New wheels on the way, which size tires?

[ctbmw1]

168's are coming 20x9.5 front and 20x10.5 rears.

275/40/20 front
315/35/20 rear

or
275/40/20 all the way around? I read a thread here of somebody who did that.

or
275/40/20 front
295/40/20 rear

Thinking about Vredestein Sessanta

If have my 131 on now that will be my dedicated winters.

[Weasel]

I would go with the OEM sizes of 275/40/20 front, 315/35/20 rear.

The same size tires front and rear would have the rear tires not as wide as the rim, which would affect tire wear and would look funny too.

The tires front to rear really need to have the same rolling diameter to work properly in the 4 wheel drive system and not cause drive system wear, so the 275/40 to 295/40 idea is out.

And I have heard nothing but good about the Vredestines so far.

Good luck and enjoy the new wheels!

[TaMbALoLoNg]

Go with the 1st option

[X5-limo]

Originally Posted by weasel56

I would go with the OEM sizes of 275/40/20 front, 315/35/20 rear.

The same size tires front and rear would have the rear tires not as wide as the rim, which would affect tire wear and would look funny too.

The tires front to rear really need to have the same rolling diameter to work properly in the 4 wheel drive system and not cause drive system wear, so the 275/40 to 295/40 idea is out.

And I have heard nothing but good about the Vredestines so far.

Good luck and enjoy the new wheels!

I like the 20" wheel look. Not knowing much about tire-wheel basics, I would like to understand how when having the same rolling diameter is necessary to work properly in the 4 wheel drive system, that a '275/40 to 295/40' front-rear tire combo would be ruled out while the sizes of 275/40/20 front, 315/35/20 rear deemed acceptable?

Thanx

[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