tuning your car: sticking to the road
In the last installment, I discussed the importance of making sure your car can stop—and making sure that when you choose brakes for your car, you choose them based on what you’re planning on doing with your car rather than what your car is currently capable of. I also discussed making sure that when you chose your brakes, to take into account any wheel and tire upgrades you planned on.
Tires keep your car on the road. It’s their job.
They provide grip and traction, help you drive confidently in wet and slippery conditions (unless you have racing slicks, but that’s another story all together), and they have a little bit of give to make your ride more comfortable. They’re like shoes for your car.
Just like the shoes on your feet, there are different tires for different needs and by choosing the correct tire for the circumstances, they can offer better performance for the conditions you find yourself in.
So, what’s the deal with tires?
Many of us have cars that came equipped with “All Season” tires from the factory. These tires are great for cars that are used on a daily basis to commute to work or go to the store. They perform moderately well in a variety of conditions (though some are often better than others). They aren’t great at anything.
All Season tires split the difference between performing in warm, dry conditions and cold, wet conditions. This means they’re not particularly good at performing in either one.
For any sort of spirited or performance driving, it’s in your best interested to invest in some better rubber.
When you’re looking at tires, there are a handful of things you should keep in mind. Speed rating, load rating, wear rating, and performance level are all ways that tires are categorized. You also don’t want to forget customer rating. I’ve noticed that tires can be labelled for a particular use, but that doesn’t really mean much if they don’t perform well in the real world—customer ratings are a great way to find out where tires excel as well as fall flat (no pun intended, but it’s a good one, right?).
First up is the performance category. This is the first stop in narrowing down your tire search. If you’re shopping online, sites like Tire Rack are a great resource. (You can also shop online with many of the national tire chains, but Tire Rack sponsors the SCCA, where I’m a member, and I feel better about shopping there because of the support they give to amateur racing.)
For my purposes, I’m going to use Tire Rack as my example. For performance categories you have a few options: All-Season, Winter/Snow, and Track/Competition.
All-Season tires are a little bit of a misnomer. While they can handle a mild amount of snow, they aren’t really meant for being used as a serious winter tire. When you see an All-Season tire, what you’re seeing is what people will call “Summer Tires”. They can handle a variety of weather and conditions, but are best suited to the warmer months and dryer conditions, though they’re most definitely safe when it’s raining.
Under All-Season, there are a handful of sub-categories: Ultra-High Performance, High Performance, Performance, Touring, Standard Touring, and Passenger. Each of these have their pros and cons, and as you work your way through the performance categories high to low, you also work your way through price.
Its important to note that which category you shop in will be determined by your own personal needs. If you’re looking to put new tires on for your daily commute with a touch of spirited driving on a nice curvy backroad on the weekends, you can probably get away with not buying from the Ultra-High or High Performance categories. If you’re just going to be commuting, you can get away with anything from Touring down through Passenger. But, if you’re going to be using the tires for daily duty as well as some track days or plan on auto crossing your car, you’ll want to stick with the High or Ultra-High Performance areas or look at the Track/Competition (this, of course, depends on the class you’re competing in).
These are exactly what they sound like—they’re tires made to be used in the winter, when it’s cold, wet, and slippery. As a general rule, you really only want to use these when the temperatures dip below 40 degrees Fahrenheit. Using them in warmer weather will not only wear them out extremely fast, but they won’t perform as well as they should and can become a safety hazard. (This doesn’t apply if you’re using your snow tires for RallyCross). The rubber used in snow tires is formulated to work best in colder temperatures.
This tire category is also pretty self-descriptive—Track/Competition tires are for racing. These tires are come in all sorts of varieties, all of them geared toward the track. Your options when choosing Competition tires are based on the conditions you’ll see on the track—wet or dry—and softness, which depends largely on the air and track temperatures you’ll be encountering.
If you’re going to be enjoying your car on the road, as well as the occasional track or autocross weekend, the performance-level tires are going to be your best bet, since they’ll work best across all of your uses, especially if you don’t have the budget for multiple sets of tires.
Speed ratings give you a general sense of what your maximum speed you can drive your car and expect the tire to continue its life as a tire.
These are labelled as a letter grade, with each letter coinciding with a max speed. The ratings are as follows: S (112 mph), T (118 mph), U (124 mph), H (130 mph), V (149 mph), Z (149+ mph), W (168 mph), and Y (186 mph).
For most cars, you’re most likely going to see S or T ratings on your tires. For your daily driver, you’re rarely going to see speeds this high—let alone higher—so there’s really no need for a higher-rated tire.
If you spend a lot of time on tracks, though, and your car can reach speeds higher than that, you’ll want to look for an appropriately rated tire. Unless you’re driving a supercar, you’ll probably not see Z or Y rated tires, or have any reason for them. You never know, though.
In addition to Speed Ratings, tires will also come with a Wear Rating. This will show up as a three-digit number followed by two letters, like 600 A A.
