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  • wheel offset

    looking at alloys with a 35 offset for my 2005 astra estate but also says in the ad that "Body rework necessary" wots the ideal offset for this car anybody??
    there 7.5j x 18
    is it just down to wot size of rubber gets fitted on to them?
    Last edited by Kev; 27 July 2009, 05:45 AM.

  • #2
    A lot depends on the difference between the Original wheels/tyres and the replacements..........The Circumference of the tyre needs to remain the same so that your speedo reads the same..........If the wheel is wider then the offset will change..........Check out http://www.carbibles.com/tyre_bible_pg2.html

    For instance my cars original size wheel was 6 x 16 with 205 50 rubber...........Its now on 7 1/2 x 18 with 215 35 rubber.........

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    • #3
      Offset doesn't affect the circumference, only the distance from the hub relative to the wheel.
      Kev was wondering if the lower offset of 35mm on a 7.5jx18 as opposed to the standard et39 fit of the 7jx17 already on the car would cause a problem

      4mm will make little difference as it will have a 225/40r18 tyre as opposed to the 225/45r17.

      This will give 804 revolutions/mile on the 18s, the 17s are 808(The point you are making). Roughly translated at 60mph, the new tyres will be reading 60mph when the "actual" speed is 60.3mph (0.5% too slow).

      Overall diameter is up 2.9mm from 634.4mm to 637.2mm....the difference from new tread to half worn tyres.
      sigpic

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      • #4
        Originally posted by Scott View Post
        Offset doesn't affect the circumference, only the distance from the hub relative to the wheel.
        Kev was wondering if the lower offset of 35mm on a 7.5jx18 as opposed to the standard et39 fit of the 7jx17 already on the car would cause a problem

        4mm will make little difference as it will have a 225/40r18 tyre as opposed to the 225/45r17.

        This will give 804 revolutions/mile on the 18s, the 17s are 808(The point you are making). Roughly translated at 60mph, the new tyres will be reading 60mph when the "actual" speed is 60.3mph (0.5% too slow).

        Overall diameter is up 2.9mm from 634.4mm to 637.2mm....the difference from new tread to half worn tyres.
        So overall diameter is up 2.9mm

        And the 4mm plus the 6.35mm from the extra width of the wheel...........Even though the tyre is the same width the shape of it will be different due to the extra width of the wheel...........Therefore the rubber will be closer to the arch; not by a lot but this is probably why they say "Body rework necessary".......

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        • #5
          The lower the offset figure, the further the wheels will sit out. The arches will need to be rolled and this is what they mean when they say that body work may be required.

          The offset figure is the distance from the centreline of the wheel to the inner hub face.

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          • #6
            So, if thats the case EVERY Astra VXR will have its arches rolled to accomodate its "standard" 8jx18 et37s with a 225/40......thats a full inch on rim width with only 2mm greater offset over the H Sri's 17s

            When I looked into the 20s on my Vec C, the body work reqd was altering a bracket for the bumper and a mod to the wheelarch liner....no ,metalwork. Ian C that owns the i500 rep said his went straight on, no mods or fouling.....irmy just covering their *** probably!
            sigpic

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            • #7
              You're absolutely right Scott on both counts. Every car would have to be in theory modified on its arches so yes i would say its definately an **** coverage exercise.

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              • #8
                Originally posted by Scott View Post
                no mods or fouling.....irmy just covering their *** probably!
                That's spot on the money Scott, **** coverage going on for sure

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