Michael Modl wrote:
> Hi Ch. Well now that I thought about it, you are right.  Whether or not the
> speedo drive is coming from the front diff or the left front wheel the speedo
> will always read    the same. I dont know why I thought it would make a
> difference. I wasn't feeling very well last night. I guess if someone with a
> REAR wheel drive vanagon wants to make the RPM lower without having to
> recalibrate the speedo, they will have to put 28" diameter tires in the rear
> only. RPM at 4000 RPM would equal 78 MPH, (3600 RPM = 70 MPH) and the speedo
> will show that speed, since nothing was done at front , right.
>  Michael Modl. 87 syncro

Hi Michael:
You and Ch brought up some good points. Every time I think about it - I almost
understand it!  The indicated speed (say 50mph) at a certain RPM (say 2000) does not
change by putting larger sized tires on the auto but the actual speed does. If I do
put on larger tires - say 2" larger in diameter - then at 2000 rpm the larger
circumference will be covering more ground than the smaller tires in a time period.
Since it covers more distance than the smaller tire in the same unit of time, the car
is going faster.   How much will the speedometer be off?  The TireRack web site has
some good info on this.

NEW TIRE DIAMETER/OLD TIRE DIAMETER x MPH at a certain RPM = ACTUAL MPH at that RPM

In my case:
       30/28 x 50 = 53.6    So when my speedo indicates 50 I'll really be doing 53.6
                            so I'll back off a little at higher speeds.

Gary
80 Westy, 88GL