I've had 31's on my (unlifted) 87 Wagoneer for about two years now, and have obviously realized that they make a difference in the speedometer. However, I have almost never gotten pulled over, and the only time I've been able to test the speedo is doing 40mph (3mph off) so I just figured that it couldn't be THAT bad at the higher speeds.

BUT...I broke out the GPS for a road trip this weekend, and it turns out that once the speedo gets to 50mph, I'm actually doing somewhere around 57. And at 65mph (the speedlimit on all the highways around here) I'm doing 73....and if I just creep up a little more to do 70mph (per my speedo) I'm actually doing 80! Both the GPS and a "speedo app" on the iPhone confirmed this....and now I don't know why I'm not rolling in the speeding tickets!!

So yes, I now have a better idea of what speed I'm ACTUALLY going and could just keep that in mind while driving...but I'd really like my speedo to reflect at least CLOSE to what speed I'm going...not ten miles off....if it's possible.

Is there someplace I can go to get it recalibrated? (Please say Midas will hook me up? ) Or I KNOW there's some at-home fix!

Thanks in advance! And out of curiousity...what have the rest of you done? Do you just keep the difference in the back of your mind and adjust accordingly? Speed everywhere? (Which was apparently my choice!) Get it fixed?

And is ten mph off at 65 pretty standard for 31s on a Cherokee?

 

now remember gps and most other things like that usually have a +2 -2 grace period. i dont exactly remember the sight, but ill see if i can find it. It tells you the exact amount your speedo is off by putting in your original factory tire size and then the new size. I think it said going from a 235/75R15 to a 31x10.5R15 would have a difference of something like 7.6666775757576% which means if your speedo says you're going 55, you're actually going 59.4 or something like that.

 

True, but that still means that it's off by quite a bit (IE anything over 5mph) if I'm really doing 80 at 70. I like to speed anyway, so I don't like to think that I've been doing 5mph over and ACTUALLY doing ~15mph over.

 

Yeah im still getting used to the whole speedo being off thing, just got my lift and 31's on less than a week ago. From what i've heard all you have to do to correct the speedo is to get a new speedo gear (whatever that is) and from what i understand it's supposed to be easy to do and not too expensive

 

http://www.yuccaman.com/jeep/speedo.html Try this out. Once you Fig. it out, there is a speedo gear on your transfer case. Its as easy to change, one bolt. Hope it helps.

 

Assuming you have the factory 3.55 gears, you will need this speedometer gear.

 

Thats seems pretty expensive. I think it could be found a little cheaper somewhere else. Mabe someone has a used one with the correct number of teeths.

 

That one is the Mopar brand. This one is $39.99, the one I meant to link.

 

I just did this yesterday. I took out my stock 34 tooth and put in the 32 tooth that I got from Morris 4x4. Easy install. Mine has the short shaft so there were 2 bolts. Yours should have the long shaft. Mine is still off on the actual mileage but the speedometer reads right. I was in the middle of needing 33 and 32 tooth speedo gears and I went up for future tire upgrades.