----------
> From: bpremack <bpremack@wavetech.net>
> To: Todd Last <Rubatoguy@IBM.NET>
> Subject: Re: Transmission question
> Date: Wednesday, October 01, 1997 12:59 AM
>
>Todd,
>
> I have also considered ways to reduce the high cruising rpms.  A quick
and
> easy way to modify your gearing is to simply increase the size of your
> tires.  If, for instance, you shift only one tire size (for example, from
> 195/70 R14 to to 205/70 R14), your diameter moves from 636mm to 652mm.
> After multiplying by Pi (3.14) to get circumference, you will find an
> increase of 7.7%.  This means that your rpm (in all gears) will drop by
> 7.7% for any speed.  If your Van is like mine, 3800 rpm @ 65-70 mph is
> reduced to about 3500 rpm, which is much better for all day cruising.  A
> shift from 195/70 R14 to 215/70 R14 will result in a reduction of 14%,
> which may be even better for engine longevity and gas economy.  Just
> remember to downshift as needed so you don't harm your engine.
Obviously, there is a size limitation based upon the Vanagon wheel
housing/suspension dimensions and the spacing available before wheel travel
will impinge upon other components.
>
> If you choose this technique, remember that your odometer and speedometer
> will also be off by the same % factor.  Your apparent readings will be
> higher than your actual speed and distance.  My speedometer guru says
that
> it is quite easy (in other words, inexpensive) to adjust the
> speedometer/odometer gears to correct for this factor.  (His name will be
> supplied upon request.)
>
> I have a table of tire diameters ( taken from this list some time ago)
which I cannot post now as I do not have a scanner.  If any listees want a
copy, I will make arrangements to have it posted to the list.
> If anyone wants any further info, or if I have omitted some relevant
calculation or logical analysis, please let me know.
>
>
> Budd Premack
> 86 Syncro, 84 Van, 73 Super
> Minneapolis, MN
> bpremack@wavetech.net