Depends on the bike. The tyres that a Yamasaki leaves the factory with we're not even completely round, but the standard Sanya tyres were good enough to touch bits (the rear brake pedal) down with confidence.
I have gone and bought one. An Orion Apollo 250 but it's not listed on any of the insurer's websites so I shall have to give them a call to get a quote. Also, I paid for it through an ebay listing and since I asked the seller for his address to organise a courier I haven't heard anything from him. I shall give it a day or so and then go crying to ebay to get my money back. Hopefully it will work out though