This is just a theory but it came from a very good source.Guran wrote: I'll leave it to him to chip in.
I bought a set of R888s at the same time as guran. This was about my fourth set of them: same size, same compound as usual. I'd always been very happy with R888s but this set was absolute crap. I spent the next year driving the car like it was speedway. Guran's came from the official distributor, mine came from a parallel importer but they were both genuines from the same factory.
I fell into a social discussion with one of the country's leading multi-brand motorsport tyre distributors. We are both of an age where we can have an extended technical discussion of whether nurses uniforms of the 60s and 70s (you remember: pinafores, starched caps, watch upside down, starched flat fronted skirt, court shoes, etc) actually made them better at their jobs or if they just looked hot in them. I interrupted this to ask him a question about tyres, specifically why guran and I both had such bad experiences.
He said he too had had a number of regular R888 customers who got a bad set at about that time. He put it down to a change in EU tyre regs when they brought in the new Eco-tyre rules. He said the key part of this, as far as competition tyres were concrned, was banning certain carcinogenic oils from the compounds. Some manufacturers (and he named Yokohama and maybe Bridgestone) got it right and immediately released a better performing motorsport tyre while others, especially Toyo, produced dog motorsport tyres for a few months until they got it sorted.
I did some googling after that to get the background on what he said and it all checked out. In 2010 highly aromatic hydrocarbon oils had to be replaced with mineral oils. Worldwide this meant an improvement in tyre life and rolling resistance at the expense of grip. So it was not a problem for 99.9% of the users but a real issue for motorsport.