would bigger tires get better milage????

[bassman]

I get 45mpg in town and 40 on the highway.
when you hit 70mph with my auto 93 injected festiva it revs real high and I think thats why the milage is less on the highway than in town ???
if I put on a 13 or 14 inch rim and a taller tire that dosent rub would I get a better mpg??
I would use a gps to track my miles as the speedo would be out .

[scottxd45]

I doubt it because they would be heavier.

[Burnrate]

Lower weight (lighter rims smaller tires) and less rolling resistance (skinnier, harder less grippy tires) are mpg improvers. If you go with a taller (not to fat) tire much lighter rim (alloy) combo to get you in the RPM sweet spot it would be ok. They will lug your car more in city driving. Remember taller tires will raise your car and might lower you Cd some. Major hot spots are created around your tires and cause drag. You want to tuck them in the car as much as possible. Also I think these engines are more efficient at higher RPM's but I know the auto isn't tall enough for interstate speeds to be efficient. Best recommendations are to leave a few minutes earlier and slow down. (Speed pulls down mpg exponentially). Or trade it out the auto tranny for a manual.

Eric

[jglutz]

Its realy easy.....gains would be directly proprtional to the circumferential increase in the tire (pi)(d2-d1).
However, the consequence of this gain must be offset buy the increased parasitic requirements associated with the rotational inertia reflected by the increase in both tire mass and radius. Though, if the new rim and tire were designed such that the net inertia equaled that of the previous, substantial gains may be seen in the net milage.

I slept at a Holiday Inn last night!

[b8kedbeans]

...at higher speeds most of the fuel is consumed to fight wind resistance of the car body so I doubt that a tire size change will make much of a difference in that case.

[dahodges]

I have 155/80/R13's on my auto. Does not really help gas milage. But does place enought of a load on the engine so that it does not sound like it's going to come apart. They also slow the speedo down abour 5 mph.