Maybe someone had installed some electronic widget to tune the speedo based on some other mods?

 

I know someone who got caught doing 100 mph in their s2000. They used this little yellow box to fudge the speedo and took it to a tester guy. It held up in court just fine. Got off with a much lower ticket.

 

When you change the rear tire size or rear end final drive, it effects your actual speed in relation to what your seeing on the dash, the dash is not re calibrating itself, it is just inaccurate at that point. The "yellow box" being referred to is sold aftermarket as a programmable calibrating tool to compensate your re gearing to match what your seeing on the dash to regain accuracy again.

 

I put 17" AP2V1 wheels on my '01 AP1. How much error am I seeing on my speedometer and odometer?

 

The wheel doesn't change the speedo the tire size does. If the tire is taller than your stock tire the speedo will show slower than what the car is going. If the tire is shorter then the speedo will read faster than the car is going. I run tires that are 3.8% more in circumference than stock so I have to add 3.8% to the speedo to get the correct speed and I have to add 3.8% to the mileage to get the correct mpg.

ROD

 

My front tires are 225/45zr17
The rear tires are 245/40zr17

I'm not sure how they measure up to original stock sizes.

 

I used a gps app on my phone and my garmin to check my speedo.