Can you trust your speedometer? Yeah, weird question. But maybe not so strange if you get a speeding ticket you thought you didn't earn.
Basic speedometers show a hand that will raise or lower, to the right and the left, when you accelerate or decelerate. Digital speedometers show the digits to display mph (or kilometers). But are these numbers accurate?
There are several ways to calculate a car's speed while driving, whether it's an old-fashioned speedometer, a GPS app, a third-party speedometer app or worst-case scenario, a police speed trap.
How do speedometers work?
Older vehicles use a mechanical speedometer with a cable that connects to the vehicle's transmission to display your speed. Modern cars have electronic speedometers that use the speed of your tires to display a reading.
What could cause speedometer inaccuracies?
There are several factors that could make your speedometer show an incorrect reading, one of them being your tires. Since modern speedometers operate electronically based on how fast your tires are traveling, if the tires themselves are larger, aren’t inflated at the right level or have low tread, that can lead to speed inaccuracies.
Another way could be the automaker intentionally making a vehicle display a speed faster than you are actually going. This is something that many cars do, especially performance cars to try to silently persuade the driver not to go too fast.
How accurate are speedometer apps?
There are several apps out there on the Apple App Store or Google Play store that have a live and accurate speedometer. Some are traditional GPS navigation apps while some are dedicated for speedometers.
Waze was one of the most popular navigation apps to use this feature. The app was purchased by Google in 2013 and some of its features have been implemented into Google Maps over time, including the speedometer feature. Google Support has a disclaimer about the feature. “Speedometers shown in the Google Maps app are for informational use only. Make sure to use your vehicle's speedometer to confirm your actual driving speed. “
After driving my personal car and several vehicles provided to the media over time, I’ve noticed the speedometer of my own car and the navigation apps are at the same mph, while some of the other cars I’ve driven are off by a few mph.
With so many ways to track your car's speed, just make sure you are going the speed limit and you should be fine.
Keenan Thompson is a car culture reporter for the Detroit Free Press. Contact Keenan at kthompson@freepress.com. Follow him on Instagram at @keenanautos. To sign up for our autos newsletter. Become a subscriber.
This article originally appeared on Detroit Free Press: Your speedometer may be miscalculating your speed. Here's why
