New wheels on the way, which size tires?

[Weasel]

The wheel sare all tied together through the drivetrain, all pushed at equal speeds by the engine. The bigger diameter of a tire, the further it rolls per one rotation. If one set of tires are bigger than the other, the bigger set will push the smaller set and the smaller set will drag the bigger set... putting LOTS of stress on the drivetrain.

The tire sizes work probably different than you think. The 1st # is the tread width in millimeters, the 2nd # is the aspect ratio and works off of a percentage of the treadwidth... so a 275/40 is different height from a 295/40 and so on. The 275/40 and 315/35 are at the same rolling diameter which is why they are the best tire size option.

If you go on a site like tirerack.com and click "specs" when looking at a tire, it will give you the overall diameter and revs per mile for each tire size. Here's some to look at.

Dunlop did their homework to make tires the same size: http://www.tirerack.com/tires/Spec.j...e1=yes&place=0

Yet look at the different #s on the yokos:http://www.tirerack.com/tires/Spec.j...e1=yes&place=0

[RichiRich]

OH YEAH! i went with the Vredestein Ultrac Sessanta

OEM sizes of 275/40/20 front, 315/35/20 rear.....

Just recentley lowered with KW coilovers.....car handles great.....even in the ice and snow...carefully of course.





RR

[TaMbALoLoNg]

[quote=weasel56]The wheel sare all tied together through the drivetrain, all pushed at equal speeds by the engine. The bigger diameter of a tire, the further it rolls per one rotation. If one set of tires are bigger than the other, the bigger set will push the smaller set and the smaller set will drag the bigger set... putting LOTS of stress on the drivetrain.

The tire sizes work probably different than you think. The 1st # is the tread width in millimeters, the 2nd # is the aspect ratio and works off of a percentage of the treadwidth... so a 275/40 is different height from a 295/40 and so on. The 275/40 and 315/35 are at the same rolling diameter which is why they are the best tire size option.
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I agree pretty much 100%, but the difference between 275/40 and 295/40 is only 8mm, which is practically nothing and you can pretty much balance it out if you have less PSI on your rear tires. It shouldn't put significant amt of stress on the drivetrain worth worrying about.

[rayxi]

Originally Posted by TaMbALoLoNg

I agree pretty much 100%, but the difference between 275/40 and 295/40 is only 8mm, which is practically nothing and you can pretty much balance it out if you have less PSI on your rear tires. It shouldn't put significant amt of stress on the drivetrain worth worrying about.

I don't know how you're doing your math but the difference in circumference is around 100 mm and the difference in diameter is 32 mm. That's a 4% difference in rolling diameter which is outside the recommended maximum difference of 3%.

There are other considerations besides drivetrain stress. DSC and ABS both rely on sensing rotational differences between tires. It's possible that introducing differences under normal driving conditions could throw those systems off.

[TwinsPoppa]

Listen to weasel and go with the stock size tires.

I used the following sizes because my wheels are smaller width than stock:

265/45-20 (front)
295/40-20 (rear)

If you're going to use different width tires, in general, remember that your aspect ratios will be different to match the rolling diameters.

[motordavid]

richirich,
Titz looking wheels and tires!
Especially like the look on your Ti Ag...
Wish I could justify a set for ours.
BR,mD

[RichiRich]

Originally Posted by motordavid

richirich,
Titz looking wheels and tires!
Especially like the look on your Ti Ag...
Wish I could justify a set for ours.
BR,mD

MD - Thank you for the comp!

LOL! I had to justify mine to the MRS. LOL!

Rich

[TwinsPoppa]

Originally Posted by motordavid

richirich,
Titz looking wheels and tires!
Especially like the look on your Ti Ag...
Wish I could justify a set for ours.
BR,mD

Hahaha ... you know what they say (and it's usually what I do) ... it's easier to beg for forgiveness than to ask for permission!

Shhh ... don't tell my wife!

[Weasel]

Originally Posted by TaMbALoLoNg

I agree pretty much 100%, but the difference between 275/40 and 295/40 is only 8mm, which is practically nothing and you can pretty much balance it out if you have less PSI on your rear tires. It shouldn't put significant amt of stress on the drivetrain worth worrying about.

The difference between 275/40 and 295/40 equals out to 18 full rotations per mile!!! I have personally seen and had to fix the problems created by this, namely... transfer case. In 2000 - 2003 X5s it usually strips the splines at the front output shaft of the case costing you a front driveshaft and a transfer case. In 2004 - 2006 X5s it causes substantial wear to the clutches in the case where it transfers torque split to the front wheels, causing once again the transfer case to need replacement.

It would be like having different gear ratios front and rear of your 4 wheel drive... you just don't do that.

[TaMbALoLoNg]

Originally Posted by weasel56

The difference between 275/40 and 295/40 equals out to 18 full rotations per mile!!! I have personally seen and had to fix the problems created by this, namely... transfer case. In 2000 - 2003 X5s it usually strips the splines at the front output shaft of the case costing you a front driveshaft and a transfer case. In 2004 - 2006 X5s it causes substantial wear to the clutches in the case where it transfers torque split to the front wheels, causing once again the transfer case to need replacement.

It would be like having different gear ratios front and rear of your 4 wheel drive... you just don't do that.

Makes perfect sense. The above is my current set up but I'm going to replace my rears to match my 275 fronts, I certaintly dont want future transfercase problems. So far I dont notice any problems right now and my X runs great. So i guess its either 275 or 295 all around. What do you think? This have been a very informative thread..great job guys