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Tyre size for 18" rim

Phlipper1 Jun 5, 2006

  1. Phlipper1

    Phlipper1 New Member

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    Most people seem to have fitted 225/40's, but surely on a wider rim you'd move to a wider tyre?
     
  2. The Slug

    The Slug Active Member

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    depends if wheel is wider, 18" audi wheels tend to be same width as 17"'s ie 225 45 17 or 225 40 18...
     
  3. madvw

    madvw Active Member

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    [ 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.
     
  4. Phlipper1

    Phlipper1 New Member

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    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.
     
  5. madvw

    madvw Active Member

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    [ 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....
     
  6. AndyMac

    AndyMac Moderator Staff Member Moderator

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    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.
     
  7. nervus

    nervus Well-Known Member

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    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.
     
  8. AndyMac

    AndyMac Moderator Staff Member Moderator

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    and wider tyres mean more tramlining and aquaplaning
     
  9. silver75

    silver75 Big Ron

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    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.
     
  10. Phlipper1

    Phlipper1 New Member

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    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.
     
  11. AndyMac

    AndyMac Moderator Staff Member Moderator

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    I think it's called rear wheel drive
     
  12. ChriS3

    ChriS3 hud at ye bam

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    [ 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?
     
  13. silver75

    silver75 Big Ron

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    [ 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
     
  14. Phlipper1

    Phlipper1 New Member

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    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.
     

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