Improving fuel efficiency with heavy vehicles

artguys wrote:
pnichols...reduced mass and friction.

Mass...less overall wheel/tire weight, or unsprung weight. Higher weights require more energy to turn.

Friction...normally a larger tire foot print as the new singles have increase friction, but because you've got 2 side walls as opposed to 4, rolling resistance is greatly reduced and that negates the foot print issue.

Thanks much for getting back to me on this.

Why isn't the unsprung weight of a huge single about the same as the unsprung weight of two smaller tires in a dual set (assuming the rims are steel in both cases) - no fair comparing some light-weight alloy to steel ... or at least close enough so as to be insignificant? However if the single does indeed weigh enough less to be significant, then the more energy required to spin the dual set is only required when coming up to speed - once rolling the energy to keep them rolling will be the same.

Also, why aren't the flexing sidewalls of two huge singles - carrying the same overall weight as the flexing sidewalls of four smaller tires from dual sets (with each carrying one-half the weight of the large single) - creating about same total rolling friction?

For kindof a counter-example related to rolling friction: On our motorhome I recently changed the stock Michelin tires to new Michelin tires of the same load class but of a taller sidewall and narrower tread width design. Michelin rates this new taller/narrower tire as a Green X tire with reduced rolling friction over their wider/lower profile old design that was on our motorhome.

I'm wondering if the new low profile truck tires aren't all about the fact that they "wallow" less under side loads because of less sidewall height (the same as in race cars) ... and the fact that they indeed do weigh a lot less than dual sets because their rims look to me to be made from a lightweight alloy (aluminum or magnesium). If so on this last rim material issue, then why couldn't the dual set rims also be made of the same lighter weight material so as to reduce their unsprung weight (which reduces the energy required to overcome their moment of inertia when accelerating)?