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Alternate tyre sizes

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  • #16
    Originally posted by PeteH View Post
    π - feel free to cut and paste
    Show off!

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    • #17
      Originally posted by Drew View Post
      Sorry responded to wrong quote, I meant these are quite different not the others, its an age thing...
      You'd definitely notice 2" compared to 0.1"

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      • #18
        Originally posted by tens6 View Post
        You'd definitely notice 2" compared to 0.1"
        That's what she said

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        • #19
          Originally posted by Drew View Post
          I thought the ride on 18s was good maybe you have worn shocks or broken springs or both?
          I did think the same, whether there's something wrong suspension wise. I do have flexride(not sure if he does) so might make a difference. I have both the 18s and 20s but don't feel an awful lot harder amazingly.

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          • #20
            Back to original op now
            I doubt any of the sizes mentioned will rub

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            • #21
              Originally posted by tens6 View Post
              I did think the same, whether there's something wrong suspension wise. I do have flexride(not sure if he does) so might make a difference. I have both the 18s and 20s but don't feel an awful lot harder amazingly.
              I doubt it's anything wrong with the car. It's the state of the roads round here.

              Maybe something wrong with me, too. I find most modern cars are really crashy over tiny bumps - the kind pneumatic tyres were invented to absorb - because they don't have fat enough tyres.

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              • #22
                Originally posted by Alex421 View Post
                I thought it was 40s fitted to 20s. Well most I've looked at buying. I'd never have 35s would get destroyed up here.
                With the gap round the arches on either 20s or 18s they would fit any of above sizes that's my point.
                The gap is one factor. What's the suspension travel, though?

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                • #23
                  Originally posted by Drew View Post
                  245 width was found to be the magic number which is why they feature on a lot of manufacturers cars.
                  As you go up a rim by inch diameter you drop an aspect ratio by 5% magically the rolling circumference (the important bit) stays very close.
                  It's not that magic. An inch is 25.4mm. 5% of 250ish mm, doubled for both sides of the wheel, gives an inch.

                  Works with reasonable accuracy from about 245 up to about 265. I wouldn't be surprised if 245 is most common just because it's the narrowest tyre that it works with.

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                  • #24
                    Originally posted by BodgeItAndScarper View Post
                    The gap is one factor. What's the suspension travel, though?
                    Not sure tbh sorry

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                    • #25
                      17" are readily available on fleabay quite cheap with tyres maybe a less stressful choice

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                      • #26
                        The aspect ratio is only relevant to the tyre not the wheel. The wheel is in inches. If you have a tyre that is 245/35 you have 88.75mm of tyre wall height. Times that by two because the tyre is there at the top and bottom of the wheel. Thats 171.5 mm. Now say thats on a 20 inch rim so 20x2.5 (to get it into cm) is 50. Times 10 is 500mm. Add that to 171.5 equals 671.5mm. Times that by Pi equals 2109.28mm rolling circumference.

                        Lets do 245/40 thats a total tyre height top and bottom of 196mm. But now you have to drop an inch on the rim to 19in or 475mm plus your tyre height equals 671mm. Times Pi 2108.28mm circumference.

                        The difference in circumference is just 1mm which as a percentage of the overall circumference is nowt. Theres a bigger difference between a new and worn tyre!
                        Last edited by Drew; 04-02-2020, 06:10 PM. Reason: Conversion to inches error!

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                        • #27
                          I’d think you’d be better dropping to 17” and keeping the oem size of tyre.
                          I’m sure I’ve read before of insurance implications when fitting incorrect tyres.

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                          • #28
                            Originally posted by Mr Wullie View Post
                            I’d think you’d be better dropping to 17” and keeping the oem size of tyre.
                            I’m sure I’ve read before of insurance implications when fitting incorrect tyres.
                            I've heard that with BMW's that have run flats

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                            • #29
                              Originally posted by Alex421 View Post
                              Yeah but are larger in diameter with tyres fitted
                              Only 0.1" .. 18s are 26.7" dia, 20s are 26.8". 2.4mm overall. Lose that I worn tread

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                              • #30
                                Originally posted by Chewy1971 View Post
                                Only 0.1" .. 18s are 26.7" dia, 20s are 26.8". 2.4mm overall. Lose that I worn tread
                                I've always been told every inch counts!

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