F1 teams' relief as Pirelli decides against changing 2014 tyre size

The F1 teams heading back to work after the enforced summer shutdown with next week's Belgian Grand Prix, will be relieved to learn that Pirelli has bowed to their wishes and decided against increasing the size of the rear tyres for 2014.

Just before the shutdown it emerged that Pirelli had requested some changes to the dimensions of the tyres for next year - they wanted to increase the rear-tyre width by 20mm to 400mm and the diameter to increase from 660mm to 690mm.

But today sources within Pirelli have confirmed to this website that the tyres will stay the same size.

JA on F1 technical expert Mark Gillan, former Williams chief operations engineer, analyses the situation:

"This was a really difficult one. On the one hand you can have sympathy for Pirelli; with new rules, no-one knows what the improvement will be in aerodynamics over the course of next season - there will be huge steps in development compared to this year for example, generating performance gains and thus significantly higher cornering loads - and Pirelli have to allow for that. They learned this lesson from the huge gains teams made with the blown diffusers, for example.

On the other hand, the last thing the teams needed now with 2014 chassis designs being finalised, was a significant last minute change like this, which would mean a lot of work in certain areas being thrown away and design teams having to start again, with very tight deadlines for producing chassis before the testing starts in January. (There is also a significant extra cost implication at a time when teams are already spending more on the new power trains)

No-one wants to see tyre failures, so Pirelli has to allow quite a margin. An increase in tyre size, as proposed by Pirelli, would have helped to produce a stronger tyre able to handle higher loads.

They don't know what to expect because there has been no testing.

But it's not surprising that 10 of the 11 teams were said to be against the change when it was discussed before the Hungarian Grand Prix. They feel that the footprint of the tyre should be fixed, as any change has a massive impact on aerodynamics and ride height.

The team's headache over last minute changes

Ride Height: Currently F1 tyres have a diameter of 660mm, while it's slightly more 670mm for wet tyres, to give more ride height to avoid aquaplaning. To change to 690mm at this stage is a real problem, as the layout of the cars will already have been done based on 660mm and to raise the cars this much is a huge difference. The rear ride height of the car is typically 100mm, so to raise it by 15mm at this stage is big.

Aerodynamic and mechanical change: The extra diameter and especially the width of the tyres will have a significant bearing on the aerodynamics of the car and the aerodynamicists would have to throw away a lot of the work they have done and start again with a different shape tyre and ride height changes. New wind tunnel tyres would have to be built with this aspect ratio of height to width, so teams can get accurate data from the wind tunnel. It will take significant time to do that with a new aspect ratio.

A change to the height of the rear wheel has an impact on pick up points of suspension, axle heights. It is very late in the day to be making that sort of change.

It is hard to explain to F1 fans just how sensitive an F1 car is to the contact patch and shape of the sidewall of the tyre, tiny differences make a big change to the numbers in the wind tunnel.

The timetable to build new cars

The issue needed to be resolved urgently as there is not a lot of time for teams to do all the new work they need to do to accommodate new tyre sizes.

The teams are up really against it in terms of getting the cars built for the earlier start of testing in 2014 (due to the introduction of complex new hybrid turbo engines, it's been decided to allow more testing time, so the cars need to be ready in January, rather than the usual February 1 date).

Working backwards from the January tests, you need 2-3 months for chassis construction, so you really need to have the drawings released and signed off in late September.

So you can see that if teams had a load of work to redo, to incorporate these changes, there wasn't a lot of time to do it.

It was looking especially tough for teams who buy in their power train, such as McLaren, Force India, Lotus and a possible advantage for the works teams: Mercedes, Red Bull and Ferrari.

The teams will be delighted to stay with the same aspect ratio of height to width as used currently.