[eddyj14]

Thanks for the explanation I appreciate it I'm just gonna
Do some research on what tires I can use to run the setup

[eddyj14]

Okay backs are two weeks old do not wanna replace.. I can replace fronts

So if I use 220-40-18 front it would give me a .8%
Or use 225-40-18 same as backs would give me .0

Is that correct? Someone help me on this?

[ammar23]

Originally Posted by Efthreeoh

So what no one has explained to you is why the tire diameters need to be the same front to back. On an all-wheel drive car there is a center differential (transfer cases are usually found in 4x4 trucks) that applies power to the front axle and rear axle. The center differential is computer controlled and can vary the amount (percentage) of engine power between the front and rear axles. It does this though a clutch mechanism.

Regardless of the amount of power that is directed to each axle (it's always 100% combined) both axles have to run at the same speed. The speed of rotation of the axle is tied to the diameter of the tire, so to have both axles rotate at the same speed the tires need to have the same overall diameter. If the tires are of different diameter between the front and rear axles, the center differential is stressed because the gearing inside it can not compensate for the difference in the speeds of each axle, so eventually the clutch mechanism takes the brunt of the stress and breaks.

Using a staggered wheel set up can create a difference in the tires diameter for the front and rear axles if the tires are not sized correctly to have the same overall diameter for all four tires (which is what you did). A tire's size specification, for the front tire example of 225/40-18, means the inside diameter of the tire that attaches to the wheel rim is 18 inches, the tread width is 225MM, and the 40 means the height of the sidewall is 40% of the width of the tread, so 225MM x 40% means the height of the sidewall is 90MM, which determines the total diameter (rolling distance) of the tire. Reducing the sidewall for the rear tires from 40% to 35% against a 20MM treadwidth difference gets a sidewall height of 89.25MM (255MM x 35% - close to 90). So the staggered setup of 225/40-18 in front and 255/35-18 rear has essentially the same tire diameter for all four tires.

If it were me, I'd get 4 wheels of the same size and correctly size the tires for an Xi car.

It's best to first understand how things work when deciding to modify them.

Brilliant response, I was just cruising through the thread not expecting to learn too much but that's with a reply like this. Anyways OP hope you find what you're looking for.

[SpeedBuggy]

Originally Posted by Efthreeoh

So what no one has explained to you is why the tire diameters need to be the same front to back. On an all-wheel drive car there is a center differential (transfer cases are usually found in 4x4 trucks) that applies power to the front axle and rear axle. The center differential is computer controlled and can vary the amount (percentage) of engine power between the front and rear axles. It does this though a clutch mechanism.

Regardless of the amount of power that is directed to each axle (it's always 100% combined) both axles have to run at the same speed. The speed of rotation of the axle is tied to the diameter of the tire, so to have both axles rotate at the same speed the tires need to have the same overall diameter. If the tires are of different diameter between the front and rear axles, the center differential is stressed because the gearing inside it can not compensate for the difference in the speeds of each axle, so eventually the clutch mechanism takes the brunt of the stress and breaks.

Using a staggered wheel set up can create a difference in the tires diameter for the front and rear axles if the tires are not sized correctly to have the same overall diameter for all four tires (which is what you did). A tire's size specification, for the front tire example of 225/40-18, means the inside diameter of the tire that attaches to the wheel rim is 18 inches, the tread width is 225MM, and the 40 means the height of the sidewall is 40% of the width of the tread, so 225MM x 40% means the height of the sidewall is 90MM, which determines the total diameter (rolling distance) of the tire. Reducing the sidewall for the rear tires from 40% to 35% against a 20MM treadwidth difference gets a sidewall height of 89.25MM (255MM x 35% - close to 90). So the staggered setup of 225/40-18 in front and 255/35-18 rear has essentially the same tire diameter for all four tires.

If it were me, I'd get 4 wheels of the same size and correctly size the tires for an Xi car.

It's best to first understand how things work when deciding to modify them.

Originally Posted by eddyj14

Okay backs are two weeks old do not wanna replace.. I can replace fronts

So if I use 220-40-18 front it would give me a .8%
Or use 225-40-18 same as backs would give me .0

Is that correct? Someone help me on this?

Have the 225/40/18 removed from the rear wheels (18 x 10) and have them mounted on the fronts (18 x 8.5). Buy new 255/35/18 and have them mounted on the rears.

This would be the stock sizes supplied by BMW, Results in 0.236% difference in diameters front to rear. (that is less than 1/4%)

18 x 8.5 is 1/2" wider than BMW stock front wheel, (18 x 8 is stock size) may provide a small amount of stretch.
18 x 10 is 1-1/2" wider than BMW stock rear wheel, (18 x 8.5 is stock size) will probably provide some stretch.

