How Accurate Is Your Car’s Speedometer?

If you’ve ever taken a trip and used your GPS device for navigation purposes, you might have noticed something about your speed. Your speedometer might be saying one thing, while the GPS device says another. That’s enough to get you thinking. “What if my speedometer isn’t all that accurate?” enters your thoughts. Then, your mind wanders back to all the speed cameras you’ve passed in recent times. Sure, you thought you were doing the limit, but what if your speedometer wasn’t all that accurate?

Car's Speedometer

Image credit: Pixabay

It’s an interesting topic of thought, and it’s one that we’re going to put to rest for you today. We’ve picked out a few key bits of information, and we’ve detailed them below.

Speedometers Must Not Have An Error Of More Than 4%

In the US, it’s determined that your speedometer should not have an error of anything more than 4% off. This could include two mph either way, and nearly every US manufacturer abides by this. Ideally, you want a nice balance. You might even find that it’s set a little higher to make sure you don’t go accidentally speeding.


Image credit: Pixabay

The European Rule Is Even More Complicated

The European Union sets a different rule for the countries which fall under its banner. There, no speedometer is allowed to read slower than the actual speed the car is going. However, it can go up to 10% above the actual speed itself. This results in quite a different speedometer reading to US vehicles in some cases.

speedometer reading to US vehicles

Image credit: Pixabay

But Is My Speedometer Working Correctly?

Ah, yes. We need to get to the bottom of this question. Well, we can’t say for sure. There are loads of ways to test it, though. We’ve already mentioned your GPS system, which is a good indicator on its own. Otherwise, why not get another GPS app for your phone and test that? If you want to go with the good old fashioned method, get a friend to use a stopwatch while you drive.

Can They Go Totally Wrong Altogether?

Yes, they can. If you’ve never experienced a faulty speedometer before, there are a few things you should know about. Of course, it can stop entirely, or it might wildly fluctuate while you’re driving. Also, that check engine light might not be a cause for massive concern just yet. A faulty speedometer can make these lights appear on the dashboard for no reason, too.


Image credit: Pixabay

But What If I Get A Ticket Because Of A Faulty Speedometer?

Ultimately, it’s your job to understand when your speedometer is faulty. That said, you could always challenge a ticket by going to a speeding ticket attorney. Whether you’ll win the case depends on the scenario. It might be worth a try, especially if you think you’ve got a good case.

Can Anything Else Affect It?

There isn’t much else you need to be aware of, but we’ll draw attention to your tires for a minute. Keep in mind that badly underinflated or overinflated tires can affect the reading, too. Keeping your tires in top working order is crucial in any case to ensure your car remains safe.