ABS 5.3.

one thing i do know, is that a nonfunctioning ABS computer is dangerous because the system defaults to the fully loaded condition.

onemoremile
03-12-2008, 03:10 PM
The wheel speeds will match unless the car is skidding. The system has to be reactionary. At least that is my limited understanding. The more I read the less I understand which is why my calipers are still stock. If my rear rotors wear out I'll probably bump up to the A6 rotors.

One thing I know for an absolute fact is that braking while in gear limits the ability of either end to slip since center diff ties the front and rear together. With ABS I slide down the hill at the end of my block but rev matching and dropping it into first slows it down very quickly with a lot more stability. Braking is much better in gear.


Antilock braking system (ABS) (http://www.audiusa.com/audi/us/en2/tools/glossary/safety/anti_lock_braking_system.html)
The anti-lock braking system (ABS) prevents the wheels from locking up during braking. Even under strong braking, the driver can better control and steer the car, potentially avoiding obstacles without having to release the brakes first. When the ABS is activated, the driver will notice a slight pulsation of the brake pedal. The anti-lock brake system is optimized with electronic brake-force distribution (EBD), and is standard on all Audi models.
A note on ABS: when driving on certain surfaces like gravel or snow on a hard road surface, ABS may result in longer stopping distances.

Electronic Brake-force Distribution (EBD) (http://www.audiusa.com/audi/us/en2/tools/glossary/safety/electronic_brake_force_distribution.html)
Electronic Brake-force Distribution (EBD) and the Anti-lock Braking System (ABS) constitute one unit inasmuch as they share a number of the same parts. EBD ensures maximum braking performance at the front and rear wheels, and under normal conditions it prevents the rear-end from braking away because of over-braking. The system also counteracts “fading” as a result of overheating.

ModifiedA4
03-12-2008, 03:22 PM
The wheel speeds will match unless the car is skidding.

well not exactly, certainly the inside and outside wheels will have different speeds when turning. and in the first milliseconds of braking. perhaps the bias proportioning happens during this time.



The system has to be reactionary.

i completely agree, but there is a period of time between braking force applied and skidding. even though it may be milliseconds...

the abs computer is always on, monitoring. for instance EDL is an active function of the abs computer that doesnt require the brake pedal to be depressed. perhaps the dynamic proportioning is similar?

hoganalley
03-12-2008, 04:28 PM
iin10ded.....BEFORE YOU BUY THE CARRIERS!!!!

I was about to do the same thing. I found a yard in CA with A8 rears. Not the same caliper, but you get the carriers.....they were $66 each. Definately look before you blow a wad on new stuff.

onemoremile
03-12-2008, 04:52 PM
^^ Great info right there!!!

onemoremile
03-12-2008, 04:55 PM
well not exactly, certainly the inside and outside wheels will have different speeds when turning. and in the first milliseconds of braking. perhaps the bias proportioning happens during this time.



i completely agree, but there is a period of time between braking force applied and skidding. even though it may be milliseconds...

the abs computer is always on, monitoring. for instance EDL is an active function of the abs computer that doesnt require the brake pedal to be depressed. perhaps the dynamic proportioning is similar?


I think the system is looking for sudden deceleration of a wheel in relation to the others. Even a sharp turn shouldn't affect the system. This may depend on whether or not the car has ESP too.

I had a good bud at Visteon that was a developer of vehicle dynamics systems but he got laid off and moved out of the country. I would love to pick his brain on this one. That dude was my Yoda until he split. There were a couple guys at Magna that could have helped too but they got canned in the big buyout. This industry is hell on a contact list.

hoganalley
03-12-2008, 06:53 PM
thanks onemoremile!

the one thing I've learned about these cars is there are so many mods done you can usually find what your looking for used, cheap! car-part.com is a great resource. you have to do some phoning to get exactly what you want, but it's worth it.

on a side note....i did the research with ETKA....a lot of the A8 braking system is shared with the A4. only difference is the booster. So, get the upgrades for front and rear, and it will almost be perfect!

genecan
10-11-2008, 12:35 PM
Lets dig this thread up...

What do you think of an upgrade of rear TT carriers and calipers and rear B5 S4 256x22mm rotors? Should this be a stright bolt in?

A little move to the fronts: would the TT carriers AND callipers fit around the A8 312x25mm? ...under 16s? Would that gain any benefit?

I think if all from above is possible and combined that should be some sort of balanced upgrade. Do you agree?

hoganalley
10-11-2008, 05:06 PM
why TT calipers when stock calipers work fine. The only time a different caliper will work is if you go to Porsche calipers. I have A8 fronts A8 rears and they're awesome. They fit under 16's and I haven't had a single problem. Get good pads that grip hard and they'll stop on a dime.

312/288 = 1.0833333
256/245 = 1.044
269/245 = 1.097

Even though the 269 rotors are a little over the front upgrade ratio, it won't throw out bias and is closer to the upgrade than the S4 rears......

genecan
10-11-2008, 06:19 PM
Why TT calipers? - Because I got a VERY good deal for TT solution for all four courners.

I do not know if the A4 and TT callipers are any different in terms of pad contact surface or piston ring size. That is why I asked if such swap would be benefitial at all.

Well, I do not think that the only factor here is the "upgrade rotor ratio". IMHO if you ugrade the pads front and rear with the same pad material, the bias will be thrown slightly towards the rear, because this way the friction coefficient will be improved on both axels but the rears will take relatively more advatange of that, due to their lesser involvement of the stopping act. May sound weird, but I think it is true. On the other hand the primary cars the rotors were designed for had diferent weigts, heights and interaxel lenghts (do not know the exact term in English), thus completely diffrent mass transfers compared to our A4s when stopping... And here I will stop, because it gets too complicated again and further thoughts are pointless. In the end I do not think there would be noticeable difference in the A8 rears you have and the TT/B5 S4 I suggest.

My question stands for mechanucal compatibility of the elements I suggest. The TTs use a 256x22mm rear rotors, but with a 5x100mm patern. The 5x112mm patern of the same rotor is in the B4 S4 rear. What bothers me is if the rear TT carier and calliper when mounted on A4 would fall on the exact spot to accept the 256 mm diameter and if the S4 rotor mounted on the A4 hub will make the exact offset to fit the "new" TT caliper/carrier assembly.

My concern for the fronts: would the TT caliper (over the TT carrier) bulge toward the weel more than the TT carier/A4 calliper in order to fit 16s.

hoganalley
10-12-2008, 08:52 AM
I do not know if the A4 and TT callipers are any different in terms of pad contact surface or piston ring size.

alright....according to ETKA.....it's the same caliper. It won't make a difference for what you want to do. May as well use stocks. Unless the calipers you got were from a new TT, they should be identical.

This leads us back to A8/TT/A4 all use the same front caliper. So go nuts......

Rears, I like the A8 rears, but the S4 rears would be ok too. Pads can't make a difference for bias if they're upgraded equally, because everything is being upgraded equally. That means nothing will change. If you put a stronger pad on the back compared to the front, then yes, I could see a bias change.

audispeed
10-12-2008, 11:59 AM
some comments I made on my various setups a while ago. take it for what you will:

A quick run down of my various brake setups and opinions:

Drilled zimmerman all around: I was young and stupid (7 or 8 years ago - wow that is long). Rotors caked with brake dust and the holes cut slots in the pads. Not worth it, but hey, I needed new rotors so I gave it a shot.

Stoptech 332/stock rear: Great setup. Stoptechs shifted the bias to the rears sligthly and provided better overall brake balance (I think the stock A4 has too much front bias). Rear rotors would get extremely hot and would actually cause the rear wheels to heat up substantially more than the front. The stoptechs are slotted and to this date I have not had any problems with the slots becoming filled with deposited pad material (probably at least 40k on them).

Stoptech 332/S4 rear: Good setup, but the S4 rears shifted the balance back forward (go figure?). I didn't like this much at all and changed rear pads to bring it closer to where I wanted it. Still a little more forward bias than I wanted.

Stoptech 332/S4 rears with ECS 306 mm rotors: My current setup. Bias is just about perfect and the setup is a good strong setup. Looking forward to more track time.

Hope this helps a little. What to take away front my ramblings - if you want a cheap upgrade stick with A8 fronts. If you want a little more I would try A8 fronts with S4 rears and a very agressive pad in the back and a milder pad upfront. Just my two cents, granted that is one setup that I haven't run. If you want a bigger upgrade, keep in mind my experiences.

iin10ded
10-13-2008, 10:04 AM
I have A8 fronts A8 rears and they're awesome.

what's the rear setup?

hoganalley
10-13-2008, 02:48 PM
269x? I think 22mm. S4 rears and A8 rear carriers.....works awesome. I love it

JumboBlack1.8
10-20-2008, 10:11 AM
Bring this back, since I don't want to start a new thread....

