One tyre or two?

Discussion in 'Wheels and Tyres' started by The CO, Apr 23, 2017.

  1. The CO
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    The CO Admin

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    Annoyingly, I need to change my NSF tyre. Wear across the two fronts is equal with 4, 5 and 4mm (inner, middle, outer) on each. Head says replace both, wallet says just the faulty one but as the car is xDrive I'm a bit wary. Just not sure how much, if any, 2-3mm difference will make. Thoughts?
     
    Last edited: Apr 23, 2017
  2. Carl W
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    All four at once.

    'Can't mess about when it comes to tyres!'

    Kindest Regards
    Carl.
     
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  3. pinewood
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    @The CO, you know the reality of X Drive. If the fronts are at 5mm then a new tyre will be at 8-9mm. You have to replace all 4 as that is too much of a difference between front & rear axles.
    Stick the remaining 3 on Ebay . I sold my rear two for £30 each
     
  4. Mieke
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    Nah, I'd buy five just to be on the safe side. :whistle:

    Seriously though, I've no idea on the acceptable tolerance for the xDrive system, but normally I would buy a pair but only have the faulty one replaced. Most tyre places will then fit the second tyre FOC as long as you keep the bill. New tyres have approx 7 mm depth, so as you say it'll be 2 -3 mm difference in radius. I'm guessing BMW recommends changing both tyres on the same axle?
     
    Last edited: Apr 23, 2017
  5. The CO
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    No idea what BMW says to be honest, having read numerous threads over the years the perceived wisdom seems to be changing them both but that's with 'conventional' 4WD systems. When it was picked up at the service BMW said change the one. Doesn't mean it's right of course!
     
  6. sshooie
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    sshooie

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    I'm a bit anal with tyres, personally I'd never replace a single tyre, 2 as a minimum.

    When I've done it I chuck the OK one on fleabay.
     
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  7. Mieke
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    The old Audi Quatro 4WD system was straight forward - 3 conventional differentials (one on each axle, and another on the prop shaft to separate front and rear). So it was all purely mechanical and any tyre tread difference would be absorbed by the drive. But the BMW system incorporates electronics, so not too sure how it works. But when you think about it, the car is not only driven in a straight line. Every time you go through a series of bends, the outer wheels will be rotating faster than the inside wheels - hence will be absorbed by the differential. This will have a bigger effect than 2 mm difference in tread depth. I would have thought that it's within the operating parameters of the xDrive system? Don't quote me on this, but I'd be inclined to accept that BMW Service Dept know what they're talking about. ;)

    YMMV of course :)
     
  8. xyzl
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    xyzl

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  9. xyzl
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  10. kleynie
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    kleynie WARLORD Site Supporter

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    I would always change in pairs at least, but I have no idea about x drive.
     
  11. xyzl
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    xyzl

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    Just for my own interest can I ask what brand and size of wheel you've got the fault with?
     
  12. Mieke
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    So that would imply that @The CO tyres would maybe over the acceptable tolerance of 2mm difference in tread depth. Makes life a bit complicated Re - tyre wear on a staggered wheel setup like I have on my 19" 403M's, because the rears have to have a greater tread depth than the fronts. So wheels cannot be swopped around.
     
  13. The CO
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    Bridgestone S001 225/40 R19 RFT

    Interesting TIS link, would suggest that I need to change them both. Don't actually have a problem with it but if I can save £200+ then I obviously will. I could ring BMW next week and ask but I suspect I'll get some scratching of chins and an err on the side of caution.
     
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  14. Mieke
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    I would also hate to throw anything away that's only half worn.
    Must be the result of being married to a Scottish lass for 40+ years. :D
     
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  15. xyzl
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    xyzl

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    Sorry should also have asked what the problem with the tyre is?
     
  16. Postman
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    Postman

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    I would change at least the front 2 and probably all 4 if the rears are more worn than the current 2 at the front (which I would expect).

    I have an AWD mechanical system on one of our cars (not BMW or Audi) and I know the diffs can get worn if you don't pay attention to tyre wear. Tolerances for different makes will of course be different, but don't forget different rolling radii will be absorbing designed tolerances within the diffs which are there to allow for turning etc. Can get costly as I only know too well.
     
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  17. Cooky
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    I would change X 2 and keep one as a spare for when one of the others gets to 5mm or so and you have to change one again:)
     
  18. Singvogel
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    I don't know about Bridgestones - but my ContiSportContact 5s left the factory with 6.9mm on the front tyres 225/45 18 and with 7.5mm on the rear tyres 255/40 18

    I'd probably be buying a pair for the front only.
     
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  19. slim_boy_fat
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    slim_boy_fat WARLORD Site Supporter

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    She must be of the same mind :love: , or you'd be history by now......:ROFLMAO: [sorry, couldn't resist....:sneaky: :oops:]
     
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  20. K777
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    Buy a used one with similar tread ?

    I heard of a guy who fooked his scooby by changing one only.
    That said I have only ever changed the tyre that needed changing, but never had a xdrive of 4wd.
    But as said many times before I am professionally tight.
     

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