suggested tire size
 

hi,
I was looking into buying some 20x8.5 rims for my 2004 A8L.
I was wondering if anyone could tell me what the suggested size tire is for a rim that dimension (20x8.5).
I found some tires in my price range in a size 255/35/zr20.
would ther be anything wrong with tires these size on rims this big on my car?
anyone know what the OEM Audi 20x8.5 tire size is?

I understand ogoing form the OEM 18 to 20in rims I will be feeling th road a bit more and gaining a slightly bit more of a bumpy ride.



thanks for your help!

My suggestion is to stay with 18's. 20's will spoil your ride quality, acceleration, braking and cornering on anything but perfect surface, wheels and tires can be easily damaged, pretty soon they will wake up all rattles around your car.

If you want real upgrade go for some lightweight wheels 18x9 wide with 45mm offset and Continental 275/40x18 tires.

We have this posting debate not infrequently. Basically 95% disagree
 

My car came with 20's factory. Very nice ride. No tire issues. In my 5th year of ownership. W12's weigh maybe 5-700 more pounds on average too. Wheel weight is in same zone as the factory 18's given forged vs. cast, etc. Audi knew what they were doing on 20's on this car. The air suspension is what makes it possible. I live in CA, which these days are not grade A roads--not the worst or best.

But, it's a user choice, that's my real point. It is a rational choice in this case. Would not do it on a steel suspension w/ conventional springs car from Audi, but that's not this one.

To the original poster, 8 1/2 will limit you to about 255's. The OEM size for 20's was 275/35, but you need a 9" wheel to run that (in addition to the right offset range). You will end up with a shorter sidewall height at 255/35, while one of the things that makes the 20's a good OEM choice with the good ride I experience is likely that slightly greater sidewall height--they pick up about .35" in radius all in the tire sidewall (OEM 275/35-20" size is 27.7" in diameter while OEM 18" and 19" size is about 27.0" in overall diameter), which makes up for 70% of the otherwise 0.5" offsetting effective drop in tire sidewall height that would happen in going from 19" to 20." Clear as mud perhaps, but if you work through the math with the rim diameters and the tire diameters (can be found on TireRack site easily), you will see how the numbers work there.

Regarding wheels: we should compare same design and production wheels of a different sizes. If guy wants to buy BBS 18" or BBS 20" than all I said is right. Can't compare 20" BBS with some no name 18" garbage. Larger wheel is heavier and mass is at greater diameter what makes moment of inertia substantially greater and ruins performance.

Regarding tires: we should keep outside diameter as close as possible. 20" tires has less than 1" of soft side wall. 18" tires has 2" of soft side wall. That's twice more dumping and twice more deformation before damaging tire or wheel. It is also more of contact patch and more flexible to keep that patch in contact with uneven road.

Let's not ignore the question of original poster. The question being what tire size would work on a 20x8.5 wheel.

Mishar is quite correct in his second post. The diameter you want to keep the same as to not affect your speedometer. Be careful on the websites that say a narrower or wider tire will work. A wider tire may work but may need a wider wheel than 8.5. There is a wheel calculator online that will tell you the diameter of your tire with different sizes.

http://www.1010tires.com/TireSizeCalculator.asp

I am sorry. I can't help there with any good advice.

Check this one.

No, don't see it that way...surprise...
 

Audi OEM wheels are what should be considered primarily. That is what most of the cars on the road have. There are real differences in construction of these OEM wheels that make rules of thumb you quote not so applicable to this car. More directly, the 18" baseline wheels are relatively heavy as a choice compared to the oft used forged OEM 19's and 20's. I'll admit too that other than the rare high end BBS forged or similar wheel with a real TUV certification specific to a D3, I think most aftermarket wheels on a nice car are ultimately a value subtract, not a value increaser, so for that reason I keep my comparison set to available OEM (including cross platform in similar weight and power domains for the 5x112 bolt pattern like the C6 RS6 and recent RS4).

On tire diameters and sidewalls, again an oddity with the A8. Audi uses two different accepted tire diameters on A8's; three if you count the S8. It's just the way it is, not some aftermarket trickery or non-stock. My experience is the 27" size used stock with 18's and 19's compromises the speedo accuracy meaningfully and unnecessarily. The one published review I know of that gets at it (in German) shows it at 5%. It is reduced w/ the 27.7" diameter 20's a fair amount. Note on the D4, they went up a bit more on effective diameter, now running a new 265/40-20 size. Net, for a specific technical reason, but also for what I recognize as a purely aesthetic judgment call, I think the marginally bigger diameter suits the car more as well. But the latter is personal choice, not hard math. As mentioned below, it has a side benefit of moving the sidewall back to near the 19" OEM size for ride and sidewall strength. Audi has moved bigger tire diameter wise on the D4 too. In fairness/full disclosure though, Audi's spare well can't handle the 27.7" tires, so those of us with 20 " factories have the painted black 18" baseline wheel with middling OEM tire as the spare.

Back though to my original point to you and for the OP. In my judgment the 20's ride well and do not suffer from the criticisms you state, specifically on the D3 A8. I have driven them 50K miles on a D3, even with stiffened bars to the S8 level, so I am describing real experience specific to this car, not generalized rules of thumb. If you haven't driven OEM 20's, you might try them. The rules of thumb you are thinking very much apply to my steel/spring suspension A6 and Mini S as the wheel diameter and tire profile change, but really not so much the D3. Having driven them back to back on the same D3 with everything else identical against the factory 18's with the middling OEM tires used on those wheels as new, the 18's are really a let down and in a different league, and the ride harshness doesn't change anywhere close to what I have seen in a conventional suspension car, even with the 2" step up. If I did that on my C5, my teeth would clearly be rattling by comparison, and I would be motion sick to boot since they softened the shocks to deal with lower profiles in a "conventional" suspension compromise. I can improve the 18's with better tires on the D3, but the grip and brake performance are still likely to be less at the limit than with the 20s's at the respective OEM sizes, and it is a heavy cast OEM wheel no matter what--built for OEM strength at a price point, not performance. And buried in that subtle point about the 20" stock tire diameter is why in terms of sidewall height and harshness, they are actually pretty close to the 19's. And yes, Audi 19's are a nice choice too, in the forged versions that is that are the lightest OEM wheel choice available.

