Correct gearing for chunky 31" tires

[Sexploder]

Hi all,
So I have been on the hunt for mpg ever since I got some new 31x10.5R15 Goodyear wrangler duratrac tires. They have a lot of rolling resistance and I have been getting less than 10 mpg with mainly city miles. I have been doing some research and the most likely solution to my problem seems to be to regear my axles from the stock 3.73 gearing. My question is is what gearing would be best for getting the best mpg mainly in the city with occasional highway driving. From my understanding, 4.56s seem to be the best option. I would like to have the option to get bigger tires in the future as well but I'm not sure what would be the appropriate gearing with my 4R55e tranny. Thanks for the help!

 

[2TimingTom]

Back when I had 3.55 gears and 30" BFG AT tires, I got like 16-18. Then I went to 4.56 gears and I didn't drive it too much but mileage didn't appear to take much of a hit. Now with 33" BFG ATs, I've been getting like 14. But I don't drive it that often and when I do, I'm usually in 4lo creeping along on a trail somewhere.

If you're getting under 10, I'd say you've either got something else wrong with the truck or you've got a major lead foot. The tires shouldn't affect mileage THAT much.

 

[MercuryMullet]

That's 2500ish at 65. That is the normal gear for 33s. It will help around town get them rolling however depending on how much you drive going from 8mpg to 12 mpg could take awhile to pay for itself if $$ is the only reason. If power, stress on trans and other things are involved that's different. Just my option. You are running close to what a stock ex with 3.55 is running 4.11 would put you at stockish for 3.73 but I wouldn't pay the money to change from 373s to 411s. I'd go 456s and be ready to put on atleast 32s or just leave it alone. My opinion only, 4.56 and 31 could be optimum depending on driving style.

 

[frankcal]

I agree with Tom I think you must have some other problem other than gearing and tires. I'm running 265/75/16 which is close to 32s on a 3.73 open diff and am gettin about 16 in the city and 18 on the hwy. even when I step on the gas really hard and jack rabbit on stops I never get as bad as 10mpg.

 

[Greg_DonWindsor]

I run tires that measure almost 31 and routinely get 22+mpg with stock gearing. Something else is wrong.

 

[Flash]

This might not be the solution for you but this is what I have.
Because my Ex is almost always used on the road I have 255/70/16 tyres with a highway pattern.
I get decent mileage, good handling and braking and they're good enough to go on the beach which is where I do almost all of my wheeling.

I have a set of 15 inch wheels fitted with 31x10.5 with a more aggressive off road pattern if I need them.

 

[biggon71]

I ride the same exact tires, and my mileage wasnt affected very much. .5 to 1 mpg. I was at 15 and now I bounce around between 14 and 14.5. I have the info center console and thats what I use to judge.

 

[RomeovilleIL]

Did you have the computer reset for the larger tires? The 31's are larger than the stock sized tires so you milage is going to read low by about 8-10% - for example speedometer shows you cruising at 60 but are actually doing 65. Total miles traveled will be off too and shift points will not be optimal. Before spending $$$ on regearing have someone with a decent computer go into the menu and change your tire size setting. Revolutions per mile should be set at 650.

That much said getting 10-12 mpg you have other issues as well. Any engine codes?

 

[slickemhoundd]

Didnt really read all the other posts. saw a bit of of inconsistencies. 4.56 are surely not an all around gear for 31s. You will scoot around town for sure. On the highway.... lets just say itll be terrible. 410s seems to optimal for 31s-33s. in my experience 456 is spot on for 35s. Also remember that with a different tire size you mpg calculations will be off due to the incorrect mile count. Hell my truck now with 373s on 33s says i get 8-11 mpg. which is waaaaay off. the truck thinks it doesnt go as far as it actually does. hell im two weeks off a full tank but by the computer shouldve ran out of gas a couple days ago.

 

[4rd4life]

Did you have the computer reset for the larger tires? The 31's are larger than the stock sized tires so you milage is going to read low by about 8-10% - for example speedometer shows you cruising at 60 but are actually doing 65. Total miles traveled will be off too and shift points will not be optimal. Before spending $$$ on regearing have someone with a decent computer go into the menu and change your tire size setting. Revolutions per mile should be set at 650.

That much said getting 10-12 mpg you have other issues as well. Any engine codes?

+1 i was thinking the same thing.

 

[Sexploder]

Did you have the computer reset for the larger tires? The 31's are larger than the stock sized tires so you milage is going to read low by about 8-10% - for example speedometer shows you cruising at 60 but are actually doing 65. Total miles traveled will be off too and shift points will not be optimal. Before spending $$$ on regearing have someone with a decent computer go into the menu and change your tire size setting. Revolutions per mile should be set at 650.

That much said getting 10-12 mpg you have other issues as well. Any engine codes?

I had no idea that needed to be done. How does one go about changing the computer for bigger tires? Thanks

 

[RomeovilleIL]

Advanced scanners and some of the OBDII software programs can access the computer menus. Its a simple change of the numbers from stock 700 revs per mile to the corrected 650. A search on the forum should turn up which models will work. I know the dealerships and some garages will do it for you for 1 hour labor charge (takes a couple minutes). Once you change the revolutions per mile, the system will do a reset of the shift points and engine controls to match the tires.

 

[2TimingTom]

Depends. On my '97, I changed the speedo gear that is on the transfer case.