Mark,

I just put two lengthy posts on the SubaruVanagon Yahoo Group about my
experiences with larger tires and gearing changes up with Suby 2.2L and,
now, a 2.5L engine.

My experiences are all with Syncro Vanagons with Subaru 2.2L and 2.5L
engines....but you can use the spreadsheet for an autobox also...

Use the Excel Calculator in the SV Yahoo Group FILES area called "3 Ratio
Tire and Gearing Calculator"...(a modified version of Tim Smiths original
spreadsheet.)

Just plug in the R&P ratio and the gear ratios for the autobox into the
first 3 gears. Ignore the 4th gear column. Be sure to get the "revs per
mile" specs from the manufacturer for the size tire you are considering.

With a Subaru 2.2L in my Syncro Westy with 14" wheels and stock tires, I
very quickly got used to being able to climb medium sized hills in
4th ...and liked that ability....and I found it annoying when I lost most
of that 4th gear climbing bility when I installed new 215/75-15 size tires.
Some who read this may find that comical..since a Suby 2.2L in any Vanagon
model can climb almost all hills in third. ...but it's just my preference.
It's very easy to get accustomed to extra power/torque quickly..and hard to
vive it up.

The gearing calculator showed the 215/75/15 size tires to give me 77mph @
4000 rpm (stock was 71mph)..so about an 8.5% increase, overall.  But from
my experience with a Syncro Westy, I don't think I would recommend a tire
size that would put your automatic's 3rd (top) gear over 75mph in 4th.
Your lighter van may not lose as much as a Syncro Westy.

You could try this....In a 2wd drive van, it's pretty easy just to borrow a
couple of larger tires/wheels from someone, slap them on the rear and give
them a try. This will give you an idea of how the gearing works out..on the
driving wheels...but will not tell you much about handling overall...since
you'll have a missmatched set.   I'm thinking of experimenting this way
with this out...experimenting with a set of 30" tires on the back of my
Syncro...decoupled, of course.

You need to drive around on them for a week or so...in different
terrain ....to see how you like the gearing effects.  A run around the
block won't do it. T

Good luck.

Warren Chapman
Moderator
SubaruVanagon Yahoo Group