Can you believe that within the first 3 weeks of owning my Jeep, I got a speeding ticket? A speeding ticket in a Jeep! Not on the back roads – on the highway! The police officer should have been embarrassed to give it to me!
I think my Jeep originally came with 16″ wheels and small tires because there was a P225/75R16 tire mounted in the spare position. When I bought it, the Jeep had 17″ wheels with larger P255/75R17 in the (4) driving positions. So as you know, when your axle spins at a certain number of revolutions, your vehicle will measure a certain mph. If you go to a larger size tire, your axle is spinning at the same number of revolutions, but because the circumference of the tire is larger, your vehicle will travel further per revolution, thus increasing your mph. I found a web-site where you can punch in (2) different tire sizes to see the mph reading given the original tire size vs the actual mph with the new tire size. For my Jeep, the difference would have been as shown below:
Before I use this information to deny any and all responsibility for my ticket, I guess I should tell you that I got ticketed for going 20 mph over the speed limit. Even if I used my new found tire conversion information to plead my case, I would have been shown to be speeding. Crap!!! After several hundred dollars leaving my wallet to avoid my insurance rates jumping way up, I needed to find a solution to this problem. Well, the problem of my speedometer not showing the actual mph…
I was thankful to meet Chris Crecelius, Hypertech’s National Sales Manager, at the 4WD Hardware Jeep Jamboree recently. Chris told me about Hypertech’s Speedometer Calibrator and offered to sponsor our Jeep Build.
The Speedometer Calibrator is vehicle specific and comes with a quick start instruction card that features a QR Code Scan to get a full set of instructions. My first step was to remove all devices from vehicle chargers and turn off windshield wipers or any other items that use power from the battery. I turned the Jeep’s key to the run position and plugged the Speedometer Calibrator into the Jeep’s diagnostic port, located under the driver side dash.
It is best to climb in and close the door so you don’t have to listen to the door open beeping the whole time. In a mater of 5 minutes, the Speedometer Calibrator walks you through a quick set of diagnostics and then asks for your tire size. I punched in 35″ for my BF Goodrich T/A KO2s and I was all set.
If you have changed your gear ratios, you can also use this unit to re-calibrate your speedometer to reflect the change in ratio as well.
This process couldn’t have been any easier and now I will be able to see my true speed while driving around town. Re-calibrating the speedometer might also prove extremely beneficial on our trek out to Vegas. I don’t want me or any of my co-pilots to get a ticket on that long long drive. Really? In a Jeep?