On 20 x 8.5,
 

it probably nets to 255/35 20. That has the 18" and 19" 27" tire diameter, though that means INCREASED rather than decreased speedo error (to the other poster's correct point to look at this too) relative to Audi's normal 275/35 fitment on its 20 x 9 wheels. At the 8 1/2" diameter, you're kind of stuck with that 255/35 fitment. The 265's (S8) and 275's (optional A8 20") call for a 9" minimum wheel from typical tire mfr. specs. Some might mount a wider tire anyway, but that isn't the tire mfr. recommendation. There are also relatively few tire choices in a 255/40-20, and that is stepping up the diameter even over the factory D3 20's, though not quite to the D4 level.

My net might actually be if the OP is serious at the 8.5 width specifically, stick to 19's, particularly in the Audi OEM wheels. There are some advantages (or non-tradeoffs) on the 20's per my other posts I'll stand behind from practical experience, but the 275 (or 265) fitment you only get at a 9" width is a strong part of that equation.

Buying OEM wheels at Audi prices is crazy. They are not any better than good aftermarket wheels half priced. Anyways, comparing apples and oranges is misleading even if they come from the same producer.

On the sidewall thinks are just the same. Comparing different outside diameter is not an option. If you think that 27.7" tires fit A8 better than you should compare 18's and 20's of that diameter. By the way, using VAG-COM speedometer can be easily adjusted and factory settings for 27's and 27.7's are not the same.

Air suspension is not that much different than conventional. It most certainly doesn't make stiffer tires smoother than soft ones. Main advantage is leveling and lifting. This is virtually only way to keep car leveled with different load. Actually there is a better one. It was used by Citroen from 60's on. I don't know if they are using it now. It was hydraulic.

More interesting "info" yet...
 

1. Did I ever say new OEM? There's one point of agreement-new OEM prices are crazy. But of course the point is...used OEM. Widely available. No questions if the car is traded in. No buyers who (like me) routinely walk for an unknown obviously modded car with who knows what history, and wheels make the top of that dubious mod list. I have bought many OEM wheels for many cars many times. Most all used, most in great shape, and most for barely more than the tire cost, or tires plus TPMS's on D3's. 90% of aftermarket is value subtract. Much of it is of questionable manufacturing origin these days. Much of it is not TUV rated, and the D3 is a heavy car, and in the case of the W12 anyway quite high torque within the 5x112 set of fitments. Same bolt pattern as a B chassis (A4) going back 15-20 years, and I've seen more than a few wheels marketed as covering from A4 to A8. Scary. Meanwhile, like many OEM wheels, Audi's tend to be heavy, but that makes them durable unlike most of the aftermarket cheapo stuff. And on the D3 as their former top of the line car, Audi also happened to offer some nice forged choices. The 19" forged and the later (new) RS4 20's are both good examples. The BBS RS GT's as a quality example with a TUV rating pull off relatively few pounds from them, are like 150% the price of even new (overpriced) Audi OEM, and are hard to find used, let alone at an attractive price or with D3 tire sizing if complete with tires.

2. Can I suggest stopping with the "apples and oranges stuff" too. OEM fitments (both tires and wheels) are directly comparable--that's how the manufacturer sells and presents them for starters. They sticker the car for tire sizings and ratings, and dealers regard cars with other sizes as non-stock/modified. The factory choices have different diameters and designs and construction, but the manufacturer, the dealer and the buyer all perceive them as directly comparable alternatives.

3. Big time wrong on adjusting speedo's via VAG COM. Care to post where those instructions are? The Fed's would like to perhaps know too, given how that area is regulated and locked down darn tight. I've only used a VAG COM for 10 years, but then maybe I missed it? Maybe in the occasional posts around that subject here or much more on the C5 or other boards, where it either goes unanswered or comes back as a no? What I am familiar with that can sometimes be adjusted for overall diameter/running circumference is the Nav calibration when it is dead reckoning in the absence of receiving the GPS sat signals, but the speedo display calibration is (way) different, off limits and big time regulated for new cars by both the Feds and their Euro counterparts. They get fined major $/Euro's if this stuff reads below actual speed, hence they consciously calibrate it conservatively and then fence it off electronically.

4. I'm familiar with the old (droopy) Citroen stuff. Novel and groundbreaking. Plush ride. Unreliable. The whole MR design (think Corvette) is more interesting in the modern era. You are missing the computer controlled electrical dampening regulation of the D3 struts inside the overall unit and the lightened aspects of various of the subassemblies involved. Both get at real ride quality--way more than the old counteracting air pump up stuff. Posts on this board rarely get beyond the compressor and ride height aspects of the system, so don't be sucked into thinking that's all there is to it if the board is somehow the reference body.There is a whole SSP on this for the D3 you could access to get up to speed if you are not familiar with it; that goes into a level of understanding way beyond what I have come across concerning the system on this board. I've got a well maintained C5 with all the later Audi aluminum bits in the front suspension and a 4.2 and about 4100 pounds overall like the D3, and run both 17's and 18's on it in various 45 and 40 fitments in the 255 range with a conventional suspension--nice car, but way off the plushness and performance of the D3 set up with 20's and 35 profile and some extra net wheel weight.