Taller rear tires on RWD vehicle

[Frank Lee]

I think old school stuff without overdrive gears and/or lockup converters are more likely to see an fe benefit than newer stuff that already has a decently tall top gear.

[Diesel_Dave]

Originally Posted by mcrews

actually dave, quite a few have.
As a general note, frank lee commented that trucks doent see a benift.
But the trick to the equation is how much highway miles you are driving vs city driving.
Also you cant be going from 15 rims to 17 rims, because then the issue is the extra wieght. But a 4-7% increase in diameter (given hwy driving) absolutely will result in betterr mpg.

Just common sense alone would have to question your 1 in 10 statement.

My "1 in 10" statement was directed at pickups. I know Big Dave tested different things, including putting an overdrive and 3:03 gears in his truck. I can't remember the particulars, but he found worse FE with larger tires. I've heard similar from other truck owners.

I do agree that the benefit (or lack thereof) would depend on city/highway mix as larger tires/rims add extra weight and rotational mass. That would likely lead to a decrease in FE in city conditions. Also, the gearing benefit would not show up much in city driving, as you're not in top gear much anyway. Of course, putting taller tires only on the rear would contribute only half the additional weight/rotational mass, while giving you all the gearing benefit.

My thinking is that taller tires only on the rear would also have little affect on aero (maybe even a slightly positive one?).

[mcrews]

on the areo idea.
someone had oposted that one of the car mags back in the 70-80??? did a econ project car over several months.
they either raised the rear or lowered the front as one of the mods.... BUT the result was slightly better mileasge.

I lowered the fron of my Q45 for this last trip to texas. about 1 1/4 inches. I broke 32mpg on the trip. last yr it was 30.9mpg
Now I also run a body kit so I'm sure that helped.

[Rick323]

Both my Tacoma and my Dodge w250 (4wd, 4.10 gears, diesel: bought new in 1992-sold in 2004) got better fuel mileage with larger tires (all four tires). Both are manual transmissions. I got the same size tires for my ford (rear only; auto trany) in hopes that it'll get better fuel mileage too. I didn't have the stock size on the ford long enough to compare the two different tire sizes for fuel mileage.

[royanddoreen]

Don,t it seem that many cars and trucks etc are probably geared for higher rpm than need be to compensate for load or 20 degree hills. If need be we could always down shift. Don't hear of anyone complaining of wind resistance when driving the max speed limit I drive my Z around rural areas.in 5th and 6th gears getting the best mileage that is without stop and go traffic. Then on the highway I'm wishing I had a 7th gear to get my revs down. Only solution I see are larger o d tires. I can always go back to stock if that don't help.