tomw via EV wrote:
Larger diameter would be more efficient.  If they don't need to carry much
weight you might look into using motorcycle tires which are narrower.

It's not quite that easy. Larger diameter is more efficient, all things being equal. But they are rarely equal.

A larger tire and its rim is going to be heavier. The extra weight pushes you in the wrong direction.

A larger tire adds wind resistance, both from its larger frontal area, and by stirring more air around it as it spins.

The tire may be constructed differently. For example, motorcycle tires are definitely not built for low rolling resistance.

Years ago, I talked to Bob McKee about his amazing Sundancer EVs. They were going up to 140 miles on a charge on just twelve 6v golf cart batteries! He said he did a lot of experiments on tires, and found that *smaller* wheels were better, because the weight savings and reduced aerodynamic losses were greater than the increase in rolling resistance.
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
        -- Antoine de Saint Exupery
Lee Hart, 814 8th Ave N, Sartell MN 56377,
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