A star tyres , myth or fact

[ommis]

So you opted for a non staggered set up
I have a staggered set up
?
I put a couple of cheap rear tyres on a e53?
When I hit the gas / it lit up the traction control light and went limp mode till I slowed down

Again cheap tyres

How can A star on the side make such a big difference/ is it scare tactics from Bmw / it just seems that my e70 x5 that that I own now
Means at a guess I will have to change the front tyres in pairs and so on for the rears
It’s a very expensive
What about
Soft compounds
Hard compounds
The transfer box is more sensitive than a woman

[graemeX5]

Hi

The reason BMW want the star tyre is so that they are matched in terms of the circumference when using staggered set ups as they know how the tyre will perform so they are within the specified tolerance of difference between the wheels which the 4wd system can cope with.

If you have a staggered set up like I did on my old E53 it had 285/20 on the front and 315/20 on the rear but with different profile and so the overall rolling circumference was within the BMW recommended tolerance and no problem.

When I went to a set of tyres with same size all round 295/22's again no problem.

Several members have had transmission wind up due to a staggered set up especially on the X3, and it can occur on any car given an excessive difference between the front and rear wheels, and can cause Long term probs with transmission as some have found.

If you do a search and have a read of the posts from Horizon about his experience with his X3 he had a staggered set up which caused transmission wind up and when he changed to a non staggered set up the car was fine once again.

I have posted a link which has a link to check the circumference of your set up and you will be surprised. If say you have 4 wheels of the same size and the same new tyres say khumo's then it would be okay as the tyres are the same the rolling circumference.

However, if say you had 2 khumo's front and and 2 bridgestones which are star rated tyres because the tyres are different then how the side walls deflect will be different and so will result in a different rolling circumferences and could cause probs if beyond the tolerance the transmission can accept.

The thing to remeber is all the 4 wheels are connect by the 4wd system, hence the problem of the two axles turning at different speeds causing the transmission to have probs. So if say you have front tyres with 1.6 mm of tread and put brand new rear tyres on with 7-8 mm on then this can cause you probs too.

I think that's why they recommend changing the tyres as a set of four,

http://xdrivers.co.uk/forum/index.php/t ... 982.0.html

Graeme

[asoni]

So it seems basically the if tyres are mis matched or some are worn more then others, it will cause a difference in the radius and therefore cause issues with transmission.

To me, that doesn't seem to have anything to do with having run flats or not. I could have run flats with worn fronts and perfect rears which will cause exactly the same issue with different radius.

[X5Sport]

Correct.  Bear in mind this issue also affects Mercedes and Audi who use their own ‘marked’ tyre sets.  Merc are marked MO.  I am jus5 wondering if an MO marked set offers the same matching as * marking?  It’s the same principle I suppose.  Staggered sets on Merc and Audi may give rise to the same problem although I thought that Audi at least used a different transmission system on their high end models (the big Q variants)?

[Spandex]

Given that these cars will wear tyres unevenly front to back, the only time a set of new star rated tyres are the same size (allegedly) is when you fit them. From that moment onwards, they will be getting further and further apart in size.. ironically, having mismatched tyre sizes could keep you within tolerance for longer as they both wear at different rates.

X5Sport mentioned a user above who had a circumference difference on 32mm - this actually only equates to 4.5mm tread wear difference (assuming the tyres started the same radius). You could easily end up with 4.5mm difference after a few thousand miles even with tyres that started an identical size.

All that being said, I’d still like to see some hard evidence. Buying £1000 worth of tyres every time one axle gets to 3-4mm difference in tread depth to the other seems like the sort of thing you’d only want to do if you were certain it was necessary.

[pvr]

Getting a nail in one tyre could work out very expensive as you would almost have to change all 4 then  :'(

[ommis]

They should of left the turret and tracks on them . Less of a head ache
So after all of our head scratching

If I put 4 new tyres on my tiger tank / all the same make / middle of the road buget/ even though my rears are wider than the fronts/ non star rated / I will be fine

      ????????????

[X5Sport]

Possibly..........or possibly not.

We’ve been looking at this for some time now and the only conclusions I think we have really got to are:

You might have a problem using non ‘*’ marked tyres, but you might not and no one has yet determined which specific makes are a higher risk.

BMW will walk away from any warranty issues where non OEM Approved RFT or non-RFT tyres are used (you can use either as long as they are approved).

As yet there has not been a reported differential or transfer box failure with ‘*’ tyres whereas there have been numerous where they haven’t been used.

Our resident non Dealer member who specialises in BMW transmissions - kkx5 - gives dire warnings based on the number of broken XDrive cars he has seen through his shop about not using Approved rubber.

Tyre sets normally wear pretty evenly across both axles so you should not see a significant tread depth variation unless one pair was changed without the other at some point in the past.

Changing all 4 as a set seems safest.

Cars with the same sized wheels and tyres all round don’t seem to suffer any problems, only the staggered setups.

E70 and E83 models are the most susceptible, others not so much with the latest models being the least sensitive - possibly due to changes in the transfer box type?

It’s completely pot luck whether you get a problem or not when not using ‘*’ tyres.

[asoni]

For me, the question mark is not so much that people get problems with non * tyres. I’ve seen plenty of posts to suggest that is true, so no argument against it.

What I really want to know is why? If I put EXACTLY the same tyre but in the non run flat version and therefore not * marked, why should there be any issues? Same rubber, same tread, same radius etc etc.

My car had staggered wheels out the factory so that part in itself isn’t the cause otherwise surely bmw wouldn’t have used staggered set ups?

[asoni]

Also for a lot of us with e70’s we don’t have a bmw warranty to worry about so that is another reason that doesn’t apply when considering whether to try non run flats or not.

[Spandex]

So how can star rated tyres never cause problems, when it’s perfectly possible (likely, even) that star rated tyres will wear unevenly to the point where they’re well past the circumference difference that apparently has caused problems for members on here?

Star rated tyres don’t magically stay the same size across both axles throughout their life. If 3-4mm tread depth difference is enough to cause a catastrophic failure of the transfer box, how are any e70s still on the road, given that all of them - even those with star rated tyres - will spend some of their life in that state?

[kkx5]

[kkx5]

[kkx5]

Just one comment to above pictures: As long as some of You will question star marked tyres, i will have a job:)
The knowledge is there for many years. Buy cheap tyres, pay high diff/gear/transfer box bills. If you can not afford to pay £900 for set tyres on high tech 4x4 BMW, go and buy a ford fiesta....

[asoni]

I’ve not seen a single person cite cost as a reason so you’ve made that up along with a silly comment about not being able afford to run these cars.