Tyre question

[Dave29]

So, I find myself in an expected positon and welcome some advice

After a puncture whilst away at the weekend, the AA fitted a non-runflat Economy tyre (GripMax) to get me home.

I'm happy they fitted a NFL, given I want to get the RF off asap anyway, but not sure whether I should fit another identical GripMax to the other side (rear) or spend out again (Gripmax cost me £200) and fit better quality tyres.

I'm not tyre snob and do appreciate that you tend to get what you pay for, but the Gripmax does get decent enough reviews.

So, do I:

- fit another Gripmax
- fit 2 better quality tyres
- fit 3 more Gripmax (assuming i shouldn't mix RF and NRF across front and rears)?
- fit 4 better quality tyres?

Naturally, I'd like the answer to be don't worry and just fit another Gripmax...but I don't want to be storing up problems for the future

really appreciate any advice

Thanks
Dave

[X5Sport]

The simplest answer is that if is doesn’t have a ‘*’ on the sidewall then the tyre does not meet the rolling radius spec that BMW need.

Does it matter?

In reality yes it needs thinking about.  Because the front and rear tyres are a different size, their rolling radii are different.  BMW (and other AWD manufacturers) have a tyre size spec that ensures the rolling radii are matched correctly.  These tyres (on a BMW) have a ‘*’ on the sidewall.

Having unmatched rolling radii increases the chances of transmission wind up, and can (and has) lead to shattered diffs or transfer boxes.  These are not covered by BMW AUC or new car warranties.

You don’t have to have RFT, but you really should have matched tyres on all corners with tread depth relatively evenly matched all round.

This unfortunately means premium tyres and usually having them changed as a set, especially if the old tyres on the car are more than 1.5-2mm lower in tread depth.

Other manufacturers with similar issues are Porsche, Audi and Mercedes.

The warning signs are odd grumbling noises from the transmission and low speed jerkiness at full lock.  Both are indications that the transmission is under excess load and could result in failure.  It doesn’t always happen, but more than a few have happened on here.

[Dave29]

Thank for the response

I don't doubt your knowledge, if that's the case, why do on line firms (e.g. BlackCircles) offer a range of tyres for the X5 if they could lead to serious failures?

[X5Sport]

In simple terms, it is because (in their opinion) it’s up to you not them to know what should be on your car.  They also won’t know if you have staggered on non-staggered.  I doubt very much if they even understand the critical connections with all of the different transmission issues  They won’t care what you fit and can’t be held accountable if you order the wrong thing.  They will simply point you at whatever the Owner’s Manual, or car manufacturer says.

Their shop systems use a very simple search engine that looks at sizes and weight ratings based on a look-up table.  Anything more is highly complex and needs careful rules written into the software database.  That costs them money to produce and maintain.  If they get that wrong then they could be in trouble so they don’t and somewhere in their Ts & Cs will be a get out of jail clause absolving them of anything and everything.

BMW themselves only ‘recommend’ but won’t help if you choose to use anything else, and will walk away if a warranty claim occurs.  A BMW dealer will only sell you the right rubber for the car, but at a really silly price that unless someone else is paying, you won’t want to pay.

[Dave29]

ok. makes sense

So, got a decent price to fit a set of star rated Non Run Flat Bridgestones all round...will that we ok for the car and, presumably, not invalidate my RAC warranty?

[X5Sport]

Bridgestone Dueller are one of the standard fit whether RFT or not.  I don’t expect the RAC will care (but they might).  As long as they are ‘*’ marked then your transmission will still be friends with you 

I think most of us on here feel that this issue should not exist with modern cars, and allegedly with the F15 series it has been largely overcome with the new transfer box in use. 

No owner should have to play Russian Roulette with choice of tyres  >:(

[Dave29]

thanks  - really helpful advice...much appreciated

hoping that fitting non RF will improve the ride...my only real grumble with the car...

[Huxsta]

Ive never bought into the different tread depth being an issue. When you drive anything other than perfectly straight all the wheels will cover a completely different distance due to the nature of how diffs work and that diffs are not permently locked. In that case, how does one wheel with say 3mm less tread than the other 3 tyres effect the transmission in any circumstance? Bring on the scientists......

[Dave29]

also, when I bought the car it had RF Dunlops on front and RF Bridgestones on rear. Both in good condition with even tread depth so presumably fitted around the same time

is that also a No No, and should I have recourse with the dealer (reputable independent) and/or be concerned about potential inherited transmission issues?

[X5Sport]

If both are ‘*’ rated then unlikely to be an issue., especially if tread depths were close anyway.

@Huxsta, I’m still trying to work that one out but I think it’s do do with the xDrive system and how each diff sends the extra turns back into the system (they have to be lost somewhere) and what the transfer box is doing with the extra loading.

[Chrispy]

I've just fitted a set of 4x non RFT's to mine this morning - Hankook Ventus S1 Evo 2's which come as standard fit to the newer X5's, just in RFT form I think.  Took a bit of a chance but the ride was driving me round the twist.

Luckily they came to my house (ordered online from Tyre Leader) before I took them to the local garage for fitting and I could measure them and get a spirit level across them to see how they fared.  Identical height/ diameter between fronts and rears when measured on a level surface with both the tape and the spirit level.  not sure how much more accurate I could get without the worlds biggest vernier calipers.



The ride difference is nothing short of astonishing and if my transfer case implodes I'll let you know......

[Digidick]

Superb info, can see me doing the same

[Dave29]

having just 'bottled it' and stuck with a new set of £900 RF Dunlops after saying I was DEFINITELY ditching the run-flats this time, I hope your diff explodes 

seriously, sounds great...look forward to the 12 month review when I need to replace mine again

[Chrispy]

Believe me I mulled this one over for a while.  Being able to measure the things prior to fitting was very nice as if they would have been out I'd have sent them back.  Plus they were £503 inc free delivery - then £48 fitting for all 4 from my local garage.  Compared to the £900 you were talking for replacement Dueller HP RFT's before fitting, and those are made of pure unadulterated concrete.....my dentures could take no more.....

[Digidick]

I could have 4 x 20" nearly new Dunlops up for grabs soon after seeing this