Now that my car is running, I'm gonna begin my F&R BBK project. I've got the boxster brake upgrade for the front, Motul 5.1 brake fluid, Stoptech rear SS lines, and I'm leaning towards going with the A8/S4 caliper rear kit....I can get the A8 parts locally for dirt cheap, but I was wondering.....did all the D2 A8 rear brake rotors come vented stock? Or will I have to buy new rear rotors. The rotors I'm going to be purchasing do not have a lot of mileage on them....I know its not ideal to buy used rotors, but if I can get them at a good price, clean them, and possibly get them turned, then I may go that route. But I forgot to ask the guy if they were vented.....someone help me out?

Also, will I be fine running PBR ceramics in all four corners?

hoganalley
10-20-2008, 11:40 AM
Anything post 99.5 (VIN 400k + I believe) came with 269, 280 or 310 discs. They'll all be vented. Before that though, there was an option for 245x10. If the year of the car you're getting the parts off of is 99.5 or later, you're good.

PBR's are fine! I love em!

JumboBlack1.8
10-20-2008, 11:53 AM
And can I get the carriers off any D2 A8, or only from 99.5+? The Brackets I plan to get are from a '98

hoganalley
10-20-2008, 01:42 PM
If the rear rotors are 269, then you're fine. If they are 245, no go. Obviously the bigger the rotor, the more likely the carrier will have to be bigger. I know the 245, 256 rear carriers don't work with 269+ rotors.

Ask and ye shall find out.......

lml999
10-24-2008, 07:20 PM
269x? I think 22mm. S4 rears and A8 rear carriers.....works awesome. I love it

This is what I run as well. Boxster S calipers over A8 (IIRC) rotors in the front, S4 over A8 in the rear. Very well balanced, the Porsche calipers have great feel. Highly recommended.

I'm putting a similar setup on my C5 A6 next week. Boxster calipers over A8 rotors, S4 over A8 in the rear.

JumboBlack1.8
10-24-2008, 07:23 PM
This is what I run as well. Boxster S calipers over A8 (IIRC) rotors in the front, S4 over A8 in the rear. Very well balanced, the Porsche calipers have great feel. Highly recommended.

I'm putting a similar setup on my C5 A6 next week. Boxster calipers over A8 rotors, S4 over A8 in the rear.

I believe you have S4 rotors in the front, since the Boxster S caliper calls for a thicker rotor (cant' remember the dimension)....i think bira.org has all that info

I'm putting on the Boxster calipers you sold me this weekend too [up]

$teady$upreme
10-24-2008, 07:37 PM
For rear, can i upgrade the whole thing with b5 s4 calipers, s4 carriers and s4 rotors on a b5 a4?

lml999
10-24-2008, 07:38 PM
I believe you have S4 rotors in the front, since the Boxster S caliper calls for a thicker rotor (cant' remember the dimension)....i think bira.org has all that info

I'm putting on the Boxster calipers you sold me this weekend too [up]


Thanks, you're right. You know, when you get to my advanced age, the memory is the second thing to go.

I can't remember the first. :)

Enjoy those pretty red calipers. I wish I hadn't sold them...figgers...I sat on them for 6 months, then a couple of weeks after you buy them, I snag the brackets I needed!

Oh well, the black calipers I picked up match the rest of the black on black car!

I did pay extra for the red Boxster S calipers for my urS6, and I'm pretty sure the reds are faster!

Militant-Grunt
10-24-2008, 09:50 PM
I guess you missed my thread.

http://www.audizine.com/forum/showthread.php?t=242134

tmljeh19
10-26-2008, 10:35 PM
So if I go with A8 rotors in the front what should i do to the backs to make up for that? Is there anything I can do without doing the a6 conversion on the back? I was thinking about doing the a8 on the front and then putting a bigger rotor on the back with the stock caliper and using the same pads all the way around. will that be ok?

rogerius
10-27-2008, 01:13 AM
I installed 4pot rear Cayenne calipers in the back on 330mm discks....on Passat,though

$teady$upreme
10-27-2008, 02:46 AM
For rear, can i upgrade the whole thing with b5 s4 calipers, s4 carriers and s4 rotors on a b5 a4?

