Analysis: How Williams have become Formula 1's pitstop kings

For after what technical chief Pat Symonds called an 'embarrassing' failure in the tyre change department in recent years, the Williams crew has been the fastest in the pitlane at each race so far this season.

Its 2.35 seconds stop in Australia, and 2.32 seconds in Bahrain was improved to 2.10 seconds in China to deliver it a hat-trick of trophies for the DHL Fastest Pitstop Award.

While one brilliantly fast stop could be put down to luck, the fact that it has been consistently at the top shows that there has been a significant change that is now delivering hard results all the time.

And it is especially satisfying for the team, after the spate of problems that has marred its recent campaigns and left it throwing away good results through time lost in botched pitstops.

In fact, a slow stop at the 2014 Canadian Grand Prix was cited by Felipe Massa as the reason he did not win that race.

Hidden progress

Valtteri Bottas, Williams FW38 pit stop

Photo by: XPB Images

The dramatic transformation has not come from a new pitstop coach, a better fitness regime or a shuffling of staff: instead its down to a simple mechanical change on its car.

Speaking to Motorsport.com, Symonds said: "If you remember, it was a real embarrassment last year.

"We had this problem with the sticking wheels, and actually we had to do a complete redesign of the hubs to get around it.

"And we took the opportunity to really analyse every part of it. It is really working well now."

Symonds claims that the issues with the sticking wheels last year actually disguised the progress the team had made in improving its pit crew.

"We had put up a lot of stuff in behind the scenes, we had our fitness trainer involved for example, so there were a lot of things going on that weren't showing because we had the mechanical problem with the cars. But now bang: we are hitting the low two-seconds."

Secret changes 

Williams FW38 front detail

Photo by: Giorgio Piola

Interestingly, Symonds will not reveal too much about what the key problem his team solved was, in case it helps rivals not go through the same learning pains.

But he dismisses the theory that it was down to the team using mismatched metal components that were expanding at a different rate – so did not fit as well when the car was 'hot' in races.

"No, it was something other than that," he said. "It was a design feature that could have been improved. It was quite subtle.

"And I'm really not going to say what it was because someone else will run in to it one day I think. I am sure they will in fact, because it was so subtle."

"But in solving the fundamental problem, we just put a broom through the whole thing. It is a very different design now with the whole hub, wheel nut, wheel. everything. Yes, it has really worked well."

Axle tweaks may hold answer

By Matt Somerfield

Williams FW37 and FW38 axle comparison

Photo by: Matthew Somerfield

Williams, like the rest of the field, use a captive nut system. This means the nut remains within the wheel, rather than being a separate item that stays in the wheel gun between changes.

In the case of Williams, the nut engages with three threads on the axle. It is possible these threads may have had their roughness modified this year to reduce the chance of galling.

Williams identified the axle as one of the key areas where it can improve performance and, as such, the FW38's axle features several differences in shape, weight and material.

All of these are likely to have been examined to reduce thermal expansion – which is critical when you consider the temperatures the axle is exposed to by virtue of its
proximity to the braking system.

Although it turns out thermal expansion was not the root cause of Williams' sticking nut issues last season, it may well have been a subtlety that contributed to the situation.

Looking in detail at the design, the base of the axle is now more deeply tapered. This allows a suction gap between the axle and wheel during engagement and release.

Meanwhile, the end cap features several changes to both its shape and the number of crevices. This changes its aerodynamic profile, perhaps in keeping with any subtle tweaks made to the front wing aero structures and/or the design of the wheel.

It is worth noting that whilst over half the grid (Ferrari, Red Bull, Haas, Toro Rosso, Force India and McLaren) utilise a blown axle, Williams has opted not to – even though it did so in 2013.

The blown axle, which can be helpful in an aerodynamic respect, does make life more difficult in terms of handling the thermal aspects of the axle, upright and braking systems though.