by Jim Kerr
They’re round, they’re black (usually), and they are made mostly with rubber. Many of us have purchased replacement tires for our cars and trucks, but what makes up a good tire and how can we chose the right tire for our vehicle? The answers to these questions and many others were explored recently during a tire testing session at BF Goodrich’s “KICK ASPHALT” dealer tour in Toronto.
Three tour locations in Canada, Vancouver, Toronto and Montreal allowed Canadian dealers to learn in the tire classroom and on the test track and pass their experience on to their customers. I was one of the lucky ones to join the dealers and learn about tire technology too.
A classroom session introduced us to handling characteristics and the basics of comparing tires. While some tire designs work better on snowy or icy roads and others are built for superior traction on dry roads, all tires have something in common. It’s called slip angle.
Slip angle is the way a tire generates cornering force. In simple terms, it is the difference in the direction the tire is travelling and the direction the tire is pointing. Keep turning the steering wheel sharper and the slip angle increases, and so does cornering force – to a point. If the slip angle exceeds the tire’s maximum grip then the tire quickly looses much of its cornering force and the car skids
You have probably experienced this action on icy roads. Turn the steering wheel too much and the vehicle just wants to keep going straight ahead. Turning the steering wheel more only increases the problem. Skilled race drivers are adept at feeling the maximum slip angle of a tire. When the tire is “past its limits” they will actually decrease the steering angle, allowing the tires to grip again for more cornering force.
Performance tires, with their low profile sidewalls and large stable tread blocks, are able to produce greater slip angles and more cornering force than regular passenger tires. However, this comes at a price. The recovery zone from where slip angles are at their limits to where the vehicle is sliding out of control is very narrow. Drivers have to be alert and react quickly to drive the vehicle at its limits.
Passenger tires have much softer and taller sidewalls and smaller tread blocks that tend to flex more during cornering. This type of tire gives the driver lots of feedback that the traction is nearing its limits. Because the transition from maximum cornering force to out of control is gradual, these tires make it much easier for most drivers to keep a vehicle in control.
Testing tires requires driving with different tires on the same vehicle under the same conditions on the same course. While tire manufacturers do some testing at high speed, much can be learned on a slow speed course. A few gentle, slow speed curves allow a driver to feel the responsiveness of the tire to steering inputs. Jackie Stewart, one of the world’s great race car drivers, told me that learning about a vehicle’s tire and suspension characteristics is best done at speeds under 50 kph! Sharp corners and lane change maneuvers test the tire’s maximum traction capabilities, while water on part of the course is used to test the tire’s wet traction and braking.
One of the tires we tested was BF Goodrich’s new Traction T/A tire for touring and sporty cars. The Traction T/A won’t be on the market until 2004, but when it arrives it will replace BF Goodrich’s Comp T/A and Touring T/A tire lineup. Advantages of the new Traction T/A are up to 15% greater traction with an increase in tire life. Against the competition, there is a noticeable difference.
The Dunlop Sport A2 and Toyo Proxes TPT tires were chosen to test against the new Traction T/A. The Dunlop and Toyo tires are highly rated all season performance tires and offered very good handling and traction. When compared with the Traction T/A, the BF Goodrich tire had better traction on both dry and wet surfaces and the steering felt more precise. Although the Traction T/A tires were faster, this was tempered with the tire’s smaller slip angle recovery zone that kept drivers on their toes. The Traction T/A is a new tire design that sets new standards for touring and sports performance all season tires.
Better traction, longer tread life, and superior handling. These characteristics are what separate premium quality tires such as the Traction T/A from economy tires. They’re worth it.