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Complications of running different profile tyres with haldex?

Discussion in 'A3/S3 Forum (8L Chassis)' started by Absolute_Jon, Dec 5, 2011.

  1. Absolute_Jon
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    Absolute_Jon New Member

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    Ive got hold of some genuine rstt's to refurb with two almost new 225 45 18 tyres. Going to get the wheels powdercoated and fit a full set of new rubber. In the meantime I was wondering if I could get away with running the 45 profile tyres on the rear of my current Reps and 225 40 18s that I run on the front? heared it could cause problems with the haldex and rolling radius etc. Anyone shine some light?

    Cheers,
    Jon
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  2. jojo
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    jojo S3 Drift King! Staff Member Moderator

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    The Haldex allows for a 5% difference in rolling radius to take into account of tyre wear, you should be fine with the above tyres, there's a 3.6% difference in rolling radius if they are both the same tread depth. I wouldn't do it personally, so entirely upto you.
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  3. beanoir
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    beanoir Sharpest Tongue in the West

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    You shouldn't mix tyres like that on any car with or without Haldex.
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  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    why not?

    Many cars leave the factory with different sized tyres on the front/rear, and a few with different sized wheels too.

    As for haldex, cant you simply disable the whole system by removing the fuse? If thats good enough for running a car on a dyno in FWD mode, i cant see why it wouldnt be fine with slightly different tyre sizes front/rear.
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  5. beanoir
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    beanoir Sharpest Tongue in the West

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    Agreed many do, but only as the manufacturer intended, suspension, geometry aligned to account for it etc.

    A tyre profile is a percentage of the tyre width, many cars with staggered wheel set-ups (wider on the rear) will have different profiles but will still maintain the same actual profile measurement and keeping the rolling circumfrance the same on front and rear wheels.

    The same cannot be said of what the OP is suggesting.
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    True.

    It might cause issues with the ABS too, depending how different they are.

    To be honest, when i first read the post i read it as 225 45 17 and 225 40 18, which are almost the same diameter, and should be perfectly interchangable.
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  7. jojo
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    jojo S3 Drift King! Staff Member Moderator

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    As a temporary measure, I think it would be ok short term. I wouldn't disconnect the Haldex for this. Actually this has reminded me! I was running 2x19" rims on the rear and 2x16" at the front whilst getting a pair of rims refurbed, only drove it like that for a couple of days pootling about, no issues whatsoever, even though the front was sat a lot lower than the back!
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  8. Alex C
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    Alex C Well-Known Member

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    could drive with the handbrake one click on to disable the haldex?
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  9. jimmp
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    jimmp Member

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    Is that true?

    does that work???!
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  10. Alex C
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    Alex C Well-Known Member

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    AFAIK if the handbrake swith shows that the handbrake is on ( i.e. your handbrake light is on) then the haldex is disabled
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  11. beanoir
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    beanoir Sharpest Tongue in the West

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    just take the fuse out, surely thats the best way?
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  12. beanoir
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    beanoir Sharpest Tongue in the West

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    just take the fuse out, surely thats the best way?
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  13. Alex C
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    Alex C Well-Known Member

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    possibly yeah, the handbrake switch being on will probably affect your ABS also
    Last edited: Dec 7, 2011
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