Tyre size and car speed

• chech01

  31 Mar 04, 11:03

  If a car is originally 205x65R16 and you change it to 225x55R16, what is the impact on the speed reading? Will it cause the speed reading to be incorrect, i.e. 90kmh becomes 100kmh or 80kmh?
  
  Reason I ask is that the circumference is now smaller so the speed and also the odometer must be affected.
  
  Any tyre or mathematics expert around that can shed some light on this?
  
  Thanks
• chech01

  31 Mar 04, 11:22

  OK found this link on the web that provides for a calculator to do just that.
  
  http://pw1.netcom.com/
  
  So it seems that for my case, my speedo is under-reading slightlly now. Pyschologically, I can drive faster and still be within the law!
• HENG@

  1 Apr 04, 03:11

  uh... if u wanted to change to lower profiled tyres, u should also change the rim size an inch larger... theoratically
• Danisdead101times

  1 Apr 04, 03:52

  Originally posted by HENG@:

  uh... if u wanted to change to lower profiled tyres, u should also change the rim size an inch larger... theoratically

  i agreed....
• w2k_83

  1 Apr 04, 20:47

  Originally posted by HENG@:

  uh... if u wanted to change to lower profiled tyres, u should also change the rim size an inch larger... theoratically

  No offence, but dun think u are answering to his question... Anyway chech01, u can get a mechanic to rectify the difference
• HENG@

  2 Apr 04, 01:21

  Originally posted by w2k_83:

  No offence, but dun think u are answering to his question... Anyway chech01, u can get a mechanic to rectify the difference

  what i mean is to maintain the calibration of his speedo, he has to do that. I think i did answer to him