<VV> Tires & Speedometers

[FrankCB]

Bill,
     Why not just hook up your GPS unit, drive the car on a straight road at steady speed with little traffic and read the GPS speed?  My Garmin 255W (thanks Jim) tells me my speedo is about 2 mph FAST at 65 mph.  So it's a little optimistic, just like me.<GGGG>
     Frank "looking for easy way out" Burkhard

In a message dated 09/23/09 15:35:54 Eastern Daylight Time, lechevrier at earthlink.net writes:
[SNIP]*IF* it is important to you, you could probably do better by figuring 
out what tire circumference gives your particular speedometer head the 
greatest accuracy, and/or by sending your speedo head out to a shop and 
get it "Certified" (used to need the whole car to do this - $$$) or at 
least calibrated, and/or by having a speedo shop build you up a  "ratio 
adapter" to give you a correct speed  for your speedo and the tires and 
gearing that you choose, rather than making tire size choices based on 
someone else's idea of how your speedo should read and what your car 
should look like.  Then when you put on your "winter tires" (for those 
that drive year round), you just change the ratio adapter, too. 

There are many shops that provide these services -- just one example is 
http://www.speedometerservice.com/services.php