mSchvOus

Hey guys, newb here

recently picked up a '12 sport 2dr / auto
complete basic...16" steelies w/ 225/75 tires
and unfortunate 3.21 gearing (bought the jeep prior to reading any forums)

this is going to be a DD for me with a posibility of land rides and slight trials (no rock crawls or mudd'n), so im not lookign to get too crazy with mods

my drive is pretty flat, locally and the ocassional highway ride

i do however need to get rid of these wheels and upgrade
im looking at a set of 15" mb72 w/ general grabber studdable in a 31x10.5 size - roughly 1.5" larger than stock

so my questions are:

1) is there going to be a power loss difference going to the larger wheel - even though its under 33"
2) am i going to need anything for the tire carrier or is this size going to fit w/o a problem
3) are there any slight mods i can do for better power with a 3.21, outside of a re-gear, i.e. intake, exhaust, tuning...
4) do i need to get the speedo re-calc'd for the new tire size or is it already in the general speed range since the sport s comes with 32's"

sorry for beating a dead horse - any help is greatly appreciated
thanks!

rattymml

If you do loose any power it will be minimal. I have a '10 with the same gears and the 255/75/17 (32's) and a much weaker engine and it gets up and goes fine. Keeps freeway speeds of 75 with no issues, so I think you should be fine. I'd actually recommend going with the 255's. You can probably find some stock wheels and tires on the forum for a lot cheaper than new.

mSchvOus

a 255 in a 17" or on a 15"?
im trying to get away from stock all together with the rims/tires - i like the wide stance with aftermarkets

rattymml

I forgot you wanted to go with aftermarket 15s. when I said 255s I meant on a 17 inch rim. I bet you could run some 33 inch duratracs no problem. They're surprisingly cheap at discount tire, especially for 15 inch rims. Just make sure the backspacing is correct so you don't rub on anything.

JE8154

I thought I would be happy with 32's when I first got my jeep. It's a decent upgrade from the stock 225's but I was wrong, and ended up losing about $300-400 upgrading the second time in a month. It made it look like a stock S package sport but with a more aggressive tread pattern. I would definitely recommend you don't bother getting 31's. If you're going to get different wheels with lower backspacing you can run wider tires than 10.5" without rubbing too. I am currently running 305/70/r16's which is like a 33x12. The power loss is minimal with a manual, the only time I notice it is going up hill on the highway and even then I only have to down shift if the guy in front of me forces me to slow down to around 60. I can't say for sure what it is like with an automatic.
You shouldn't need a tire carrier for anything lower than a 37 but depending on the weight of the tire/wheel you should consider one. but for a 31 no. a 31x10.5 general grabber with a wheel would probably only weight around 65-70lbs. Just make sure your rubber tailgate bump stops make good contact with the new tire sidewall.
you shouldn't even consider upgrading anything other than the tires if you're only going to a 31/32 as you really wont notice any difference on a 2012.
With an automatic transmission you will need a programmer for the shift points going to a bigger tire. A 31 might not throw it off too much but it will probably be noticeable since yours is currently calibrated for a smaller tire. Your odometer and mpg calculator will also be off.

My advice would be don't go with anything smaller than like a 33x10.5. Anything smaller and you won't really notice a difference in the way it looks. I'm not saying it will look bad, but to me something about mine just didn't look right sitting on the 32's. Look around the show and tell section on here, and find something that looks how you want yours to look and go from there. If you haven't seen any pictures of a JK on 31's you should definitely find one before you consider going to that size, or any size for that matter.

mSchvOus

after i bought the jeep i started doing my homework, shoulda been the other way around

so i spoke with someone at DTD, the rims/tires would fit (the 15's w/31x10.5)

then i started reading threads about the gearing - thats how this all came up

im just assuming, that the new rim is going to be lighter than the steel stocks - so their might be a slight change in the unsprung weight on the new setup. so im hoping the lighter weight of the rim plus going up almost 2" in diameter on the tire, might not make any negative difference with the gearing.

if it were, thats where the part about any upgrades would help make up for it...exhaust/intake/programmers and such

i just want to keep things simple for now
once the warrenty is done, then ill go nuts with this thing...lift, 35"s, re-gear, ect...

mSchvOus

im probabaly going to be killed for this, but im not a fan of the 33" on an unlifted jeep
i dont like how the wheel well gets filled
i like the look of open space in there.

in the prior post, once the warrenty if gone, then its a free for all...lift, 35's, re gear. im just looking for something that'll make me content for the next couple years while save $ for all that, lol

i was just hoping that the 31's beig wider than the 225's, on a lower back spaced rim, would give a move appealing look for the time being. ive seen a 31x10.5 on a 15" crager - granted it was on a cherokee sport - but i liked the set up

JE8154

Whatever floats your boat, It's your jeep do what you want to it. For me I felt it sat a little too low and the tires didn't give me enough of a change from a stock JK so I went bigger. I'm lifting mine soon but didn't want to make the jump to 35's so I have 33's with no lift currently. I'm only going with a 2.5" lift so I'll gain back the space in the wheel wells but I also like the way it looks now with the wheel wells being a little more filled. One thing you might want to consider is the tire size difference from printed to inflated. with a 32" tire you end up with about a 31" tire when its inflated and under vehicle load. JK's also have a lot more space in the wheel wells than a cherokee.

I think you'll get the look you're going for with the lower back spacing and a little wider but it just didn't do it for me. To each his own though. Good luck hope it works out how you want it to.

This is a 265/75 R16. Under vehicle load it measured about 31" but was listed at 31.7" diameter. Just subtract 2 doors from mine.

mSchvOus

i see what you mean about the 31's
guess i gotta look around a bit more

my father in law has a sport as well with 32' stock
ill get a chance to check it out tomorrow - maybe ill look that route

just to confirm, you also have the 3.21 gearing, but in manual, right?

JE8154

yes, 3.21's, 2012 6 speed, 305/70 R16 on 16x8" wheels with 4.5" BS, No lift until my new drive shaft comes in.