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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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    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. quattrojames

    quattrojames Moderator
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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.
     
  4. vorsprung dork

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    its width not depth im looking at 235 v225!
     
  5. vorsprung dork

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    its 235 v225 james this would make no diff to rolling radius
     
  6. stu_m

    stu_m Well-Known Member
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    your speedo will be 1.4% too fast so when its showing 60 you would be doing 59.2 :)
     
  7. quattrojames

    quattrojames Moderator
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    Oh really? So 45% of 235 is the same as 45% of 225 is it?
     
  8. vorsprung dork

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    width!!!!!
     
  9. quattrojames

    quattrojames Moderator
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    I think you need to go away and read up exactly what tyre profile means.
     
  10. vorsprung dork

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    how could my speedo be out when both tyres are 45s ?????????????????????/
     
  11. stu_m

    stu_m Well-Known Member
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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. quattrojames

    quattrojames Moderator
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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.
     
  13. quattrojames

    quattrojames Moderator
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    Beat me :hi:
     
  14. vorsprung dork

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  15. Paul100

    Paul100 Member

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  16. vorsprung dork

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    1 milimeter how very sad sir!
     
  17. quattrojames

    quattrojames Moderator
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    Whats 1mm, and are you calling me sad?
     
  18. Paul100

    Paul100 Member

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    according to that tyre calculator I linked to the 225's would have a 9mm smaller rolling radius..
     
  19. Paul100

    Paul100 Member

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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. vorsprung dork

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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!
     
  21. vorsprung dork

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    its .9 of a mil sorry dont think this will help your s4 !
     
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  23. Paul100

    Paul100 Member

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    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...
     
  24. quattrojames

    quattrojames Moderator
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    Put the right size tyres on, that's what it's designed to run. Stop being tight.
     
  25. vorsprung dork

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    you know what your right! im going too! cheers
     
  26. vorsprung dork

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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!!
     
  27. stu_m

    stu_m Well-Known Member
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    really??

    thats a worry for a "tyre" fitter!
     
  28. vorsprung dork

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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!
     
  29. stu_m

    stu_m Well-Known Member
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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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