LONDON, England - Formula 1 must allow in-season testing to avoid the risk in 2013 of tyres lasting only a handful of laps and races being cut.That's the view of Pirelli motorsport director Paul Hembery who is taking flak because his company's quick-wearing tyres caused a procession of pit stops during the 2013 Spanish F1 GP on May 12. He warned that a current-testing ban made it harder for the Italian company to meet significant technical challenges expected in 2014.'UNDERESTIMATED THE IMPACT'He raised the possible scenario of a race "where you can only do five or six laps on every single option that we bring because we've totally underestimated the impact (of the new regulations)"."I don't think we'll have an issue with structural integrity but we could end up with the wrong compounds for the track or (not know) the influence of the powertrain on the tyre. There are championships, less visible than F1, where those sorts of things have happened and you've ended up having to take 10 laps off the race distance."Team managers held a working group meeting during the Spanish GP weekend and voted to maintain a ban on in-season testing, despite opposition from some teams. McLaren's sporting director Sam Michael said they had decided to stay with the limit of 12 days pre-season but testing in January was allowed and could be outside of Europe.Pirelli currently has a 2010 Renault, as much as five seconds a lap slower than current cars, for testing. The company is expected to continue as sole tyre supplier in 2014, although a deal has yet to be signed.A defensive Hembery said at the weekend as criticism mounted: "We have no in-season testing, we can't have access to the cars going around now, and have to run around in a 2010 car. It's all rght to sit there and criticise but you're not exactly given the tools to do a precise job."NEW ENGINES FOR 2014The Spanish GP put Pirelli even more in the spotlight with four pit stops turning out to be the norm, a number of failures in practice, and the race that saw tread stripping from tyres.Pirelli has gone more aggressive with the tyres for 2013 and has now agreed to change both the structure and compounds to make them last longer and reduce the number of pit stops. It said on May 14 that the modifications could be made from Canada, race seven of 19, in June rather than the end of that month.2013 will see a switch from the 2.4 V8 engines to new 1.6 V6 units with kinetic energy recovery systems and turbocharging.Hembery said: "We are getting varied data from different teams which means there are going to be some surprises. We don't want to be as a tyre maker in a situation where we come up with some surprises when we get to Melbourne (for the start of the season). We want to know before."Ferrari, whi has its own test track and one of the biggest budgets, has long pushed for a return to the in-season testing that was banned in 2009 to cut costs. Hembery said Pirelli had different reasons and needed to test with current cars, now and in future."Next season, if all we have available to us is a 2011 car, that's going to help us with nothing when you've got a very different power train. I think the teams are going to have to go back and revisit the ban) I don't think Ferrari and some of the other teams are going to let it go."I hope we can have some sort of compromise, with some sensible, limited, in-season testing."