It's all about the tires: Pirelli plan on hold

(CNN) -- Formula One is supposed to be about drivers racing fast cars, but this season it seems to be all about the tires.

There have been complaints from teams and drivers, with an official investigation also underway over a development test, while the latest twist involves Pirelli putting its plan on hold to introduce new race tires at next month's Canadian Grand Prix.

Instead, each of the 22 drivers will be given two sets of development medium compound tires to try out during the first practice session at the Gilles Villeneuve Circuit in Montreal on 7 June.

A statement by the Italian manufacturer explained: "The Formula One teams will have an opportunity to test the new range of Pirelli tires during free practice at the Canadian Grand Prix, while the tires used for the actual race will remain in their original 2013 specification.

"Following feedback from the teams and drivers, the new specification of tire is then set to be introduced from the British Grand Prix at the end of June, and will remain in place until the end of the year."

Often dismissed by the sport's protagonists as the "black things in the corners," those spheres of rubber have very much moved to F1's center stage.

After the last race in Monaco, it emerged that Mercedes, who won the race thanks to Nico Rosberg, faced an official investigation over whether it carried out an illegal tire test.

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The German team, who are based in Oxfordshire, England, helped Pirelli carry out a three-day tire test in Barcelona immediately after the Spanish Grand Prix but controversially the team used race drivers Rosberg and Lewis Hamilton and their 2013 car.

In May, Pirelli had asked the sport's ruling body -- the FIA -- if it could carry out testing with an F1 team.

The sport's rules state that 1,000 kilometers of testing with any marque is allowed during the season -- as long as every team is offered that opportunity.

But rival teams Red Bull and Ferrari protested to the FIA, arguing the Barcelona test contravened the rule banning in-season testing.

The FIA is now investigating the matter but neither the governing body or Pirelli expect a resolution before the Canadian GP.

Read: Mercedes faces FIA tire probe

Even prior to Monaco, tires had already been drawing plenty of heat.

Red Bull and their triple world champion Sebastian Vettel complained the 2013 rubber meant they could not push the car to the limits of its top-speed because the tires had to be so carefully managed.

There were further criticisms after the Spanish Grand Prix was won by Ferrari's Fernando Alonso on a four-stop strategy.

Like Spain, the race on Canada's temporary race circuit, which combines high-speed straights and slow corners, could well see teams make multiple pit-stops.

There were also more serious safety concerns following a spate of delaminations -- where the tire layers separate -- which affected Hamilton, Felipe Massa and Paul di Resta's cars.

Pirelli wants to introduce new tires that are not prone to dangerous delaminations as quickly as possible.

The Italian company is also aware it must protect its image both for its road car clientele and also as it hopes to sign a new deal to continue as F1's official tire supplier.

"The aim of introducing the new tire is to prevent any instances of the tread detaching itself from the structure," the Pirelli statement continued.

"However, the performance and wear characteristics of the new tire will not be significantly different, with the aim of keeping up the spectacle and retaining a strategic element to all the races."

In theory, the FIA does not interfere with decisions on tires.

"We only step in on safety concerns.," an FIA spokesman told CNN: "For us safety is paramount.

"When they decide to bring a new tire, it is normally given to everybody. The tire has to be the same for everybody... it is evaluated afterwards."

But with Mercedes facing an official investigation over its involvement in testing, the subject of tires has become an issue where everyone in F1 must now tread carefully.