275/40R20 ideal tire pressure?

[osideaudi]

Alright so I can't find a middle ground on the ideal tire pressure. Seems like the 41/41 of the 21's is way too stiff but common pressures for 275/40R20 are around 30/32 which seems really low for the speeds I run ()

Anyone have any recommendations on what pressure to run?



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[riceboy22]

Have you tried something right in the middle? (I swear I'm not intentionally being a smart a$$ lol.) It really depends on your driving style and the kind of driving you're doing (highway, backroads, city, etc). I am running my 20x9 wheels (255/45r20) at 36 front and back, so in-between the Q5 and SQ5 recommendations, because I do mostly highway driving but don't want to feel every single road imperfection when I'm in the city. You can check out this thread http://www.audiworld.com/forums/q5-s...2870406/page2/ on AudiWorld as well, although nobody has a final "answer," because it's largely a personal preference thing.

[SQive]

Try 36. I've had similar-sized tires on a different vehicle, and that worked best for me.
Of course, you could use the old "chalking-the-tire" technique to get it perfect.

[osideaudi]

I'm at 36.5 right now and it feels rather slushy. I believe the book says for 255/40R20 it's 39/39 but that's a more narrow tire. Not sure what that translate into for a wider tire... I guess ill give that a shot


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[osideaudi]

Have you tried something right in the middle? (I swear I'm not intentionally being a smart a$$ lol.) It really depends on your driving style and the kind of driving you're doing (highway, backroads, city, etc). I am running my 20x9 wheels (255/45r20) at 36 front and back, so in-between the Q5 and SQ5 recommendations, because I do mostly highway driving but don't want to feel every single road imperfection when I'm in the city. You can check out this thread http://www.audiworld.com/forums/q5-s...2870406/page2/ on AudiWorld as well, although nobody has a final "answer," because it's largely a personal preference thing.

You don't feel like there's too much give in handling at hire speeds? I took it for a joy test ride at 70-80mph and it had mushy sway over imperfections


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[riceboy22]

For how I'm driving with a one-year old in the back, it didn't seem particularly mushy to me. I doubt I'm taking any long sweepers at the same speed as you though. And most of my high speed driving is on the NJTP which is a remarkably straight road. I was initially at 41 front and back but that was a bit high for me once I hit some NYC roads.

[riceboy22]

In thinking about this some more, with a wider tire than stock, you should probably be a bit below the factory spec for pressure to get to the same ride quality. If you're an "enthusiastic" driver though, 39 psi is probably going to end up being right. You may also want to run the front a bit higher than the rear.

[SQive]

This is true. As a typical rule-of-thumb, wider tires will run a slightly lower pressure. Of course, if you're coming from a 21-inch (or 22"), the 20" is going to seem softer regardless of the pressure. If you want to get it just right, in addition to what you feel is right, read up on how to chalk the tires. That's the best way to ensure the best wear. If the pressure is too high, it will be hard riding. If it's too low, it will be soft and your MPG will suffer slightly.

[osideaudi]

In thinking about this some more, with a wider tire than stock, you should probably be a bit below the factory spec for pressure to get to the same ride quality. If you're an "enthusiastic" driver though, 39 psi is probably going to end up being right. You may also want to run the front a bit higher than the rear.

I'll give 39 a shot and see how that works. Initially the main reason for my tire pressure inquiry was that I had all four wheels balanced and was told they're in spec/road force is good. I was still feeling a vibration from 70-80mph so I thought it possible that the tire pressure was causing it. While I've fluctuated pressures and still haven't remedied the vibration, I'm starting to wonder what the right pressure is anyway. I'm going to get it back to 39psi and then see if something else could be causing the vibration (bolts, rotors, suspension, etc.). Thanks for the tips though

[Silverarrow240]

I'm sure you've got this worked out Vic, as thorough as you are... but are you running different spacers on your 20x10's than your 21's (or any at all)?

Bad spacers can cause a pain-in-the-ass-to-disgnose vibration at speed... You are probably aware of this, but just a thought. :)

[riceboy22]

Funny enough, I'm dealing with something similar, as I have some vibration above 70mph after installing new wheels and the H&R springs. I'm not sure what's causing it either, so I was going to throw my stock 21s back on to see if I can eliminate a variable (no vibration on the stock wheels and suspension before). If you've got the time and inclination to do it (and the extra set of wheels), it'll at least help you to narrow down the root cause.

For tire pressure, I'm going to try bumping the front up a couple PSI so I'm at 38F and 36R.

[osideaudi]

I'm sure you've got this worked out Vic, as thorough as you are... but are you running different spacers on your 20x10's than your 21's (or any at all)?

Bad spacers can cause a pain-in-the-ass-to-disgnose vibration at speed... You are probably aware of this, but just a thought. :)

No spacers on the 20's, thanks for the suggestion though. That would have been one of the first things I'd check

Funny enough, I'm dealing with something similar, as I have some vibration above 70mph after installing new wheels and the H&R springs. I'm not sure what's causing it either, so I was going to throw my stock 21s back on to see if I can eliminate a variable (no vibration on the stock wheels and suspension before). If you've got the time and inclination to do it (and the extra set of wheels), it'll at least help you to narrow down the root cause.

For tire pressure, I'm going to try bumping the front up a couple PSI so I'm at 38F and 36R.

I just came off the 21's actually and didnt notice any sort of vibration that I can recall. but after having the wheel guy say that they're balanced and road force is good, I'm starting to wonder if suspension/linkages are playing a part. I've had the KW HAS on for about 15k miles, I doubt it's caused any issues this early. I'm taking the wheels to another tire shop this afternoon, we'll see what they say and what I'll do next. Let me know if you have any difference in ride quality after switching wheels, I'm interested now.