^^^is this setup right or i got the wrong stuff?

According to Audiworld, I need A8 rotors and A8 carriers? Now, bring into the question of is A8 carriers and A8 rotors same as B5 S4 rotors and carriers?

Two Audi A8 caliper brackets: Audi Part# 4D0-615-425-B

hoganalley
10-27-2008, 09:15 AM
Originally Posted by $teady$upreme
For rear, can i upgrade the whole thing with b5 s4 calipers, s4 carriers and s4 rotors on a b5 a4?

^^^is this setup right or i got the wrong stuff?

According to Audiworld, I need A8 rotors and A8 carriers? Now, bring into the question of is A8 carriers and A8 rotors same as B5 S4 rotors and carriers?

Two Audi A8 caliper brackets: Audi Part# 4D0-615-425-B

No, S4 rear carriers won't fit. Everything else will but the carriers are different. S4 part # is 8D0 615-425. That "B" makes all the difference. The S4 rear carriers won't fit over a 22mm wide rotor

hoganalley
10-27-2008, 09:19 AM
putting a bigger rotor on the back with the stock caliper and using the same pads all the way around. will that be ok?


I installed 4pot rear Cayenne calipers in the back on 330mm discks....on Passat,though

You can. I'd ask around to see what putting on different calipers and rotors have done to the braking of the vehicle. Most people don't recommend it because if the bias switches to the rear too much the car becomes very unstable under braking. When you see other vehicles with bigger rear brakes they've been designed that way. Our brake system wasn't designed to have huge rear brakes.

Always try to upgrade in scale. Never throw the front/rear relationship out too much or you'll be asking for trouble.

tmljeh19
10-28-2008, 10:35 PM
What is the cheapest way to go with a rear upgrade and what are all the parts that i need to get for that?

Squarrl
10-28-2008, 10:52 PM
No, S4 rear carriers won't fit. Everything else will but the carriers are different. S4 part # is 8D0 615-425. That "B" makes all the difference. The S4 rear carriers won't fit over a 22mm wide rotor

S4 rear carriers do work on A4 and S4 uses 22mm wide rotors.

$teady$upreme
10-29-2008, 12:43 AM
So what is your rear setup like?

B5 S4 calipers, S4 rotors and S4 carriers?


S4 rear carriers do work on A4 and S4 uses 22mm wide rotors.

rogerius
10-29-2008, 02:07 AM
You can. I'd ask around to see what putting on different calipers and rotors have done to the braking of the vehicle. Most people don't recommend it because if the bias switches to the rear too much the car becomes very unstable under braking. When you see other vehicles with bigger rear brakes they've been designed that way. Our brake system wasn't designed to have huge rear brakes.

Always try to upgrade in scale. Never throw the front/rear relationship out too much or you'll be asking for trouble.

I balanced the fronts too with Cayene 6pot calipers with 350mm disks.I based the upgrade on :
1. computed OEM front/back braking force ratio differs by 2% from computed UPGRADE front/back braking force ratio
2. car has an automatic Electronic Brake Force Distribution System (EBD) which will take care of the 2% initial bias difference. IMHO

edit: Oh,the bias is to the front 2% more than it was OEM.Tell me what do u think.

hoganalley
10-29-2008, 07:39 AM
^^ I'm impressed! It seems to make good sense, nice choice.

I would've loved to go bigger but I have to run 16" stocks in the winter so I needed something that would stay inside that. If I could go bigger, I like your setup

hoganalley
10-29-2008, 07:42 AM
Quote:
Originally Posted by hoganalley
No, S4 rear carriers won't fit. Everything else will but the carriers are different. S4 part # is 8D0 615-425. That "B" makes all the difference. The S4 rear carriers won't fit over a 22mm wide rotor

S4 rear carriers do work on A4 and S4 uses 22mm wide rotors.

You know what.....you might be right. I swear S4 Carriers didn't work for me, that's why I had to get they A8 carriers. I always thought it was a hole issue when putting the carriers on the spindle.

Damn I wish I could remember now......

Squarrl
10-29-2008, 12:19 PM
So what is your rear setup like?

B5 S4 calipers, S4 rotors and S4 carriers?

Yes

$teady$upreme
10-29-2008, 12:33 PM
Perfect thank you. I just got S4 carriers and S4 calipers, going to get rotors and PBR ceramics now.


Yes