After adding larger tires and rims to my '09 JKU, I knew my speedometer was off. After a quick search, I found the "Neo Speedometer" App on my iPhone and decided to give it a shot. While I was waiting for my AEV Procal (wonderful product by the way!) to arrive, I tracked the Jeep's speed several different times. It seemed to be pretty accurate. Once the Procal arrived and I re-calibrated to the correct tire size, and I took more readings. Again... no complaints.

Just to see how accurate the Neo Speedometer actually was, I checked it against the RADAR in my patrol car. To my surprise, it was spot on! I did this at various speeds and I can honestly say it was never more than 1 mph off. I am in no way affiliated with AEV Procal or this App, but I would definitely think about getting it if you are running larger tires. Obviously, your cellular strength and/or other variables will have some bearing on the accuracy, but I thought some of you may find this useful until you are able to re-calibrate your speedo.

 

that's cool ill check that one out. I use ihudlite, its a heads up display that shines on ur windshield and its free