Theoretically, it the two tires have the same aspect ratio, it's a
percentage difference of the two sizes. 195/185 * 100 = 5 percent.  However,
the theory does not hold true as different tire types and different
manufacturers will have different circumference for the same tire size.
Your best bet is to measure circumference of the front tires at full
operating pressure and compare to the new tires.

You can always set your cruise at 60 MPH and time how long it takes to go a
mile, and that will give you an estimated speedo error.  It should be very
close to 60 seconds.

Chris.

----- Original Message -----
From: Roy O. <keepsake@pangea.ca>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 17, 2000 5:51 PM
Subject: Tires: 185 vs 195

> Anyone out there know what percentage my speedometer will be out if I put
195
> R14 tires on my '87 Westy instead of the OEM size185 R14 tires?
>
> Roy O.
> '87 Westfalia GL
> (till death do us part)