Tires and Rims
by Joel Jacobson
If you’ve ever needed to buy new tires and rims for your vehicle, but were totally confused by the nomenclature and gobbly gook associated with buying them? Well, do not feel ashamed, because most people are confused by all the extraneous information provided on sidewalls of tires.
Click on the Image for a Bigger Tire Diagram
Let’s take a look closer at how tires and rims are measured. For example, you have a P18570R14 tire. The P means it’s a passenger tire. European tires typically don’t have the “P” designation, and if the designation starts with LT, this is a higher ply tire and stands for “light truck”.
The section width, when measuring tires and rims, is measured in millimeters, which is 185. If you would like to convert to English, take 185 divided by 25.4, which equals 7.28”. Also known as the section width, this is the width from sidewall to sidewall when mounted on the recommended rim.
The next number, 70, is the Aspect Ratio when measuring tires and rims. It is calculated by dividing section height by section width, multiplied by 100. In this example, the sidewall will be 70% of 185.
The “R” designation stands for radial construction. Other designations include “B” for belted, and “D” for diagonal.
Lastly, the final number when measuring tires and rims is rim diameter. In this example, the rim diameter is 14, in inches. This is the EXACT size rim the tire will fit. There are some older rim designations called TRX, which is a metric conversion. You CAN NOT mix TRX rims with regular tires. They will not work!
Now that you have the correct tire size for your vehicle, it’s much easier to pick out the type of rims you would like. Tires and rims are usually sold together as a package for standard tires (like when you buy a vehicle). But if you want something aftermarket, customized, and REALLY cool, there are a ton of custom rims that are available to choose from.
Changing the tires and rims is the number one single improvement modification that can be done to a vehicle. The reason is because the modification is visual. It’s what everyone sees first. You can get spinners, lo-pro, aluminum, polished, and spokes, just to name a few.
So if you’re into pimpin’ your ride, or just trying to get a decent and dependable set of wheels for your car, it’s essential that your after-market dealer or your nearest tire dealership gets the correct size tires and rims. Otherwise, you may as well just take the bus!
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Mr. Jacobson is a freelance writer, web designer, and product design engineer. He's an avid fisherman who loves to northern and musky fish. He and his wife recently adopted two infant girls from Russia, and that keeps them quite busy.