|The Right Tire for Your Porsche
By: Ken Koop – The Yellowstone Region (Old Faithful Newsletter)With winter rapidly approaching, I thought it would be a perfect time to discuss how to choose a proper tire for your car (whether it is a Porsche or another manufacturer). The actual choice of tires comes down to how you will be using them and in what type of conditions they are going to be driven. This article will begin with the highest performing tires (race tires), progress through other tire categories and end with the preferred choice for the winter driving, snow tires. Without getting bogged down with the technical details of tire construction, I will try to focus simply on the practical applications. Hopefully, this article will help you understand that there is no perfect tire for all driving conditions and the tires you have on your vehicle are designed for a very specific purpose.Tires are very complex structures. The “black part” of the tire is not just rubber. It is a compound composed of varying amounts of rubber, silica, carbon black, silanes, nano-composites (aluminum silicates), oil and other components that give the tire its desired performance characteristics. The internal structure of the tire can be composed of Kevlar, steel, nylon, polyester and many other exotic materials. These materials are layered in belts or cords to give the rubber compound a framework to bind with. This structure affects the tire’s ride quality and contributes to the performance characteristics as much as the rubber compound itself does.With racing tires, grip is one of the most important elements. The more tread you put on the ground, the more grip the tire develops. This is why there are no grooves on racing slicks. Race tires also perform their best over a specific temperature range. Tire engineers like to have the rubber on these tires at a temperature of approximately 180-220 degrees in order to provide maximum adhesion (a passenger car’s tire would have disintegrated long before ever reaching this temperature). If the temperature of the air or track is too cold, the tires never heat up to their desired temperature. In this case, a softer compound would be chosen to help generate more heat (unfortunately, when we drive our cars on the street, we don’t have the luxury of having a pit crew to change our tires to match the driving conditions). If the race track temperature falls from 100 degrees to 80 degrees, the tire temperature is reduced as well. As a result, the performance of the tires on the race car will fall off dramatically. If you have ever watched any racing series, the driver has to be extremely cautious when exiting the pits until the tires come up to their operating temperature. Otherwise, the tire’s grip is low and there is a lot of TV time showing some exciting footage of what the driver should not have done (usually going through grass and gravel before hitting something solid). By the way, a race tire’s life expectancy is around 100-300 miles.
|Most race tire manufacturers protect their technological innovations very carefully. For instance, Michelin Racing Tires are not sold to race teams. They lease the tires to the team for around $1000 a tire. The tire has its own bar code that is scanned and then assigned to the team. When the race is over and before leaving the track, the team must return every tire that has been leased to them back to Michelin. It does not matter if the tire has been completely used up, destroyed by a puncture, or was never even used during the race. Michelin still wants the tire back to examine the tire carcass and the rubber to continue to improve their product. More importantly, they do not want their innovations falling into the hands of their competitors.For very high performance cars, such as the Porsche GT3, tire manufacturers provide what are called “DOT legal Competition Tires”. These tires are manufactured for the race track but are allowed to be used on the street. They have just enough grooves/tread on the tire to provide traction in wet conditions to make them street legal. This type of tire can withstand the stresses that the race track will place on them and provide exceptional grip in warm, dry conditions. However, if there is standing water on the road or the air temperature falls below 55 degrees, the tire compound becomes hard and grip becomes very poor to non-existent. Therefore, extreme caution is required when driving on the street with this type of tire. Due to the softness of the rubber compound, their longevity is only around 5,000 miles.|
|Porsche currently provides “Max Performance Summer Tires” on most of their sports cars. They provide very good handling on dry roads and acceptable resistance to hydroplaning in the rain. For summer use, they are an excellent choice. However, once the temperature reaches 50 degrees, these tires will lose their ability to stay soft and traction is drastically reduced. A car using this type of tire on a cold day will see their braking distances (from 50 MPH to 0) increase by 38% over the same car using winter tires. This distance grows exponentially if driven on wet or icy surfaces. Even though these tires have a considerable amount of tread/grooves on them; just try backing your car out of the garage on a winter day with snow on the ground. You will soon find yourself looking for some friends to help push the car back into the garage. Temperature has a very dramatic affect on all of the performance tires. Max Performance tires, depending on how you drive, will last from 10,000-15,000 miles.|
