Just bring a GPS deal in your car and see if it matches your speedo. There are phone apps out there too for GPS speedo, for your phone. These are great tools to see if the speedo in the car is accurate, or if you need to change pinion gears. I found that my car's speedo was WAY off, but using the GPS speedo in my phone, I was able to eventually get my car's speed pretty close to accurate, and what should have been in there for pinion wasn't even close to what I ended up with.............and no, I didn't get the second pinion right the first time either -- I believe I went through 4 different pinions to get the closest one. But it worked............

Good luck!!!!!!!!!!