Williams "couldn't afford" to put together a mule car to run in Pirelli's 2017 tyre test program this year, according to Pat Symonds.

Pirelli asked teams to produce modified cars in order to simulate increased levels of downforce, allowing it to test the 2017 tyres before next year's cars hit the track. Mercedes, Ferrari and Red Bull will carry out a number of tests from August until November, with all three testing two days after the final race of the season in Abu Dhabi.

Williams was one of the teams to originally signal its intent to take part but Symonds - who is the team's chief technical officer - says the costs were too high.

"Not second class, but we don't have the money to do it," Symonds told the official Formula One website when asked if missing out makes it a second class team. "We wanted to join, but then we worked out the costs and it showed that we couldn't afford to do it.

"Pirelli will disseminate the information as best as they can, but it will never be the same as running it on your car. And we certainly don't have a strategic relationship with any other team!"

And Symonds believes the change in tyre regulations next year will be the "most crucial" difference in 2017, but says tyre strategy will continue to play a part in races.

"Not eliminated - that would be a too strong word - but if Pirelli hit the target then I would expect that two-stop races turn into one-stop races and three-stop races turn into two-stop races. We will see wider windows to make the pit stop - so the strategic element will be less, but not eliminated.

"Of all the changes for 2017 the tyres will be the most crucial I believe. All teams aside from the three that do testing will have no knowledge of what the 2017 tyres will look like until they run them in February. Only Ferrari, Mercedes and Red Bull are testing - the rest, we need to see."

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