[05Unlimited]

Tires will need to be replaced next spring/summer and I was considering switching up to 31x10.5 from my stock 30x9.5 on my 2005 LJ (4.0) 6-speed. I have stock 3.73's. The 6-speed has a relatively low 1st gear and really all of the gears are somewhat low so maybe a slight gearing increase due to a mere 1" in tire height won't negatively affect throttle response so much? Any issues going to 31x10.50 with stock suspension/fenders? I realize I could search on this but thought I'd ask in case someone doesn't mind answering specific questions. Here's what I suspect the overall effect to be when switching to 31x10.5 from 30x9.5: Mileage will hopefully be unaffected; tires are an inch wider and create more rolling resistance and wind drag, yes it's a negative effect on MPG. However, tires being taller increases gearing which likely will have a slightly positive effect on MPG ....so it's a wash with MPG hopefully. Handling will likely be unaffected if not ...improved; yes I realize the center of gravity goes up a little bit, however, there is more of a percentage increase in tire width than height with this switch ....which should be beneficial to handling in two ways, less "tire roll" in turns and a greater contact patch. Performance on the road may suffer very slightly if any at all due to the taller gearing and increased tire/road friction/resistance (however off the line traction will improve). Perhaps not though because this transmission seems geared a little too low for optimal street performance (especially 1st gear). Maybe say a 0 - 60MPH run will actually be quicker with taller tires due to the gearing better matching the torque curve of the engine for street use? Performance off the road will be a wash because IMO it's a negative in that you're gearing it higher, but it's a positive that you have greater ground clearance and more of a contact patch. I realize 1" in tire size is not going to change gearing very significantly ....but it's still there none the less. This is an overkill amount of analysis for going up one tire size but I always think things through vastly before I ever start. So those of you with 31x10.5's on otherwise stock LJ's ...how do you like them and what are your answers about performance on and off the road? Have you noticed an impact on MPG? Surely it looks better with 31x10.5 tires ....that has to be the one thing most all would agree on BTW in case it's pertinent to my questions I WILL NOT be doing any suspension upgrades other than future stock-type shock replacements that are a step or two over stock (like a Koni or whatever), this Jeep is slated to be my daily driver once I sell my Buick Riviera. Haha I'll shut up now ....anyone care to tell me how they like their 31x10.50
s on their otherwise stock LJ's? Thanks.

[RogueSpear2023]

I don't think you will notice any difference in any of the above, may here run 31s with 3.07s and don't complain. I have 31s with 4.10 gears, 42RLE, and a 4.0L, I get about 16-17city, and 18-19hwy. Go for 31s you won't regret it.

[CB3]

I think a 31 or 32 X 10.5 would be much better for you.

I am an advocate for 10.5 wide tires for an LJ because I've tried 33 X 11.5 and 33 X 10.5 on my LJ. The 11.5 floated to much, and the 10.5 floats just perfect. I think that a 9.5 would not float enough (unless a 34+ tall).

So for you a 31 or 32 X 10.5 R15 would be ideal for amount of flotation, IMO.

For gearing and braking, it'd be fine. You probably wouldn't notice any difference from stock.

[hawk3ye]

Imho, you seem to be over thinking this tire choice but the funny part is I totally thought along the same lines as you when I first got my jeep.

31s were my first upgrade on my TJ (sorry i know you asked about LJs)...I guess the main question to you is, what do you plan on doing with your jeep? are you going to wheel it on easy or moderate (or higher) trails? If you're just going to use the jeep as a daily driver and for weekend warrior trips to some dirt roads, the 31s will be plenty fine for that type of use without loss of highway performance either.

Personally, I just joined a jeep club and we've hit up some trails about once a month now - my 31s are holding up okay on my stock suspension setup but in about a year or so I'll look to move onto some 33s and prolly a 2.5 inch lift.

[mdm]

You are WAY overthinking this. The difference in COG, steering, MPG, ... between 30" and 31" tires is just about unnoticeable. 3.73 gears will handle 31" tires with no problem, you'll barely notice the difference. The biggest difference is that your speedometer will most likely be more accurate with the 31" tire.

[05Unlimited]

Originally Posted by mdm

You are WAY overthinking this. The difference in COG, steering, MPG, ... between 30" and 31" tires is just about unnoticeable. 3.73 gears will handle 31" tires with no problem, you'll barely notice the difference. The biggest difference is that your speedometer will most likely be more accurate with the 31" tire.

Awesome ...I figured I'd have to deliberately drive a little slower to not get speeding tickets. So from what you're saying with stock tires when my speedo says 75 MPH I'm really going more like 74 MPH, and the 31" tire will probably correct this without overcompensating much if any, that's nice to know. Well I realize I over thought this but what the heck why not since I have time to (not replacing them until spring or summer ...whenever they're worn down).

To the other posters yes, it will predominately be a daily driver and I probably won't get into serious wheeling. Mostly ridge running along easy to moderate pipeline trails maybe a dozen times a year ....and I won't be doing lots of "mudding" because I hate cleaning it up and causing rust/corrosion. Of course, I've only owned this Jeep a couple months and have already had it off road twice and loved it both times ......

...so anyway 31 x 10.50 it will be when the time comes, thanks for the input.