Since a 20" tire is larger in circum than a 14" tire, and thus go further on each rev. wouldn't mpg be better

Question

Since a 20" tire is larger in circum than a 14" tire, and thus go further on each rev. wouldn't mpg be better

Answer 1

yes mpg would be better and the vehicle would look way better than with 14"

Answer 2

Depends on where the vehicle is driven. A taller/shorter tire changes the final drive ratio of the vehicle.

If the vehicle is used on the highway, using a larger (taller/larger circum) tire will usually net you an increased mileage per gallon. This is because the engine rotates slower to do the same amount of work (distance). It is like overdrive in a tranny.

If the vehicle is used in the city or stop and go driving, a taller tire could decrease your economy. This is because the engine need to work harder to initially get the vehicle moving (leverage). So the shorter tire would work better in town. Just as David P.L said, the weight is harder to hold the more you outstretch your arm; same effect with the larger tire.

Answer 3

Not likely.  The rim diameter is only part of the equation.  It's the aspect ratio and width of the tire, in combination with the rim diameter, that determines the outside diameter.  For instance, a 195/70-13 and a 195/50-15 may well have the same outside diameter.  Also, the lower the aspect ratio, the harsher the ride, unless the car is specifically designed for low profile tires, or you have a TON of money to spend on hopefully decently engineered suspension kits.  Additionally, the wheels and tires will be heavier, taking more energy to roll, and your stopping distance may well increase.  The wear and tear on your brakes will certainly increase.

Answer 4

Your theory is correct, until you factor in the fact that it takes more power to turn a larger wheel, and there is more rolling resistance.  Due to the added demand for power, you do not gain any fuel economy.  To prove this point, put a weight in your hand, hold it out by your shoulder, then extend your arm fully.  Where does the weight feel heavier?  When it is heavier, you need more power to hold it out all the way.  This is due to the greater radius of the tire(the distance from the center point to the tread).