"might sound weird, but when I went from 255/60/15 to 255/55/17 RT rims
and
tires, I noticed that I can't go over 20mpg on my overhead anymore. I
used to get 21 doing 60mph or less on the hiway, I can barely get 19.5.
This
could be due to the difference in tire size has thrown off the
calculations,
but I think the RT has the same overall diameter as the stock tires,
255/65 (mine were 255/60)
Dunno, could be wrong. I am sure there are others than can answer."
-Interesting thing to note. The stock 255/60R15's should have an
overall diameter of approximately
687mm. The R/T size 255/55R17 stands about 712.3 mm tall, roughly 2 1/2
cm., or almost exactly 1 inch
taller. Who's the math wizz on the list? If you have a taller tire
that at the same rate of revolution as the smaller
size, will travel further in distance due to an increased
circumference. The fuel mileage on the computer
would read lower, but the distance traveled would be further than what
the computer thinks, due to it taking
its reading off the speed sensor on the transmission.
So, is the gas mileage affected? Only if the replacement tire is
shorter in diameter, not taller in diameter. Being shorter will raise
the engine rpm at any given speed, increasing fuel consumption.
Patrick
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