View Full Version : Wheel diameter difference
Outie Essex
01-22-2020, 06:15 AM
I know this has been discussed before but I haven't seen a verifiable answer. I just bought a set of new wheels. 20x9 fronts with stock size 255/35/20s and 20x10.5 rears. I don't like the look of stretched tires so I want to go with something like 285/35/20s or 285/30/20. One main reason is that I LOVE the Michelin PS A/S 3+ tires and those are the largest ones they make. So the total diameter difference between OEM 255/35/20 and 285/35/20 is ~3.06% (upsized rear) and between OEM and 285/30/20 is ~1.1% (downsized rear). I am confident that the 285/30/20s will work just fine with that 1.1%, but I can get a super deal on the 285/35/20s.
I have read that Audi quattro can handle up to 3% difference so the 3.06% is stepping over that red line just a tad, but is that 3% a legitimate number? Is this what Audi claims or just from prior experience? This thread (https://www.audizine.com/forum/showthread.php/396882-Different-size-wheels-on-a-quattro-is-it-bad)is where I got that number from.
If there is a comparable tire to the Michelin PS A/S 3+ in a either of the 2 sizes already discussed or in a 295/30/20, I would love to hear about it. Something with a high UTQG rating (~500+) and excellent wet weather traction.
The diameter difference isn't OE to replacement diameter. Rather it's the diameter difference between the front and rear tires that are installed on the car. If all 4 tires are the same it won't negatively affect the quattro system. But, may affect speedometer accuracy .
Audi permits the following tread depth variance from front to rear:
Longitudinally mounted engine: 2mm (or roughly 5/64")
Transverse mounted engine: 3mm (or roughly 1/8")
Audi "recommends" the same tread depth left to right (especially with the sport diff)
In your case the OE tire is 770 revolutions per mile (RPM).
285/30-20 is 777 RPM.
285/35-20 is 746 RPM.
So, the 285/30 will have a negligible effect on speedometer accuracy.
Hope this helps.
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Outie Essex
01-22-2020, 11:51 AM
The diameter difference isn't OE to replacement diameter. Rather it's the diameter difference between the front and rear tires that are installed on the car. If all 4 tires are the same it won't negatively affect the quattro system. But, may affect speedometer accuracy .
Audi permits the following tread depth variance from front to rear:
Longitudinally mounted engine: 2mm (or roughly 5/64")
Transverse mounted engine: 3mm (or roughly 1/8")
Audi "recommends" the same tread depth left to right (especially with the sport diff)
In your case the OE tire is 770 revolutions per mile (RPM).
285/30-20 is 777 RPM.
285/35-20 is 746 RPM.
So, the 285/30 will have a negligible effect on speedometer accuracy.
Hope this helps.
Sent from my SM-G950U using Audizine mobile app (http://r.tapatalk.com/byo?rid=87676)
Ok somehow I confused a few people in my post. I am keeping the front tires the same as OEM, 255/35/20. The other sizes are only for the rears and what I am asking about in comparison to the OEM fronts. Yes your info helped. I haven't seen the 2mm and 3mm specs before so thats good info.
Both of these tires are out of the allowable variance and will negatively affect the quattro system. You only have 4mm total to play with.
The 285/30 vs OE is approximately 5.1mm
The 285/35 vs OE is approximately 22.9mm
You might want to consider changing the front to 255/40. Doing this with 285/35 on the rear gets you to 2.5mm difference and within the allowable variance.
Ok somehow I confused a few people in my post. I am keeping the front tires the same as OEM, 255/35/20. The other sizes are only for the rears and what I am asking about in comparison to the OEM fronts. Yes your info helped. I haven't seen the 2mm and 3mm specs before so thats good info.
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Outie Essex
01-22-2020, 02:11 PM
Both of these tires are out of the allowable variance and will negatively affect the quattro system. You only have 4mm total to play with.
The 285/30 vs OE is approximately 5.1mm
The 285/35 vs OE is approximately 22.9mm
You might want to consider changing the front to 255/40. Doing this with 285/35 on the rear gets you to 2.5mm difference and within the allowable variance.
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That is one possibility had considered. The other is to go with 245/35 and 285/30 or 255/35 and 295/30.
The 1st combo is spot on. I didn't see a 295/30 on Michelin's site. One other possibility if you have the OE size tire for the front. And that's to have the tread shaved down to match the 285/30 diameter. The would only need about 0.100" removed. I know it sounds odd, but this is commonly done in the truck industry.
I hope whatever you decide to go with works out.
That is one possibility had considered. The other is to go with 245/35 and 285/30 or 255/35 and 295/30.
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Outie Essex
01-22-2020, 06:34 PM
Yeah I’m thinking that’s the one I will most likely go with, 245/35 and 285/30
So, I take it that you previously had the Michelin PS A/S 3+. I'm thinking of getting these this spring for my A4. What's your experience with tread wear and wet traction?
Yeah I’m thinking that’s the one I will most likely go with, 245/35 and 285/30
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Outie Essex
01-22-2020, 07:15 PM
Yes my current tires are the PS A/S 3+. I live in central Florida where is rains like a monsoon and these never broke loose once. Love them. Totally comfortable drive in wet and dry weather.
Nice. Thanks for the feedback.
Yes my current tires are the PS A/S 3+. I live in central Florida where is rains like a monsoon and these never broke loose once. Love them. Totally comfortable drive in wry and dry weather.
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Outie Essex
01-23-2020, 06:04 AM
Anytime. I wish I didn't like them so much. It would open up so many more options for my setup.