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      01-13-2012, 03:57 PM   #1
Cory1970
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Will this mess up my transfercase?

I need to put snow tires on my Type 162 (Front: 18x8 ET34 225/40 R18) (Rear: 18x8.5 ET37 255/35 R18).

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2007 335xi, sport package, 6speed

According to Gary at TireRack I can run 225/40R18 all the way around. While I am sure he is correct and they will fit, will this damage my transfercase?

My thought is that the rear tire will be slightly stretched on the rim causing a difference in diameter between the front and rear wheel.


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I'm just going to mount tires on my factory 18" Sport wheels because I have aftermarket wheels for summer or just don't want to buy another set of wheels. Can I use 225/40R18 on all four wheels even though the rear is now 255/35R18?

Yes, you can use 225/40R18 on both the front 8" wheels and the rear 8.5" OE wheels with no problem. This is actually very common to do. Eliminating the stagger in this way works very well for winter and results in better winter traction.
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      01-13-2012, 05:43 PM   #2
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According to the offset calculator at the top of the wheel and tire section, the difference in rolling diameter between your 255/35 series tire and a 225/40 series tire is 0.235%, so in that aspect you should be fine.

However, I don't know if I'd personally risk stretching a 225 series tire on a 18.5" rim. It will have a stretched look and provide less protection for the rim face. I use my stock rims (same sizes as yours) as my winter wheels, but my winter tires are 225 front and 255 rear. While it may not be the optimal size for snowy conditions, it still provides enough traction for safe driving. And there are only a few snowy days per year where I live anyway. The rest of the time it's just cold, so I prefer a staggered tire for more grip.

Last edited by Patrick719; 01-14-2012 at 03:06 PM.
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      01-14-2012, 11:01 AM   #3
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Quote:
Originally Posted by Cory1970 View Post
I need to put snow tires on my Type 162 (Front: 18x8 ET34 225/40 R18) (Rear: 18x8.5 ET37 255/35 R18).

Car:
2007 335xi, sport package, 6speed

According to Gary at TireRack I can run 225/40R18 all the way around. While I am sure he is correct and they will fit, will this damage my transfercase?

My thought is that the rear tire will be slightly stretched on the rim causing a difference in diameter between the front and rear wheel.

The rear tires will be slightly stretched, but it won't change the rolling diameter, only the width - which is good in this case since you want skinnier tires for snow.

FWIW I'm running 225/40/18 Dunlop 3Ds on 8.5' wheels. The tires look slightly stretched, but not too bad. Just have to be careful around curbs etc.
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      01-14-2012, 01:57 PM   #4
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I am running that winter size.
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      01-14-2012, 03:57 PM   #5
Cory1970
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Quote:
Originally Posted by zipstic View Post
The rear tires will be slightly stretched, but it won't change the rolling diameter, only the width - which is good in this case since you want skinnier tires for snow.
Here is my thought process:
  • Tires are stretched when the bead is pulled further out.
  • This extra width comes from deflection of the sidewall causing it to be a less steep angle.
  • A sidewall at an angle less than one on a narrower rim would be shorter in overall height.
  • The shorter sidewall height would equate to a smaller rolling diameter.

This smaller rolling diameter is what worries me.

Thoughts?
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      01-14-2012, 09:47 PM   #6
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Rolling diameter does not change ( enough to matter) when put on different width wheels. This is due to modern sidewall construction. You'll be fine for snows.
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      01-15-2012, 01:14 PM   #7
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Quote:
Originally Posted by Patrick719 View Post
According to the offset calculator at the top of the wheel and tire section, the difference in rolling diameter between your 255/35 series tire and a 225/40 series tire is 0.235%, so in that aspect you should be fine.

However, I don't know if I'd personally risk stretching a 225 series tire on a 18.5" rim. It will have a stretched look and provide less protection for the rim face. I use my stock rims (same sizes as yours) as my winter wheels, but my winter tires are 225 front and 255 rear. While it may not be the optimal size for snowy conditions, it still provides enough traction for safe driving. And there are only a few snowy days per year where I live anyway. The rest of the time it's just cold, so I prefer a staggered tire for more grip.
This is incorrect. I have the very setup you mentioned (stock sport 18s with 225 winter rubber on all corners), and it doesn't looked stretched at all. You can't tell the difference between fronts and rears at all.

I did have my transfer case replaced under warranty though...

I hadn't thuoght stretching it would make enough of a diameter difference to matter. from .22, what's the worst it could have become, doubled to .44? Even still it'd be okay... The problem with my case wasn't a wear and tear issue though. I had a defect, at least they said. Interesting.
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      01-15-2012, 02:25 PM   #8
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I have 235/40/18's all around on my stock wheels with 10mm spacers in the rear and the car runs great.. my winter tires are Blizzak ws60's.. there is one thing that I have noticed is at high speeds when turning I feel a bit of vibration in the wheel, almost feels like torque steering.... The tires in the rear are a bit stretched but doesnt look bad at all.
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