It should be the simplest thing in the world: How big are my tires? There can’t be that many tire sizes, right? It’s just like buying a pair of shoes for your car. Easy. Unfortunately, we have many more tire sizes than shoe sizes (which seems odd). There are different specs for width, sidewall height, and wheel size. Oh, and by the way, if you’re buying wheels, it’s even more complicated. But for now, let’s stick with the tires.
First of all, this is important info to have on hand. If you’re somewhere civilized like Kansas City or Dallas, we here at Zohr can help you find the right tires. Just let us know what you drive and if your wheels are stock. But if you lose a tire in the middle of Nowhere USA, and you limp on a donut into Bubba’s Discount Tires, Bait, and Video Rental, you should be able to tell Bubba what tire you need.
Check the Side of the Tire
If you can see your existing tire, just look on the side. You’ll find the tire measurements there. Simple, really. Tell Bubba to get a 235/65 R17.
But let’s say you’re away from your car for some reason. Or perhaps someone stole all your tires… Just open your driver door and you should see a sticker on the sill. This sticker has the stock sizes for your front and rear tires, as well as the manufacturer recommended pressure specs. And if some complete walnut painted over this sticker like the guy who used to own my WRX, you can always just look it up online. Wheel-Size.com is a great place to start, or you can always use Zohr’s tire search tool.
But what do these numbers mean?
Your tire size contains four key pieces of information: Tire width, aspect ratio, construction, and wheel diameter. Let’s start with an example size:
235/65 R17
235 is the width. This is measured sidewall to sidewall in millimeters. Our tire is 235 mm wide. Some cars, namely performance cars, have different tire sizes front to back. For example, the 2019 Corvette ZR1, the last cool Corvette, has 285 front tires, but chonking 335 tires in the rear. This is to help transfer its 755 horsepower and 715 lb-ft of torque to the road.
Width is important to know, because if your tires are too wide, they simply won’t fit. You might think they will, but once you bolt up your front tires and try to make a turn, you might hear a deep rubbing sound. That’s a too-wide front tires scraping away the plastic on your inner fender. There is usually some allowance with tire and wheel width, but that’s something you’ll have to research for each car.
65 is the aspect ratio. This measures the height of the sidewall relative to the width of the tire. Yes, it would’ve been simpler to just measure this in millimeters, but whoever came up with this system was probably very bored and decided to mess with us. So a 65 sidewall is 65% of the width. Again, it seems a bit lazy to not just say “153,” but there we are.
Again, knowing the aspect ratio is key. Often, if you want a tire with a taller sidewall than stock, you could encounter rubbing. Remember, wheels move up and down, so just because something fits when the car is up on a jack doesn’t mean it won’t chew up your fenders when you hit a bump. Skinny sidewalls might look cool (if you’re into that kind of thing), but they can lower your vehicle and mess with your ride quality. Just stuff to consider.
R is the composition. Most drivers don’t even need to know this, but you’re here to learn, and I’m going to shove this knowledge into your brain like it’s carry-on luggage.
Most passenger tires on the road are “R” tires, which means radial. This refers to how the steel belts within the rubber are arranged. Radial tire belts run in parallel lines across the rolling axis of the tire, while the other type of composition, bias ply, uses a diagonal arrangement. Radial tires generally have a longer tread life, while bias ply tires offer stronger sidewalls. Almost all passenger cars use radial tires. Bias ply tires are often found in off-road performance vehicles.
Finally, 17 refers to the wheel size. This is measured in inches, not millimeters. Thanks again, bored tire industry founders. Obviously, an 18-inch tire won’t fit on a 17-inch wheel. But it might look like a 16-inch tire might. This is how tire beads (the part that seals against the rim of the wheel) get torn. And there’s no repairing them. Use the right size and you’ll be good to go.
So now you know how to find your tire size, what those numbers mean, and exactly how inconsistent this silly measurement system is. No, buying tires isn’t as simple as buying shoes. But imagine how comfortable your next walk would be if your shoes were this customizable.
As always, count on Zohr for the right size tires, delivered and installed by our mobile tire technicians at your home or office, on your schedule.
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