Analysis: Why is Robert Kubica only the reserve driver at Williams F1 team?

Williams has finally made its long awaited driver announcement, pairing Sergey Sirotkin with Lance Stroll as the race drivers for 2018.

Robert Kubica is confirmed as reserve driver.

Many Williams fans will be dismayed, while neutral F1 fans will be wondering, why is it that Kubica, a race winner and a big name in F1, is only the reserve driver?

The obvious conclusion most will draw is money: Sirotkin's backers are believed to have offered €15m a year for two years to Williams on top of the funding from the Stroll family.

But it is also the case the in the Abu Dhabi tests, 22 year old Sirotkin did a good job and swayed the team towards thinking of him, rather than Kubica, who had been trying to build the case for a comeback from his arm injury.

Sirotkin was faster, especially on the single lap runs, although Kubica was strong on the long runs.

Time on track is very limited in F1 and Sirotkin had certainly had more than Kubica in the build up to the critical test at Yas Marina, after which the decision was made.

Kubica believes that he has more to come, as he said on his appearance at the Autosport Awards in December.

Sirotkin has been knocking on the door of F1 for some time, without landing a race seat. He orbited Renault, taking the reserve driver role last year, driving partly in tests and Friday practice sessions. Some will wonder why he didn't get a chance, especially during the period when Jolyon Palmer was struggling.

But Renault had their eyes on Carlos Sainz from 2016 and when McLaren and Honda split with Toro Rosso taking the Honda engines, that opened the door for Renault to move in on Sainz.

Williams now has the youngest driver line up in F1, ahead of Sauber with Charles Leclerc partnering Marcus Ericsson next season.

But Williams has managed to convince Kubica to take the reserve driver role, which allows him to get more track time as well as regular simulator time and will reveal whether there is more potential, as he believes.

Stroll has two more years on a three year contract and Sirotkin a two year contract, so on the face of it there is no opening for 2019 for the popular Pole. But things can always change, for a variety of reasons - as Valttei Bottas' shock move to Mercedes in 2017 demonstrated.

The main reason why Kubica is in the reserve driver role, however, is the engineers.

All F1 engineers need pushing; even the ones at the top of the tree at Mercedes or Ferrari. History tells you that F1 drivers who go into the real details with the engineers on everything from damping, to aero to fuel mixtures and make demands, push the team forwards.

A rookie line-up, however talented, doesn't know what it doesn't know and so an experienced and demanding driver like Kubica is important to keep them stimulated and to challenge them.

Also with both drivers under 25 and not exactly household names, it helps with the sponsors to have a driver with star quality like Kubica. He can fulfil obligations for Martini, which the youngsters couldn't do as well.

It will be good to have Kubica around again and it will be interesting to see how Sirotkin does.

F1 paddock wisdom is that Williams will slip back behind McLaren and Renault in the pecking order this season, despite having a Mercedes engine and a chase overseen by technical chief Paddy Lowe.

That outcome would not reflect well on the drivers or on the decision makers who put them there. We will find out soon.

What do you think of Williams' move on Sirotkin? How much of a role can Kubica play from the reserve driver position? Leave your comments in the section below

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