Tyre advice

[Sjl]

By accident I’ve ended up in a mess with my tyres ….

NSR PZero (PZ4) 275/35 R19 100Y XL Run Flat >6.3mm

OSR PZero (PZ4) 275/35 R19 100Y XL >3.5mm

NSF PZero (PZ4) 245/40 R19 98Y XL >5.6mm

OSF PZero (PZ4) 245/40 R19 98Y XL >5.8mm but has side wall blister 20mm diameter

what should I do, given new PZ4 tread depth is 7.1mm ?

option 1 - replace NSR with non run flat and OSF & sell NSR run flat here/eBay and live with big tyre tread difference on rear

option 2 - replace NSR & OSR with non run flat and OSF & sell NSR run flat here/eBay, no tyre tread difference on rear

option 3 - replace the lot with non run flat from different manufacturer e.g. Michelin or another suggestion?

note: I’m not so worried about a 5.6mm - 7.1mm tread difference on front of the car 

I live in the south east so don’t need winter tyres …..

Any other suggestions ….. 

Edited October 28, 2022 by Sjl
Typo

[Lobster Pot]

No idea what your set up should be but just be careful if it’s a xdrive I’ve just had to have a brand new transfer box due to last owner putting wrong tyres on apparently it’s recommended to be star rated and change all 4 together as they need to be within a certain tolerance tread of each other otherwise it confuses the transfer box which it did in my circumstances an expensive lesson learned 

[Sjl]

4 minutes ago, Lobster Pot said:

No idea what your set up should be but just be careful if it’s a xdrive I’ve just had to have a brand new transfer box due to last owner putting wrong tyres on apparently it’s recommended to be star rated and change all 4 together as they need to be within a certain tolerance tread of each other otherwise it confuses the transfer box which it did in my circumstances an expensive lesson learned 

Thanks for that info - not heard that before … and it is xDrive !

Edited October 28, 2022 by Sjl

[Matthew]

As it is xDrive, I'd replace the lot to protect the transfer case as has been mentioned. I had similar on my old F11 (non-xDrive of course) and sold 2 of the removed tyres that didn't have the bulge nor the cut! As for RFT vs non-RFT many will tell you to replace with non-RFT, I've never had an issue with RFTs and have always replaced like-for-like.

[Lobster Pot]

I’ve just had 4 run flats can’t really tell a difference I went for Goodyear suv asymmetric which are bmw star rated be careful not all premium brands are star rated if you go on the wonderful online tyre sales they say which are I got mine off tyresavings.com £761 fully fitted 

[Mr H]

On 28/10/2022 at 21:56, Matthew said:

As it is xDrive, I'd replace the lot to protect the transfer case as has been mentioned.

tbh I don't quite understand this. My G31 xD with 29k on the clock has 4mm tread on the rears and 6mm on the fronts (so currently 2mm difference and no issues); assuming wear rates stay the same, when the rears are at 2mm, the fronts will be at 5mm i.e. 3mm difference (and hopefully no issues). So why can I not replace rears with 8mm new and leave the fronts at 5mm i.e. still a 3mm difference (albeit rear to front rather than the other way round) so should be no issues? Or am I looking at this too simplistically?

[Procion]

You can, safely.

A lot of persistant myths about X drive, the technology has moved on since first introduced. 

Yes, stupid differences in tyre size would cause serious issues very quickly but 5 or 10mm won't.

If the car left the factory with 245/40/19 tyres on the front and 275/35/19 on the back you straight away have a diameter difference of 3.5mm!

Play with the pressures and get at least another 2/3mm.

If the system was as delicate as some make it out to be then BMW would be supplying spare transfer boxes instead of spacesaver wheels.

[Matthew]

Probably the extreme but the official, and current, statement from BMW:

Additionally for all-wheel drive vehicles:
   The tyre size, manufacturer and tyre tread must be identical on all wheels; different tyre sizes between front and rear axles are only permissible if mixed tyres are fitted.
   The tyre tread difference between tyres in all wheel positions must not exceed 2 mm (normal quality of the wheel control systems and wheel alignment requirement)

However, the OP has one axle with mixed RFT and non-RFT tyres and the other axle with a tyre with a sidewall bubble. If I were seriously cash conscious, I'd replace the OSR with an equivalent RFT and replace both fronts for the same spec and sell the remaining good tyre. 

[Procion]

1 hour ago, Matthew said:

Additionally for all-wheel drive vehicles:
   The tyre size, manufacturer and tyre tread must be identical on all wheels; different tyre sizes between front and rear axles are only permissible if mixed tyres are fitted.
   The tyre tread difference between tyres in all wheel positions must not exceed 2 mm (normal quality of the wheel control systems and wheel alignment requirement)

No disputing the words of the maker Matthew! I nevertheless find that incredible, a 2mm tolerance is nothing.

My tyre consumption is 1 set of fronts to 2 rears (sometimes 3 if I've been having fun). I always replace when the treads are down to 3mm so I can be running 7mm+ tread on new rears and 3 or 4mm on the fronts or vice versa. Simply inflating a tyre or loading the car will also change the radius, I've never attempted to measure this but visually I would say a tyre can easily "rise" 2-3mm.

Checking a tyre size calculator for a non square set up like my old G31 530 DX it shows a difference of 0.5% or 3.5mm. On my B5 it is 1% or 7.5mm front to back. Those figures would be true for a car leaving the production line. The wording of the text reads "different tyre sizes between front and rear axles are only permissible if mixed tyres are fitted" Well yes, mixed tyres are fitted in my case. Does the statement about 2mm relate more to general handling & safety or is it to do with protecting the transfer box from big front to rear variations? 

I'm now totally confused. )-: