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jbone303 01-31-2006 10:47 AM

will 31 10.50s change the speedo?
Just put new rims and tires on. Went from 10 speed tires to 31 10 50 super swampers will this change the speedo Jeep seemes like it's driving slower than im really goping but cant tell the whole new tire and wheel thing Thanks for any help.

amerijeep 01-31-2006 10:55 AM

I did a little math, which I am not good at, and when your speedo says 60, that should be just over 67 mph. Hope this helps you.

khenderson 01-31-2006 10:58 AM


Originally Posted by jbone303
Went from 10 speed tires to 31 10 50 super swampers...

hahaha. that's pretty funny. i'm asuming by 10 speed tires, you mean the stock 215/75's, then you're speed will change, probly by five or so mph. here's a link for changing the speedo Speedo change

edit: looks like someone else actually did the math. woo-hoo for them! :flipoff:

amerijeep 01-31-2006 11:04 AM

I could set up a little conversion chart that could be refered to here on WF. I'm not sure if I can do it on a wide range of tire sizes though. I'll have to do some numbers and see how it comes out. I said before that I am not good at math. I'm actually good at it, but it gives me a headache.

RWsJeep 01-31-2006 11:29 AM

I went from 225/75R15's to the 31-10.5's. At 70mph my spedometer shows about 66mph.

amerijeep 01-31-2006 11:52 AM

Well, there is no way to make exact calculations when you don't have all the variables. That is pretty close to what I come up with. You are going a little faster than what tyhe speedo says. I'm in the same situation, but I don't worry about it.

The easiest way to check your own speed is to get on the highway and cruise at 60 mph. Time yourself between mile markers as to measure one mile in 60 seconds. Whatever the variance is is how much you are off.

I have comrade on the police force and I had him clock me to check how much I was off.

Tdad 01-31-2006 06:53 PM

Here's another good page that shows how to change the speedo gear. They cost like $15 at the dealer. Remember, your computer uses the vehicle speed as one of the inputs while it makes mixture, timing, etc adjustments, so it's not just that your speedo is wrong.

kbart 01-31-2006 08:20 PM

I went from the stock 30x9:50's to 31x10:50's, I checked the speedo on a 10 mile straight section of road with the mile markers posts. In 10 miles my odometer said 9.8 miles, so my speedo was 2 tenths slow or 2% slow (at an actual 60mph the speedo showed 1.2mph less or 58.8mph. That's not enough for me to worry about correcting. Your difference will probably be worth correcting because of the greater change in size. It's all percentages at 30mph my speedo is only .7mph slow. Hope this helps.

+spook+ 01-31-2006 08:43 PM

On Jan 20th, I went to Nashville, Tenn and purchased a 2001 TJ , 4 cyl, 5 speed with only 19002 miles and a one owner. We went in my wife's car and when we got back home, my wife's car showed 442 miles and my new TJ showed 398. I was running 31-10.50/15. My speedo was about 5 mph slow at about all highway speeds. Was also going to check the gas mileage but forgot to write down the mileage when I filled up about half way home.It had BFG mud tires on and now has BFG 31-10.50/15 AT/KO. Less sound and a great ride.

SouthTJ 02-02-2006 04:19 PM

Well, I think it depends on what you started with. My 04 came with the 30in package and I upgraded to the 31 MT/Rs. I checked my speed and mileage against my GPS and my spedo is dead on. Before the new tires, I had noticed my spedo being a little off but not anymore. But since you started with the smaller tires that would account for it feeling slow. Check it with a GPS if you or a friend has one.

jeeperx2 02-02-2006 10:36 PM

i started with an 04 x model also 10 speed went with 33x12.50(also 4" lift) and it slowed speedo about 7-8 mph.

jeepmutt 02-03-2006 03:59 PM

I run 31's as well. I used my handheld GPS and find that I run about 2-3 mph off what the speedo reads. If it says 50mph, I'm doing about 53mph.

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