having trouble with my rear tyre. On a ride on sunday it felt skitterish, on monday i checked tyre pressure and it was a fair bit down (22psi), pumped it back up to 34 and went about life for a few days, but i took it for a decent ride yesterday and it feels the same. Tyre's a michelin pilot activ, new last november, done maybe 800km. it feels fine when cold, but feels crap once it has some heat in it any ideas???