***uming it is in a car and working, get a GPS unit and travel at a set speed say 60 to make it easy. The GPS will show the speed, take a reading off the speedometer and compare the differance. If you have a cable drive you can count the teeth on the gear and change to the correct gear. TCI sells gears and can tell you which one you need.
If the available drive gears don't get you close enough it is possible to get a small gearbox that goes inline with the cable. Those can be ***embled with a wide variety of ratios. Depending on what you need and where you get it, cost ranges from u8nder $100 to $150+.
If you don't have a GPS, just use the mile markers on the interstate. At 60mph indicated, it should take 1 minute to travel 1 mile. If your time is off, you can calculate your actual speed by using the formula of: Speed=Distance/Time. Once you know your actual speed, you can get the correct gear for the cable.
there used to be a speedo shop down in the industrial park areas between Marginal Way and toward town on one of the long numbered streets (3rd/4th Ave S/etc). Should be in the phone book if they're still there. Started using their services when I moved to Seattle back in the late 60s....
Most speedometers are calibrated to a standard ratio. Are you looking to have a ratio box built to compensate for tires, etc, or is the speedometer itself doing anything funny?
If having the incorrect gear for the rear end is the problem you idea will work great. If the speedometer is the problem (such as losing its magnetism, needing lubrication) changing the gear will correct the speedometer but you will then have an odometer problem. A little more history might help. Here in California the AAA has a unit that travels to the different offices and will calibrate your speedometer for free. You might call the highway patrol and see if they can suggest anyone, tell them you are trying to make sure you obey the posted speed limit. Charlie Stephens
The Jalopy Journal
