F1's defining question: What is more vital, a driver or his tyres?

As Michael Schumacher and Fernando Alonso prepare to take the Formula One championship to the wire in Suzuka tomorrow, David Tremayne considers an issue that goes to the heart of grand prix racing in the 21st century

Formula One enthusiasts the world over have been pondering one prime question for the past two or three months: who will be the world champion this season? Will it be the reigning champ Fernando Alonso who hangs on to his crown for another year? Or will the outgoing legend Michael Schumacher stage one of the biggest comebacks in history to snatch a remarkable eighth title at the 11th hour? Or will the alchemists at Bridgestone or Michelin be the true champions? Has the importance of tyres, and the influence they exert on performance, got so out of hand that the skill of faceless scientists, rather than that of fearless race drivers, will dictate the outcome?

Traditionally, tyres are dismissed as round, black and boring. But not racing tyres. Every little sensation and behavioural nuance that a Formula One car relays to the driver comes primarily from the little rubber contact patches at each corner. A special, grippy compound here, a blister or graining there (where the rubber tends to roll across the tread), can make all the difference between success and embarrassing failure. Look at how serious graining on Alonso's replacement front tyres in China last week turned what was going to be a crushing victory for him into a battle for survival as he instantly lost four seconds a lap to his pursuers, Giancarlo Fisichella and Michael Schumacher. The problem may even have lost him his championship crown.

The tyres give the car its footprint on the track, and while you need a lot of other things going for you too - not least a strong engine, plenty of aerodynamic downforce and good handling balance - if your tyres are not up to it, you are never going to get the job done.

Failing to get the best out of them can have a similar effect, as Williams-BMW and McLaren Mercedes demonstrated in 2002 when they did not make the best use of their Michelin tyres and Ferrari and Bridgestone romped away with the world championship, or Ferrari discovered a year later until a helpful late-season "reinterpretation" of the wear rules helped Bridgestone to strike back at Michelin.

"The four tyres dictate everything, and unless you are kind to them and don't take too much out of them, you're going to be in trouble," says the former Jordan and Jaguar designer Gary Anderson. "They are the biggest thing, to be honest, the biggest individual component on the car, which gives you grip. You must look after them. It's what this business is all about."

Renault's executive director of engineering, Pat Symonds, says: "If you consider the five primary factors in the performance equation - engine, chassis, tyres, driver and team - the tyres account for at least 30 per cent of the performance package. A bigger separate percentage than any of the other factors, for sure."

The tyres are the mechanical prima donnas. Their compound (the mix of the rubber) and their construction (the precise way in which they are made), exert major influences on their behaviour. But they are also sensitive to temperature, track surface and driving style, not to mention the car's inherent handling characteristics (understeer or oversteer), grip level (a product of aerodynamic downforce) and traction (a product of suspension efficiency and traction control electronics).

When your tyres are working in your corner, fighting for you, there is no cheaper or quicker way to make a big jump in lap speed. A set of tyres can be worth half a second a lap. To achieve a similar performance increment, an engine designer would have to find between 100 and 150 extra horsepower, at a time when a 20bhp increase is a big deal and significantly expensive. Similarly, a half-second jump in performance due to aerodynamic improvement would be regarded as a major achievement.

In Hungary, when Alonso was asked about Renault's capacity to improve their car to Ferrari's level, or whether the rest of the championship would depend purely on the tyres, he replied: "I think mainly only on the tyres. I think Ferrari and Renault are at the maximum of the capacity of the car. I think car development has been constant all year and it's difficult to get something more from them. It can be a tenth or something like that, but no more than that. I think the tyres are making a big difference every weekend and I think we are probably in Michelin's hands."

Similarly, Schumacher said: "The championship is so close that it is going to be settled on tyre performance."

So is this total reliance on the efficiency of four bits of rubber a healthy thing for the sport?

