When you shop for tires, or even if you are in the auto parts store for something other than tires, you’ve likely seen tire ads with specs listed on them. A handful of numbers, letters, and facts are listed like speed rating, quality rating (UTQG), size, style, load range, and so on. You might even see a p-metric or euro-metric. Here's what they mean.

What’s the difference?

The tire size 215/60R16 is a euro-metric size, and P215/60R16 is a P-metric size. So what’s the difference? They both have the same measurement. The tire is identical in physical dimensions, however their composition can be different in many cases.

Euro-metric tire ratings began in the 60’s. It’s a simple way of measuring a tire in millimeters, and a straightforward calculation shows the aspect ratio, or height, of the tire compared to the width. Because different vehicles have different load requirements, automotive manufacturers would have tires developed to match their needs. Over time, several combinations of load capabilities and sizes emerged to fit those needs. A broadly used system was needed to create uniform sizing.

The P-metric system began in the 1970’s in the US. It rates a tire according to its load-carrying abilities, physical size, and its tire pressure capacity. P-metric tires are used for passenger-carrying vehicles such as cars, vans, and small trucks. It uses a formula for the load rating, so all auto manufacturers are able to engineer vehicles around a specific tire size or ability.

This article originally appeared on YourMechanic.com as Converting Euro-Metric and P-Metric Tire Sizes and was authored by Jason Unrau.

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