Right so I have the tyres and whilst they were an absolute **** to fit they are now on. The front is pumped up and seems to be holding pressure (ill check it tomorrow and chuck in some sealant). The rear however will not hold pressure, air seems to be rushing out of the valve where the round bolt thing is (I'm sure there's a technical name). I have tried loosening it and tightening it, I have even tried wiggling the valve but nothing stops the air coming out. Any ideas or is it new valve time?