I'm no mechanic, how the hell do you change the gear ratios,
is it done by computer??? and can you tell me what i should change it to??? tires are 31x10.5x15,

Are you talking about correcting the speedometer? Changing axle gears requires just that, changing the axle gears, not for the average mechanic. With 31s and a 4.0 3.73s would be fine.

I got a stock explorer and I can get a good deal on 31" tires, I just wanna make sure I know what i'm doing before i do, I'm not to worried about the speedometer as I am gas mileage, so basically i'm asking if I upgrade the tires do i have to change the ratios.???

I got a stock explorer and I can get a good deal on 31" tires, I just wanna make sure I know what i'm doing before i do, I'm not to worried about the speedometer as I am gas mileage, so basically i'm asking if I upgrade the tires do i have to change the ratios.???

Check your door plate and post up what it says for your axle code. Then youll know what gears you have now.

it says 45, do i gotta change it for 31's???

You have 3.55's. It should be ok for 31's, but if you want to swap axles to one with a better gear ratio its not that hard. Are you 2wd or 4wd?

the ex is 4wd but i drive in 2wd, i'm low on funds so if i can get by with out changing thats cool. I'm not gonna screw up my gas mileage or nothing am I?

You should be fine, but I'm sure you will lose a little bit of gas mileage. Improve the exhaust and intake, use synthetic oils, keep tires balanced/proper air....etc and you will pic up what you lose and more.

thanks Utah, one more question and I think i'l be good to go...
can i put 31x10.50R15LT tires on 15 X 7 rims???
im not 100% sure and i'd like to verify before I try.

yes you can.. You can run up to 11.5" wide tire.. Some have gone to 12.5 on a 15x7..

good, is there (any) modifications I have to make on the stock explorer to run 31's???

Every Explorer is a little different but generally you should be able to fit 31's (stock) with no problems.

Not to hijack this thread but how much difference will there be in the speedo with 31's. I am thinking of getting some when my 235"s wear out. I have the 3:73 and not that it matters but I think it's the limited slip diff.

You should be fine, but I'm sure you will lose a little bit of gas mileage. Improve the exhaust and intake, use synthetic oils, keep tires balanced/proper air....etc and you will pic up what you lose and more.
Doubt it... I lost 2-3 MPG average moving to 31s, I've even re geared and didn't see millage improve, drivability yes, millage no. I run synthetic oil in my engine (Mobil 1) and rear end (AMSOIL) and have a very free flowing exhaust. A 4.0 will not be affected as much as my 2.9 was though.

With mine, GPS actually reading shows spedometer as closer to actual speed with stock 31's. It reads 1-3mph high depending on the speed, where as the stock read 3-5mph slow.

Gas mileage didn't change much for me, either.

As for changes needed, none. It should fit a stock explorer fine. You might have minor rubbing, but if you want, you can always do a TT and shackles to avoid any minor rubbing, if you have any rubbing at all, that is.

God bless you fellas, I just got some $40 rims, for the $40 set of 31's. about to paint them black, can i get some recommendations on doing this?