Different tyres sizes?????
 

Hi guys, i have just realise after all this time i have been running my x5 on two different size tyres :(

the two at the front are different to the two at the back. i have 295 30 22 and 285 35 22. Im worried now that it might have damaged the trans, do i need to replace two asap or is this ok untill i get paid (a few weeks). A friend says two need to be replaced asap as it will break the transmission. Another said it should be fine as it a 4x4 and they supply different power to different wheels.

i did a google search and it says different things about "the rolling radius would be different"

i dont really get the rolling radius thing, does 5mm make that much difference, are they ment to be different (like race cars)

i would be very gratefull of any advice, many thanks kind regards Jon

A couple things to consider.

Using rolling diameters different than stock will affect the speedometer - reading higher or lower than actual.

Driveline damage, as it relates to using different rolling diameters front to back, are dependent on your model X5.

2003 and below (non-xdrive) have a locked front/back torque split. If your X does not have xdrive then match your front & rear tires. If I remember correctly they can only be within 3-4 revs/mile tolerance difference.

If you use a site like this Tire Size Calculator, you can compare tire specs. There are differences between mfgrs even with the same sized tires. So, while the dimensions are nominal, and not actual, they are fine for our purposes.
Tire Size Calculator - tire & wheel plus sizing?

According to that site your current setup has about 21 revs/mile difference.

2004 models and up have x-drive. These allow for more tolerance as the torque split is not locked. However, I can't remember right now what is the tolerance.

What year/model is your X?

Twins:

A couple of comments.

You say that the pre x-drive has a locked torque split. That is technically true, but a little misleading IMO. The transfer case has a fixed torque split, but it is certainly not locked. The transfer case is open, and one drive shaft (front or rear) can rotate at a different speed than the other without too much issue. If you have a very large difference, for a long time, then damage can result. Towing with one axle raised and the other axle on the ground is an example; you are limited to a certain speed and distance by BMW.

Tire size differences can certainly cause damage with the pre x-drive transfer case. I would strive for 3-4 revolution per mile difference, but I don't think that is a hard cutoff. When BMW came out with the x-drive transfer case (in the X3) there were actually more problems with tire size differences. X3 models are famous for it, as they have a lighter transfer case than the E53. So I would be just as concerned with an x-drive transfer case and tire size differences, including on the E53/E70, probably more so than with the pre x-drive.

Correction, the non-xdrive transfer case has a fixed front-to-rear torque split.

So, in general and all things being equal, you feel the non-xdrive transfer case would fare better when it comes to using mismatched rolling diameters in the front vs. rear? I'm probably missing something and don't know it.

thank you for your replys, wow i didnt realise different tyre sizes made so much difference, my other cars a alfa spider and i have never had to look into this much info about tyre sizes, but hey its always broke down lol!........... (not really)

my x5 is a 2001 e53 3.0l petrol so its not a xdrive so not looking good, im going to have a play on the website now to see what it come up with................ps nice cars

You should run all the same sized rolling diameters. Maybe just run the 285 on all four corners - as long as they are the same rolling diameter.

Stock some X5s came with a staggered setup of 275/40-20 front and 315/35-20 tires. However, they still had the same rolling diameter.

If you want to run staggered wheels and/or tires you can - just make sure they are the same rolling diameters.

Thanks for the compliment. :thumbup:

ok so i used the website and its say the rev per miles on the 295/30/22 are 718
and the 285/35/22 are 697 so there is a difference.

the rolling radius for the 295 is 14.48 inch
and the radius for the 285 is 14.92 inch

so for future use if i go for different tyre brands, whats the variance you can have?

Ideally you want the same but try to be within 3-4 revs/mile max. Try to have the same tire brands too. Why would you want to use different tire brands?

the ones on the X are nexens, not a brand i know, i will replace two tyres with a better brand and then replace the nexens at a later date. thats the plan lol!

An old pick up or Jeep has a locked up transfer case in 4wd, simply dividing the power front rear but not allowing any speed difference. That is a very different type of transfer case.

I don't have data to back it up, but yes, for the following reasons

*The non x-drive (nxd) is an open diff. It can handle speed differences
*The xd has clutches to wear
*The X3 (which only came with xd) had more problems with transfer case failures, attributed by BMW to the use of different sized tires.
*BMW has a towing limit, with one axle raised, of 150 km at 50 km/hr for the nxd. Towing the xd with one axle raised is not permitted due to the risk of transfer case damage.

I had the same questions and had a staggered setup and was toying woth the idea of different tires , in the end i bought a set of used alloys 17" and tires are the same all the way round and the correct tires as you see them listed on the fuel cap flap

Standard Vs Z on an X3
 

Hey guys, does anyone know if having a standard tire and a Z tire on the same car makes a difference/has an effect on this?

We bought our 04 X3 in August, and now when I drive it, I dont like how the transmission feels. It is a hard shift at low speeds sometimes and I get a weird RPM "flutter" when slowing down/coasting at approx 30mph.

