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It has emerged that tyre wear will be critical in Sunday's race - making the smartest choice of tyres and then managing them cleverly will decide the weekend, particularly for the top 10 qualifiers who must start the race on the rubber on which they set their best grid time.

This is a change from carrying race fuel in the final session of qualifying and is intended to lessen the chances of the quickest cars disappearing into the distance.

Lewis Hamilton in action in his McLaren in Bahrain - Photo: Getty

Some teams believe the softer of the two tyre compounds could be as much as half a second quicker than the harder compound, depending on a car's characteristics.

But the learning process has been slow because under the new regulations, the teams have fewer tyres to work with over a weekend. So teams have to ration their use of tyres.

Because of the desert setting of the first race, they've limited their mileage while the track conditions improved from underneath a blanket of sand and dust.

In the recent past, qualifying high up the grid has been a major advantage for drivers - but here in Bahrain qualifying fastest on the lightest fuel may not be the key to success in the race.

According to one team's race simulation, the biggest potential gamble for qualifying would be choosing the soft tyre for the final dash for grid positions. That might get you on to pole position, but there is a risk of a sudden performance drop-off during the race.

That would force an early pit stop and a sure-fire descent into mid-grid congestion.

The more likely option for the leading teams is to choose the harder tyre for qualifying, leaving them to make the one mandatory switch to the softer tyre for the run to the chequered flag.

Reacting to the consequences of the refuelling ban will also be crucial.

One leading team official described the demands of the new race strategies as "very stressful".

It'll be no good hedging your bets for a couple of laps after a rival peels off into the pit lane - by the time you decided to come in, the advantage your rival had got from fresh rubber could have lost you the race.

But however it plays out on Sunday, that will not necessarily be the ideal strategy elsewhere. The teams will be learning to adapt to the new rules over the opening races.

For , for example, where there's a far greater chance of a safety car, the best call could be to start on the softer tyre, make up positions and then be ready to pit if and when there's an early incident.

Currently, in Bahrain, look to have the kindest car on tyres. Their greater concern is finding a better balance.

and posted the more impressive times on race fuel loads but both have problems to solve.

Ferrari found they lost time on the softer tyres. McLaren lost performance on their rear tyres generally.

on a shorter lower fuelled run, but the current world champion found his mark on the longer race runs.

The idea of a central engineers' island within the McLaren garage, where the drivers gather to analyse the data together with their engineers, is so far having the desired effect of making the drivers work as a team.

Likewise, there seems little to choose between Ferrari drivers Felipe Massa and .

The front-end grip they both enjoyed through the twisting middle section of the track set them apart from the field.

Fernando Alonso hopes to make a winning debut for Ferrari in Bahrain - Photo: Getty

Alonso would certainly have enjoyed his sweep past Sebastian Vettel late in the afternoon but that was just before the Red Bull driver found his day blighted again by last season's malaise, unreliability.

Vettel suffered a brake-disc failure. Mark Webber had already been sidelined by a driveshaft problem.

Quick over short bursts, both are still struggling for a set up which doesn't chew their rear tyres with a heavy load of fuel. Like last year, they're still seeking better performance through slow-speed corners.

That's exactly what's required through the new eight corners in the middle section of the circuit, and that could cost them over a race distance.

The extension is also very bumpy and will be a severe test for the cars on full tanks.

The most significant movers outside the top four teams were . Adrian Sutil's Friday morning performance at the top of the timesheets was done with a respectable fuel load.

Their long runs on full tanks - around 160kg - during the afternoon stood up favourably against those expected to be comfortably faster.

They're expecting to score points on Sunday.

Sauber's belief that they have a strong car remains unshaken despite their low-key performance so far, having concentrated on long, heavy fuelled runs on Friday.

, the other team to catch the eye in Barcelona testing, enjoyed rookie Nico Hulkenberg's unflustered start but veteran Rubens Barrichello lost ground with electrical problems.

A telling factor in their progress will be the fuel economy of their Cosworth engine.

There's one added complication for all front-runners on a weekend that promises so much.

Backmarkers could decide early calls in the strategy battle. Newcomers have been almost 12 seconds off the pace, and could be lapped before one quarter distance.

Even more than usual in Formula 1, nobody can afford to be held back when they're getting up to speed with change.

UPDATE AT 0845 ON SUNDAY:

On race morning, the stage is set for a showdown between Sebastian Vettel's Red Bull and the two Ferraris.

Red Bull's Renault engine has the better fuel efficiency and the car could start 10kg lighter than the Ferrari, which is the most thirsty car despite plenty of work over the winter.

But concern remains that Red Bull will be much harder on their rear tyres than Ferrari who've shown greater consistency over longer runs.

Brake wear shouldn't be as much of an issue as it has previously been in Bahrain because the new layout of slower corners reduces the demands on the brakes.