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Do I really need to replace all 4 tires at one time?

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Old 02-07-2011, 08:27 AM   #1
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Default Do I really need to replace all 4 tires at one time?

I blew out one of my Nokian WR snow tires in a pothole. Problem is they don't make them anymore. I keep seeing you need to replace all four tires when you have all wheel drive. I believe just the front two may be OK. Here is my reasoning: While having different tires/wear levels side to side might present some issues given the nature of the quattro system, front vs back should not, precisely because of the vaunted Torsen system, which mechanically adjusts continuously for difference in traction, etc. Am I crazy or will I ruin the transmission if I put Nokian WR-G2's on the front?

Any opinions?
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Old 02-07-2011, 08:52 AM   #2
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I blew out one of my Nokian WR snow tires in a pothole. Problem is they don't make them anymore. I keep seeing you need to replace all four tires when you have all wheel drive. I believe just the front two may be OK. Here is my reasoning: While having different tires/wear levels side to side might present some issues given the nature of the quattro system, front vs back should not, precisely because of the vaunted Torsen system, which mechanically adjusts continuously for difference in traction, etc. Am I crazy or will I ruin the transmission if I put Nokian WR-G2's on the front?

Any opinions?
Having driven with different sized tires in the past I would say no, a minute difference due to new thread will not affect the system.
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Old 02-07-2011, 09:41 AM   #3
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Depending on how worn the opposite side is, you will probably be OK with two, at the most. Put both new ones on the same "axle", of course. If the tire 'on the other side' still has a lot of tread. maybe you're OK with just the one new.

BUT....

I would be a little cautious about running tires with two different tread patterns on the same "axle" (front or rear), since their traction performance might be different enough give you handling problems.
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Old 02-07-2011, 10:24 AM   #4
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Default $.02

I used to have a Subaru Legacy Outback Wagon with manual transmission and awd. It had a torsen center diff, similar to the Audi design. This was a hotly discussed matter on the Subaru boards. People who ran different sized tires front and rear pointed to a condition known as "torque binding" where the car would buck and jump while going around tight corners, esp in parking lots, etc. The theory was that constant work by the center differential would cause stress and overheating, which in turn led to torque binding.

There were also those who had run 200k miles, never paid attention to matching tires, and never had a probleem.

I never had the torque binding condition with my Subaru, but I always ran tires that matched. When I bought an Audi, I looked into the mfr recomendation for tire size, and Audi is more liberal when allowing a different sized tire than Subaru. Maybe Audi's system is more forgiving?

Be sure to explore all options. Sometimes you can find a discontinued tire online, tirerack.com etc. Be sure the tire is the same size, and if you are really worried, you can have a new tire shaved to match the existing.

Good luck.
John
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Old 02-07-2011, 10:27 AM   #5
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I think two are fine. But here are the issues:

1) you need - both front to back and side to side - similar (not exact, close) rolling circumferences or else there will be constant motion in the diff. It matters not if its open or Torsen - motion is motion.

2) Similarly, both ABS and ESP (stability) operate based on relative rotational speed of the various hubs/axles. If the rolling circumferences are different enough, ABS or ESP could be confused.

3) On any car, FWD, RWD or AWD, if you have worn tires at one end and good at the other, you will either make it understeer more or oversteer more. Typically, people say "put the good ones on the front because they steerr". True. but that also means the rear end can snap out mroe easily - and most people panic when that happens. You choose.

Yes, i have even replaced ONE tire on a quattro and all was fine. The others were only worn about 3/32"

G
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Old 02-07-2011, 10:46 AM   #6
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Also check on eBay to see what's available. You'd be amazed at the odd-ball tires and stuff that people want to sell.
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Old 02-07-2011, 01:09 PM   #7
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Also check on eBay to see what's available. You'd be amazed at the odd-ball tires and stuff that people want to sell.
Very good point here. Also check your local used tires places. They usually have thousands of misc tires lying around, you might just find the right tire for yourself.
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Old 02-07-2011, 02:03 PM   #8
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Very good point here. Also check your local used tires places. They usually have thousands of misc tires lying around, you might just find the right tire for yourself.
thats what i did to pass the time till i needed 4 new tires
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Old 02-07-2011, 04:01 PM   #9
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tire size doesn't matter one little bit.

Its the difference between tires that matters.

I run all 4 tires + 2.8%, which is a lot. But the sensors and the differentials don't know the difference. All they know is how fast the axle's rotate.

