The last few weeks have been an eye-opening experience for us, especially the time spent at the track witnessing the results of our Camaro suspension upgrade (covered elsewhere in this issue). We say eye-opening because up to this point we'd never given serious thought to the importance of tire selection could be when it came to making the most of performance suspension upgrades. We now realize that we've been remiss in the fact that we've neglected this important factor, and we're hoping that we're not the only ones who have not given this important performance vehicle handling aspect its due. With this in mind, we've done a bit of research, and we'd like to share a bit of what we've learned.
Tires, like all performance automotive components, are constructed to meet very specific requirements. Sport tires are designed to provide maximum performance at the expense of tread life. Conversely, general-use (semi-performance or touring) tires trade some of that handling potential for a bit of extra comfort and longer life. With this in mind, the selection of the right tire requires some careful thought. Tires should be viewed as every bit as important as hard-part upgrades when it comes to performance. Their return on investment cannot only be measured in their ability to allow your suspension components to perform to their maximum potential, but to provide possibly lifesaving traction in extreme conditions, as well.
It is a vehicle's tires that employ friction against the road surface in order to transmit chassis forces, and as a result, the capabilities and limitations of those tires will almost always define the limits of acceleration, braking, and cornering. In other words, you could have the best engineered chassis and suspension components available on your car, and if you're running on crappy tires, the benefit you'll receive from those components will end up falling well short of what those components are actually capable of providing. This is precisely what we'd, up to this point, never fully realized. OK, we'll assume a lot of you knew this already, so we're going to beg your indulgence while we go over some basics that will help bring others up to speed.
There are quite a few levels of performance tires available on the market, from full-on race tires to general use passenger car tires. With a bit of investigation, this assortment of choices allows us to choose the best tire to serve our needs. The Nitto NT-01, the tire we used in our aforementioned Camaro testing, is a DOT-approved competition radial with an asymmetrical, non-directional tread pattern optimized for dry racing conditions. The NT-01 features a tread depth of 6/32 and a tread compound formulated to deliver extreme cornering power for not only fast and consistent track times, but exceptionally impressive handling for aggressive driving, as well.
The main objective of a performance tire is to increase traction. Thicker tread blocks provide more contact area with the road. A softer rubber tread compound and small-channel grooving provide a smaller void ratio contribute to increased grip on the road. With this in mind, there are some trade offs associated with running extreme high-performance tires on a streetcar. Beyond a bit of increased noise and stiffer ride--minor drawbacks for a performance-bred vehicle--the most important is less-than-optimum performance in the wet stuff (true dry erformance tires are terrible in the rain, so use extreme caution). Since performance tires are designed to maximize the contact area with the road, there is less "void area" for water to be directed away from the contact patch, which can lead to hydroplaning in wet conditions. Another consideration is wear. True performance tires are manufactured using softer compounds that wear quicker than the average street tire, so expect to compromise tire life with outstanding handling characteristics.
READING TIRE SIZING
One plus when tire shopping is understanding tire sizing and specifications. These sizes, ratings, and specs are found molded into the sidewall of all tires. The side information consists of the tire manufacturers name, the tire model name, the tire size, the tread wear indication, the traction rating, and the temperature grade. The sidewall also has the U.S. DOT safety code, load limit information, maximum inflation pressure information, and the tire construction composition.
The tire size code is read like this (using, say a 255/50VR17 for example): The first number is the overall width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4. In our example size, the width is 255mm or 10.04-inches (overall width: 255 [mm] / 25.4 [mm per inch] = 10.04 inches wide). The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 255 mm or 10.04 inches wide, multiply that by the aspect ratio to find the height of one sidewall. In this case: section height (sidewall height): 10.04 inches x 50% = 5.02 inches high. The speed rating is the letter designation indicating the high-speed durability of a tire. In our example, the speed rating is "V". The letter to right of the speed rating is an "R" designating radial. The last number is the diameter of the wheel in inches.
To figure the overall diameter of a tire, take the sidewall height and multiply by 2, (remember that the diameter is made up of 2 sidewalls, both above and below the wheel) and add the diameter of the wheel to get your answer. In our example case the overall diameter would be: (5.02 inches x 2) + 17 inches = 27.04 inches tall.
There's lots more to learn about performance tires and what's available for your performance vehicle than there's room for here, so I strongly suggest hitting the Nitto Web site (among others) to get a more in-depth look at tire availability. Arming yourself with a bit of background from these sources will go a long way to help you utilize all those horsepower and suspension upgrades you've performed to their full potential. You'll be amazed at the result!