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evo 9 spare tire

Old Dec 29, 2018, 10:42 PM
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evo 9 spare tire

Is it safe to run the oem spare tire on the evo awd system? Or will it destroy the diffs? I know usually you don't want a spare on your drive/power wheels.
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Old Dec 30, 2018, 07:49 AM
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I wouldn't 'run' it long like that. Use it for emergencies only.
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Old Dec 30, 2018, 09:02 AM
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I would say, its def not safe to run the spare longer than it takes to get to a tire shop ASAP. Keep the speeds super low & only drive a few miles

You should measure the circumference of your spare vs whats on the car. Im not sure, at this point, what is the acceptable variance is, but you should know how much the difference is

Ill measure mine today

Edit:
  • My 265/40/17 tire measures approx 79" in circum
  • The spare measures approx 76 1/2" in circum (3% diff)
  • The stock 235/45 tires has approx circum of 76 1/2"
Bottom line: My setup is not right for running the spare for any length other than to get it off the road

The tire guys seem to use 3/32nd of tread depth diff between tires as the limit on AWD cars

Last edited by MinusPrevious; Dec 30, 2018 at 04:24 PM.
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Old Dec 30, 2018, 05:07 PM
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Originally Posted by MinusPrevious View Post
I would say, its def not safe to run the spare longer than it takes to get to a tire shop ASAP. Keep the speeds super low & only drive a few miles

You should measure the circumference of your spare vs whats on the car. Im not sure, at this point, what is the acceptable variance is, but you should know how much the difference is

Ill measure mine today

Edit:
  • My 265/40/17 tire measures approx 79" in circum
  • The spare measures approx 76 1/2" in circum (3% diff)
  • The stock 235/45 tires has approx circum of 76 1/2"
Bottom line: My setup is not right for running the spare for any length other than to get it off the road

The tire guys seem to use 3/32nd of tread depth diff between tires as the limit on AWD cars
Great info. Thanks a lot!
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Old Dec 31, 2018, 11:48 PM
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Originally Posted by MinusPrevious View Post
I would say, its def not safe to run the spare longer than it takes to get to a tire shop ASAP. Keep the speeds super low & only drive a few miles

You should measure the circumference of your spare vs whats on the car. Im not sure, at this point, what is the acceptable variance is, but you should know how much the difference is

Ill measure mine today

Edit:
  • My 265/40/17 tire measures approx 79" in circum
  • The spare measures approx 76 1/2" in circum (3% diff)
  • The stock 235/45 tires has approx circum of 76 1/2"
Bottom line: My setup is not right for running the spare for any length other than to get it off the road

The tire guys seem to use 3/32nd of tread depth diff between tires as the limit on AWD cars
great info! I used my spare once. I drove less than 4 miles and ended up getting 4 new tires. I drove on a flat and didnt notice till the tire was tore up.
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Old Jan 1, 2019, 01:23 PM
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When I first got my Evo, January 2004, the weather was clear. Then it started snowing. Well, I had seen the door placard tire warning but I figured it was nonsense. So, I took the car out in deep the snow and found the placard was an understatement. What to do? I had four new snow tires on 16 inch steelies that fit a DSM. I was able to mount two on the back. On the front, on one side, so I could steer, I mounted the spare. So, with 16inch wheels on the back and the OEM wheel, plus whatever size the spare is, mounted on the front, I drove until spring and nothing bad happened. I've now had the car for 15 years and the differentials have never been touched. For next winter I had snow tires.

Running the spare will cause additional wear on spider gears. But remember, these gears are moving to some extent any time the car is underway anyway. Just use common sense.
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Old Jan 1, 2019, 01:50 PM
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I think what we are dealing w/here is more than just gearing. We have to consider the clutch plates in the rear diff & the plates in the front diff (ACD equipped)

Heres a visual of what happens w/mismatched AWD tires. You are forcing the difference in circumference through the drive train. Its all figured in RPM (revs per mile)

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Old Jan 8, 2019, 08:19 AM
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Having one smaller diameter tire is basically like driving a car with matched tires in a giant circle - you're forcing the differential clutch plates to deal with the smaller wheel turning faster than the opposing wheel even when going straight. Every time you go around a turn with matched tires, the outer tires travel further and turn faster than the inner. The plates in the differential deal with the mismatch during turning for hundreds of thousands of miles. The mismatched spare is not the end of the world as it's only supposed to get you home or to the tire shop. Or for BarneyB, thru the winter

BarneyB- I was going to ask why you didn't mount all the DSM snow tires but realized they were 15s and wouldn't fit in the front. I had a 92 TSI AWD that I bought new and drove for 313K miles. I loved that car and it never let me down or left me stranded.
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Old Jan 8, 2019, 12:13 PM
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Originally Posted by Steve_P View Post
Having one smaller diameter tire is basically like driving a car with matched tires in a giant circle - you're forcing the differential clutch plates to deal with the smaller wheel turning faster than the opposing wheel even when going straight. Every time you go around a turn with matched tires, the outer tires travel further and turn faster than the inner. The plates in the differential deal with the mismatch during turning for hundreds of thousands of miles. The mismatched spare is not the end of the world as it's only supposed to get you home or to the tire shop. Or for BarneyB, thru the winter

BarneyB- I was going to ask why you didn't mount all the DSM snow tires but realized they were 15s and wouldn't fit in the front. I had a 92 TSI AWD that I bought new and drove for 313K miles. I loved that car and it never let me down or left me stranded.
Two blocks from my house and running North to South across town is this very frost heaved arterial. Using that road I hear the center differential working all the time. Each end of the car travels a different distance as the car moves over bumps. Well, you might think the movement is tiny but constant tiny movements is what wears out u-joints.

I believe DSM's came with 16 inch wheels. With 55 series snow tires they looked to be the same diameter as the stock OEM Evo wheel and tire assembly. So, not a major sin.

Last edited by barneyb; Jan 8, 2019 at 12:20 PM.
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