Whatever vehicle you use, whether it has two wheels or four, and whatever horsepower you have on your ride, most people fail to realize that the only things responsible for putting all that power down to the road, are your tires.
Tires are a critical part of your vehicle as it directly affects the handling, grip, traction and maneuverability. It’s not just the dynamics of the vehicle that are dependent on your tires, but also the fuel economy and life of the tires themselves. Tire pressure is something to be taken seriously, and regular checks are necessary for those vehicles that are not equipped with a tire pressure monitor. So enough about tires, and lets talk about the tire. If you’ve looked at your tires, you’ve probably noticed many numbers and if you’ve wonder what they all mean, this is where you get all your questions answered.
The tire size meaning is dependent on four factors – width or tire section, height or tire profile, type of design and diameter. Let’s consider a common car tire size which is used on most sedans 225/50 R17. Here, 225 signifies the width of the tire in millimeters. It’s interesting to note that a motorcycle tire size always ends with a 0, while that of four wheel vehicles ends with a 5. That means, you can have a 190-section for a motorcycle, but a car will use a 185 or a 195-section.
Now onto profile. In the above example, 225/50 R17, 50 is the aspect ratio, or the profile of the tire as a percentage of it’s width. The higher the profile, the taller the side wall of the tire will be. The side wall is the rubber between the outer belt that is in contact with the road and the outer edge of the wheel rim. So, a 225/45 R17 tire will have a lesser diameter across than a 225/55 R17 tire.
“R” signifies that the tire is a radial. Which means that it has steel belt across the section, or circumferential width. This provides added strength or durability and improves the life of the tire. If the tire is not a radial, it will have a number of plies. This is mentioned in the ply rating on the tire. In that case, the tire size would read, for example, 225/50-17 8PR.
Finally, “17″ signifies the wheel rim diameter on which the tire is mounted. This has to be the inner diameter of the tire. You cannot use an R18 tire on a 17″ wheel rim or vice versa. Another important aspect, is the width of the rim, which is usually mentioned in inches as 8.5×17. 8.5 inches is 215.9 millimeters. Which means you can have 225, 235 or even 245 section tire sizes mounted onto this rim. However, you have to ensure that the tire isn’t too wide for the rim, and be doubly sure it doesn’t rub along the wheel arch or the underbody.
In case you’ve seen tires on some older vehicles, specifically motorcycles, you may notice something like 3.50-19 6PR, which until recently was the tire size used by classic motorcycle manufacturers. Here, 3.50 is the width of the tire in inches, 19 is the rim diameter and the tire has a ply rating of 6.