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tyre size??????????

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by vorsprung dork, Feb 23, 2012.

  1. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    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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  2. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 23, 2012]
    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.
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  3. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    its width not depth im looking at 235 v225!
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  4. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    its 235 v225 james this would make no diff to rolling radius
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  5. stu_m
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    stu_m Well-Known Member VCDS Map User

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    [Feb 23, 2012]
    your speedo will be 1.4% too fast so when its showing 60 you would be doing 59.2 :)
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  6. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 23, 2012]
    Oh really? So 45% of 235 is the same as 45% of 225 is it?
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  7. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    width!!!!!
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  8. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 23, 2012]
    I think you need to go away and read up exactly what tyre profile means.
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  9. vorsprung dork
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    [Feb 23, 2012]
    how could my speedo be out when both tyres are 45s ?????????????????????/
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  10. stu_m
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    stu_m Well-Known Member VCDS Map User

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    [Feb 23, 2012]
    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
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  11. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 23, 2012]
    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.
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  12. quattrojames
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    quattrojames Moderator Staff Member Moderator

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  13. vorsprung dork
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    [Feb 23, 2012]
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  14. Paul100
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    [Feb 23, 2012]
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  15. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    1 milimeter how very sad sir!
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  16. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 23, 2012]
    Whats 1mm, and are you calling me sad?
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  17. Paul100
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    [Feb 23, 2012]
    according to that tyre calculator I linked to the 225's would have a 9mm smaller rolling radius..
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  18. Paul100
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    [Feb 23, 2012]
    just a thought along these lines, if you increased the radius then in theory would mpg improve? (yes im an ever hopeful S4 owner.....)
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  19. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    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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  20. vorsprung dork
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    [Feb 23, 2012]
    its .9 of a mil sorry dont think this will help your s4 !
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  21. Paul100
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    [Feb 23, 2012]
    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...
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  22. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Feb 23, 2012]
    Put the right size tyres on, that's what it's designed to run. Stop being tight.
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  23. vorsprung dork
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    vorsprung dork Member

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    [Feb 23, 2012]
    you know what your right! im going too! cheers
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  24. vorsprung dork
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    [Feb 28, 2012]
    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!!
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  25. stu_m
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    stu_m Well-Known Member VCDS Map User

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    [Feb 28, 2012]
    really??

    thats a worry for a "tyre" fitter!
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  26. vorsprung dork
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    [Feb 28, 2012]
    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!
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  27. stu_m
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    stu_m Well-Known Member VCDS Map User

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    [Feb 28, 2012]
    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!
    #27

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