Anyways a local mechanic pointed out to me that the tires in the front are different sizes than those in the rear. The measurements are all the same (235/35/17), however the rears are Z rated. I can really see a difference in size though. The fronts definitely look bigger.

Can tires have the same measurements on their side walls but really be different sizes?

Can this cause issues?

1. Having different tire brands with different tread patterns can create a different feel/response from each axle
2. Yes, tires with the same measurement on their side walls can actually have different overall cirucmference/diameter

TIP: spending approx 30 minutes on a site like Tire Rack - Your performance experts for tires and wheels educating yourself to various tire technology & info can go a long way in expanding your knowledge about the questions you asked. You can come away with a lot of information about the tire industry and what all the specs & stuff mean that is provided on tire sidewalls...and you can actually compare many tire brands & specs side by side and see exactly how different some tires may be even though they are the same size, same category, etc.

I've got a 2001, non-xdrive, NV125 transfer case, 19" style 63 BMW wheels, 285/45R19 107V rear, 255/50R19 103V front. The spare is of course a 235/65R17 with zero wear.

My rear tires are worn. That is a fairly rare size, but I can get a pretty good deal on some lightly used, nice 275/45R19 tires, but of course I'm concerned with causing TC problems.

I know that buying a new set of 4 Michelins at the dealer, and replacing the never used, but 14 years old spare as well will work, and many here would do just that. Not me.

So first question on the TC tolerance on difference in rotations front to rear - JCL quotes 3-4 per mile should be good, and I think I saw that somewhere else too. But then the quote on towing (also confirmed in the owner's manual) - that seems EXTREMELY more stressful than the 3-4 revs/mile difference for driving. It would make me think that the real limit may be higher than 3-4. Comments?

Also, I ran some numbers for myself calculating the differences in tire diameter and revs per mile for different tires. Following is the output for my current situation.
1 - 285/45R19 on rear, with about 8/32" of wear gone (not remaining)
2 - 255/50R19 on front, 4/32" worn
3 - 235/65R17 spare, 0/32" worn
4 - 275/45R19 candidate replacement for rear, 2/32" worn

revs_per_mile =
705.2 700.5 694.8 704.7
diameter_mm =
726.4 731.3 737.3 726.9

Comments - the candidate tire fits better than the existing one due to lower wear. The spare is further out.

BTW, if I did not account for tire wear, here are the results (assuming all tires were brand new with no wear):

revs_per_mile =
693.1 694.5 694.8 701.6 (brand new, all specified tires are in a tight range)
diameter_mm =
739.1 737.6 737.3 730.1

I know this does not account for manufacturing tolerances, inexact tire design, inflation, load, etc.

Does this seem like a safe plan? BTW, the TC is pretty new, dealer installed by the PO a year before I bought it.

I don't have a single answer for you, but I can give you some data points and a suggestion.

The BMW workshop manual lists a 1% maximum allowable difference between tires to avoid transfer case damage, on the x drive transfer case. I don't have the published figure for the non x drive transfer case. 1% works out to about 7 revs/mile, so that is their hard limit. I have used 4 revs/mile as my own limit, based on previous discussions with dealer service personnel and my own experience with other awd vehicles.

I deal with a good tire shop. I recently had a tire receive a cut to a sidewall on a lightly worn Pirelli Scorpion on an x drive vehicle. They supplied one new tire to replace it. I had purchased 4 tires from them not too long ago. Turns out they covered most of the cost via a road hazard warranty I had, but that was a bonus. They checked the other tires, and told me I was OK with replacing only one. I asked, and the limit they used was 40% wear on a same size tire compared to the new one. Not sure how many revs/mile that is, but your calculator would tell you. I guessed it was around 5 revs/mile, but I didn't calculate it.

You can see from your calculator how tightly BMW aimed to have them grouped when new, less than 2 revs/mile.

It appears that with your worn front tires, the used tires you found would work.

It appears that if you do that, when you next replace your front tires you may need a plan B. Perhaps change the front size to match the rear if the tread wear is close.

I wouldn't worry as much about the spare.

Good luck

Jeff

Thanks for the confirmations - everything you say makes sense to me. BTW, I expect that if I get these ~new ones on the rear now, they will wear out when the fronts do and I'll get 4 new ones at that time.

To the guy that asked about the 285/45 and 255/55 combination. These are identical in over all diameter. One of them makes 693 revolutions per mile, the other makes 694. The 255 makes the extra revolution.

The overall diameter is 29.098 and 29.039, respectively. These are identical for any practical purpose. You have no worries about the drive train using these two sizes.

And, to dot the i and cross the t, The 235/65x17 is also in there at 695 revs. per mile. All of these sizes are suitable for use at the same time on your car. That is, the spare can be used anywhere and will play well with the other three.

As with any spare, you will want to get the damaged tire repaired or replaced as soon as is practical.