An interesting twist to the Pirelli testing saga has emerged, and it throws a little more light on what Mercedes might or might not have done at Barcelona.

This blog can reveal that since the start of the season some teams have routinely being swapping the left and right rear tyres, having discovered – in some cases as early as winter testing – that they found an overall performance advantage by doing so.

The 2013 steel belt tyres are ‘handed,’ meaning that they are marked left and right and are intended by Pirelli to be used on that side of the car.

However there is nothing in the rules to stop teams from using them on the ‘wrong’ side, if they find it works better. However it’s not something that can be done without a considerable amount of attention to set-up and so on, in order to make the change work effectively.

Indeed in the case of some teams it even goes back to the design stage as they worked with data during the winter, having run prototype tyres in Brazil, and decided – in effect – that Pirelli had got its sums wrong in defining the left and right side tyres.

Intriguingly sources have told this blog that in Monaco Mercedes used the swapping technique for the first time – or at least it was the first time that it was spotted by keen-eyed observers.

It would thus be very easy to speculate that Mercedes took the opportunity of the Barcelona test to try swapping the rears around.

However while it may have helped Mercedes in Monaco, it might not do so in Montreal – assuming that Pirelli follows up on its promise to switch from steel belts back to Kevlar, as used last year.

As is well known, the move has been touted on safety grounds, as a result of several cases of delaminating treads, which have caused embarrassment to the Italian company – even though many observers consider that a delamination is potentially safer than a complete tyre disintegration, as it allows the driver to carry on back to the pits.

Pirelli has insisted that the change won’t have a major impact on the competition.

However, Kevlar belted tyres are not ‘handed’ meaning they are identical on both sides – in other words there is no point in swapping them around.

And that means the teams that have been routinely swapping will lose the advantage they currently have, and that in turn explains why they a) they are now fighting with Pirelli and the FIA over the planned change and b) why those teams who have not been able to make tyre swapping work, or have general tyre issues, are only too happy for it to go through…

It’s also clear that the change of belts represents a change of specification, which usually has to be cleared by all the teams.

If the change does happen it will provide further ammunition for Red Bull and Ferrari given that it is widely accepted that Mercedes tried the revised tyres in Barcelona, and thus have the huge advantage of being the only team to have already run 2013 Kevlar-belted tyres.

Inevitably the speculation is that Mercedes didn’t just try tyres in Barcelona, but also its own components. It’s even been suggested that the team ran a gearbox with revised suspension geometry in attempt to get to the bottom of its tyre problems. However a Mercedes spokesman says that no new parts were tried, and it was only about tyres.

This story is far from over yet…