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Tyre size for 18" rim

Discussion in 'A3/S3 Forum (8L Chassis)' started by Phlipper1, Jun 5, 2006.

  1. Phlipper1
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    Phlipper1 New Member

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    [Jun 5, 2006]
    Most people seem to have fitted 225/40's, but surely on a wider rim you'd move to a wider tyre?
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  3. The Slug
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    The Slug Active Member VCDS Map User

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    [Jun 5, 2006]
    depends if wheel is wider, 18" audi wheels tend to be same width as 17"'s ie 225 45 17 or 225 40 18...
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  4. madvw
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    madvw Active Member

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    [Jun 5, 2006]
    [ QUOTE ]
    Most people seem to have fitted 225/40's, but surely on a wider rim you'd move to a wider tyre?

    [/ QUOTE ]

    An 18" rim doesn't necessarily mean that the rim is wider, the width of the rim is quoted in inches and specified as a J figure, for example 8J. The quoted figure is the distance between the fitting faces of the inner and outer beads.
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  5. Phlipper1
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    Phlipper1 New Member

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    [Jun 5, 2006]
    Assuming that the standard s3 rim is 17 x 7.5 the 18" rim maybe 8 or 8.5 wide (i.e. RS4 rim)? You would have to try and maintain the original circumference of both wheel + tyre so as not alter the speedo settings. What sort of profile would I need if I went to 235 or 245. I'm guessing 235/40 for 8" and 245/35 for 8.5.
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  6. madvw
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    madvw Active Member

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    [Jun 5, 2006]
    [ QUOTE ]
    Assuming that the standard s3 rim is 17 x 7.5 the 18" rim maybe 8 or 8.5 wide (i.e. RS4 rim)? You would have to try and maintain the original circumference of both wheel + tyre so as not alter the speedo settings.

    [/ QUOTE ]

    absolutely, but maintaining the same rolling radius has nothing to do with the width of the tyre, you just need to make sure you use the correct section tyres.


    edit: oops - stand corrected as normal....
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  7. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Jun 5, 2006]
    Yes, but as you move to a wider tyre the options on tyre size give you a less accurate rolling radius. 225/40/18 gives you the most accurate rolling radius (within 0.5%), if you then move to 235 or 245 widths this moves to 1.7% or 3% respectively unless you're gonna drop down to a 35% profile which gets expensive.
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  8. nervus
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    nervus Well-Known Member

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    [Jun 5, 2006]
    The profile is quoted as a % proportion of the width so obviously as width increases then profile number decreases.

    My factory tyres were 225/40/18's so this yields the optimum rolling radius.

    You could fit say 235/35/18's but why would you? I think the tyres are wide enough at 225.
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  9. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Jun 5, 2006]
    and wider tyres mean more tramlining and aquaplaning
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  10. silver75
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    silver75 Big Ron

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    [Jun 5, 2006]
    Anything up to 8.5/18 I wouldnt go over 225 wide tyres. 9/18 or wider would need wider tyres but you dont need wheels that wide on a 3... unless its just for the looks?? then you get rubbing and handling issues.
    #9
  11. Phlipper1
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    Phlipper1 New Member

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    [Jun 5, 2006]
    Lets just say you were having a play with a Boxter. According to some people the S3 is going to struggle due to the comparative balance and neutrality issues of it's handling (ees_three's comments). A colleague at work has just got a Boxter. I happened to notice the 265/35 19's on the back. So surely physical grip must be a factor.
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  12. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Jun 5, 2006]
    I think it's called rear wheel drive
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  13. ChriS3
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    ChriS3 hud at ye bam

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    [Jun 5, 2006]
    [ QUOTE ]
    Lets just say you were having a play with a Boxter. According to some people the S3 is going to struggle due to the comparative balance and neutrality issues of it's handling (ees_three's comments). A colleague at work has just got a Boxter. I happened to notice the 265/35 19's on the back. So surely physical grip must be a factor.

    [/ QUOTE ]

    Ever seen the size of the tyres on an Elise?
    #12
  14. silver75
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    silver75 Big Ron

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    [Jun 5, 2006]
    [ QUOTE ]
    Lets just say you were having a play with a Boxter. According to some people the S3 is going to struggle due to the comparative balance and neutrality issues of it's handling (ees_three's comments). A colleague at work has just got a Boxter. I happened to notice the 265/35 19's on the back. So surely physical grip must be a factor.

    [/ QUOTE ]


    The Porker has wider rear wheels to stop it oversteering and spinning. Wider rears on the 3 would cause more understeer I think
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  15. Phlipper1
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    Phlipper1 New Member

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    [Jun 5, 2006]
    I guess the rwd explanation is obvious, particularly as the S3 is primarily fwd. Perhaps the Haldex upgrade would redress the balance. I assume an 18" rim with 225's gets more scuffs.
    #14

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