Try the following link for the "xi" forums, seems to be a lot of info also.

http://www.e90post.com/forums/forumdisplay.php?f=197

[Frenk]

On my XI , i have :

265/35/R19
245/35/R19

[eddyj14]

Thank you guys I appreciate the help I will do that mount the rears to fronts and I will be picking up some 255-35-18's tonight
Thanks

[Frenk]

then if the 4x4 lights doenst go off, I would go get it checked

[eddyj14]

I'm sure it will go off I drive it sometimes and light never comes on just as sometimes I do and it does come on it's an on an off thing

[paddy335]

Originally Posted by Envuks

You likely blew your transfer case by putting on the wrong size wheels. A rwd car could handle that for for Xdrive thats not a good setup at all. It's rare that it would happen so quickly after you out them on. Perhaps it was on its way out anyway.... The stretched look might be the dumbest thing to hit the automotive world since glow lights under the car. It looks like crap, handles like crap, and can lead to situations like this. Get a normal setup

+1 million. I just shake my head at the inanity. OP you are well outside recommended tyre ranges on front and rear for the width, as well as different rolling diameters. Go to a good shop and get some professional assistance.

[Frenk]

well i just realised I have 2.13% of difference on my XI

265/35/R19
245/35/R19

Been driving like that for 2 years not in winter tough (never had any issues or warning lights)

[eddyj14]

I think my lights may be more of the battery because I played around with battery and fuses that same day plus my battery is not good either so
I might have left something loose and that could have lead to my warning lights I heard.. But yeah better of being safe then sorry

[eddyj14]

I think my lights may be more of the battery because I played around with battery and fuses that same day plus my battery is not good either so
I might have left something loose and that could have lead to my warning lights I heard.. But yeah better of being safe then sorry

[romanonj]

Originally Posted by eddyj14

I think my lights may be more of the battery because I played around with battery and fuses that same day plus my battery is not good either so
I might have left something loose and that could have lead to my warning lights I heard.. But yeah better of being safe then sorry

What do you mean "played around with batter and fuses"?

[eddyj14]

I have had my tire pressure light on and thought I could take it off by fuse or disconnecting the battery... Mind you I had not yet driven the car with this tire or wheel setup after I pulled out fuses and checked them I turned on the car the light went on the 4x4 and traction... Disconnected battery the negative only then plugged it back on light still was on drove the car it went off this was the first time..

Now the light occasionally goes on only when car is driven not at start up

[Meeni]

You are going to break your car. Just have the proper tires installed. It's not the battery, using different rolling diameters will damage the central diff.

Good luck. You seem to need it.

[parabola]

My recommendation would be to fit the proper tires with TPMS and leave the battery and fuses alone.
Seems like you'll mess something up beyond your diy repair skills and then end up forking over $$$ at the dealership.

[eddyj14]

I knew what I was doing with the fuses there's oviously a diagram can't be that dumb and thanks to everyone's advice I just picked up two rear tires 255-35-18 that I didn't know about in an awd BMW thank you guys

[alex35i]

Could def. be because of the battery. When I replaced my battery car had 4x4 malfunction light on upon startup and I had stock staggered setup on my XI. Took it for a spin around the block and light disappeared, never came back.

[Amini77]

I have a 330xi and I have 0 problems regarding the 4x4 system. I think its something electrical.

Stock setup:
225/45/17 all around

New setup since 2 years ago:
(front)235/35/19 10mm spacers up front , (rear)255/35/19 12mm spacers in the rear. Plus I'm lowered on KW V1.

[scotty_miller]

Originally Posted by alex35i

Could def. be because of the battery. When I replaced my battery car had 4x4 malfunction light on upon startup and I had stock staggered setup on my XI. Took it for a spin around the block and light disappeared, never came back.

The reason that light went away is because you set the steering angle sensor. When that light comes on after a new battery is installed you turn the wheel lock to lock to make the computer reads your steering movement correctly. Just throwing that out there for anyone

[Alohaaaaa]

Originally Posted by matraks

No. They are original sizes. I think that stretch will not be good for any 4x4.

Not to be that guy, but when I was an Audi driver... We mostly ran hella-stretch on Quattro's.

[eddyj14]

Originally Posted by alex35i

Could def. be because of the battery. When I replaced my battery car had 4x4 malfunction light on upon startup and I had stock staggered setup on my XI. Took it for a spin around the block and light disappeared, never came back.

How long did you disconnect your battery? Did you only disconnect the negative or both?