Hi
I've had the same problem with an IRC going flat as soon as you hit even the smallest of steps. I switched to a Michelin X-lite and have had no problems. The bike is a Scorpa which is virtually new and the rear wheel is completely true. I took the tyre back to the dealer, BVM, and they admitted that they have had loads of returned IRC tyres. The rumour is that the latest batch of IRCs bought into the UK have some kind of problem. Some are Ok but many aren't.