Have you ever looked at your tires? I mean really looked at them! If so, you might have noticed there is a strange sequence of letters and numbers on the sidewall. Perceive this “code” like a shoe size for your tires, although it’s a bit more complicated since there are more factors at play besides length and width. Here are seven essential things to know about your tire code.
Let’s Dig Deep into the Meaning of Your Tire Code
Here’s an example of what a tire code looks like:
P195/55R16 87S
(Note: I will bold the letter or number I’m referencing throughout this blog for the purpose of clarity.)
The first letter describes your tire’s purpose in life. In other words, what work is your tire meant to do?
“P” stands for passenger vehicle. Unless you drive for a living (or own a boat), this might be the only tire code you’ll ever see since it covers cars, vans, trucks, and SUV’s.
Just in case you’re curious, I’ll share a few more examples. “LT” stands for “light truck.” If you tow or drive off-road in your truck/SUV, these might be the most functional tires for you.
Understand: Some trucks and SUV’s can operate with “P” or “LT” tires. The best choice depends on how you use the vehicle. If you haul heavy loads or drive on gravel roads, consider switching to “LT.” Otherwise, you can expect better fuel economy and a smoother ride from “P” tires.
“T” stands for temporary. You’ll find a “T” on your spare tire, because it’s only meant to be used when you get a flat (and replaced with a “P” tire as soon as possible!). Lastly, “ST” stands for special trailer. These tires are designed for utility trailers that haul boats, cars, and assorted heavy objects.
How Wide Are They?
P195/55R16 87S
Next, let’s look at the first three digit number on our imaginary tire. This means the tire’s section width is 195 mm. Section width is calculated by measuring the tire’s sidewall at its widest point.
How Tall Are They?
P195/55R16 87S
On the opposite side of the slash (/), we have a two digit number. This represents the tire’s aspect ratio. It’s not measured in millimeters like section width. Instead, this indicates your aspect ratio is 55%.
How’s that? It’s simple math. Aspect ratio is calculated by dividing a tire’s height and width. In other words, our hypothetical tire’s height is 55% of its width. Here’s an equation to illustrate what I mean: 195 mm (width) x 0.55 (aspect ratio) = 107.25 mm (height).
How Were They Created?
P195/55R16 87S
I’m not going to spend much time on this point, because 98% of tires are made in the same exact way. “R” stands for radial construction. Unless you’re an auto professional or enthusiast, don’t worry about what that means.
That said, you should be mindful of one more possibility. “D” stands for diagonal construction. This designation is reserved for light truck and spare tires. They heat up quickly and result in a bumpy ride, so don’t use these them unless you have a good reason!
How Wide Are Your Wheels?
P195/55R16 87S
This two-digit number signifies your wheel diameter. It’s similar to measuring your tire’s width; but unlike section width, wheel diameter is measured in inches.
How Much Can Your Tires Lift?
P195/55R16 87S
Do your tires even lift? (They’re bearing thousands of pounds every day, so I hope so!)
This number reveals the tire’s load index. The higher the load index, the more weight a tire can support.
In this case, 87 translates to 1,201 pounds. Here’s an interesting chart of different load indexes available for the curious.
Note: one tire can carry 1,201 pounds (or whatever fits your load index). So you’ll need to multiply the load index by four to determine the maximum weight your vehicle can handle.
For most drivers, this isn’t a big deal. If you’re hauling a boat to the lake or RV to the park, that’s a different story. Make sure to do your math and confirm your tires are strong enough to bear that load!
How Fast Can Your Tires Move?
P195/55R16 87S
We’re in the home stretch! The last part of your tire code describes its speed rating. I’ll make it easy to remember. Family sedans and vans typically have a speed rating of S or T.
While you shouldn’t drive recklessly (unless you want to end up on an episode of Cops), those types of tires can travel 112-118 MPH. To compare, spare tires (speeding rating: M) can only go 81 MPH safely.
Why make tires that can go faster than is legal? Remember: we’re not the only country that drives cars. Germans drive too; and unlike us, they don’t have a strict speed limit! Thus, the need for a speed rating. Here’s a list of every speed rating on the market. If you’re trying out for Nascar, I recommend a Y or Z!
I hope you learned something new about your tires!
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