saabSean

Well, that's a different story. Carry on!

Capt William

A speedometer is an extremely simple device is this age of electronics. There is a sensor that counts the passage of either a piece of metal or a magnet that is rotating with the output of the tranny or possibly the wheel hub/brake disk. A crystal time base, which is accurate to better than 0.005% looks at the time it takes for each rotation or a number of rotations. The only significant source of error is the tire size, due to wear or non-standard tires. The speed signal sent to the speedometer is probably extremely accurate (excluding the tire size issue) but the analog meter movement is not likely to be nearly as accurate as the signal. There may even be an intentional error added into the system to cause you to believe you are going faster than you actually are.

The speed limiter only looks at the raw data from the rotation sensor so it will not have any of the inaccuracies that you see on the speedo and will cut the power at exactly the correct wheel rotational speed (not MPH).