BigD_S8

I've got a 2008 A8L with the 20 inch sport package. I'm running Dunlop Sportmaxx 275-35-ZR20 tires. The sticker on the door jamb says: 275/35/ZR20 should have an inflation of 41psi in the front and 44 psi in the rear. According to the manual, the sticker on the door jamb is for max load.

The manual on the other hand shows 275/35/R20 tires with a normal psi of 33 front and 30 rear and at full load it should be 36 front and 39 rear.

I'm typically by myself so I don't need to run them at max load PSI but I'm confused as to why there is such a discrepancy between the door jamb and the manual. Any thoughts on which is correct? Thanks.

uberwgn

BigD, welcome aboard!

There was a major change a number of years ago and the label shows MAX LOAD only. Ref.: FMVSS 110 for the specifics.

You need to see your Owner's Manual for detailed info on normal load conditions. Audi still provides highly specific info, most other mfrs no longer provide normal load info in the manual and leave it up to chance.

MP4.2+6.0

That stickering change is courtesy of the Ford Explorer rollover debacle, and came into force by 2007. You can actually find the "real" manufacturer recommendation by either referencing 2006 or earlier (when the recommended pressure sticker was still on the gas tank lid), or finding the Euro equivalents.

Net, I would definitely NOT run anything in the 30-33 range with the 20's. That is asking for wheel issues and especially sidewall bubbles. Having run the Dunlop Sport Maxx'es specifically for a full life cycle (and currently Michelin PS2's nearing end of life) on my W12 also with 275/35-20's and the sport wheels (assuming you mean the twin 7's--a.k.a. "new RS4 style"--though 20 x 9 and the tire fitment is what matters), I would concentrate between 38 and 41 PSI. I tend to go with 40, and if I see the edges scuffing off early bump it up a bit. That should tend to agree with about the mid point between the lighter and heavier load recommended PSI's that is the Euro type spec the car had through 2006. I tend to run the same pressures all the way around--my experience across many Audi's is it is the rear where the ride deteriorates more at high pressures FWIW. You might shave the overall setting a little if you favor ride given 4.2 vs. 6.0, but my suggestion would be not under 38 PSI. From experience over 5 years now with the W12 and 20's, and my prior eight years with my A6 4.2 with 255/40's, it's been clear to me pressures right in there optimize wear and handling and protect the rims and sidewalls pretty well. Above that is mostly making the ride harsh, and the tire center starts to wear early. Down below 35-36 is a set up for tire sidewall bubbles on a low profile tire from pothole strikes. Maybe even more so on a summer tire like the Dunlop that tends to be somewhat more lightly constructed than an all season tire.

mishar

Agreed, but have to add: anybody reading this between lines can figure out that 20’s are wrong choice. If you have to pump them 10psi above recommended pressure in order to prevent premature wear of edges, bulging of sidewalls and bending rims, something is very wrong with this setup. OEM or not it is just fashion. Doesn’t feel or work good but it looks nice. Everything for the looks.

FlyTyinFool

Yes, but to temper this statement, it really depends on your local road maintenance conditions. Although I've never driven in the Northeast, I would suspect 20" wheels would be a poor option due to poorly maintained roads. Midwest too?

Here in the Northwest I could get away with 20" during summer months without much worry at all. During Winters though, there isn't much road maintenance that takes place and potholes actually become an issue.

Point taken though. I freely admit that 20" wheels (for me) are mostly for looks.

Carry on...

mishar

Local roads absolutely perfect, yet ...

I like the looks too.

MP4.2+6.0

I don't know why you feel compelled to post this each time someone, or I, posts something thoughtful about 20" wheels, or try to help someone out with a question. I disagree with you, as I have before. Can I suggest you find positive things to say here, and move on and let people enjoy their cars, and wheels, particularly when dealing with OEM configurations.

On point, the pressures I cited in my post above are all right in the middle of the tire pressure sticker provided by the factory on my car for 2006, glued right to the gas door. Thus this statement you made appears to be wrong: "If you have to pump them 10psi above recommended pressure in order to prevent premature wear of edges, bulging of sidewalls and bending rims, something is very wrong with this setup." And that's a 2006 sticker before the manufacturers cranked up the pressures (and sticker location, style and content) to address the regulatory change. Instead, you pump them up to the manufacturer's recommended settings--before the regulatory bias crept in--to get exactly the expected very strong performance. FWIW, I wouldn't even run 55's or 60's down at 30 PSI on a newer car, SUV, minivan or much of anything else--for much the same reasoning--and indeed the Explorer scenarios of heavily loaded vehicles, lower pressures and high road and operating temps. can start to be more relevant.

Sounds like you may not be aware of that factory recommendation (pre mandated sticker and standards change), nor from my prior post where we went around on this did you respond that you have on the road experience with 20's on the car (as I do w/ 18's). And once again, it's a fabulous set up on my car. For others who love 18's great, and as I have also posted the 19" factory pie plates are a great wheel too, forged and light at that.

mishar

OP: “The manual on the other hand shows 275/35/R20 tires with a normal psi of 33 front and 30 rear ...”

You: “I would concentrate between 38 and 41 PSI.”

Me: Sorry, not 10psi. Actually between 8psi and 11psi. May be 9.5psi?

Nevertheless, I agreed with your advice about pressure, but I always feel compelled to post against illusions. Especially if they are potentially harmful.

By the way, as I remember, last few times it was you who jumped in with glorifying OEM wheels contrary my advice against big wheels and shallow tires.

No need to be mad when you are wrong. At least not at me.

BigD_S8

Thanks for all the valuable insight! It's good to hear some real-world experience. I'm in an area where the roads are pretty good, I'm driving primarily on highways and I can run summer tires year-round. I was getting some unusual wear on the inside of my front tires but just replaced them and probably need to have it aligned.

Thanks again!

mishar

Do it ASAP.