|Next-the so called “All Season Tire”. For this tire group, the phrase “jack of all trades and the master of none” really does apply. The All Season Tire is designed to provide acceptable traction in the summer for acceleration, cornering and braking. For winter use, they are designed for “light or occasional snow”. Their grip in snowy conditions is marginal since the rubber is not able to stay soft enough once the temperature falls below 40 degrees. Also there is little to no “siping” on the tread to provide grip in slippery winter conditions. Once the tires become hard (due to temperature), they are no longer able to react to the snow and will lose their ability to grip onto the snow surface. They do however, offer people living in the city a product that will give respectable wear during the summer. In addition, they will provide some traction in light snow. If they are used during extreme winter driving conditions (such as what we experience in eastern Idaho or Wyoming), braking distances will be dramatically longer than those of a winter tire. Directional steering is also drastically reduced. Unfortunately, these tires give the SUV owner a false sense of security while driving on snow. Tire life will be in the 30,000 mile range depending on your driving style.|
|The “Mud and Snow” (M&S) or “All Terrain” tires fill another niche that fits in-between the All Season and Winter tires. These tires provide tremendous grip on rocky or muddy surfaces because of their large blocks of rubber. They are able to self clean themselves because of the large spaces between the rubber tread blocks. Their rubber compound is fairly hard in order to withstand the punishment they must take off road. For use in snow however they are not a good choice because of the following reasons (the rubber becomes hard around 45 degrees, there is no siping on the tread and the spacing between the blocks is too wide to compact snow). These tires have a tendency to float across the snow rather than grip it.|
|Now, let’s examine the snow/winter tire. These tires have a rubber compound that will remain pliable at temperatures down to -20F degrees or lower in some cases. They are designed with siping (small cuts) across the tread for optimum grip on snow and ice. Each of these tiny cuts in the tire provides a biting edge that increases the tire’s grip. They also have blocks of rubber and enough space between these blocks to compress the snow (similar to packing a snow ball). By compressing the soft snow as the tire rolls across it, the snow is compacted and semi-fused to the surface below. This enables the tire to bind with the packed snow and allows the tread a surface it can adhere to. This is what actually gives snow tires their “grip”. Their biggest drawback is their sensitivity to heat. Since they stay soft at very low temperatures, they wear very quickly with the heat of summer or high speed driving. Also, because of the larger blocks of rubber and siping, the tire tends to “squirm” during cornering and braking. This not only reduces the tire’s cornering and braking ability, but increases the tire temperature. This tends to shorten its lifespan even further. A snow/winter tire can be identified by the extreme weather “Snowflake-on-the-mountain” symbol, stamped on the side of the tire. To obtain the “snowflake” symbol, the tire has to exceed a set industry standard of traction on snow by 10%. If used year round, expect at most two winter seasons out of these tires (around 20,000 miles).|
|Studded tires are still available for some car models. However, most manufacturers of higher performance cars and SUV’s do not recommend them. Many countries have also banned their use on public roads and most states in the USA now allow the use of studded tires only during specific months of the year. The two primary reasons are the speed rating of these tires is fairly low and the studs tend to chew up the pavement when snow is no longer present. Since the studs are made of tungsten carbide, they tend to cause the tires to over-heat on dry roads. At higher speeds, these studs can become dislodged from the tire or potentially even puncture the tire itself. If you are traveling at highway speeds (without snow for long periods of time) they can become hazardous.On a side note: The U.S. National Safety Council completed a study by siping “All Season Tires”. The study compared the same tires both before and after sipping. Tests were conducted on glare ice and packed snow. Stopping distances were reduced by 22%, breakaway traction improved by 65%, and rolling traction improved by 