JKtak

I have an '07, 6-spd, 2 dr with 295 Cooper SSTs on 17" steelies and 4.88s and averaging around 12.5-13 mpg. I got the 4.88s because I wasn't totally against getting 315s in the future and don't mind the low-end torque as I mostly do city driving.

My question is when I move to the 315s (thinking Duratracs) will my mpg continue to slope dramatically or stay relatively the same since my Jeep will be more properly geared?

Maertz

id think it will stay relatively similar, but a small drop.

TheEngineer13

A big part to properly answering your question is knowing what size your tires are. 295 defines the width, the second part of that (295/??) defines a percentage of the 295 as it relates to the sidewall height.

Going with a larger diameter wheel does not necessarily directly correlate to better or worse MPG, the larger factor at play here is the overall rotational mass. Generally a taller, wider tire means more weight. A deeper tread pattern will also mean more weight. More weight (rotational mass) means more force (torque) required to move the tires. To create more force at a given RPM (say 1000 RPM) you either have to add more fuel (push the pedal further; i.e. get worse MPGs) or re-gear.

Seeing as how you are running 4.88's; unless you go with insanely heavy tires, you may drop a tenth or two off your MPGs.

JKtak

They are 295/70/r17. Looks like they come in just under 65 lbs! One of the heaviest 33s out there and pretty comparable to the weights of the 35" ATs I was looking at.

Thanks for the advice gents.

TheEngineer13

Just remember to re-cal your ecu after the switch. There is about an 8% difference in size between these tire diameters. This means (if you do not recal) you will be driving at 108% the displayed speed and your MPGs will be 8% lower than they are.

Invest2m4

At 12.5-13, what's another .5?! What's crazy is that Peterbilts new full-size Semi-truck with trailer, gets 10mpg. To be fair, at 65,000 lbs, it is pretty light.

waterboy222

That's also measured at "company truck speeds" of 55 mph.. I know my drivers are ready to kill someone when we had them limited to 67 mph. With speed limits here being 75 and 85 mph, 55 is deadly! lol

2012JKNY

Just a point to note (one of the reasons they have become so popular), even though they are not quite 35s (they measure 34.4), the Duratracs are among the lightest tires out there. I actually think that the 315/70/17 size is about the same weight as your current tires, maybe even a couple of pounds less.

Invest2m4

x2. I average 19 mpg (2013 JK) and have the 315/70/17 Duratracs.

Weight is much more a factor if you do a lot of city driving or have hills. Two other main factors are drag (wider tires have more surface area to push through the wind) and rolling resistance. The Duratracs do well in weight and rolling resistance.

metaldemon

My son has those tires on his truck. He calls them Duraslicks in the rain, but he does have a heavy foot like his Dad. I tried to tell him before he bought Goodyear. He didn't listen. Bullheaded like his old man.
If you drive like they teach you. You will be OK. That being said I have Rubicon take offs on a 3.6 manual. I get about 17 mpg in the winter if I drive like a girl. Any off-road and that goes below 15 mpg.
Can't wait to get my 4.56 gears, and 35s.