Those of us that find joy in a country road’s curves and elevation changes often want to enhance the experience by increasing our car’s handling capabilities.
There are a lot of options out there these days. Springs that lower the car’s center of gravity and give a tighter gap between the tires and fenders are everywhere. Aftermarket shocks and struts offer a stiffer ride that promises to keep the tires in more constant contact with the road. Body lean can be controlled with larger anti-roll bars. Many options exist and because there are so many it can be confusing and complex to get the kind of handling you are looking for.
Add to this the fact that we all have to work within a budget, be it large or small. The most “bang for the buck” in terms of handling improvements is by far upgrading the tires. These days many factory sports cars come with some exceptional tires. My Evolution MR came with Yokohama Advans that stick like nobody’s business. They also wear as fast as they corner. I was lucky to get 14,000 mile out of the first set. Ugh. My replacement tire? The same Advans. Since the whole car seems to have been designed around these tires it was difficult to go to anything that might be less sticky. Aside from wear there are other drawbacks. In winter temperatures the compound that provides such exceptional coefficient of friction the rest of the year, can turn to a slippery let down. So in the northern climes people convert to a winter set of tires for their Evolutions.
Most cars come with tires that are a compromise in many ways. Often car manufacturers shod their automobiles with tires that are quite inexpensive and are specially made just to keep the cost down. In extreme cases tire companies produce tires for car manufacturers that are not available other than on new cars.
Fortunately the aftermarket provides some fantastic tires to choose from. One of the first areas to improve the handling of a car is to explore tires that have better performance and likely are wide in their profile. Your stock tire might be sized as a 215/50-16. If you are lucky you could have room under your fenders for a wider tire in a size that offers higher performance options. So you could move up to a 235/45-17 sized tire. What do all the numbers mean? The first number is the width in millimeters. The number after the slash is the sidewall height. Not in millimeters. This two digit number is a percentage. In the last tire size it means that the sidewall is 45% of the width of the tread or 45% of 235 millimeters, or about 160 millimeters high. The last number refers to the diameter of the wheel that the tire mounts to. In this case we go from a 16″ diameter wheel to a 17″ diameter wheel.
Why go to a larger wheel? Well, this can help as well as hurt. A larger diameter wheel can move your tire size options into an area where there are a lot of great choices in the way of performance tires. It can also provide you with room to upgrade to larger diameter brakes. All of this sounds positive, but there can be a downside, and that is added weight. Weight is the enemy of handling performance. Make your car lighter and it performs better. It stops easier, accelerates faster, and corners better. Most of the car’s weight is suspended by springs, but perhaps the most important weight is not. That is called unsprung weight. It is the weight that consists of wheels, tires, brake components, and everything that are not supported by the springs.
Why is unsprung weight so important? Ask the people who make their money at it, the race car engineers. Reducing unsprung weight will improve acceleration, braking, just about all aspects. The exotic race cars have ultralight wheels, tires, move the suspension springs into the body and operate them with rocker arms and linkages. They have carbon fiber brake rotors and try everything they can to get rid of unsprung weight.
I have seen many “formulas” that claim getting rid of a pound of unsprung weight is the same as getting rid of 100 pounds of sprung weight that may not hold up to scientific scrutiny, but there is truth to the fact that unsprung weight reduction pays off.
So what does all this have to do with tires? As you go to wider tires guess what? You can increase your unsprung weight. Wider tires will require a wider wheel. Changing to a larger diameter tire will require a different wheel as well. So while you are looking at all those choices in replacement wheels try to find the lightest wheel you can afford. Unfortunately the sources for aftermarket wheels don’t generally make wheel weight easy to find out. I find that Tire Rack (http://www.tirerack.com/) does have that information for most of the wheels and you can call them directly if it is not listed on-line.
Eighteen inch diameter wheels will weigh more than seventeen inch diameter wheels. So before you go crazy with the bling factor of having 20″ diameter wheels on your ride keep in mind the price penalty you will have to pay. With huge brakes you will need the space of larger diameter wheels, but don’t go any larger than you really need.
Keep to a tire and wheel size that will effectively give you the same total diameter as your factory wheels and tires. A handy site to find out what choices are open to you is http://www.miata.net/garage/tirecalc.html.
For the tire size I picked in the paragraphs above and eight inch wide wheel is ideal. Seven and a half inch is acceptable, but not desirable. Assuming you go looking for a seventeen inch diameter wheel that is eight inches wide you will have another factor (besides weight) to deal with. That is offset. What this refers to is how much the actual mounting surface of the wheel is off-set from the center-line of the wheel. This is important for a couple of reasons, not the least of which is being able to fit under the fender.
Often you will have to do quite a bit of research to determine what offset you will need. Many car forums will be able to provide you with this information. I wish there was a general rule here, but while a 38mm offset will work for one brand and model of a car another will require a 48mm offset to clear things.
While picking the “right” wheel you should keep a couple of other things in mind as well. You will have to clean these wheels from time to time so think about how complex a spoke design you want to live with and what it will take to get brake dust off it. You might want to pick a grey wheel color so that your brake dust doesn’t show up as fast as it would on a white wheel. Chrome can really set off a wheel, but often mean that the wheel is brittle compared to a painted wheel. And we do live in a world of pot holes.
Tires have many qualities that you need to consider. The trouble is that you cannot have a tire that has every quality you might want. I guess the ideal tire would last 100,000 miles, have a coefficient of friction that would allow you to park on the ceiling of your garage, shed water so well that you could transverse 10″ deep puddles at 120 miles per hour and get you through snow like and Artic Cat. All costing you less than $30 a tire. Unfortunately no such technology exists today that can provide all those extremes. There are some amazing tires out there that will allow you to corner with confidence through the summer and spring, but will have to be replaced or at least treated with respect in the off seasons. An ultra-high performance all-season tire is usually a great compromise. If you just want to have the best cornering possible, dam the wear and cold weather, then extreme performance summer tires are it.
When reviewing your tire choices you must be realistic about the environment you really have to deal with. Keep in mind wear rates and how noisy a tire is. Some tread designs are quiet to begin with and get noisy later on. Tire Rack offers customer feedback and ratings that can be very helpful
To sum it up the most rewarding place you can invest your handling improvement money is in tires and wheels. Get as much tread on the road as practical and keep things as light as possible. Be realistic and enjoy the vast improvement.