You know what they say (or rather Goodyear said in its ad’s in the 60’s) “Where the rubber meets the road.” And that is indeed one of the most critical interactions in F1. Tires have always played a huge roll in F1, and while some new rules have slightly diminished that importance, the talk in the paddock during practice is always about the tires and how to find more grip.

In the past, teams were free to run whatever brand of tires they wanted, provided the size of the tire meet basic requirements. The start of the modern ‘tire war’ in F1 was in 2001, when Michelin entered F1 to challenge the then monopoly of Bridgestone.

In physics terms, all tires work basically the same. The idea is to create a tire that will have high friction in all directions. You need longitudinal grip (along the direction the tire rolls) for good acceleration and braking, and lateral grip (sideways) for cornering. Your typical street tire accomplishes this through mechanical friction. The more rubber that touches the road, the better as far as grip is concerned. So you may wonder why your street tires have various grooves and slots; the “tread pattern”. The street tire is designed with the voids to channel away water (and snow and mud) from coming between the tread block (the part that touches the road) and the pavement, which helps to avoid hydroplaning. Hydroplaning happens when water builds up between the pavement and the tread block, leading to a loss of traction.

So it should be clear that a racing tire, designed for maximum dry, warm-weather conditions will be a ’slick’ or have no voids (no tread pattern). And in most racing series, this is still the case. However, in F1 the speeds were getting too fast, so the FIA attempted to slow the cars down by mandating that the tires have several grooves molded into them, reducing the effective area of the tire.

We’ve talked before about the aero loads (downforce) that the cars achieve. Ideally, we’d want our wings attached directly to the wheel hubs or suspension, which would then push down only on the tire, and leave the body of the car free to move up and down to absorb bumps. However, due to some spectacular failures of suspension-mounted wings, these were quickly banned and now any aero surface must attach to the body of the car. This means that the downforce pushes the body down, which then compresses the suspension of the car. In order to keep the car from bottoming out, the teams must run a very stiff suspension, which has a travel of only a few inches.

Ideally we’d like to have a softer suspension to deal with bumps on the track, but since that’s not possible, teams turned to tires. You’ll notice that the sidewall of the tire is quite tall in F1. Contrast this to the very short sidewalls on this LMP Porsche in the Le Mans series at right. This is because the tire actually is the majority of the suspension of the car! The tire is designed to deform to absorb bumps and maximize grip. This means that since the tire is also largely the suspension, understanding and having correct tires is critical in F1. Most teams partnered with a tire supplier and designed their cars around getting maximum use out of the tire.

During the tire war from 2001-2006, the tire engineers went nuts. They developed special compounds for each race of the season, sometimes multiple compounds for different air temperatures at the track. The tires are quite sensitive to heat, and need to be at the proper temperature to work. Too hot or too cold and the grip will be less than optimal, and the surface of the tire may start to degrade. You’ll see whenever the cars change tires, the tires are wrapped in special blankets. These are tire warmers that heat up the tires to near track temperature, so when the driver goes back out, there’s at least some heat in the tires.

During this period there were several changes in the tire regulations. For a while, the cars had to qualify and complete the race on a single set of tires. This rule was designed to make the teams run harder tires, which have less grip, and therefore slow the cars down. The result was actually more dangerous, as the drivers would still want to run as soft of tire as possible, even if it meant risking a failure, and eventually this lead to the US-GP debacle in 2005.

Now for 2007, the tire war is officially over, with Bridgestone becoming the sole supplier of tires. Bridgestone has developed five tire compounds that will be used for the entire season, and all teams get identical tires. These compounds range from super-soft to hard. For each track, Bridgestone selects two of these compounds. The harder of the two will be designated the ‘prime’ or ‘hard’ tire for that race, while the softer tire will be referred to as the ‘option’ or ’soft’ for the race. This can be a little confusing in some cases, like Monaco, where Bridgestone brought their super-soft and soft tires, which were then called “soft” and “hard” respectively, for that particular race. The “prime” and “option” terminology is better, and its what most of the teams use.

The rules specifiy that during the race each car must use both types of tire at least once. The option tire is distinguished by a white stripe painted in one of the grooves on the tire. Most teams have said that the option tire tends to be a little faster, but doesn’t last nearly as long. They tend to be good for one or two fast laps, and then begin to degrade. Most teams have found the prime tire to be more consistent over many laps.
Unlike many other forms of motorsports, particularly those that compete on ovals, F1 races are not usually cancelled or stopped due to rain. Hence, Bridgestone also supplies ‘intermediate’ and ‘wet’ tires for non-dry conditions. (At night is a full wet tire).
The intermediates have a shallow tread pattern, and tend to work best on a damp track without standing water or rain. The full wets work quite well in heavy rain and standing water, but on a drying track they can quickly overheat and start shedding chunks of rubber.
The changes in F1 are many, but for Bridgestone, the most significant change is the return of slicks.

“Slicks are a big change for Formula One, and it brings the sport back in line with most circuit racing formulae we see around the world,” says Bridgestone Director of Motorsport Tyre Development, Hirohide Hamashima. “A slick has a bigger contact patch than a grooved tyre of the same size and requires a softer tyre compound, so it gives more grip.”

Whilst the tyres give more mechanical grip, the cut in downforce means that the grip provided by the cars being pushed down into the road from their wings is significantly reduced which should mean an overall increase in lap time.

“The new cars, combined with our new tyres, mean that many variables have changed,” says Hamashima, “and learning how to gain the best advantage from these variables will be the challenge of the season.

“The front tyre now has a bigger contact patch relative to the rear tyres. This is because the grooved area on the front tyre took up a larger proportion of the tread area than on the rear tyre, so the removal of the grooves changes the balance.

“On top of this there is the aerodynamics change with a lower and wider front wing, combined with a taller and narrower rear wing, which also moves the balance in the direction of more aerodynamic grip at the front, and less at the rear.”

Source: F1n00b.blogspot.com & F1complete.com