As the latest round of 2017 tyre testing is about to get underway - with Mercedes testing the wet compounds at Paul Ricard from tomorrow - Pirelli has revealed that it fears the tests are unrepresentative with the mule cars providing insufficient data.

In view of the new regulations for 2017 which will see increased downforce levels, Pirelli, which will be introducing tyres 25% wider than their 2016 counterparts, put together a ten date programme that would see three teams (Mercedes, Ferrari and Red Bull) test its wet and dry tyres at a variety of venues.

For the purpose of creating the sort of downforce levels expected, each team has provided a 2015 mule car modified to help create the 2017 levels.

However, with six tests remaining, including that in Abu Dhabi where all the teams will have the new rubber, the Italian manufacturer fears that while the downforce levels being created are 10% up on 2016 levels they fall at least 20% short of the levels that can be expected at the beginning of next season and as much as 40% by the end of the year.

Consequently, Pirelli is in talks with the FIA to try to discover how realistic 2017-spec downforce levels might be created, bearing in mind there are just six tests remaining before the teams run the new rubber in anger next season (at pre-season test venues yet to be decided).

"What is still missing is some downforce from the mule cars," admitted Pirelli's racing manager, Mario Isola, according to Motorsport.com.

"The teams are working to increase this downforce level for the next test," he continued. The problem of not having the downforce at the right level is that you don't stress the compound at the level that is required and expected for next year, so you evaluate the degradation that is probably not the right one.

"When the performance and downforce is increasing you have higher degradation, so now we have some numbers, but we need cars with higher downforce to have a proper number."

Asked to clarify the anticipated discrepancy, he admitted: "It's difficult to say. It depends if you consider the beginning of 2017 or the end of 2017.

"During 2017 we will have quite a big development of the cars that means we are even more far from that target. But it is probably around 20 percent that is missing.

"We don't have a lot of time," he continued. "We know they are working on the car to generate more downforce. They know they have to react quickly and we know they are doing their best to do that. I am not saying they are not doing their best, it is not easy to have this kind of car that is different from 2017 car but has to generate this level of downforce.

"We are working with them in order to have some cars that are really representative of next year's conditions, so everybody can test and we can provide a tyre that is next year in line with data collected."