28%. So when siping an All Season Tire, you can increase the tire’s performance for winter driving. However, they still won’t perform as well as a dedicated winter tire (because of its softer rubber compound and dedicated tread pattern). Other tire tests have compared winter tires against studded tires. These tests show that winter tires actually perform as well or better than studded tires on ice and packed snow. With advanced rubber technology, the need for studded tires becomes almost irrelevant for today’s winter driving.Tire manufacturers recommend replacing snow and DOT legal competition tires at an interval no longer than three years from the build date (stamped on the tire). Snow tires and competition tires lose their suppleness much sooner because of their softer rubber compound. As a result, after three years, they have already become hard and are unable to perform their intended job. These tires may look incredibly good from the outside and have virtually no mileage on them, but do not depend on them. Non-specialty tires should be used no longer than eight years from the build date. The reason for this is that all tires begin to degrade from the moment they are produced. The oils mixed with the rubber during the manufacturing process begin to dissipate and the tires slowly lose their elasticity after leaving the factory. To ensure that all of Michelin Race tires are kept “fresh” (this means, keeping the tires at the same consistency as when they were first built); they are stored and shipped in refrigerated containers until they arrive at the race track. It is an expensive and elaborate procedure, but it ensures that the tires are 100% ready, consistent and predictable for the race teams.|
|Many people, especially those with SUV’s, would like to have one set of tires to utilize during the summer and winter season (myself included). Unfortunately, those tires do not exist. In our region of the country, an All Season or Mud & Snow Tire is a poor compromise. I know it is a hassle to change tires or to have two sets of rims and tires for summer and winter driving conditions. From my experience and the recommendations from tire experts, everyone should have a set of dedicated winter tires to guarantee optimal safety on snow covered roads. Once spring arrives, pull out those summer tires again and place them on the vehicle. It may not be the most convenient option, but it is the safest!By reading and understanding the basics of tires in this scintillating article, I hope it becomes apparent that there is no BEST all around tire. There are only compromises. If you want the safest tire for winter driving (to be able to stop and corner safely), then you will need a winter tire. (Remember: It only takes one accident, to make up for a lifetimes cost of switching out your summer and winter tires) If you drive your car primarily in the summer and do a few track days, then a Max Performance tire is a great choice. If you want the maximum traction for racing, then you will need a racing slick or a DOT approved competition tire. There is a veritable plethora of tires to choose from. Choose the tire category that best fits the condition that you are planning to drive in.|
|A couple of important safety tips for winter driving;1. Be sure to use the same brand and model of tires for the front and rear of the vehicle.
2. Never install wider or larger diameter tires than are recommended. In fact, it is generally suggested to use the narrowest approved wheel/tire combination recommended by the manufacturer.
3. Use Porsche approved N-spec tires. Why? The answer is that tire manufacturers make their tires for general purpose consumption (generally for front engine cars). Since most Porsche’s have rear or mid engines, more of their weight is over the rear tires. Porsche N-spec tires have been designed with a higher load rating (by having more side wall rigidity and strength) to compensate for this factor. Secondly; Porsche tests and approves every tire that they recommend and guarantee it will meet their performance and safety standards.
4. Do not use cruise control on snow or ice covered roads. When a vehicle is going up a hill, the cruise control will sense a decrease in speed, and inadvertently apply power to compensate for the loss of speed. This can cause wheel spin and result in the driver losing control of their vehicle.
5. If possible, select a gear that will allow the engine to run around 2,500-3,500 RPM’s. By selecting that RPM range, engine braking has some beneficial effects in slowing the vehicle down when needed and provides for a more positive/quicker throttle response in emergency situations.
6. If your vehicle is equipped with an adjustable suspension, set the suspension to the softest position; this allows for more suspension travel, greater roll of the vehicle’s body and provides for better tire to road contact. 7. Check your tire pressure often and keep them at the manufactures recommended pressure. Generally a tire will lose (or gain) one pound of pressure for every ten degrees change in outside temperature.