World champion Fernando Alonso admits he must rely on guesswork as he bids for a first Monaco Grand Prix win this weekend.

The Enstone-based Renault F1 team driver arrives in the principality with a 15-point lead over Michael Schumacher in the standings but cannot afford the kind of slip which hit his chances last year.

The wrong tyre choice in 2005 wrecked his hopes of victory, but Alonso admits the Monaco streets are too unpredictable to guarantee a similar mistake will not happen again.

He said: "It is nearly impossible and in Monaco sometimes you have to guess a little bit with set-up and make changes thinking about qualifying and the race, not the immediate moment.

"The circuit starts the weekend very dirty and cleans up with every lap, getting better and better all the time. So you have to have some guesses and put a set-up on the car, then work from there."

The Spaniard admits he is no great fan of Formula One's only true street circuit, claiming the tight confines make it impossible for drivers to clock a perfect lap.

He added: "Monaco is different to anywhere else, completely different.

"First of all, we run a special set-up to cope with the bumps and tight corners, so the car feels very different and is quite hard to drive.

"The circuit is so tight that it is hard to get the car and tyres to the maximum, or to use maximum power on this track.

"At the end of the day, from the point of view of getting maximum performance from a Formula One car, this is not my favourite circuit."

The unique characteristics of the track, which is a main road through the principality for the rest of the year, mean drivers face a step into the unknown when practice begins today.

Alonso's team-mate Giancarlo Fisichella expects to take his time before he dares go flat out on the concrete-lined streets.

He said: "It is really unusual. The feeling is very different compared to the first laps of the weekend at a normal circuit.

"You go round the first few times and you're telling yourself that it's impossible to drive on the limit at this track.

"Then, after ten or 15 laps, you get more confidence, you feel more comfortable, you start braking later, and you find the limit.