bmorrow

I currently have a 2013 S8 with 21" wheels and 265/35/21 ContiSport tires on it. I'm not very happy with the road noise and am thinking about going to a 20" x 9" wheel with a 265/40/20 tire. Has anyone done this and if so, did it help with tire noise on the freeway? I have confirmed a 20" wheel will fit as will a 40 series tires, but I'm concerned about spending the money to swap and it not making a difference with regards to the road noise. Below are the rims on my S8 as well as the new wheels I'm looking at getting. I'm also a little concerned about how the car will look with a 40 series tires versus a 35. Input is appreciated.

MP4.2+6.0

I have posted on this a fair amount on this board. Search if interested beyond this reply. I went from the stock 21" 5 spokes to the factory 20 x 9 twin 7's on a 2015 S8. Mine came with 275/35-21's. But in my case I went off the play book a bit and used 275/40-20. And I would again...

Mine came new with one of the noise reducing fitments (Dunlop), though I went with a more generic Continental DW summer when I dropped to 20's. Noise was never a primary issue to me, though I would basically say having gone from the OE 275 noise reducing fitment to a same nominal width 275 without that designation, I really did not notice any real change. Pretty quiet in both cases, and summer to summer for direct comparison. Car only had 3200 miles though at CPO delivery, so my 21's were hardly worn as far as possible road noise later in a tire's life.

I went 275 among other things because there is a lot more choice in tires in the 275/40-20's than 265/40-20. Said bluntly, 265/40-20 is a one off Audi oddball fitment (also seen on A7/S7) that means limited choice and generally more cost.

My other posts also explain how with a careful wheel choice you can get a lot of unsprung weight off the car at the same time. I was more after that, and the not quite sorted handling the 21's seemed to exhibit. Satisfied on all those counts. I took about 9 pounds off per corner, which is a whole lot in unsprung rotating weight terms--the worst kind of pork to carry everywhere. Your wheel choice I'm guessing is a knock off. Looks like the S8 Plus OE (21") design, which I like. But many knock offs are on heavier side and most are cast (not forged) unless you pay up a lot.

And yes, you do want to think about the appearance if super important. I suspect the 265/40's might look just a little better. The 275/40's have a bit taller sidewall than the 265/40's and of course yet another ½" more than the 21's. A good thing to me (275 vs. 265 in 20's) real world wise since it filled wheel wells a tiny bit more and at same time gave another couple tenths of ground clearance--which is so so on S8 at stock. Qualitatively I would say it has just the beginnings/slightest of the "cop car" bulge thing going on. Very subtle for most though, and I think it is more the basic shift to the 40 profile when you go to 20's. Just look at any D4 V8 A8 with 20s though and judge for yourself--they will have the 265/40-20's, but just ride a little higher with a bit more fender gap.

20's of course clear, at least in any OE wheel. Just like they do on the V8 A8's since front brakes are still the same. Even the right 19's can clear--for winters perhaps for some owners. I think the 20's do a better job of highlighting the brakes up front as an aesthetics matter too; even for their massive size they get a bit lost in inside the 21's.

bmorrow

MP. Thanks a bunch for the feedback. The two issues I'm try No to figure out are the look considering a 35 series sidewall is 3.8" versus 4.3" on a 40 series. The height difference is .1" so the height of the car really doesn't look like it would change. I'll definitely go look at the 20's on the a8's and see how the appearance is, but I'm sort of hoping the 40 series provides more cusion and looking at the choices of tires like the DWS continental which are quieter tires that it will be less road noise. I'm moving to a 275 width tire either way.

MP4.2+6.0

Yes, the 40 series does provide more cushion at the margin with the greater sidewall. I would say it is not dramatic, but you can feel it. That it is not greater is maybe a testament to the Dunlop SportMaxx's the car came with being well designed. I still leave the car on the softer settings, but the others are tolerable. With the original 21's, another notch stiffer and the sport settings were not my cup of tea. And to be clear, this from a guy who always went up on wheel sizes and down on profile on prior Audi's, and fitted stiffer roll bars, including 10 years and 100K miles on 275/35-20's on my D3 W12.

Hard to explain exactly, but the 21's did not feel settled on the car. A combination of a little too jittery, a little too twitchy, stuff like that. Having weighed the 21's, they really were unacceptably piggish in weight and I think that was a fair part of my sense rather than just ride alone--it affects the dynamics too. And, if you find almost any recent review of an S8 (particularly the ones from the facelift) in either print or web, they all basically seem to say, fast as hell, beautiful constructed, somewhat cold and ... ride not quite...sorted. And every picture I have seen of the given review vehicle or accompanying text says the car was on 21's.

FWIW, I'm running Conti DW's now in the 275/40's. No interest in going back to the 21's except to sell car in (distant) future or trade it back as "stock" for dealer resale. For shoulder season I will go to some Conti DWS's you mention--the later and better reviewed "06"'s. I'm in a weird situation where I live near coast and zero chance of snow or any road ice, but then go to a second home in Sierra's over the 7000 ft. plus summit and settle in at 6700 feet. 150-250 inches per season, and like the Donner Party experienced it can happen as early as Oct 1. Thus interest in the DWS's. I have used dedicated snows in past for trips up there in winter, but then 95% of miles going on tires are on dry pavement and at 50 degrees plus. Will still probably get some Dunlop 3D's, which are well priced in (only) the 265/40 fitment they offer.

Last, on diameter, it's subtle but sounds like you are looking at it so I will mention. On the 265's in either 20's or 21's you end up at 28.3" on many other tire choices you would likely look at. If I read your post correctly, this is where you are now with your 21's. The 275/35 21's fit to mine originally are 28.5". The 275/40-20's will be at 28.7", at least for the Conti's I mention. Thus, you do step up another 4/10" on diameter and 2/10" on radius/ride height and fender gap closing. The 265 to 275 change is what is really driving that when you multiply by the aspect ratio for height, give or take a bit for specific tire manufacturer design tweaking. Actual numbers are from TireRack specs if you look them up for various tires. Net, I'll take that. Speedo error also went from approx. 1mph optimistic at highway speeds (using a GPS phone app) to dead on post switch.

I can post some pic's later on more focused on wheels and tire look.

MP4.2+6.0

One P.S.: You might weigh a wheel and report back. Easiest is just complete tire and wheel, since you can usually just look up tire weight and subtract to get pretty close. I was never able to find a weight for the 21" OE wheel in your picture.

What makes me more curious back from when I looked at all the available D4 OE wheels is in some obscure articles Audi said it had developed some new technology lightweight wheels that were some kind of composite or plastic sort of material with a conventional finish. And...the picture that ran with the story...was of those wheels. Not clear to me if they ever went to production, if it was just a stock photo, or what. My guess is those are conventional cast with those unusual slender chrome spoke trim appliqués. Probably typical OE Speedline/Ronal, but I am not sure. If cast, the handful of forged choices offered for D4 (none in 21's AFAIK) are definitely lighter. But, without a weight of overall wheel or first person inspection of one loose from tire, hard to be at all sure. If it were the little known special design actually implemented, something to consider.