Fernando Alonso admits it's "impossible" to follow a race, Jenson Button calls it a "right mess" while several other drivers are also not happy with the tyre situation.
Ferrari driver Alonso came from fifth on the grid to win the Spanish Grand Prix ahead of Kimi Raikkonen and Felipe Massa on Sunday, but the big debate after the race centred around the Pirellis.
Raikkonen, Mercedes' Nico Rosberg and Button were the only three drivers in the top 10 to stop three times while the rest were forced to change their tyres four times.
The general conclusion in the aftermath of the race was that four pit stops are too many for Formula One and Alonso believes it is becoming difficult to know what's going on due to the number of stops.
"I'm happy to win from whatever position to start," the Spaniard said. "Here, I think this historically has been difficult to overtake and starting off the front row was hard for the race but now with this year's degradation and this year's tyres we see the races keep changing all the time.
"Whatever car keeps the tyre alive normally is on the podium at least - or winning the race. So, happy for this.
"If it's too much confusion for the spectators? There is no doubt. I think it is impossible to follow one race now. Here it's good because you have the tower and I think you follow the race on the tower with the numbers and you see who is first, who is second. But in some other circuits, if I'm sitting in the grandstand, without any information: radio, telephone or something, you only see cars passing."
Raikkonen initially thought he could battle Alonso for the victory late in the race, but he decided not to put up much of a fight when they were side-by-side due to the tyre issue.
"It is too easy to overtake, so no point to really fight again because you cannot hold him behind," the Finn said.
Button, who came from 14th on the grid to finish eighth thanks to his three-stop strategy, was quite critical about the current situation.
"It is a right mess. The problem is that a lot of people watching will think there's a lot of overtaking [so] it's great, isn't it?" he said. "But when we're going round doing laps three seconds slower than a GP2 car did in qualifying, and only six seconds quicker than a GP3 car did in the race, there's something wrong. This is the pinnacle of motor sport.
"We shouldn't be driving round as slow as we have to to look after the tyres. It's so complicated. It is very confusing. The whole time the engineer is on the radio saying: 'The temperatures are too high or too low, you've got to go quicker in this corner, you have to go slower in this corner, to look after this tyre.'
"When I see a car behind I let it past because I'm doing a different strategy and I don't want to damage my tyres. If I block I might destroy my tyres. It's the same thing we had in China, waving each other past so we don't destroy our rubber while hoping that the guy who's overtaking will."

Mercedes will face an investigation from the FIA's International Tribunal regarding its recent secret tyre test with Pirelli, while Ferrari has been cleared over its test with a 2011 car.

The Mercedes test at Barcelona was referred to the stewards of the Monaco Grand Prix when Red Bull and Ferrari lodged a protest on that weekend.

The FIA had been waiting for a report from the Monaco stewards before deciding if Mercedes had a case to answer, and it has decided to pass the matter on to the International Tribunal.

The sport's governing body explained that it requested information from those involved and rival teams before coming to its conclusion.

Ferrari's own test with Pirelli, conducted at Barcelona in April with a 2011 car, was deemed not to breach the rules.

An FIA statement said: "In the light of all the replies received and in view of the information gathered during this inquiry, the president of the FIA, acting as the FIA prosecuting body, has decided:

"To close the case as regard to Scuderia Ferrari Team considering that its participation in a tyre test organised by Pirelli in Barcelona on 23-24 April 2013 using for this purpose a 2011 car is not deemed to contravene the applicable FIA rules.

"To bring the case concerning the tyre testing session carried out by Pirelli and Team Mercedes AMG Petronas F1 in Barcelona on 15-17 May 2013 before the FIA International Tribunal because it results from the inquiry that the conditions of this testing may constitute a breach of the applicable FIA rules.

"The FIA International Tribunal is called upon to make a decision in compliance with the FIA Judicial and Disciplinary Rules."

THE FULL STATEMENT FROM THE FIA

The Monaco Grand Prix Stewards raised in their report to the FIA an issue concerning a tyre testing session carried out by Pirelli with the participation of Team Mercedes AMG Petronas F1 in Barcelona on 15-17 May 2013[1].

The FIA requested clarifications from Pirelli and Team Mercedes AMG Petronas F1 in this respect.

The FIA also asked questions to Scuderia Ferrari Team, which took part in a tyre test with Pirelli in Barcelona on 23-24 April 2013.

The FIA requested all the other F1 Teams to provide the FIA with information they may have regarding any tests carried out by Pirelli during the 2013 season.

In the light of all the replies received and in view of the information gathered during this inquiry, the President of the FIA, acting as the FIA prosecuting body, has decided:

* To close the case as regard to Scuderia Ferrari Team considering that its participation in a tyre test organised by Pirelli in Barcelona on 23-24 April 2013 using for this purpose a 2011 car is not deemed to contravene the applicable FIA rules.

* To bring the case concerning the tyre testing session carried out by Pirelli and Team Mercedes AMG Petronas F1 in Barcelona on 15-17 May 2013 before the FIA International Tribunal because it results from the inquiry that the conditions of this testing may constitute a breach of the applicable FIA rules.

The FIA International Tribunal is called upon to make a decision in compliance with the FIA Judicial and Disciplinary Rules.

[1] The Stewards' report follows the protests made by Red Bull Racing and Scuderia Ferrari Team on the occasion of the Monaco Grand Prix against Mercedes AMG Petronas F1 concerning its participation in the Barcelona tests (15-17 May 2013).