Quote:
Originally Posted by Big Dave
Increasing tire OD almost always backfires and MPG is reduced.
It might work if you were a long-haul trucker who can maintain the same speed hours on end, but most of us have to deal with stop-and-go situations.
Rotational moment of inertia goes up with the square of diameter. That means those four "flywheels" have to absorb more energy to increase their RPM. Until the tire RPM increases road speed doesn't increase.
Another evergreen myth that deserves a sticky.
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Dave, I think i see what your saying, but wouldn't the tread of the short tire and the tread of the tall tire be going the same ft/sec. at x MPH. The axle would see more torque but at a lower RPM. If the tall tire was wider, more aero drag, or heavier more vehicle weight, or caused more air under the vehicle, then i could see obvious losses. But what if the tall tire was the same width, same weight, the vehicle height could be lowered to stock. And the engine efficiency at the lower RPM was the same. Wouldn't the MPG be the same. Of course, how often could we find a tire that weighted the same.
On the other hand i could see where a narrower, lighter tire that lower the engine RPM to more efficient speed could be beneficial.