Reply to "How to tell if speedometer is way off?"

Being a former Georgia State Trooper and Accident Investigator, the proper and most accurate method to check your speed is..

Maintain a constant speed, any speed, and measure the seconds per 3 miles. Divide 10,800 by the number of seconds it took you. The answer is your speed. This will also work with a tachometer as well. The formula is taken from 60 seconds per mile or 3,600/60 where 3,600 is a constant and 60 is the seconds it took at 60 miles per hour. The formula 10,800/(seconds per 3 miles) is simply more accurate. 10,800 is simply the constant of 3,600 multiplied by 3. To fix the problem will require mechanical means such as changing your tire diameter or by reducing the speedometer cable ratio. Most guage or speedometer service centers can make up a reducer. You will need to take your speedometer so they can match up the threeds to the head and you'll also need to tell them the results of your speed test so they can come up with a reduction ratio for your setup.

[This message has been edited by Pantera1252 (edited 02-26-2002).]