09/11/2004
NEWS STORY
Earlier this year (May to be precise), regular reader, former F1 driver, Le Mans winner, rally driver and all-round motorsport legend, Vic Elford, sent Pitpass the following:
"Yesterday on the SPEED TV's coverage of Barcelona, David Hobbs and Steve Matchett referred to the ability of modern tires to 'create' their own molecular grip with a given road surface. In other words they don't just resist sliding, but have a positive gripping effect when in contact with the surface for which they are designed.
"How about telling us what goes into modern tires (I don't suppose there is any rubber in there any more) and how it works?"
We got in touch with Bridgestone, and although it took them a little time - we got the response on Thursday, five months later (sorry Rachel) - we did get an answer to Vic's question.
"First of all, here is a basic explanation of what a racing tyre consists of, excluding construction materials," explains Hisao Suganuma, Bridgestone Motorsport's technical manager.
"Tread compound is the part of any tyre in contact with the road and therefore one of the major factors in deciding tyre performance. The ideal compound is a compound with maximum grip but which still maintains durability and heat resistance. A typical F1 race compound will have more than ten ingredients such as rubber polymers, sulphur, carbon black, oil and other curatives. Each of these includes a vast number of derivatives any of which can be used to a greater or lesser degree. Very small changes to the mix can change compound performance.
Polymers: 2 basic groups: natural or synthetic rubbers.
Carbon Black: A black powder substance produced by burning oils in a furnace. Carbon black has a reinforcement effect in rubber and its chemical make up can vary by using an assortment of oils to create different physical properties. There are hundreds of kinds of carbon black for use in compounds and each will produce a compound with certain properties: improved traction, heat resistance, wear and so on.
Processing Oils: The oils mix with the other ingredients to yield particular tyre characteristics. A race tyre will use several types of processing oil. ie more oil = softer rubber.
The amount of carbon black and oil, and its curing time, will determine the hardness of the rubber.
Curatives: Sulphurs and accelerators: curatives induce the vulcanisation process of rubber and generate the cross-linking of molecules. This process finalises the characteristic physical properties of the rubber.
"Tyre grip is a result of adhesion and hysteresis loss," Suganuma continues. "Adhesion comes from the interaction between tread rubber and the road surface on a molecular level. As rubber softens it has a larger contact area with the road surface producing stronger interaction been them and therefore increasing the friction (grip) force.
"Hysteresis loss, on the other hand, is related to what is happening within the composition of the rubber. When cornering for example, the tread rubber is repeatedly distorted. This generates heat in the rubber which also increases the friction coefficient (grip) levels."
We hope this answers Vic's question... we'll be asking questions later in the day.
Note: Hysteresis - n [NL, fr. Gk hysteresis shortcoming, fr. hysterein to be late, fall short, fr. hysteros later] A retardation of the effect when the forces acting upon a body are changed (as if from viscosity or internal friction).