Nope, the great misconception. It actually requires more energy to
turn those larger diameter wheels/tires. More than you get from them
propelling your further. If you look at almost all the high fuel
economy vehicles, one thing they'll have in common is small diameter
tires. Narrower tires aren't necessarily better, but because they have
less mass, they also help. In the end for best fuel economy you want
the least amount of unsprung weight (the unsprung weight is the weight
of the tires/wheels, brakes and other suspension stuff that is BELOW
the springs. The rest of your car/van is sprung weight (above the
springs).

Of course with our Vanagons, you have a balancing act to get small
tires/wheels, with sufficient strength rating to handle the weight of
the van.

On Sep 9, 2009, at 7:30 PM, Edward Maglott wrote:

> I thought a larger diameter would be better for mpg by raising the
> effective gear ratio.  Engine turns fewer revolutions/mile.  'course
> if you are figuring your mpg using the stock odo, smaller diameter
> tires would make it look like you had better mpg because the actual
> distance would be fewer miles than the odo says.   You would also be
> travelling slower than indicated on the speedo and saving some fuel
> there too.  I think that makes sense.
> Edward
>
> At 01:41 PM 9/9/2009, Kim Brennan wrote:
>
>> 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.)