johnd64

When shopping for rotors I noticed that there is a 360 mm and a 385 mm disc.
Does it matter which ones I buy?
Are the brake pads the same size regardless of the rotor size.I understand that the big rotor can dissipate more heat but if the pads are the same size I don't see the braking power being significantly different.Advice?

Thank you

mishar

S8 has 385 x 36 mm front rotors and yes it does matter.

Bigger rotors has more braking power for a few reasons: friction force acts on a bigger lever so it creates bigger torque, they have bigger mass so they can accumulate more energy and they have bigger surface to dissipate that energy. If they are ceramics they can withstand much higher temperature so dissipate energy much faster.

MP4.2+6.0

As Misha says, for S8 always 385mm fronts. 335 backs FWIW.

Lille known pad trivia you are getting at: In Audi dealer pads, they will actually be a different part # for 385's vs. 360's, even though caliper, pad backplate and sensor connector are all the same. The difference is only in the size of the mounting bracket. In EBC and probably the other various aftermarket pads out there it will all collapse to a single part #. The difference is on the dealer pads for 385mm fitments, they are bonded to the backplate a mm or so inward. On my W12 that also have the 385mm rotors, I have run all of dealer 4.2 (360mm), dealer S8/W12 pads (385) and EBC one # fits all, and they all work. In a one size fits all or 4.2 fit, it just leaves little to no lip at outer edge of rotor, which to me is sort of a plus. Covered actually in my linked post in auto sig about my cosmetic upgrade years ago now when I stumbled into this.

johnd64

Thank you, I was planning to get the 385 mm anyway.
Just to make sure I get the pads right, can I go with any pad ?
Or how can you tell the pads are for the 385 mm rotor?

MP4.2+6.0

So again, from Audi (dealer) the S8/385mm has its own pad set part #. But for EBC as an example, in 385 mm (S8 or W12) fitments EBC specs the same pad number as they do for the 360mm 4.2. I couldn't take you thru every pad player out there (Hawk, Ferodo, sometimes Brembo, Ate, Akebono, Porterfield and many, many others), but using EBC as an example they just collapse it to one pad number for either 360mm or 385mm rotors. Also know/remember the factory pads have built in sensors that plug in to a connector at each front hub area. So do the EBC's from my experience installing those. But some pad offerings don't, where you either have to fit a sensor to the inner pad or wire around it. For obvious reasons I prefer one that integrates same as factory/OE.

johnd64

Thank you for all the info.I just talked to a fellow at AutoAnything and he said the EBCs(pads) do not have the built in sensors.I thought they did.He recommended the Wagner Thermoquiet.
Would you guys go with a Centric Premium rotor?It's made in USA he said.I know it's only a little less than the original rotor, so I'm debating it, but the overall package is a great deal.I did use Centric once (I think) on my SAAB and they worked well.

Thanks

MP4.2+6.0

EBC does have the built in sensors. Zero doubt about it, if you mean fronts in EBC red. Not sure if yellows do, but reds definitely. In fact, in rears they even put a set of loose sensors in the box, but car doesn't use them in back for at least the D3 fitment. I bought and installed like 3 sets over time for the W12/S8 size, so I am 100% sure--so much so that I would suggest buying elsewhere indoor you talked to does not have reliable and correct info--which they don't. Not to personal file--nix on AutoAnything... Look at Amazon BTW; not a huge fan of car parts from there necessarily, but at various times their EBC prices are as good or better than anyone's, fast shipping and easy returns if something not right. Look for it by the EBC part # if possible.

I would--and do--use EBC pads. EBC Red results in noticeably less dust FWIW. If I don't use EBC Red, it would then be stock from discounted dealer. More dust but good feel, decent wear, always correct fit, etc. I mostly OE rotors, which are not particularly expensive and well made. Dealer pricing on rotors if you use one of the on line discount dealers is fairly reasonable; similar to EBC rotors for example. Anytime you buy rotors on line, watch the shipping. Pricy, and fronts in 385 weigh 39 pounds, each. If pricing and brand right, free shipping on rotors is a meaningful savings.

johnd64

My situation is more complicated.I live in Canada so I have to get this shipped to a friend in US or to a shipping company near the border.Since there is a free shipping within US offered by a lot of these parts suppliers I decided that buying in US might be the most cost effective.I'm about 3 hrs from the border.
Sounds like this guy from Autoanything has got it all wrong as far as the EBCs are concerned.(the pad sensors).I will put them back on the list.
Any comment on the Centric rotors?