Most people don't think too much about their car's tires - all they know is that they're round, hold air and essentially keep the car on the ground. In fact, most people don't even care about them, until it's time to replace the tires, then they make comments like "Gosh, my tires are worn out, now I have to replace them!" and "It's a hassle to get a whole set of new tires."
As a result, people end up searching for the "best" deal, often getting the cheapest tires possible.
If one would stop and think about their tires a little longer, they would realize that they are the only contact their vehicle has with the road. Therefore, stopping distance, cornering ability, ride comfort and fuel efficiency are all affected by the tire choice.
The most sophisticated braking and steering systems could be rendered useless by inferior tires. But by the same token, a good set of tires can considerably improve every aspect of even the most basic automobile.
Now that we've acknowledged the importance of tires, how do we go about making the correct choice? As with any purchasing decision, knowledge is power.
The first step is determining what size of tire you need. Just like how different people need different sized shoes, different cars need different sized tires. But unlike shoes, which are largely defined by a single number and restricted by your feet size, tires are exponentially more complicated with an infinite combination of size, diameter, compound type, and character.
Let's look at two examples: P225/60R16 97T and LT265/70R17 121R. Admittedly, these appear a bit like a "code," but after breaking the measurements down, it's not so bad.
The prefix, a P or LT, simply indicates that the tire is designed for either passenger car or light truck application. Some SUVs and smaller trucks are fitted with P rated tires for improved ride comfort, but if you are routinely carrying heavier loads, a LT rated tire would suit your needs better.
The next group of digits, 225 and 265 in our examples, tells you how wide the cross-section of the tire is in millimetres. The bigger the number, the wider the tire. But keep in mind this measurement is from the widest point to widest point and not just the surface of the tread.
The following number is the aspect ratio. This tells you the height of the sidewall as a percentage of the tire's width. So, the sidewall of our passenger tire is 60 per cent of 225 mm, or 135 mm. Understanding the aspect ratio becomes most important when changing wheel sizes.
The R lets you know that it is a radial tire as opposed to a bias-ply tire, which would be designated by a D. Bias-ply tires are no longer used in passenger vehicle applications.
The rim size in inches is noted next. In our examples, the car has 16-inch wheels and the truck has 17. Obviously, a 16-inch tire will not fit on a 17-inch wheel or vice versa.
Next is the load-carrying capacity. As you can see in our example, the LT has a higher load rating at 121 verses 97 for the passenger tire. It is highly recommended that you never select a tire with a lower load rating than the manufacturer's specifications.
The last item is the tire's speed rating. This reflects the tire's ability to dissipate heat. Driving at high speeds for extended periods of time, like on long highway commutes, creates heat buildup within the tire. Too much heat increases the likelihood of a failure.
Some questions you need to ask yourself are: would you prefer a harder, more performance-oriented tire or a softer, more comfortable one. For performance seekers, upgrading you tires offers a quick and cost effective means for improvement. The most common practice is plus sizing. This is the concept of increasing the wheel size by an inch or two while lowering the aspect ratio of the tire. This makes the sidewall shorter and more rigid. Typically, the width of the wheel and tire are also increased. Mixed with high performance rubber, the driver will notice quicker steering response and cornering ability.
Using the example car tire size, we could switch to a 235/50R17 or even up to a 245/45R18 from the original 225/60R16 size. As you can see, the width of the tire and wheel diameter are increased while the aspect ratio is decreased to keep the tire's overall diameter the same.
Keeping the overall diameter as close to the original as possible is important in order to maintain sufficient ground clearance, appropriate driveline gearing and accurate speedometer/odometer readings. Large changes in diameter could also affect the car's ABS, traction control and vehicle stability systems.
The last point to consider is price. Tires may seem quite costly, but you need to keep those costs in perspective. You will likely only need to purchase a new set of tires once or twice over a car's lifespan.
With so many tires to choose from, even armed with this knowledge, selecting a specific tire can still be a daunting task.
Recently I had an opportunity to experience what it would be like to upgrade a set of tires. Two experiments were performed: upgrading a 2012 BMW X1's 18-inch Good Year tires to 19-inch Continental DWS tires (with a lower profile) and replacing original 2013 Audi S4's Continental summer tires with a set of high performance Continental DWS all-season tires (of the same size).
In the first case, upgrading to larger, lower aspect ratio tires in the BMW X1 produced sharper capability around corners, quicker steering feel, and a more "planted" feel. This happened with very little loss of comfort or noise level.
In the second case with the Audi S4, it was surprising to find out that the high performance all-season tires from Continental (DWS) performed almost as effectively as the summer Continental tires from the same manufacturer (DW) in all kinds of road conditions. And of course, the ExtremeContact DWS all-season tires have an added advantage that it can be used all around the year here on the West Coast so that I don't have to worry about replacing the tires each winter with a set of snow tires.
This experiment allowed me to conclude that if you buy a set of highly capable tires, you can have the cake and eat it too in the sense that you get best of both worlds: high performance character with all-year-around capability.
