Bridgestone switched its MotoGP rear tyres to a stiffer, heat-resistant construction at the start of last season. Highly dependent on edge grip at full lean for his corner-speed style, Lorenzo was hit hardest by the change.
Work by the Spaniard and his Yamaha team improved the situation, but it still took until round 14 for the double MotoGP champion to claim a victory last season.
Despite four wins this year, it seems Lorenzo's performances are sensitive to use of a special 'modification' to soften the tyre edge.
While a choice of rubber compounds are on offer at each circuit, the mysterious edge modification (sometimes referred to as a 'treatment', Bridgestone isn't keen to disclose its trade secrets) is not always available.
"At many circuits we provide rear slicks that feature a slightly modified cons truction to improve edge grip, but the severity of the Assen circuit means we are unable to provide this specification of rear slick," Bridgestone's Masao Azuma explained at the recent Dutch round.
Assen was where Lorenzo's run of four successive wins, leading every lap, ended with a distant third place finish. The edge modification also wasn't suitable for the Sachsenring, where Lorenzo dropped from first to fourth on Sunday.
"It's like a tennis player. If a tennis player doesn't like a surface and suddenly he has to play three of four tournaments on it for sure he cannot perform at the same level," said Lorenzo, 13 points from Yamaha team-mate and title leader Rossi as MotoGP heads for its mid-season break.
"This is what happened to me. We have some problems. My good point is acceleration and corner speed and with this tyre, at the moment, I'm not able to ride at the same level as Valentino."
Lorenzo has been competitive without the edge modificat ion, at Mugello for example. It also depends on circuit grip, citing the upcoming Indianapolis round.
"At Indy I finished second, so it also depends on the tarmac if I have more or less [tyre] problems. We hope to be able to fight for the victory like last year," he said. "Then Brno is a track where I go very fast and we will have the tyres with the softer edge part, so it should be better."
The #99 will not face the same issue next year for obvious reasons.
"Next year MotoGP will go with another brand [Michelin], a different kind of rear tyre, so for sure I will not have the same kind of problems. But for the moment I try my best to be as competitive as possible."
The Spaniard scored more points than any other rider during the second part of last season, but is taking nothing for granted in 2015.
"I don't know what will happen in the future. Every year the performance of the riders is different. Last year I was consistent, I was quite fast, I could win two races and finish on the podium in the rest. Also Marc made a lot of mistakes. That is why I was the one with more points," he said.
"This year is different. Marc cannot make any more mistakes and it seems that he is competitive again. It's just a matter of time until we arrive at a track with a good tyre for us. When this happens we have to win, finish in front of Marc and Valentino, and recover the points that I'm going to lose in some other races.
"The good thing is that in a bad race for me, Vale could only finish third. Three points is not so much, for how many problems I had in this race. In the future I will be faster than in these two races. It's going to be difficult to wait three weeks for Indianapolis..."
Bridgestone told Crash.net that its tyre allocation for each event sometimes features a mix of specifications - meaning some with, and some without the edge modification - and that Phillip Island is the only remaining round where a ll rear options will be without the edge modification.
