[fefo25]

I just purchased a set of oem e90 m3 wheels and tires. The tire sizes are 245/40/18 front 265/40/18 rear. Before I installed these wheels the car had a set of 16 inch stocks and the car was running great, no issues.. Now I install these wheels and the car is out whack. When I give.hard acceleration the whole car.vibrates.. Feels very unstable most of the times. The wheels were just balance so its not that. Could it be that the rear tire is too big? I know the xi's are sensitive to this. What could this be?

[pue174]

yes the rears are a larger diameter causing a problem with all wheel drive

[fefo25]

Originally Posted by pue174

yes the rears are a larger diameter causing a problem with all wheel drive

Would a 255/40/18 fix it?

[pue174]

yes or a 265/35
Use this to figure out diameters- multiply first number by .0392 then multiply second number then multiply x 2 then add the wheel diameter. Example 255/40 18
255x.0392=9.996x.40=3.9984x2=7.9968+18=25.996. 25.996x9.996
sorry to be confusing

[Chris@codemybimmer]

i think its just needs balancing.
i dont think tire difference will cause vibrations like that.

[Amused]

Originally Posted by 1lyfe

i think its just needs balancing.
i dont think tire difference will cause vibrations like that.

A transfer case that is trying to spin at two different speeds will. He will grenade his transfer case if he keeps driving with those tires.

[Chris@codemybimmer]

Originally Posted by Amused

A transfer case that is trying to spin at two different speeds will. He will grenade his transfer case if he keeps driving with those tires.

oooo
didnt know that

[fefo25]

Originally Posted by Amused

A transfer case that is trying to spin at two different speeds will. He will grenade his transfer case if he keeps driving with those tires.

Would I be safe with 245/40/18 all around??

[fefo25]

I changed the rear tires from 265/40/18 to 255/40/18 and I still get a vibration under hard acceleration. I had that same setup on this car before and it never did that. What can this be?? Now I have the stocks back on and its back to normal.

[Amused]

What are your factory size tires?

[gaberoll]

Originally Posted by fefo25

I changed the rear tires from 265/40/18 to 255/40/18 and I still get a vibration under hard acceleration. I had that same setup on this car before and it never did that. What can this be?? Now I have the stocks back on and its back to normal.

running 235/40/18 and 265/35/18 will bring the difference in rolling diameter below 1%, that should help.

[fefo25]

Originally Posted by Amused

What are your factory size tires?

205/55/16

[Alpineweiss e90]

Originally Posted by Amused

A transfer case that is trying to spin at two different speeds will. He will grenade his transfer case if he keeps driving with those tires.

The transfer case has a multiclutch setup that will adjust to different speeds.

I'm not saying a huge difference in rolling diameter won't damage it, but it won't grenade it, it will wear faster over time.

[UltraRacer13]

@ 245/40 and 265/40 there is a 2.3% difference in the diameter. You should try to stay within 1%, though 2% may be allowable.

Here are the facts-

F- 245/40
R- 265/40 = diff of 2.3% = BAD

F- 245/40
R- 255/40 = diff of 1.2% = BETTER, but not good

F- 245/40
R- 265/35 = diff of 1.63% = Not Good

F- 235/40
R- 265/35 = diff of 0.39% = GOOD!

Use the tire size calculator on the wheel forum. Most likely, you have a balance or mounting issue, but you need to pay attention to this as well.

[fefo25]

Originally Posted by UltraRacer13

@ 245/40 and 265/40 there is a 2.3% difference in the diameter. You should try to stay within 1%, though 2% may be allowable.

Here are the facts-

F- 245/40
R- 265/40 = diff of 2.3% = BAD

F- 245/40
R- 255/40 = diff of 1.2% = BETTER, but not good

F- 245/40
R- 265/35 = diff of 1.63% = Not Good

F- 235/40
R- 265/35 = diff of 0.39% = GOOD!

Use the tire size calculator on the wheel forum. Most likely, you have a balance or mounting issue, but you need to pay attention to this as well.

Cool, thanks

[Alpineweiss e90]

I think it's a mounting issue. Make sure the wheel is dead on before putting it on the ground. Hand tighten the lugs so the wheel is sitting directly up against the hub.

I had a buddy not this and he got vibrations.

[fefo25]

Originally Posted by Alpineweiss e90

I think it's a mounting issue. Make sure the wheel is dead on before putting it on the ground. Hand tighten the lugs so the wheel is sitting directly up against the hub.

I had a buddy not this and he got vibrations.

Maybe that was the case. Like I mentioned earlier, I had the exact tire setup with the E46 m3 wheels and the car ran smooth.

[UltraRacer13]

Originally Posted by fefo25

Maybe that was the case. Like I mentioned earlier, I had the exact tire setup with the E46 m3 wheels and the car ran smooth.

XI man- you have to respect the transfer case. This ain't no E46 M3.

[Alpineweiss e90]

Why are you all obsessed with the transfer case? A transfer case is designed to allow the front and rear axles to rotate at different speeds. It synchronizes them.

[nomile]

Originally Posted by Alpineweiss e90

Why are you all obsessed with the transfer case? A transfer case is designed to allow the front and rear axles to rotate at different speeds. It synchronizes them.

If the transfer case was an open diff your statement would be correct, but it isn't. Since it's a multiplate clutch (i.e. more or less locks front and rear together), different speeds front and back will cause xfer case clutch to slip continuously, heating up, then overheating, then failing.

[fefo25]

Originally Posted by UltraRacer13

XI man- you have to respect the transfer case. This ain't no E46 M3.

What I meant was I had E46 M3 wheels on my xi withe the same tire setup and it ran perfect. That why this makes no sense of why the car is out of wack now.

[UltraRacer13]

Originally Posted by fefo25

What I meant was I had E46 M3 wheels on my xi withe the same tire setup and it ran perfect. That why this makes no sense of why the car is out of wack now.

oh...gotcha. then most likely this is mount/balance issue.