Larger tires for better gas mileage (Feb 6 show)

Can’t believe that Tom and Ray told Angelina that bigger tires will get better mileage. Yes, the car will go further for every engine rotation, BUT the engine will have to work harder meaning burn more fuel (everyone who’s ever ridden a geared bike knows that). There might be a SMALL net gain or there might be a small net loss, but if there is any gain it won’t be anywhere near the ratio of the increase in tire circumference.

True, but I had a 1984 Chevy Impala with a trailer towing package which had a 3,21 rear axle as compared to the standard 2.55 or so. The car went like stink, pulled great, but my gas mileage was less than other cars in the company fleet. I did not worry about the mileage, since I was not paying for the gas but wanted better trailer towing ability.

Increased internal friction in the engine and drive train is the prime cause for the lower mileage.

Bigger tires – having less curvature – would roll more smoothly along the surface of the road, decreasing tire/road friction and bouncing effects. Mt Bike tires used to be 26 inch diameter, but most mt bikes now come with 29 inch tires for that reason. I think that’s the reason they’d have better mpg, more so than the engine not having to turn as many revolutions per mile.

Wouldn’t a 3.21 rear differential be more similar to smaller tires rather than larger?

Some similarity, yes, but the difference between the axle ratios is 25%!!, while the difference between the tire sizes is a very much smaller percentage.

On the farm years ago we had a Chevy pickup truck with standard tire size 6.70x15 on the front and my dad put 7.10 size on the rear to increase load capacity.

That difference was (7.10-6.70)x22/7 in circumference. or only 1.26 inches in a circumference of 89.3 inches. or 1.4%!! Needless to say, we never noticed any difference in gas mileage.