[502dakotaV6]

i have a 2wd dakota with the 3.9 and i currently have goodyear wrangler authority's on it they are 31x10.5. My question is would putting the 215/75r/15's back on give me better fuel mileage or would i really even see a difference?

 

[critical_level2]

Yes, putting the smaller tires will help improve gas mileage. The smaller tires are probably about 20 pounds lighter each than the 31x10.5r15s.

When I had 215/75r15s on my 4wd 3.9 Dakota, I could get around 20-22mpg if I really babied it.

 

[502dakotaV6]

i love the look of my 31's but i feel its kinda useless having such an aggresive tire on a 2 wheel drive truck

 

[caulk04]

Do you have the speedometer corrected for the larger tires?

I'm not saying that smaller tires won't help mileage, because they will but, if the speedo is uncorrected you're actually going farther than the truck thinks it is.

 

[Shatto]

Stock size Michelin tires lasted almost twice as long as Goodyears for me.

I don't recall any significant MPG change with different tires, and I kept very accurate records, so, for me, tire life was the important criterion.
In fact, the only add-on to my Dakota that improved mileage was Gibson Headers, which gave me a bit over 1 MPG improvement......and scary acceleration.

Larger diameter tires should give better MPG. Should. Because larger diameter tires rotate fewer times per mile, thus the engine runs slower, ergo uses less fuel...
But the computer keeps the engine running within certain parameters so it is possible you'll experience a drop in pep
because of the 'longer legs' and no improvement in mileage.

If you drive mucho miles or have money to burn experimenting, you might invest the money you don't spend somewhere with a better return. Like a girlfriend

 

[98R/T]

i dont get this whole tire to mpg thing...

take my truck for example, stock comes with what 28" tires, i put on 25" tires, this will make the mpg's worse because of the higher rpms turned no?
but if i had a 4x4 and had 31" tires and down graded to a 29" tire i would get better mpgs?

 

[Shatto]

K.
We must talk about tire diameter and the number of revolutions per unit of distance.

Rims, chrome, laser headlights and such have nothing to do with the arithmetic of calculating the fewer rotations of a wheel, the fewer revolutions of the running gear and engine.

Simple theory.

The problem, I've learned, is the computer. My Dakota was simple and quaint compared to my newer Tundra which managed to keep the mileage at the same average in spite of the larger diameter tires.

 

[critical_level2]

Larger diameter tires should give better MPG. Should. Because larger diameter tires rotate fewer times per mile, thus the engine runs slower, ergo uses less fuel...

But you are also forgetting, larger diameter tires are heavier than smaller diameter tires. The stock 215/75r15 tires on my Dakota were around 27-28 pounds. The BFG 31x10.5R15s on it now are around 48-49 pounds each. That is an extra 80-84 pounds my Dakota now has to push around.

Same holds true for larger wheels with smaller profile tires. A 17 inch wheel is heavier than a 15 inch wheel, 20-inch wheel is heavier than an 18 inch wheel, etc. just raiding the wheel size will increase the weight of the wheel/tire combo.

It uses more power to turn heavier wheel/tire combo, which in turn uses more gas.

 

[Shatto]

But you are also forgetting, larger diameter tires are heavier than smaller diameter tires. The stock 215/75r15 tires on my Dakota were around 27-28 pounds. The BFG 31x10.5R15s on it now are around 48-49 pounds each. That is an extra 80-84 pounds my Dakota now has to push around.

Same holds true for larger wheels with smaller profile tires. A 17 inch wheel is heavier than a 15 inch wheel, 20-inch wheel is heavier than an 18 inch wheel, etc. just raiding the wheel size will increase the weight of the wheel/tire combo.

It uses more power to turn heavier wheel/tire combo, which in turn uses more gas.

Which sort of makes the point that there isn't much to be done that will make a significant difference.
Because I drive between 150 and 350 miles a day, a 1 MPG improvement would pay for itself in a year or so. To me it is Return On Investment (ROI) and I would gladly pay for something that worked. Except for the larger diameter tyres, when I needed new ones anyway, Clude The Ride, my Tundra, is stock.

 

[hskrRT]

One could argue that smaller diameter tires will give better mileage due the the effectivve gear ratio change meaningg the truck can get moving easier than with larger tires. And in the difference in weight and you might notice significant difference in gas mileage. Remember, rotational weight has more effect on performance than static weight. Meaning 10lbs difference on each will. Will affect performance more than 40lbs in the bed.

Along with tire size, making sure you keep proper psi in each tire helps as well. And if you are going to make a long road trip, you can bump up the pressure in each tire 5psi and it will help with your mpg.

 

[9t9-5.2]

One could argue that smaller diameter tires will give better mileage due the the effectivve gear ratio change meaningg the truck can get moving easier than with larger tires. And in the difference in weight and you might notice significant difference in gas mileage. Remember, rotational weight has more effect on performance than static weight. Meaning 10lbs difference on each will. Will affect performance more than 40lbs in the bed.

Along with tire size, making sure you keep proper psi in each tire helps as well. And if you are going to make a long road trip, you can bump up the pressure in each tire 5psi and it will help with your mpg.

That can be true around town, out on the open road the lower effective ratio will cause a loss of mileage.

Wider, stickier tires will return lower mpgs than narrower harder tires.

 

[hskrRT]

That can be true around town, out on the open road the lower effective ratio will cause a loss of mileage.

Wider, stickier tires will return lower mpgs than narrower harder tires.

I'm getting the same gas mileage with my 4.10 gears as I was with my 3.92 gears on the "open road" cruising at 80mph.