I know this has been answered in different versions. I know i would prefer not to do it...my jeep is good for driving, but not where i want it, but it's getting pressed into emergency service tonight and tomorrow.

leaving it in 2wd, and driving it for about 40 miles at street speed, 45 mph and under.

fronts are 225 45 18
rears are 245 40 18.

These are used wheels i bought because i liked them, and they fit. the person i bought them from had staggered sizes. all the wheels are the same wheel. just the tires are different. Before regular use, i'm buying the same size tire for all. I just haven't driven the truck since january mostly.

Is the emergency use of 40 miles or so in this state going to hurt the truck, diffs, trans, or etc? the rears at 245 40 18 are a little taller than the fronts at 225 45 18...

Again, this isn't long term. I know i need four identical tires. I just didn't plan on it being on the road until i got that done, but i need the truck to do truck things tonight.

As long as you have factory diffs and it is in 2wd you should not have any problems.

I think even 4wd would be ok AS LONG AS as your xfer case has 4WD full time mode (part time would link the front and rear drive trains mechanically with no ability to spin at different rates - bad idea with different sized tires).

I don't have the full time 4wd. i have the one with the 4 lo, 4 hi...i don't remember which case that is, but I know better than driving it in either 4wd setting on dry pavement, let alone with different sized tires. I have the factor diff/tcase setup.

It's 80 and sunny, so 2wd will get me wherever I need to go. My girlfriend is moving in with me, and she loses her apartment tomorrow basically. My daily driver is in the shop, and so i needed my jeep to help out. she only lives 5 miles away. Push come to shove, I could find a substitute vehicle, but it would be VERY hard on such short notice. We didn't think she'd be able to so soon, so we weren't ready for the sudden deadline.

So, you've got the 231 with 2wd, 4wd and 4lo, correct? As long as you keep it in 2wd, you'd be okay. Even if you HAD full time 4wd, you'd put a strain on it. Not enough to break something, but enough to not make the t/case happy.

Thanks guys. I knew there could be trouble based on details. I think given the circumstances, i'm going to do what i have to do then park it again. I'm happy with where it's gotten during my project, but real life has gotten in the way too often recently.

The main thing I was worried about was friction during 2wd operation or something like that.

A quick search says that the tires are off about .25" in diameter. Thats not really enough to worry about. Leave it in 2wd and go drive it!

No, the only thing is the engagement sleeve inside the t/case for the front axle will be turning at a different rate than the output shaft for the rear axle. It'll only be turning because it's driven by the front diff. Not a problem unless you try to shift it while in motion. Keep you hands off the t/case shifter and you're golden.

Front shaft doesn't spin at all if you have the vacuum disconnect, so a minor difference if you don't have the disco shouldn't matter.

You're exactly right, especially since we don't know what year jeep he has.