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Running odd tyres on a quattro.

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by sonnyjim, Jun 15, 2010.

  1. sonnyjim
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    sonnyjim Member

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    [Jun 15, 2010]
    After the other half getting a puncture while I was away working she got the tyre replaced with a new one that has far more tread depth than the ones that were already on the car. I know that all tyres should be of similar tread depth on quattro cars but will it do any harm short term? Reason I ask is I am getting my wheels refurbished in the next couple of weeks and will fit new tyres all round then. Don't plan any long runs just some things to do locally.

    Thanks

    Sonnyjim
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  3. Q4
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    Q4 Member

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    [Jun 15, 2010]
    If it's for a short term and you are not doing many miles then it shouldn't be any problem.

    The Differential is designed to allow wheels to turn at different speeds to each other (when the car is turning for example). You only run into problems when both tyres are replaced on one axle and not the other hence the loading on the rear diff crown and pinion wheel.

    The only effect you may find with the new tyre is strange handling if it's fitted to the front axle.

    Regards.
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  4. paul20v
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    paul20v Audi fanatic

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    [Jun 15, 2010]
    You started it sensible , then finished by saying that fitting a pair on one axle and not the other will effect the rear crown and pinion !!!
    dont think so .
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  5. nanafagis
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    nanafagis Member

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    [Jun 15, 2010]
    I was told that I would be OK if I changed tyres in sets of 2 as long as they are on the same axle. That said I've developed a clunk when I pull away so by fitting 2 and 2 at different times it seems I've probably knackered my diff. Nifty.
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  6. paul20v
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    paul20v Audi fanatic

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    [Jun 16, 2010]
    Ive run quattros for years and never had any issues from any of the models run when changing tyres at different times ,
    the tyres wear at different rates anyway and you still wear fronts out before rears
    but if your worried about it in the future swap the wheels front to rear half way through the tyre wear at the front and get the 4 to wear out at roughly the same time then change them all .
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  7. Q4
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    Q4 Member

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    [Jun 17, 2010]
    Firstly the manual actually tells you to only change all 4 tyres at the same time to keep the same tyre depth and overall rolling radius the same per axle. The crown and pinion will wear because of incorrect pre-loading and backlash on the diff due to the different rolling radius of one axle to another.

    Secondly the a4 quattro system is a permanent mechanical 4wd system not to be confused with hydraulic haldex types as fitted to S3'S and TT's which is only 4wd when wheel slip is detected. This is why you can get away with different tyre tread depths on cars running this system.

    If your current A4 is a quattro then I suggest you read the manual and believe what audi tell you unless of course you know better.
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  8. mikeh126
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    mikeh126 Member

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    [Jun 18, 2010]
    I have a 2003 Avant 2.5TDi Quattro, and the Owners Manual says:
    "Tyres should be replaced at least in pairs and not individually (i.e. both front tyres or both rear tyres together".
    And then, crucially:
    "On vehicles with four-wheel drive, all four tyres must always be fitted with tyres of the same type, make and tread pattern, as otherwise the driveline can be damaged by continuous differences in the wheel speeds."
    Then later in the same paragraph:
    "The use of tyres with varying degrees of wear will, however, not affect the four wheel drive transmission".

    So, it says that tread depth doesn't matter, as long as the same type, make and tread pattern are fitted.
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  9. Q4
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    Q4 Member

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    [Jun 18, 2010]
    Well that quote is a contradiction, the only way you can get a continuous difference in wheel speeds is by having different rolling radius which itself can only happen by having different tread depths !

    Go figure that one out.....

    The one thing that hasn't changed in all this is that my rear diff is still worn.
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  10. paul20v
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    paul20v Audi fanatic

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    [Jun 18, 2010]
    Hi
    In the "manual" Audi tell you to go to a dealer at every given chance do you ? they want you to replace your tyres all at once and with them,

    Im not stupid i know how quattro and haldex work etc ,
    ive been running them for 20 years and even stripped a quattro box and torsen diff ,
    there is no way your REAR diff was worn because of a difference in tread depth on the same make model and size tyres ,
    are you telling me that with the wear difference between front and rear of quattros which does happen that when the front tyres are getting lower that its going to destroy your torsion centre diff or any other diff for that matter ,
    another example in different tyre wear is when you connect a diagnostic machine that will enter the ABS system and read actual wheel speed values,
    i have never seen a difference in wheel speeds of any significant amount at any speed with any worn tyres .
    As you mentioned haldex also there is a constant between front and rear 97.5% torque goes to the front, and 2.5% goes to the rear under normal conditions this can change with upto 100% lock so they are connected at all times but not mechanically.
    Im not being funny here but you seem to be reading more in manuals than you actually have experience with the above mentioned systems .

    PS . your pre load and backlash on a diff is not altered by the tyre or wheel speed pre load and backlash are setup when the diff is being built and only alters if diff bearings wear and get play in them you should read that in a manual somewhere .
    Last edited: Jun 18, 2010
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  11. paul20v
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    paul20v Audi fanatic

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    [Jun 18, 2010]
    There is only 6.5mm between a new tyre and a illegal tyre this is not enough to alter rolling radius by any amount that is noticeable ,
    different sizes or aspect ratio will do this not tread wear.
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  12. mikeh126
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    mikeh126 Member

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    [Jun 19, 2010]
    I agree with paul20v - tyres wear at different rates - front to back - so, as my manual says:
    "The use of tyres with varying degrees of wear will, however, not affect the four wheel drive transmission".
    Does that mean that worn tyres can be used with new ones, on different axles???
    Confused of Preston. . . . . . . .!
    #11

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