[darcane]

Originally Posted by Big Dave

Pickup truck guys try this all the time and invariably it backfires and they get WORSE MPG, even after speedo error is corrected for.

.....

Empirical data shows thar gearing works and bigger tires are counterproductive.

Invariably?

I saw noticeable gains (~3%) by switching to taller wheels/tires on my truck. Steel 16" wheels to Aluminum 17" wheels with 5% taller tires. Overall weight was the same, but taller, heavier tires means the moment of inertia still increased.

I can see it go either way, but it certainly helped on my truck.