Since I won’t be able to explain this better, here is Tire Rack’s description of the numeric wear part of the wear rating:
UTQG Treadwear Grades are based on actual road use in which the test tire is run in a vehicle convoy along with standardized Course Monitoring Tires. The vehicle repeatedly runs a prescribed 400-mile test loop in West Texas for a total of 7,200 miles. The vehicle can have its alignment set, air pressure checked and tires rotated every 800 miles. The test tire’s and the Monitoring Tire’s wear are measured during and at the conclusion of the test. The tire manufacturers then assign a Treadwear Grade based on the observed wear rates. The Course Monitoring Tire is assigned a grade and the test tire receives a grade indicating its relative treadwear. A grade of 100 would indicate that the tire tread would last as long as the test tire, 200 would indicate the tread would last twice as long, 300 would indicate three times as long, etc.
The first letter of the rating is the G-Force that the tire can withstand. Listed as AA, A, B, and C, the G-Force ratings are listed below:
|Traction Grades||Asphalt g-Force||Concrete g-Force|
|C||Less Than 0.38||0.26|
The second letter is another speed rating, this one for temperature resistance. Rated A, B, and C, the speeds the tires can be rated to are as follows:
|Temperature Grades||Speeds in MPH|
|B||Between 100 and 115|
|C||Between 85 and 100|
The Wear Ratings can give you a fairly good idea of how soft and/or how quickly the tires will wear down. Lower ratings tend to be softer and wear faster while higher ratings tend to last longer. These ratings are determined under test conditions, so your driving style—and what you’ll be doing with the car—will need to be taken into account.
As an example, I’ll use the tires I use for my Volvo 240 Wagon. The tire on this car is listed as: 195/60R15. The numbers mean the following:
(Section Width in Millimeters) / (Aspect Ratio – percentage of the section width) (Radial Construction) (Wheel Diameter).
This gives the section of 195mm, the a sidewall that is 60% of the section or 117mm, Radial construction, and wheel diameter of 15 inches. Some High Performance tires will also have an additional letter, 195/60ZR15. This is for high speed ratings.
When you’re choosing a tire, the size you choose will be partially determined by the wheels you’re using. Rim width and diameter are the limiting factors for the maximum tire size you can select. If you’re using the factory wheels, you can easily replace the tire with a matching size what’s listed on your old tire (provided it’s a factory size). You don’t need to just replace your factory tires, though, there are plenty of options for changing your tire size.
Ideally, when changing wheel and tire size, you’ll want to make sure that the overall diameter is close to the factory dimensions to keep your speedometer as accurate as possible. If you’re planning on increasing the overall diameter, there are always options like adjusting the programming or installing a switch that compensates for the increase.
For more performance-oriented applications, increasing the wheel diameter and decreasing the aspect ratio will help to reduce the tire’s propensity to flex or roll in hard cornering. However this will also increase the feeling transmitted through the car when you run over bumps in the road. If your tires are going to be both daily driven and used for performance, a balance should be found between comfort and tire performance.
The wheel width can also be increased when looking to improve grip and performance of the tire. Wider tires allow for more rubber to sit between your car and the road, increasing the area of the tire called the contact patch. The more contact the tire makes, the more grip you have, the more speed you can carry through a corner. Since the tire width is limited to how wide your wheels are, there are some considerations you’ll need to make when choosing whether to increase your wheel width to accommodate a wider tire.
Because the wheel that you’re planning on using will determine the tire size that you need, you’ll want to choose a wheel the fits not only the application, but also your car.
Many of the wheels on the market can be used for both daily street driving and some moderate performance. If you’re looking for a wheel and tire combination that’s for dedicated duty on the track, you’ll want to make sure that the wheels are able to stand up to the stresses of racing.
Things you’ll need to keep in mind about wheel size as it relates to your car, though, are the overall diameter, width, and the backspacing of the wheel.
The diameter and wheel width are important because your car was designed for the wheel and tire combination that came with it. Making this combination larger can result in the tire rubbing against the wheel well or the fender. If you’re going to be using a taller or wider (or both) combination, you’ll need to make some modifications to the wheel well or fender (or both) to make sure that the tire doesn’t come into contact with other parts of your car. Of the issues you may run into with a wider or taller wheel, this one is more annoying to accommodate than it is a safety problem. Just make sure to check for clearances before you take the car for a drive so you can deal with any issues before you make a mess of some brand new tires.
The backspacing is incredibly important because this keeps the back of the wheel and tire from rubbing against the rest of the suspension components. The backspacing of the tire is the amount of space, normally measure in millimeters, between the backside of the wheel (that contacts the hub) and the outside edge of the backside of the rim. From the factory, the backspacing of your wheels provides enough space between the inside of the rim and your suspension so that your wheels and tires don’t come into contact with them, damaging both.
Increasing the width of your tire, you’ll want to make sure that the backspacing is taken into account and adjusted to allow for at least the same amount of space. If this isn’t done, you may find that you need to add spacers to your wheels so that they fit properly. While spacers can be perfectly safe, they aren’t recommended for daily use and may even be illegal where you live. Getting a wheel that fits properly from the start is always a better plan.
There are a ton of wheel size calculators on the internet that will help you determine how the dimensions of the wheel compare to the stock one, but just make sure that you’re taking your specific vehicle into account when you’re using these when looking at the changes due to backspacing and wheel width.
Your tires keep you planted on the road. They provide traction during acceleration, provide grip in corners, and help your car come to a safe stop. Choosing the right tire for your car is an essential part of both the performance of your vehicle as well the safety of it. The types of tires that exist today can allow you to fine-tune that choice and combining the right tire with your chosen wheel can give your car a bit of personality and style while also providing all of your performance needs.