37s giving 2.5 MPG better than stock?

[Chans4x4]

Drove on the stock 33s on a Rubicon and got around 17.5 MPG with half city and 2 desert trips so 65 MPH most of the way for the desert half. With 35s got about 17.0 This was multiple trips. Switched to 37s and the MPG shot up and was super shocked as got just above 20 MPG and what was equal to my all highway MPG on the other 2 tires. In comparison the 37s took a beating on city only driving and stock got 15.8, 35s 15.3 and 37s 14.9. The 33s were the stock Falken Wildpeak AT3W, the 35s the Falken R/T 01 and the 37s the BFG KO2. Anyone else notice the 37”tires getting better highway mileage?

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[Gladiatorx2]

I had 37's on my Rubicon and averaged about 2 MPG better than 35's on my Max Tow. I did the math on the effective gear ratio with the OEM tires was 4.10. The increase in diameter dropped that to 3.73 or the same as a Sport S. With the 37's it's closer to 3.45 or around there ( not calculating... just guessing. In town that hurts but on the highway that helps.

 

[Chans4x4]

Guess with it covering more distance per rotation it would get better highway MPG. Pretty wild the difference it makes.

 

[Stuntman Mike]

Did you adjust the speedometer to the new tire size?

 

[Mtpisgah]

The smaller Falkens are probably heavier than the BFG.

 

[Volksparts]

Did you adjust the speedometer to the new tire size?

That's what I thought. If you don't adjust the tire size in the computer say using a tazer it's going to give an inaccurate reading making it appear on the MPG calculator that you're getting better. With all my weight I carry with my rack and my 37s I only get like 13 to 15 MPG.

 

[GI Grandpa]

It is an illusion if you have told the computer you changed your tire size. Also, changing tire size doesn't actually change your differentials gear ratio. Your 4.10s are still 4.10s

 

[Chans4x4]

Did you adjust the speedometer to the new tire size?

Yes have the AEV ProCal. Also should have mentioned I calculate the MPG when filling up and using the trip meter.

 

[Gladiatorx2]

It is an illusion if you have told the computer you changed your tire size. Also, changing tire size doesn't actually change your differentials gear ratio. Your 4.10s are still 4.10s

That's where the word "effective" comes. The taller tire has less revolutions per mile. In this case just ( my Jeep) just under 10%. That's why the speedometer is off by the same 10%. That's also why acceleration is slower, because by the tire change you have effectively changed the final drive ratio. Yes the 4.10 gears are still 4.10s but effectively feel like stock 3.73 gears with the OEM tires after going to the larger tires.

 

[Gladiatorx2]

Also I have hand figured my fuel economy on all three Gladiator's as well as tracked it on the EVIC which is pretty close to accurate. With the larger tires and no other changes your RPM is lower at any given speed. On my Rubicon w/37's I drove it nearly 500 miles to trade it in on this Gladiator with Max Tow. This was through East Tennessee up to Norfolk, Virginia on far from flat ground. I got 23 MPG hand figured. On the Max Tow coming back OEM 245/75r17's I struggled to even hit 21 MPG. Same route, same gear, same driver. The change was in RPM at say 65 was 350 to 400 RPM higher depending upon torque converter lock up.

 

[gladtohave]

Answer is no .

 

[Gladiatorx2]

In my case the answer is yes. This is a picture of my Rubicon's dashboard on arrival at Norfolk, Virginia to trade it in. I stopped midway and filled up knowing how many miles that I had left. I hand calculated it on that stop and it was 22.7 MPG. This Rubicon's on 37's and is fairly heavy ( 5780 w/driver). Should note the EVIC was the same.

 

[Gladiatorx2]

Oh, and that was actually under my lifetime average. On the Max Tow that I traded it in for with OEM tires the day I put 315's on it. Just a little better than the Rubicon. A few hundred pounds lighter but higher RPM at any given speed.

 

[gladtohave]

Oh, and that was actually under my lifetime average. On the Max Tow that I traded it in for with OEM tires the day I put 315's on it. Just a little better than the Rubicon. A few hundred pounds lighter but higher RPM at any given speed.

Anytime you go up tire size you go down in MPG and if you can figure it to where you get better MPG when you go up in size then bless your little heart LOL

 

[Gladiatorx2]

The previous owner averaged a little over 12...seems like it was 12.49 or something like that. The difference is only in the driving style, terrain and traffic. If you can't understand how the difference in RPM's vs road speed (which is changed by tire size)....well, I won't even go there. Bigger man than you. I will avoid being condescending and will continue to share information with anecdotal evidence not just rhetoric. Have a great day!

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