LONDON, England - Lotus principal Eric Boullier said on Thursday (May 16) that Pirelli's decision to change the Formula 1 tyres after just six races penalises those who have done a better job than others in getting the existing ones to work.Boullier said on the team website: "Just imagine for a moment that because a football team can't run as fast as its opponent, the dimensions of the pitch are changed at half-time. That there are changes to come can be seen as somewhat frustrating and I hope they are not too extreme."FRUSTRATING CHANGEPirelli announced after Sunday's (May 12) 2013 Spanish GP that it would change the tyres starting with the Canadian GP in June, Round 7 of 19, to make them last longer and reduce the number of pit stops.Ferrari's Fernando Alonso made four stops on his way to victory in Barcelona, with Lotus's Kimi Raikkonen second after three visits.Ferrari and Lotus are the two teams which have got the most out of the quick-wearing tyres, rubber heavily criticised by Red Bull; McLaren and Mercedes have also struggled with them.UNDER PRESSUREBoullier said Pirelli was clearly in a difficult situation and under pressure: "As with every season, some teams do a better job than others with their designs and some drivers are more adaptable than others to the changes of both car and tyres."It is frustrating when you've developed a car from a set of tyre specifications which are available to everybody - for tyres that are the same for everyone - to then be told that they are being changed mid-season."Boullier said Lotus, which won the season-opener in Australia with Raikkonen, would be working "twice as hard" to adapt to the changes. Raikkonen is second in the championship, four points behind Red Bull's triple World champion Sebastian Vettel. Stay with Wheels24 for the 2013 Formula 1 season – fresh reports every day.