Upsizing brakes on a D3

[NightOwl]

Hi folks.

I’ve bought my second A8 a few weeks back, a 2006 3.0 TDI with sport suspension. Unfortunately it seems like it got the smallest brakes witch have been delivered on the D3. According to my research the front brake rotors fitted on the D3 are either 321mm, 323mm, 360mm and 385mm, while the rear rotors are 280mm, 310mm and 335mm. Without measuring closely on the rotors, it looks like from outside the rim that I’ve got 321mm in the front and 280mm in the back. Using 19 inch wheels for summer and 18 inch for winter, it obviously gives room for bigger rotors.

After studying the parts needed to upsize the brakes, it raises some questions.

1. How big rotors with accompanying caliper fit under 18 inch rims?
2. The calipers in the front have different part numbers according to rotor size, while in the back it doesn’t. Is it really necessary to have "the right" caliper according to the rotor size in the front?

Help and experience are much appreciated!

[NightOwl]

Did some more digging and deciphered the PR-codes for the car and could then confirm that from the factory the car was fitted with 321mm breaks in the front and 280mm in the back.

Also found that 321mm and 323mm rotors have one piston calipers, and 360mm and 385mm rotors have two piston calipers. Obviously then, I can’t reuse my old one piston calipers with bigger rotors.

Haven’t mentioned the carriers as there is no secret that they need to follow the size of the rotors and are not interchangeable with other sizes.

[NightOwl]

1. How big rotors with accompanying caliper fit under 18 inch rims?

After some more research I've found out that A8 D3 with W12 engine has 385x36 disks in the front, and 19 inch rims as standard, but 20 and 18 inch as option. Sure it has to be tight between the rim and the caliper with 18 inch rims.

[BrianC72gt]

I've got D3 A8 360 mm brakes on my D2 behind my stock 17" fat fives. I can fit the tip of my finger between the caliper and rim. It was a total bolt up affair. For 385 mm rotors, 18" should work.

[NightOwl]

Thanks for your reply Brian! I've got an opposite answer on another forum saying it didn't fit with his 18" aftermarket rims and 385mm. Might as well jump into it and if it doesn't fit, buy 19" for the winter too.

[BrianC72gt]

I know 360mm work with the stock 17" fat fives on my 2000. ASSUMING the 18" rims have the same dish profile etc...then that is one inch more clearance and last I checked, 1 inch is 25.4 millimeters. 360 + 25.4=385.4 Should work and be very tight, but I've never actually done it with that size. I recall i had to mount the bracket, then the rotor, then slide the caliper into position. I couldn't pivot it into position with one bolt still attached like I could with my original puny 312 mm discs.

I bought 18" potato peelers that I still haven't used - just in case the 17s wouldn't fit, but they do...just barely. Guy at my local tire shop couldn't believe they actually fit when I brought it in for new rubber. He had a heck of a time getting the wheels back on the car...hack.

[NightOwl]

Thanks for clarifying Brian!

Seems like the OEM 18" will fit, but no guarantee that the aftermarket rims will.

[somedude]

I have D2 17" A8 wheels and just for shits and giggles I tried to throw them on my 05 W12. not surprisingly they didn't fit but they were absurdly close. I think 18's would go without a problem. FYI the brakes are stupid heavy on the W12 and even though you will have abnoxiously strong brakes your money would be MUCH MUCH better spent on good rotors and aggressive pads rather than the massive W12 brakes. the W12 brakes with not so great ceramic pads (low dust not performance pads) I made 3 155-40 stops back to back racing a B8 S4 and they were fading pretty heavily by the 3rd stop. It was single digit temps outside, and brake feel did restore quickly.

on a comical note laying W12 brakes next to a F350 (truck) or corvette brake rotor really puts into perspective how huge they really are.

[NightOwl]

Regarding size and weight, you are very true, the front disk (one disk only) will be between 15 and 18 kg (33 to 39 pounds). I've been looking into RS4 front brakes but even used they double or tipple the price of the W12 set up.

Also do no forget that the W12 and the S8 breaks are exactly the same, only the S8 badged retainer spring is different. So I guess good disks and pads are available, and together will give some improvement compared with whats on the car now.

[somedude]

a 2 piece rotor would be awesome for ride quality. I wonder if you look into porsche brakes if you would come across somehting that would be a good lightweight solution.

[NightOwl]

Indeed a two piece disk would have been awesome to save some weight, but I don't know enough about other brands brakes to be 100 % sure it will fit with offset and other things. The car is in daily use, so I can't rely on trail and error, as I haven't found any reliable info regarding what fits on a A8 D3.

As mentioned, I went for the W12/S8 setup and I've already got the front calipers.

[somedude]

just to compare. the rotor on the floor is a C6 corvette rotor and at 13" it is not small. The W12 rotor makes it look like a toy

[NightOwl]

So it should give great stopping power.

As a quick update, I've ordered all parts needed and some have already arrived. If it fits under my 18" rims, it will be mounted in a couple of weeks.

[NightOwl]

Just for fun I can mention that on the D4 (last generation A8), the fronts are 356mm, 380mm or 400mm, and the rears 330mm or 356mm depending on engine. So my wish to have something in between on my D3 shouldn't be too bad?