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  1. #1
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    tyre size??????????

    i have sport 5 spoke 17" alloys on my car they currently have 235/45/r17 on ! can i fit 225/45/17 to this rim coz tyres are much cheaper in this size and i need to buy 4 on saturday because all of mine are borderline i dont know what the j rating is wheels came of a 2.5tdi avant

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  3. #2
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    You can fit them, use a tyre calculator to check the difference in rolling radius. It won't be much but will throw out your speedo a bit I expect.
    Ingolstance Read about my A6 HERE.

  4. #3
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    its width not depth im looking at 235 v225!
    Quote Originally Posted by quattrojames View Post
    You can fit them, use a tyre calculator to check the difference in rolling radius. It won't be much but will throw out your speedo a bit I expect.

  5. #4
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    its 235 v225 james this would make no diff to rolling radius
    Quote Originally Posted by vorsprung dork View Post
    its width not depth im looking at 235 v225!

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    your speedo will be 1.4% too fast so when its showing 60 you would be doing 59.2 :-)

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    Quote Originally Posted by vorsprung dork View Post
    its 235 v225 james this would make no diff to rolling radius
    Oh really? So 45% of 235 is the same as 45% of 225 is it?
    Ingolstance Read about my A6 HERE.

  8. #7
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    width!!!!!
    Quote Originally Posted by stu_m View Post
    your speedo will be 1.4% too fast so when its showing 60 you would be doing 59.2 :-)

  9. #8
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    I think you need to go away and read up exactly what tyre profile means.
    Ingolstance Read about my A6 HERE.

  10. #9
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    how could my speedo be out when both tyres are 45s ?????????????????????/
    Quote Originally Posted by quattrojames View Post
    Oh really? So 45% of 235 is the same as 45% of 225 is it?

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    as above

    245 is the width but the 45 is an aspect ratio of the width in a percentage which gives the hight of the sidewall of the tyre so a 235/45 will be taller then a 225/45

  12. #11
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    If you have a 235/45 x 17 tyre the 45 reading is a percentage of the width (not a mm measurement.) So 45% of 235mm is obviously more than 45% of 225mm. As such the rolling radius of your wheel will be different, which will affect your speedo.
    Ingolstance Read about my A6 HERE.

  13. #12
    quattrojames's Avatar
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    Beat me
    Ingolstance Read about my A6 HERE.

  14. #13
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    [QUOTE=quattrojames;1504578]If you have a 235/45 x 17 tyre the 45 reading is a percentage of the width (not a mm measurement.) So 45% of 235mm is obviously more than 45% of 225mm. As such the rolling radius of your wheel will be different, which will affect your speedo ah ha ! thank you for explaning im not a tyre specalist im a mere layman! so thats how it works! so if i chose a 19" rim with 235 width what would the other size be to get a correct speedo reading ?

  15. #14
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    have a look here (one of many I suspect)

    TYRESAVE: Tyre Size Calculator

  16. #15
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    1 milimeter how very sad sir!
    Quote Originally Posted by quattrojames View Post
    Beat me

  17. #16
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    Quote Originally Posted by vorsprung dork View Post
    1 milimeter how very sad sir!
    Whats 1mm, and are you calling me sad?
    Ingolstance Read about my A6 HERE.

  18. #17
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    according to that tyre calculator I linked to the 225's would have a 9mm smaller rolling radius..

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    just a thought along these lines, if you increased the radius then in theory would mpg improve? (yes im an ever hopeful S4 owner.....)

  20. #19
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    been looking at that calculator thing and it gives a diffrence of 1 mil total! just pointing out how sad it is that my speedo will be wrong so i need to spend an extra £25 a corner over .8 of a mph or something!

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    its .9 of a mil sorry dont think this will help your s4 !
    Quote Originally Posted by Paul100 View Post
    according to that tyre calculator I linked to the 225's would have a 9mm smaller rolling radius..

  22. #21
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    Quote Originally Posted by vorsprung dork View Post
    been looking at that calculator thing and it gives a diffrence of 1 mil total! just pointing out how sad it is that my speedo will be wrong so i need to spend an extra £25 a corner over .8 of a mph or something!
    I think you might want to check, when i put your tyres size choices in it came back 9mm total 1.4% different. Still well within recomended max difference to be fair...

  23. #22
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    Put the right size tyres on, that's what it's designed to run. Stop being tight.
    Ingolstance Read about my A6 HERE.

  24. #23
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    you know what your right! im going too! cheers
    Quote Originally Posted by quattrojames View Post
    Put the right size tyres on, that's what it's designed to !run. Stop being tight.

  25. #24
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    put 4 new tyres on this weekend the correct size!! and i gave the tyre fitter a lesson in side wall % as like me he didnt have a clue!!

  26. #25
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    Quote Originally Posted by vorsprung dork View Post
    and i gave the tyre fitter a lesson in side wall % as like me he didnt have a clue!!
    really??

    thats a worry for a "tyre" fitter!

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    yes i know! there are red dots on the tyres that since i had them fitted i have found out should be bang in line with the valve because the tyres are made slightley lighter on one side to accomidate the extra weight of the valve! he didnt know this either as the red dots are not lined up at all! i know the wheels ar in ballance and dont really care! but maybe they should!
    Quote Originally Posted by stu_m View Post
    really??

    thats a worry for a "tyre" fitter!

  28. #27
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    red dots are supposed to be the heavy spot and yellow is the light spot

    to be honest it doesn't matter where you put them as they should balance the wheels anyway theres not a lot of weight in it

    and yes he should have known that too!

 

 

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