How to Read a Tire Sidewall
There are many misconceptions out there about how to read a tire sidewall, and knowing what all those markings mean can save you plenty of headaches. Our best recommendation for your car, truck or SUV is to use the original tire sizing that the car was equipped with off the dealer floor. Doing this will help quite a bit in selecting the right tire for your vehicle, but that isn’t the entire story. There are many types of tires out there: some are best for certain conditions, others can be downright dangerous and all tires wear at different rates. You need to know what all of those markings on your tire’s sidewall mean for the safe operation of your vehicle – it may even save you some money in the process.
First off, you have to select the right tire. If you are located in a warm climate like Florida, you can get away with a summer only tire like the one we have photographed here. This is a performance tire made by Falken Tires called the Azenis RT-615K. Clearly visible on the tire sidewall are ‘Falken’ and ‘Azenis RT-615K’denoting the make and model of the tire. These raised markings are usually the most prominent part on any tire since the manufacturer wants other motorists to know what tire your car is rolling on. But what about the other smaller markings, what do they all mean?
The next most important marking is the sizing numbers. This particular Falken Azenis RT-615K tire is a 205/50R15. Wait, what? Well that a blend of Metric, Imperial and a ratio that we’ll try to explain in detail. First off, the ‘205’ means 205-millimeters in width of tread that makes contact with the road, and for those unfamiliar with the Metric system (and most of us are) that equates to roughly 8-inches wide.
Why is the tire width not listed in inches? Well, let’s just say the majority of the world uses the Metric system; plus the Metric system is divisible by 10, making it easier to display different widths opposed to fractions like 29/32nds. The Euro-Metric standard uses varying width increments of 10-millimeters like 195, 205, 215, 225, 235, 245 and 255 to list some common tire widths. The widest tire commercially available is made by Pirelli – the PZero Nero maximum size is 405/25R24. At 405-millimeters in width, this tire is 16-inches wide!
Now the complex part comes in, which is the profile sidewall height. The sidewall height is neither millimeters nor inches but rather a percentage measurement. That ‘50’ seen here is actually indicating the sidewall height (measured from the edge of the tire to the edge of the rim) as 50-percent of the tread width. We know that the width of this tire is 205-millimeters, so the sidewall height is 50-percent of that equaling 102.25-millimeters, or about 4-inches. The higher the percentage, the more balloon like the tires appear, while the lower the profile the more slim it appears.
The lowest profile tire in the world is the Kumho Ecsta 385/15R22, which – using our math – has a sidewall profile height of only 2.2-inches. We have seen many tires changed in our day and tire techs struggle with the really low profile tires. Surely, a tire with a 15-profile would take well over an hour to mount as they just don’t have the elasticity of the tires with taller sidewalls. The other drawback of a lower profile tire is its effects on ride quality, as there just isn’t as much cushion to absorb all of the bumps and imperfections in the road. For better or worse, today’s trends point toward lower profile tires becoming the norm – it isn’t uncommon for companies to put on outrageous rolling hardware from the factory. The Cadillac Escalade was the first to feature 22-inch wheels from the factory, meanwhile the Dodge Viper rolls on 355/30ZR19 rear tires.
Next in the sequence is a letter that describes the construction of the tire. In this case the ‘R’ designates that this is a radial tire, as most tires on the road today are as a result of this designs strength and longevity. Typically steel-belted radials integrate thin steel wires to achieve the durability, however, this particular Falken tire uses polyester and nylon belting to save weight.
Lastly, there is another number that is easily the simplest of the bunch. The ‘15’ means this tire is mounted on a wheel that is 15-inches in diameter and will not fit on any other wheel. A 15-inch wheel is a bit of a dated size these days as, larger diameter wheels are the current trend. Some popular sizes also include 16, 17, 18, 19, 20, 21 and even 22-inches on stock vehicles, while the aftermarket has gone wild with 24, 26 and grown to 28-inch wheel diameters.
The second set of numbers, located to the right of the size, are the Load Index and Speed Rating. Each tire is designed for a different vehicle and purpose. The weights of vehicles vary and so do the speeds a vehicle is capable of. Tire sidewalls include numbers that can be decoded on corresponding charts to determine these capabilities.
On our Falken tire here, we see ‘89W’ after the sizing. The 89 refers to the Load Index of the tire, or simply put, how much weight the tire can handle on each corner of the vehicle safely. If we refer to the chart we see that ‘89’ equals 1,279-pounds (580Kg) as the maximum laden amount on each tire. So for this demo car, which weighs a little over 3,000-pounds with two passengers, we are well within that maximum load even with quite a bit of cargo.
The second part of that ‘89W’ refers to the maximum speed the tire can attain safely. This is our favorite part, as you can tell a lot about a car by the tires. In this case, the W refers to the second fastest tire that is manufactured, and as such can reach 168 mph (270km/h) in a safe manner without losing traction or having catastrophic failure. Of course, this should be achieved on a closed course or in a country like Germany, where the AutoBahn highway has no speed limit and you may even be passed by another motorist if you happen to be doing even 100 mph. But as you can see from the chart, each speed rating letter has a corresponding maximum speed, which the car should adhere to for safety and of course traffic laws.
You tire also tells you what pounds per square inch (psi) of pressure operates best at. Under-inflate and your tire can overheat and blow-out. Over inflate and the tire will handle strangely, wear very fast and can also fail without warning. On the sidewall, the tire will tell you what pressure the tire should be inflated to, which on this tire is 50 psi. Many modern cars have accurate Tire Pressure Monitoring Systems (TPMS) that inform the driver if there is a problem with tire pressures.
Since this is a performance tire, it should not be driven in anything below 50-degrees F. We know it is a performance tire by the UTQG-rating or Universal Tire Quality Grating, which in this case is 200-A-A. Basically the lower the first number the stickier the tire. We would go into it more but that’s a topic for a whole different article.
Your sidewall says a lot about your tire, and we’ve covered the basics here so you can tell your friends and coworkers all about what your car is rolling on. Chances are they have no idea what all those numbers mean either!