Tire Size Comparison: What You Need to Know (2023)

If you think that most vehicles—especially your own—would look better fitted with a set of larger wheels-and-tires, you're in good company—just ask any car designer. No wonder so many drivers outfit their ride with new, stylish footwear. For passenger cars and crossovers this almost always means going to larger-diameter wheels and lower-profile—and often wider—rubber. For trucks, larger can also mean fatter and knobbier, a look that says “I can conquer any terrain.” Ready to swap your vehicle’s shoes for a new set? Here’s how to find the right, larger tires that will fit properly, look bad-ass, and work well.

Three Things You Need to Know to Choose the Right Tires

Though a lot of the sexiness of upsized wheels-and-tires comes from the aftermarket wheels you’ll be bolting on, you first must pick the right rubber. After all, no one wants to waste their hard-earned dollars on tires and wheels that either don’t fit, hurt the performance of their vehicle, or pose a threat to safety. Whether you are looking for tires for a car, crossover, or truck, there are three important things to consider before you purchase your new tires: how you’ll be using your vehicle; the new tire’s overall diameter; and the width of the new tire. Also, you should be sure to consider the downsides of larger, heavier wheels and tires. Your vehicle's ride quality (and susceptibility to wheel or tire damage by potholes) as well as braking distances may be negatively impacted, potentially severely so, depending on how extreme you get with your wheel-and-tire size.

How You’ll Be Using Your Vehicle

Will you be taking your car to track days or competing in autocrosses? Or will you be driving it strictly on the street? If you’ve got a pickup, will you be going off-road, and do you want all-terrain capability?

If you are replacing tires on a passenger car, crossover, SUV, or truck how you answer those questions will determine whether you opt for all-season touring-style tires, high-performance summer donuts, or even track-capable rubber—though rare is the SUV or crossover that will see track time. Truck owners will need to decide whether they want strictly on-road light-duty truck tires or more aggressive off road-oriented tires. Sites such as discounttire.com and tirerack.com have detailed descriptions of the hundreds of tires they offer that can help you decide. Also of note is that Tire Rack tests tires constantly at its own on-site test track, so it has first-hand data on how many of them perform along with a comprehensive database of performance results and sizing options. As you narrow your tire choice, we suggest giving either of these tire retailers a call.

Tire Diameter

No matter what type of vehicle you’re picking tires for, one of the most important specifications to consider is the tire’s overall diameter. Tire diameter refers to the height of the tire from the road to the top of the tread. Tires with lower aspect ratios—shorter sidewalls—look cooler and generally perform better, so they’re what most people want when upsizing their cars’ tires and wheels. But your new, lower-profile tires’ overall diameter—which determines their circumference—needs to remain as close as possible to the diameter of the tires that came with your vehicle. Same for truck tires.

Why? A tire that’s too large or too small in circumference will affect the overall gearing of your vehicle; will throw off the speedometer reading; change the under-car ground clearance; might adversely affect the handling; and can potentially compromise the performance of safety systems like anti-lock brakes and stability control—which are engineered to work with tires of a specific diameter. Happily, there are dozens of lower-profile passenger-car and truck tires that you can choose from that will be close in overall diameter to those that originally came on your vehicle. The same goes for off-road oriented truck tires, which may not have lower aspect-ratio sidewalls.

If you’re going to larger wheels, Tire Rack offers a good rule of thumb for picking the right lower-profile tire to go with it—which we agree is a good starting point: for each one-inch increase in wheel diameter (going from, say, a 17-inch to an 18-inch wheel) decrease the sidewall height by five-to-ten percent and increase the tire’s width by 10 millimeters. It’s not a perfect rule, but it’ll get you close. You can see how it works in this comparison tool that’s on the tirerack.com site. Discounttire.com has a useful tire-size conversion calculator that enables you to compare the diameter (listed as “tire height”), width, and sidewall height of different tires that might work on your vehicle. Still, we advise giving their experts a call to discuss your choices before you buy.

Tire Width

Wider, lower-profile tires look hot, but be careful: this is the one dimension that’s both the trickiest to determine and the easiest to screw up. You need tires sized to clear the suspension components, the inner fender wells, and outer fender sheetmetal. If your tires (and the wheels they’re mounted on) are too wide, you’ll be miserable—even if the setup looks great when your vehicle is parked.

Tires that are too wide simply won’t fit within the wheelwells of your car; they might not allow you to turn the wheels to full lock for parking without rubbing on the fender lips or suspension, potentially damaging both the tires and wheels. They could also rub against the insides of the front or rear fender wells or against suspension pieces as the car moves up and down through its suspension travel over bumps or when it leans in corners—ultimately causing a tire failure. And as a matter of taste, too-wide tires might stick way out and look, ahem, dumb (though that look has nonetheless found favor with some car and truck owners).

When it comes to tire width, consulting forums focused on your make and model of vehicle can provide some insight about the tire sizes that will—or won’t—fit from others who have tried them, but it could also lead you astray. Again, the major tire retailers like Tire rack and Discount Tire have information that will help.

“We’ve digitally scanned a large number of vehicles’ inner fender wells to measure for tire clearance,” says Eric Vance, Tire Rack’s department manager of tire information, testing, and education. Those detailed measurements are stored in a database that powers the vehicle-specific wheel and tire fitment options on Tire Rack's site. Discount tire has a similar but less sophisticated database of fitment possibilities. But since Discount recently purchased Tire Rack, they too will soon have use of the database of scanned vehicles.

Also be sure to confirm that the tires you’re considering have the proper load rating for your vehicle, which ensures the tires can handle your vehicle’s mass. Lastly, ask the tire retailers for the recommended inflation settings for your new tires. When tire size changes, the required safe inflation pressure can sometimes change with it—so you’ll want to know the proper cold inflation pressure. Determining the correct psi (pressure per square inch) number “is a complex calculation,” says T.J. Campell, Tire Rack’s tire information and testing manager. “That’s something our sales reps can figure out for you.” Get the size right, and you should enjoy many happy miles of driving on your new set of cool-looking tires.

Find more information on tires at Car and Driver’s Tire Guide.

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