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Old 11-29-2008, 07:13 PM   #1
817bimmerfanatic
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Can 2 different size rear tires screw up transmission?!

Yesterday i bought 2 new rear tires, i had a plug in one(255) and them a screw in the side wall in the other(265). since i had a warranty on the tire with another so i was talking to the guy at firestone about getting it replaced. i have M3 wheels so the rears are wide. so i wanted to get a set of 245's in the rear to stop the rubbing. ANYWAYS when i was talking to the guy at firestone i was telling him that i had a 255 and a 265 in the rear, well he told me having to different sizes will screw up my transmission or rear end. Is this true?!? after getting the tires my car rides ALOT smoother so i didnt know if it was true.
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Old 11-29-2008, 07:15 PM   #2
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It wont affect the transmission, but it will affect your differential. The two different sized tires spin at different rates, cause the the differential to work at all times instead of just during a turn
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Old 11-29-2008, 07:17 PM   #3
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so how will i know if i screwed anything up?!
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Old 11-29-2008, 07:38 PM   #4
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You'll be fine. That's such a minuscule difference. Your wheels are still the same width.

How will you know if you screwed anything up?

You'd feel it.

You'll be fine. That guy was just scaring you.
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Old 11-29-2008, 07:41 PM   #5
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Width aside, the diameters of the 2 tires were probably pretty close so not much to worry about. You also have an open diff so it's not like you were wearing out clutch packs in a LSD. If you can't tell something is messed up, then nothing is messed up.
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Old 11-29-2008, 07:41 PM   #6
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yeah....smart @ss seller
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Old 11-29-2008, 07:41 PM   #7
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Ya i had a feeling that he just wanted me to buy some more tires, cause at first i was just gonna get the tire i had a warranty on replaced
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Old 11-29-2008, 07:42 PM   #8
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the 255 and the 265 are the widths of the tire so as long as the diameter of the tires are the same like one 255 40 18 and a 265 40 18 then you would be ok...If you were running say a 255 60 18 and a 265 40 18 then it might cause undue wear to the rear end...
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Old 11-29-2008, 07:53 PM   #9
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Guys I have a similar question http://forum.e46fanatics.com/showthread.php?t=628760....

Will size difference of 225/45/18 and 235/40/18 tires in the back affect my differential? Please help!!!!!
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Old 11-29-2008, 09:43 PM   #10
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Originally Posted by kpeng View Post
You'll be fine. That's such a minuscule difference. Your wheels are still the same width.

How will you know if you screwed anything up?

You'd feel it.

You'll be fine. That guy was just scaring you.
You are wrong. The width of the tire has nothing to do with it. The rolling radius is what matters. Yes two different size tires will cause damage to your diff. As far as your transmission not likely, in the front this wouldn’t be an issue unless you have an XI. The amount of damage can be very little to extreme depending on factors like driving style, miles driven, speeds and so on.
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Old 11-29-2008, 09:45 PM   #11
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I meant the wheels are the same. Same size, same width, so it doesn't matter. The wheel is what matters. If he had two different sized wheels in the back (i.e. 17 and 19), then that's what matters. If he had the same wheels in the back (i.e. both 19"s), he wouldn't be able to have a tire width discrepancy large enough to really matter now would he?
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Old 11-29-2008, 10:02 PM   #12
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SIMPLY PUT TWO TIRES ON THE DRIVE AXLE WITH DIFFERING DIAMETERS (HEIGHT) WILL POTENTIALLY HURT OR RUIN YOUR REAR END! talk to the 4x4 owners and see if they run different size tires on their rigs. width is fine but height you have to keep.
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Old 11-29-2008, 10:09 PM   #13
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I meant the wheels are the same. Same size, same width, so it doesn't matter. The wheel is what matters. If he had two different sized wheels in the back (i.e. 17 and 19), then that's what matters. If he had the same wheels in the back (i.e. both 19"s), he wouldn't be able to have a tire width discrepancy large enough to really matter now would he?

You are wrong... Again. I am only going to say this one more time. The rolling radius of the tires is what matters. Wheel size is not the issue, tire size is. The thing is you can have 2 tires the same Number size but the rolling radius is different due to wear and age etc. So in fact just because the sidewalls say it's this big, doesn't in fact mean they are the same. This will tear up a diff. That is why you buy 2 tires when replacing drive tires, or rotate the new tire to a non powered axle. I really am not interested in a pissing contest on a forum with you.
Yes this will eat your diff. don’t be cheap, buy tires in sets.

