You're going to be limited in how wide a tire you can go to anyway, by
the offset, and whether nor not you care if your sliding door hits the
rear wheel/tire. If you go with a 205/65R15 tire, you're still dealing
with a "stock" width (and pretty close to stock diameter).

If you go up to a 215 width tire, you're only tallking about less than
5% increase in width, it really isn't going to be any significance in
your rolling resistance as the front section of your van accounts for
more drag than your tires ever will.

Larger DIAMETER in your tires will have a more significant impact on
mileage (adversely) as it will take more energy to spin your tires
(even though you are traveling further on each revolution, your net
will be an overall drop in fuel economy.)

On Sep 9, 2009, at 1:26 AM, Jeff Palmer wrote:

> Hi all,
>
> It's getting to be time to replace the 14 inch tires on my 85
> Westfalia.  So I'm thinking about an upgrade to 15 inch wheels.  I
> know on my hybrid bicycle the tires are much narrower than on my
> mountain bike, and the rolling resistance is much lower (empirical
> testing from an arts student!).  So I'm wondering how moving to
> larger/
> wider wheels and tires would affect my fuel economy.
>
> Thanks in advance
> Jeff in Winnipeg (hey summer just arrived!)