Do Lower Profile Tires affect Speedometer Reading

[Arthur Marks]

The main requirement in a the sizing of a snow tire is that it be narrower to cut a smaller path through the snow. So if you have only one set of rims you can get a tire that is slightly narrower (1st number) to fit on those rims and the profile (second number, a proportion; %) should be higher so that diameter of the tire is nearly the same as your standard tires. In that case the height of the tire is appox. unchanged even though the second number is larger. If you have a set of winter rims you can get them narrower (and it probably makes sense to get them an inch smaller in diameter with a higher sidewall to avoid denting a rim on the stuff you may blindly hit in the winter). 

Tirerack.com lists the rev/mile which is the number that affects the speedometer. Note that even different brands of tires marked with the same size may have slightly different circumferences. That site will also give size recommendations for your vehicle.  

--Art
  ----- Original Message ----- 
  From: mboucher70 at hotmail.com 
  To: quattro at audifans.com 
  Sent: Wednesday, November 09, 2005 8:03 AM
  Subject: Do Lower Profile Tires affect Speedometer Reading


  I'm looking at a pair of 'performance winter' tires.  The size is 195 55 R15.

  My car's original equipment is 205 60 R15.

  I've read that for winter you should change the sizing by one each - that is either

  205 60 R15 or
  195 65 R15 or
  185 70 R14 if load capacity allows.

  I'm a bit confused by this rule.  I understand that the tire profile change is ofset by a rim size change.  So then, wouldn't 205 60 R15 and 195 65 R15 give different speedometer readings, since the rim size is the same but the profile is different?

  Bottom line question is will moving from 205 60 R15 TO 195 55 R15 work on my car (1990Audi100) or will it change my speedometer readings?

  Other question, where is a good place to get inexpensive winter rims (Wal-Mart, etc)?  It uses 6Jx15 rims.  Are these standard rims, or specialized Audi rims?  I've noticed that most Audis use the 5-bolt tires, but mine uses a 4-bolt.

  Thanks

  Charles
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