so i have a 01 sport, and just recently put a 2" budget boost on it, as well as some 30x9.5 tires. i was curious as to how much my speedometer would be off after the changes, so i grabbed the gps out of my wifes car and hit the interstate.

now on the inside of the door it says that the factory tires should be 225/75/15, so one would assume that the speedo would be calibrated accordingly to that specific tire size.

as it turns out with the new 30" tires, the speedo is DEAD ON!!! i tested this out at a variety of different speeds , from slower 25-35 mph stretches all the way up to 80mph.

just thought that it was interesting that my speedo was off at the factory tire size. it was bone stock when i got it, so the chances of someone swapping the speedo gears is very slim.

has anyone else found their speedo to be off like this??
kinda strange.
perhaps it was a jeep ploy to keep people driving under the speed limit!!

 

haha thats odd. I do know that when i drove with my 30s it felt like the jeep was set up perfectly for them, where as the 225 were too small as i could easily spin them in the dry with all terrains at lights and not really try and with the 30s i could still spin them but i knew that i was instead of it just happening you know?

 

Pretty weird, though mine is pretty close with 31's. Only off by 5 mph at 70

 

Mines off by 8.7 percent.

 

As far as the speedo goes, I read a thread on here speculating that the speedo is a little generous in order to keep speeding down. I don't know how likely that is, but I do know that mine is off about 2 MPH over 60MPH, so I think 30's would be about perfect for that.

 

My speedo also was dead on when I ran 30" Revos on the XJ. Thought it was odd, but I was pleased.

 

Grrr! I'm on 2" BB w/30's and mine reads about 2 mph slow.

 

I drive by one of those laser speed things that tell you how fast you are going every morning on my way to work, every single time I pass it, I am doing exactly 3 MPH less then what my speedo says, and I am running stock size tires.

 

Spedo was overstated on the stock tire, now running 31-10.5x15, run by the roadside radar, speedo is right on, there are not answers to some questions