My GPS unit says differently!!  My Weddle tranny with 4.57 r/p  and .082
4th gear with Agilis tires shows 3400rpm @70mph on the spedo, just exactly
what the GPS says I'm doing.  do you think Big Brother would lie to
you??  70 and 60 series tires will definitely give you a false sense of speed.

DM&FS

At 07:11 PM 9/6/2004, Wade Yorke wrote:
>You may not actually be going as fast as your speedometer indicates
>since the Vanagon speedometer is at least 15 miles per hour optimistic
>at the higher speeds.  In the Bentley it states that at 1000 rpm in
>high gear you are going 18 miles per hour (29 kilometers per hour) with
>the 4-speed transmission.  I don't think the 5 speed has a higher ratio
>in 5th, just different spacing of the gears.
>Divide your indicated rpm by 1000 and then multiply that by 18 and you
>will get your true miles per hour.  For example: your engine rpm is
>4,500.  4500 divided by 1000 = 4.5.  Multiply 4.5x18= 81 miles per
>hour.  My 1.9TD conversion (with gas transmission) shows 80 miles per
>hour at about 3,700 rpm.  It sounds and feels like 80 but is really 67
>miles per hour.
>
>Wade Yorke
>Nova Scotia
>'84 Westy 1.9TD