Tire Size and Safety Tips

Reader question:

I have a truck and changed from the smaller tires that came with it to a larger sized tire. Will this affect the reading that the speedometer gives?


That’s not the main problem.

Changing from the tire that is recommended for a vehicle can have a lot of negative effects, and some might not manifest, but some may, and the least important of all is whether or not the reading on the speedometer will change. There are more important things you should concentrate on in a case like this, such as what will change about the safety of the car or how the car will handle itself with the different sized wheels.

Manufacturers test their vehicles for things like safety, the way that they handle cargo and their ability to handle a certain amount of it, and the way they handle with a certain kind of tires. If you change the tires, then all of this research goes out the window and you can’t be sure that the truck will continue to behave and have the same capacities that you were promised when you purchased it. That doesn’t mean that a different kind of tire is necessarily bad and will get you into a car accident. It may be fine. It just hasn’t been tested, so you can’t know for sure.

If you want to replace your tires without running into a problem, you should get the kind that have the same, not similar, specifications as the old ones. Your manufacturer might have certain suggestions when it comes to tires, such as that you should avoid wider ones, so always check your owner’s manual or head to the internet and look at the website of the manufacturer before making a big decision. Watch it when you go to get a new tire, because the tire seller might just try to pawn off what they have for you, even if it doesn’t work for your truck.

To answer your original question, though, the speedometer reading will only change if your new tires have a smaller aspect ratio. If they due, the speedometer will say that you’re going faster, probably by about five miles, than you are really going.


Fashun Guadarrama.

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."