Pirelli has admitted that predicting the number of pit-stops to be expected in this weekend's Canadian Grand Prix will only be possible once the teams have hit the track on Friday.

The tyre manufacturer is under fire to rein in the number of pit visits after the Spanish Grand Prix was won with a four-stop strategy, but has canned plans to introduce a revised tyre for this weekend's race following the furore over its three-day test in Barcelona, which saw Mercedes running its 2013 car and both regular race drivers in a bid to help Pirelli get on top of wear issues.

The Gilles Villeneuve circuit, which plays host to the Canadian round, features a mix of long, fast straights and slow corners, placing a premium on braking and traction, but is also susceptible to cool conditions, prompting Pirelli to opt for its medium and supersoft compounds, both of which have a low working temperature range.

One of the reasons why Canada is so demanding for the tyres is that the cars tend to be run in low downforce configuration to maximise speed on the straights. This means that the tyres are doing all the work when it comes to getting the car round the corners, putting the emphasis on mechanical rather than aerodynamic grip.

The rear tyres are particularly challenged, due to the heavy traction demands out of slow corners and the hairpin. It's very easy to produce wheelspin if drivers are too eager on the throttle, while the bumpy surface also provokes wheelspin as the rear tyres break traction.

As a semi-permanent track not used extensively during the year, the venue also presents a real risk of graining, particularly with cold tyres sliding excessively against the track surface instead of finding grip, causing an unusual pattern of wear. This phenomenon is mostly seen at the start of the weekend when the track is at its most slippery, without any rubber laid down.

"Canada is always one of the most unpredictable races of the year and this is partly because it is so challenging for tyres, mostly due to the heavy braking and traction demands of the circuit," motorsport director Paul Hembery confirmed, "Coupled with a high degree of track evolution over the weekend, effective tyre management has always been a key to success in Montreal.

"We'd expect two to three pit-stops per car, but we'll only be able to make a precise forecast after Friday, once we've seen some running out on track."

Along with Singapore, Korea and Monaco, Canada also has a high propensity for safety car periods, adding further weight to the need for flexibility when it comes to strategy.

"Because of the high degree of tyre wear and degradation, we would expect to see a number of different strategies at work, as was the case last year - with teams deciding whether to go for a 'sprint' strategy or to do fewer stops and put the accent on endurance," Hembery continued.

"Last year, the 'sprint' approach won the race but, with so many different parameters at work, the teams will have to analyse the data - not to mention the weather forecast - very carefully before committing to any particular tactics. Often a flexible approach works best in Canada, so we can also expect many teams to be leaving their options open, allowing the drivers to really make the difference when it counts."

The 2012 race, run on the soft and supersoft compounds, was won by Lewis Hamilton, who stopped twice, while the second and third-placed finishers - Romain Grosjean and Sergio Perez - stopped only once. The strategy choice throughout the top ten was split half and half, with five drivers stopping twice, but the tactic did not pay off for either Fernando Alonso or Sebastian Vettel, who were both passed by Hamilton in the closing stages.

As the teams found in 2011, adverse weather conditions can also play a key role in the Canadian Grand Prix, and Pirelli will bring both its intermediate and wet compounds in the expectation of at least one wet session.

The revised medium compound tyres planned for introduction in Montreal will now not be raced until Silverstone, although each team will get two sets per car to evaluate during Friday free practice in Canada.


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