How accurate does a speedometer have to be?

How accurate does a speedometer have to be?

How accurate are speedometers? Dan Edmunds, an automotive engineer and the director of vehicle testing at, says that speedometers cannot have an error of more than 5 percent (typically expressed as plus/minus 2.5 percent relative to the actual speed) according to federal law.

What is the tolerance on speeding?

Most police forces have a tolerance of 10% plus 2 mph above the limit before a speed camera ‘flashes’. So on a 30 mph road, a camera wouldn’t normally activate unless a car drove past at 35 mph or faster.

Is it possible to make your Speedo and odometer inaccurate?

You just made your speedo and odometer inaccurate. Here’s how to fix them both. If you’ve ever modified a car with smaller or larger tires or, perhaps, a different final-drive gear, you’ve immediately screwed up your speedometer. This is, of course, annoying, but for modern cars with a digital speed sensor, there’s a relatively easy way to fix it.

What should I do if my speedometer says 52?

“If you need to slow down the speedometer, you need more teeth on the driven gear.” For example, if your speedometer is showing 60 mph and it should be showing 52 mph, you will need to use a driven gear with more teeth to spin the speedometer cable slower.

How do you change the gear on a speedometer?

Clip the new driven gear into place on the speedometer cable. Replace the gear housing cover and secure it in place with the bolt you removed in Step 1. Secure the speedometer cable back into position. Determine the distance of the test drive needed to recalibrate your speedometer.

How many teeth are in a GM speedometer?

The Turbo 350, Powerglide, and GM four-speeds have driven gears that have anywhere from 17 to 25 teeth. Speedometer driven gears in the Turbo 400 and 700R4 have between 34 and 45 teeth. In these transmissions, each tooth added or deleted changes your speedometer reading.