"I think this is Formula One, and it is a lot more than that," Alonso said in Suzuka. "Yes, we say that because the difference that the tyre makes to the car is bigger than anything else that you can change, and for sure now, with the cars at their maximum level of development and maximum performance, the two or three-tenths that you can find in the tyres one weekend can make you win or lose.

"I think that is what we mean when we say that we are dominated by tyres, the key factor of the championship now in the last races. But from the beginning of the season the championship is very long and you have to take a more general view of the championship - over 18 races you need to be constantly on the podium and you need to perform well all through the season and it is not only a tyre factor. I think it is fair because Formula One is technology and everything motor sport, so you know that to be in Michelin or Bridgestone's hands is also quite normal."

Next season Bridgestone will enjoy a monopoly, however, as Michelin will withdraw after the Brazilian GP later this month. As the French company discovered when its rear tyres proved unable to withstand the extra stresses of a resurfaced banked corner at Indianapolis in 2005, and all 14 of its drivers were forced to withdraw from the race after the grid formation lap, public failure can be every bit as embarrassing as success can be valuable, in publicity terms.

The cessation of the current tyre war may prove to be a double-edged sword, however. "The influence that tyres have is massive," Jenson Button confirms. "You can easily gain or lose three to four-tenths of a second through tyre performance. Look what happened to me on my second set in China; the car was horrible. On my third set, it was fantastic again. But you accept that they are part of the package, and that they are by far the most dominant part of it.

"Personally, I have mixed feelings that Michelin are pulling out at the end of the season. On the one hand it'll be good that we are all on the same tyre, because that will be one less thing to go wrong. But Bridgestone will run harder compounds because they won't have to fight anyone, and that means the tyres will be slower. When you have competition between two manufacturers it's great fun because they tend to go for the softest compounds, which means you go a lot faster."

Tread carefully: The bald facts about Formula One tyres

* HOW BIG ARE THEY?

Formula One tyres have a maximum diameter of 660mm (26in) front and 675mm rear, and a maximum tread width of 355mm front and 380mm rear.

* WHAT ARE THEY MADE OF?

Formula One tyres are made principally of rubber, chemical polymers, Kevlar and steel.

* HOW MANY CAN TEAMS USE?

Drivers are allowed seven sets of dry tyres per weekend, four sets of wets and three sets of extreme wets.

* HOW MUCH DO THEY COST?

Teams do not pay for their tyres, but if they did the cost would be around £2,000 per tyre.

The big two: Who's the slickest of the manufacturers this season?

* BRIDGESTONE (USED BY FERRARI)

The Japanese company entered Formula One in 1997, and have generally held the upper hand over Michelin in recent years. They struggled in 2005 when only one set of tyres was allowed per race, but are more competitive this season now that tyre changes are back. They emulated Michelin by adopting a stiffer construction, and the tyre change rule allowed them to run softer, and therefore grippier, compounds. At Indianapolis they made a big step forward, as their teams started to get the best from their tyres. Arguably they now have a slight advantage in the dry.

A history of burning rubber How tyres have evolved in Formula One

Prior to 1971, Formula One tyres had treads and had steadily grown wider since the mid-Sixties to increase grip. Then came the pure slick. It had no discernible tread since the tread extended across the whole surface; there were no grooves. Grip was increased significantly, unless it rained. Then the tyre had zero ability to squeegee away water, and the driver was in trouble. In the 1975 British Grand Prix at Silverstone a breakers' yard developed at Club Corner when a late rain shower caught out driver after driver running on slick tyres.

In 1997, anxious to curb cornering speeds and spotting a cunning way of bringing tyres out of the area of the technical regulations (where any changes required unanimous agreement of the teams) and into the sporting regulations (where changes could be made on safety grounds without unanimity), Max Mosley, the president of the sport's ruling body, the FIA, hit on the idea of reintroducing grooves. This would reduce tread area again, and cut cornering speeds. "Stirling Moss started me thinking along these lines," Mosley admitted, "when he was talking about historic cars and said that you should never allow historics with treaded tyres and historics with slicks to race at the same time, because the performance gap is so enormous."