Do Lower Profile Tires affect Speedometer Reading

[Ameer Antar]

   Thanks for the link. The visual aid is nice. You know I never heard people recommendng smaller tire width for snows, but I guess it makes sense b/c I've heard that for rainy climates. Do you think that difference in width will really make much difference though? I've heard of going to smaller rims and higher profiles for winter b/c the tires are cheaper and sometimes gives you more tire options. Is there anything bad with that, other than brake clearance issues?

-Ameer

----Original Message----
From: Mark R <speedracer.mark at gmail.com>
Date: 11/9/05 7:26:45 PM
Subject: Re: Do Lower Profile Tires affect Speedometer Reading


    Here's the tire calculator I always use:
   
   http://www.miata..net/garage/tirecalc.html
   
   
   
    This will explain the differences in size variations. Again, different manufactrurers have slightly different actual measurements, but using the theoretical numbers is close and &quot;precise enough.&quot;
   
   
   
    The reason you go to a narrower tire in the winter is actually quite simple.PSI.Yes, pounds per square inch.The weight of the vehicle (or the transferred weight if the body is in motion) divided by the contact patch of the tire.A narrower tire has a smaller contact patch and therefore the edges on a snow tire (siping and tread) have more force to &quot;bite&quot; into the surface.Assuming same rim diameter, when you go narrower, the caluclator will clearly show you also need to go to a taller profile to maintain the same or similar circumference.Hence the common reference that &quot;You need a taller tire in the winter.&quot; 
   
   
   
    Going narrower has some trade-offs.Usually less weight capacity rating of the tire (not really an issue for most) and less lateral grip on dry pavement.I go narrower by 10 mm (or occasionally 20 mm when possible), but don't go for a 135 width tire on an S4 sedan!=) 
   
   
   
    Best to all,
   
    Mark Rosenkrantz