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Old 02-08-2011, 05:50 AM   #10
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Default To be clear - not changing tire size just tire model

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tire size doesn't matter one little bit.

Its the difference between tires that matters.

I run all 4 tires + 2.8%, which is a lot. But the sensors and the differentials don't know the difference. All they know is how fast the axle's rotate.

G
Still going with 235/45-17's just going with the latest generation Nokian's since the ones I have are not made anymore
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Old 02-08-2011, 07:01 AM   #11
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Even with the same size tire, rolling circumference can be different, especially with different brand/model tires. Even same brand/model tires can have different measurements due to uneven wear and inflation. Traveling at a set speed in a straight line with different rolling circumference tires will cause axle rotations per minute to be different from axle to axle. How much depends on the degree of difference. The greater the difference, the greater the strain on your drivetrain/differential/clutch pack/torsen. More strain=more risk.

Good luck,
John
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Old 02-08-2011, 11:29 AM   #12
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Default Within 2/32" - 3/32" difference is usually maximum accepted difference

Here is a quick calculation to show the difference of 3/32" on a tire. My tires are 255/40R17, so I will use the numbers for it. The results will be different for other tire and rim sizes but it illustrates the point. Results depend on the radius from center of wheel to surface of tread.

17" diameter rim is an 8.5" radius which is 215.9mm. Tire section height is 40% of section width (255mm) which is 102mm. Adding rim radius and tire section height gives total radius.
215.9mm + 102mm = 317.9mm.
317.9mm/25.4mm = 12.52"

Circumference of tire = 12.52"x2xpi = 78.67"/12" = 6.56 Foot circumference
Circ. of tire with 3/32" wear = (12.52-0.09375)x2xpi = 78.08"/12" = 6.51 foot

Number of revolutions a tire makes in 1 mile is 5280 feet/circumference

New tire: 5280 feet/6.56 feet = 804.88 revs
3/32" wear: 5280 feet/6.51 feet = 811.06 revs

Difference = 811.06-804.88 = 6.18 revolutions

In this case, a the tire with 3/32" wear will have to rotate 6 more times than the newer tire in one mile. A wheel setup with a smaller overall radius will actually see an even larger difference in revolutions (you can imagine that as a radius gets larger and larger, that taking 3/32" from its radius will eventually become negligible, while as a radius gets smaller and smaller, taking 3/32" from the radius takes a larger and larger percentage of the radius).

You can make your own conclusions as to whether or not 6 revolutions in a mile is a "strain" on the drive-train. Certainly in any turn the difference in revolutions between the inner turning wheel and outer turning wheel is far greater than that shown of the tread wear difference. However the tread wear difference is always there, and while I don't believe it puts a tremendous strain on the drive-train, it is still extra work for it and should be minimized whenever possible.
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Old 02-08-2011, 11:45 AM   #13
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You can make your own conclusions as to whether or not 6 revolutions in a mile is a "strain" on the drive-train. Certainly in any turn the difference in revolutions between the inner turning wheel and outer turning wheel is far greater than that shown of the tread wear difference.
I would think you could induce more than a 6 revolutions per mile discrepancy by having a tire (or two or three) that is over- or under-inflated relative to the others, as I'm sure many people do. It's not like the cars are set up like pick-up trucks (and old Audis for that matter) used to be where the center differential locked and you could really make the car buck if you tried to drive it on dry pavement and turned too sharply, etc. Then again, I can imagine that taken to an extreme, there IS a problem with having an odd-size tire on the car, hence Audi's decision to supply full-size spares (I mean, if Audi had its way, I imagine they would have rather put in a lighter weight spare than to go to the trouble of putting on an aluminum front end, as they did on the 4.2).
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Old 02-08-2011, 12:09 PM   #14
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Default circumference probably never the same in the real world

The math above looks correct to me but various real world variations may swamp that difference. The auto engineers are aware of that variation exists and allow for some variation in the systems they design (out of round, inflation, differing tread wear, etc.). At the same time it is also correct to say you don't want to push the limits and unncessarily put stress on your car. I have located a used tire of the same tread pattern that had 5/32 tread vs the 6/32 I have on my car now, so my current plan is to go get that tire, ride one more season and swap out for an all new set of four, unless global warming has made snow tires superfluous (not seeing it here in Boston).
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Old 02-08-2011, 01:07 PM   #15
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probably fine if they are intended to be direct replacement. Perfect? No. Close? Likely.

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