would there be any ill/positive effects of this i know the usual gears for 31 are either stock or 4.10 i have a 99 4.0 auto 4wd

 

your fuel economy will suffer some and you'll lose your top end power on the highway, that's a little over-geared for 31's. not such a bad thing if it's only a trail rig though.

 

Actually youll have some pretty good power. I know people who like that combo.

I say go for it.

 

pretty good LOWER END power... no high end... not the best for highway speeds... good for crawlin...

 

right! if it's your d.d. i'd steer clear, just to clarify! spot on that the low end would be exceptional...

 

How you figure? Gonna be in the power band and all at highway speed too...

 

My buddy ran 4:56s and 32s. It was really peppy. Im sure itd be worse though on 31s.

How long you plan on running only 31s?

 

I ran 4.56 with 32's for a bit but mine is a manual so the final drive ratio is a little lower, but with the 32s i struggled to get above 60 mph without redlining. I ended up switching to 35's and i still wind out the engine at highway speeds. 70 mph is the max i push it. IMHO 4.56 would be too low for 31's...33's would be a lot better

 

It all depends on what you use it for. If it's your daily driver either go 4.10's or step up to at least 33's to run 4.56's. Trail rig it would be all right. It will give you a good crawl ratio.

 

friend of mine ran 5.13's on 31's

you won't die or anything

 

5.13's on 31's? I thought my 37's, and 6.18's were bad lol. Between the two gearing ranges is night and day difference but 5.13 and 31's probably screamed as bad as mine do.

 

I ran 4.56's and 31's for over a year.
Rig is my daily driver and spends time on freeways and interstates.
If I remember 75mph was up handy 3000rpm, and 65mph was handy 2500rpm.
Mine is a 5spd, so an automatic would turn slightly less rpm.

I can assure you there was a boat load of power at highway cruise. We've got some pretty steep grades into the mountains around here, and I never had to shift into 4th to maintain speed, and at 65mph there was no need to downshift to pull out and pass on two lane roads.
Crawl speed was awesome.
People who say you loose top end power are mis-informed.

 

the input was great I was thinking i would buy the 31s and regear to 4.56 so i would not have to regear when i could afford 33s maybe ill just forgo the 33 and run 31s on 4.10 all depends on how much cabbage i have thank for info

 

just consider getting 32s andeither way you'll be fine. I say GOFERIT!

 

Re-gearing is probably one of the best mods you can do - and most of us don't do it. If you are going to do a re-gear, I'd go for it and worry about the tires later. Tires can be switched around pretty easy.