If only I could... Lease Co doesn't let me, they want to stick wih original tyres...

Hey Eagle eye.. you are joking right... :bustingupcome here in Greece were most of our roads are crap with full of bumps and dirt and you'll find out if you can focus 100% on the road for objects while driving with 140km...

So the wifey says tire pressure warning on rear driver side tire. Doh! This is the 2008 X5 4.8i we have had for less than 3 weeks!
And sure I do see a nair/screw stuck in it. The Michelin run flats are pimp, and lucky for me it was not in the side wall.
I spoke to 3-4 tire shops and they all said they don't fix run flats and there would be a cost associated if they did, suggesting replacement, blah! Got voicemail at Classic BMW's service when i thought i'd ask their opinion. After reading several blogs getting a run flat fixed vs. replaced later, I called up my fav. Discount Tire Co. shop in Sachse, TX. They confirmed Michelin Runflats can be fixed.
It took less that 15 mins for the work (plus the 2hr wait), but they did do it from the inside, and its as good as new: COST : $0.00, yep that is Zero! vs. having to change the tire - priceless!
And yes I watched the enitre process where they not only removed the tire from the Rim, but did infact fix it from the inside (they also used some liquid polymer kinda substance), and without getting in to the details, we're good to go.
So don't fret if your Run flats have a nail, find a discount tire co, store ;)
Cheers!

Hi Roadster, or anyone else. Does the space saver tyre have to be the same size a the original. For example can a 17" spacesaver be used with a 20" tyre. I read that rolling circumference difference can damage driveshafts, etc. Is this true?

Overall rolling diameter is important (tire + rim).

In an emergency situation you would want them to be close (within mm's? NOT inches).

If they are not close, you will probably do damage to the awd system.

A 17 inch donut ***IS** the same od as ALL of the stock BMW. Wheel/tires combinations,


Look at the od, not the rim size!

I have had a further think about this…

To the Godfather, when a vehicle is turning a tight corner is the outer wheel not turning faster than the inner wheel. And therefore the reason for a differential in the axle. Does this not then mimic the different speeds of two wheel sizes? If different wheel speeds can damage the AWD system, then too much cornering would or should have the same effect.

To Ard, I don't understand your statement. Are you saying that a SINGLE 17” space-saver spare is the same od as a 18”, 19” and 20” rim and tyre??

Any idea what BMW recommend?

Thanks again for any thoughts and advice.

i have factory 20" rims, staggered... the spare is 19" donut... from the factory... as all 4.6/4.8iS (E53) - nothing smaller than 18" will not fit over the brakes...

outside diameter is the key, and there is speed limit, about 50MPH/80kmh on a donut


PS - some non-US distribution "iS" had 19" rims from the factory...

Yes, that is PRECISELY what I am saying.

Tell you what, go to tirerack, look up your car. Select tires for "OE"..look at each of the OE tires, and write down the DIAMETER of the OE 19", the OE 20" etc...all of them will be the same diameter.

Why?

BECAUSE BMW DOESNT WANT TO HAVE TO RECALIBRATE CARS AS THEY ARE BUILT, ordered with different tire/wheel combos!

So the OE donut spare will work on and OE wheel size.

And I do have and idea what BMW recommends: the OE donut spare

The issue with damage to a diff is TIME and SPEED. Effectively mismatched tires will heat the diff and diff fluid. On turns you simply CANNOT geenrate enough continuous mismatch at speed to damage the diff. Put mismatched tires on and drive 70mph in a straight line for 2 hours and you can.