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Old 11-29-2008, 10:12 PM   #14
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Nevermind...I'm not even going to argue...

The total diameter of a 255 tire and a 265 tire is not big enough to cause damage or be disastrous like you think it is. You are dreaming and completely wrong. Like I said before, it's not like he's running 16" and 19" on each side. And even then, it takes a while for just a bit of damage to occur. We're talking mm's, not even inches. It's an open diff anyways.

Last edited by kpeng; 11-29-2008 at 10:51 PM.
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Old 11-29-2008, 10:23 PM   #15
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You guys are acting like the difference in diameter of the tires in question is soooooo huge.

Answer this.
What happens when u run a spare? Does the manual say move the flat drive wheel to the front and put the spare on a non driven wheel?

What happens when the run flat tire is at 0 psi, doesn't its effective rolling diameter become less than the fully inflated wheel, how come nothing happens?

If the cars diff was so fragile that the smallest difference in diameter will hurt the diff then how come our owners manual doesn't say, in case of flat call a tow track, why does our car come with a spare. And even with the full size spare, how come on zhp and other cars with staggered wheels, it only comes with a size that matches the front axle. What happens when you put that 225 spare on the rear drive wheel where a 255 was?

Oh wait, maybe the size difference is so small its harmless. Just maybe.
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Old 11-29-2008, 10:26 PM   #16
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you guys are acting like the difference in diameter of the tires in question is soooooo huge.

Answer this.
What happens when u run a spare? Does the manual say move the flat drive wheel to the front and put the spare on a non driven wheel?

What happens when the run flat tire is at 0 psi, doesn't its effective rolling diameter become less than the fully inflated wheel, how come nothing happens?

If the cars diff was so fragile that the smallest difference in diameter will hurt the diff then how come our owners manual doesn't say, in case of flat call a tow track, why does our car come with a spare. And even with the full size spare, how come on zhp and other cars with staggered wheels, it only comes with a size that matches the front axle. What happens when you put that 225 spare on the rear drive wheel where a 255 was?

Oh wait, maybe the size difference is so small its harmless. Just maybe.
thank you!!!!!!!!
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Old 11-29-2008, 10:33 PM   #17
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As long as the difference between tire circumference is within 3% you should be ok

Use calculator here
http://www.1010tires.com/tiresizecalculator.asp
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so 2004 bmw's dont come with a diff?
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Old 11-29-2008, 10:41 PM   #18
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Originally Posted by snikwad View Post
You guys are acting like the difference in diameter of the tires in question is soooooo huge.

Answer this.
What happens when u run a spare? Does the manual say move the flat drive wheel to the front and put the spare on a non driven wheel?

What happens when the run flat tire is at 0 psi, doesn't its effective rolling diameter become less than the fully inflated wheel, how come nothing happens?

If the cars diff was so fragile that the smallest difference in diameter will hurt the diff then how come our owners manual doesn't say, in case of flat call a tow track, why does our car come with a spare. And even with the full size spare, how come on zhp and other cars with staggered wheels, it only comes with a size that matches the front axle. What happens when you put that 225 spare on the rear drive wheel where a 255 was?

Oh wait, maybe the size difference is so small its harmless. Just maybe.

The spare is designed for short term emergency use. It's better to have a narrower tire than have no tire at all when you have a puncture. That doesn't mean it's ok to drive with that kind of set up at all times. The narrower tire would have lower grip. If certain driving parameters are exceeded, then the effect of tire width disparity would become noticeable. Even if no mechanical parts are immediately damaged, the car could well travel like a crab - side ways.

Last edited by GoingNuts; 11-29-2008 at 10:44 PM.
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Old 11-29-2008, 10:48 PM   #19
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Originally Posted by Dninty9 View Post
the 255 and the 265 are the widths of the tire so as long as the diameter of the tires are the same like one 255 40 18 and a 265 40 18 then you would be ok...If you were running say a 255 60 18 and a 265 40 18 then it might cause undue wear to the rear end...
You don't know much about tires, do you?
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Old 11-29-2008, 10:50 PM   #20
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An open diff is nothing more than gears which by design allow the wheels to spin at different speeds, there's nothing to harm. Every time you even slightly turn your steering wheel, the rear wheels spin at different speeds. Locking differentials (such as in the 4x4 world) are a completely different beast and matching tires becomes a serious concern. A clutch type LSD would incur a bit of undue wear but probably not enough to ever get concerned about.
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