Need Speedometer for RC car or something to record max speed
I'm trying to record the max speed (mph) of how fast my rc car is going. I have an iphone I tried every app I could find and none of them are giving me accurate readings, some not recording any speed at all. I bought a Garmin Forerunner 201 it looks like it's tracking the speed on the device while it's running because when it slows down and I catch up to it I can see the MPH decreasing. However when I check the history, it always gives me the same stats like 3 mph one time I got 10 mph and there's no way my jato is going 3 that slow. I guess it could be the device itself since I bought it used but, not sure if I should buy the same thing again or buy a different device.
What can I use? I probably need a GPS device that will record max speed. I don't want to install telemetry or anything that has to be actually installed into the vehicle and plugged into the receiver etc. I have some other things that I need to measure the speed on that are not hobby grade rc cars.
Any suggestions?