By Andrew Benson Motorsport editor

This year's F1 cars are hiding a raft of rule changes

Formula One has undergone its biggest revolution in years over the winter.

An extensive series of rule changes will ensure that this year's cars are very different from those that raced at the end of 2004, even if they do not look it.

The biggest novelty is the use of a single set of tyres for both qualifying and race, so that while last year's tyres needed to last only about 45-60 miles, now they must run for 200.

Aerodynamics have been severely restricted, engines must last for two entire race weekends on pain of severe penalties and the format of qualifying is radically different.

BBC Sport details what effects the changes will have in 2005.

The requirement for one set of tyres to be used for qualifying and race - with the only exception being if the track changes between being wet and dry - has had a huge impact.

2005 TYRE RULES Only one set of tyres to be used for both qualifying sessions and the race Only a damaged tyre may be changed during a race - unless conditions change between wet and dry No refuelling allowed when a car pits for a tyre change - unless conditions change between wet and dry

Along with the changes to aerodynamics and engines, this was introduced to stop the alarming escalation in cornering speeds and lap times that has accompanied the tyre war between Bridgestone and Michelin.

Drivers have reported that the cars slide around more, but in itself that does not make much difference - they adapt.

More profoundly, Grands Prix have been transformed from a series of short sprints between pit stops into marathons in which drivers have to look after their tyres to ensure they remain in good shape until the end of the race.

As a result, the rule has already promoted overtaking and the quality of racing, especially later in races, as drivers who have looked after their tyres by pacing themselves in the early stages look for a way past those whose tyres are worn out.

Ultimately, the beneficiaries will be the more intelligent drivers, who are sensitive enough to use their tyres in the best way.

Unsurprisingly, most expect Michael Schumacher to prove to be the most adept at this.

Drivers braced for rules revolution

Teams also have to choose the tyres they will use very early on in a race weekend, and this has already led to some making wrong decisions and ending up racing with tyres that did not last the distance.

That further increases the chances of overtaking later in races, as teams who were more conservative in their tyre choices end up in better shape.

F1 bosses have introduced restrictions on design as a further way to control the speed of the cars by dramatically limiting the amount of aerodynamic downforce that engineers can extract from the cars.

Interactive guide to an F1 car

The aim was to cut downforce by 25%, although leading designers say that they have managed to claw back a "significant" amount of that.

AERODYNAMIC CHANGES Front wing height raised Rear wing moved forward Diffuser made less effective

It was hoped that a by-product of these aerodyamic restrictions might be that overtaking was made easier.

One of the problems drivers routinely face in trying to pass another car is a loss of grip because the car in front disrupts the airflow over the one behind, reducing its ability to create downforce.

In theory, if the amount of downforce being generated is reduced as a proportion of the total grip of the car, then this effect will be reduced.

However, although it is too early to form a comprehensive picture, this appears not to be the case.

Toyota driver Ralf Schumacher has reported that the new cars "lose even more downforce" than did last year's.

Instead of a single qualifying session on Saturday afternoon, grid positions will now be decided by aggregating the times from two sessions.

In the first, on Saturday afternoon, cars will do a single timed lap, running in the reverse order from which they finished the previous race.

Will the new qualifying format mean drivers make more mistakes?

Teams can run with as little fuel as they like, which has not been the case since single-lap qualifying was introduced in 2003.

But there will be an additional qualifying session on race morning, after which the cars cannot be refuelled before the race.

The spectacle of the Saturday session has been improved.

That is because drivers will be able to push their cars closer to the limit because they are lighter and may therefore be more likely to make mistakes, and therefore shake up the grid order.

But the downside is that the interest in that session has been reduced, as it does not set the definitive grid.

And the TV companies have been reluctant to show both a qualifying session and the race on Sundays.

Teams now have to make engines last for two entire race weekends - and will suffer draconian penalties if they need to fit a new one.

A broken engine will now mean a penalty of 10 grid positions

A driver who needs a new engine during practice at a Grand Prix will be relegated 10 places on the grid. But if the change takes place after first qualifying, he will start from the back.

Long-term, this change is likely to play into Ferrari's hands - they were the only team last year who already had an engine that could last two races.

Every other team has had to do a lot of hard work over the winter to try to make their engines last, and some are still on a knife-edge.