Grouseguy

I get worse mileage in MN than I do after I fill up in another state. The 10% ethanol mandated by law in MN really does have a negative effect. It's not unnoticeable like the bureaucrats who mandated it said it would be. I know it should be marginal, but its noticeable.

balreadysaid

if the different size tires raise the vehicle slightly it will effect mileage. also bigger tires in a city environment will drop mileage. I run lifted trucks for work and my trucks get 7 mpg in the city. I run metric tires that are over 33" when well used and measured when they are mounted on the vehicle under the vehicles weight. which is not how the tire companies measure tires. 3.73 isn't a real low gear anyway if you had lower in both truck the difference would be much less between the two, even though it would be lower overall. thisis if the tires are different in diameter/circumference. sometimes lower gear doesn't make mileage worst but that isn't the case 98% of the time. I have talked to guys with the new 6.4 in the ram and the 4.10 gears seem to net them the same if not better mileage by a small margin. when I was looking at ram trucks to buy the tire size from 17" to the 20" was about a inch and a half. that means the truck can be almost 1 inch taller so it pushes more wind, taller tires are harder to turn from a stop.

Pandaz3

I agree of course the frontal area of the truck itself has not changed, but the bigger tires have more exposure to the wind and this underside of the truck is that much higher above the ground witch will allow a little more aero resistance

Fastskiguy

So is there any consensus on dropping the truck and inch or two and mileage?

Pandaz3

Are you going to use smaller skinnier tires to lower it, they have less rolling resistance and drag so that way there might be a infinitesimal MPG gain. Of course it would look odd and reduce the weight carrying capability and likely make a harsher ride and handling would be who knows where.
The only reason to do it with lower springs is because you like the look. You are messing with the suspension geometry though.
How much would you have to save to cover the cost?
I'm just guessing, doesn't mean I'm correct.

Fastskiguy

Well that's what my wife says…."you're going to take a suspension created by a team of engineers and mess it all up" so I hear you there. Maybe finding the lowest rolling resistance tires of the same size would be best when my stock tires wear out. My truck is a grocery getter so capacity doesn't matter but skinny tires would like kinda weird.

Alweeja

The Ethanol is Only good for the farmers not the vehicle. :-)

rmorris1953

My original tires were Hankook 235/75/17's. I got 80,000 miles on them before taking them off. At 70,000 I bought my friends GoodYear 265/70/18's from him and my mileage dropped about 2-3 mpg. I ran them for about 4,000 miles and put my originals back on. Mileage went back up. I finally decided not to push it and put the 18's back on and mileage dropped again.

Achigan

Just starting here...If your tires are taller, they are bigger around. one rotation = a few more inches in distance traveled. Our odometers don't know we have bigger tires, they record fewer revolutions of the tires, driveshaft, tranny. I learned that one with low profile tires on a Vdub. Check your odometer against mile markers on your next long distance highway trip.

rmorris1953

By GPS the smaller tires (17") I was running 2 mph fast on odometer and with the bigger ones (18") 2 mph slower (odometer says 58 mph and was going 60 mph) by GPS..... I will say computer is closer with the fill up with the 18" than it was with the 17".

But even with the computer being off by a little I wasn't getting near the mileage between fill ups with the 18".