31" tires how bad will this hurt mpg and perf

[dukes98]

i have a 98 with the 4.0 single ohc. i am putting 31" on and will soon be doing a poor mans lift, tb and shackles. how will the tire affect the mpg and will i loss a ton of power?

 

[corkey]

it won't be too bad,, i have just a bit smaller size tires than you do, and i get over 22 on the highway . it takes off a bit slower but the truck isn't a rocket to start with , check the door tag to find out what rearend gear you have, that will make the most difference,, there is a listing of the axle codes in here somewhere,,

i also have the same lift as you,,

oh yeah,, edit this to add , i have the 373 axle ratio,

 

[James909]

As corkey said the axle ratio will have the biggest effect on how the truck performs with these tires. So take a look at what the ratio in your truck is. The lower the gearing (numerically higher) the better.

Edit:Here's the link to the chart of axle codes.

 

[XLT]

I just switched to 31" tires and on my 98 ex sport with the SOHC. I could tell i lost a little power but not much. I also have the 4.10 gears as well as a shackle and tt lift on mine. Still seems to accelerate pretty good.

 

[yellowford]

I actually saw an improvement on highway mileage after switching to 31's, it dropped the rpm's by about 400. I didn't really notice a difference in power but I have the V8.

 

[storlied]

3.73LS here, 5.0L.. Lost a bit of torque, I want it back... on the plus side.. my speedo is right on now.

As for mpg, dunno... never checked it since I've owned the vehicle.. it'll always guzzle gas.