Remember kids... always wear a helmet. (The almighty bikeradar helmet thread)

well from my experience the bern runs true to size

they dont appear to make one big enough for your head...

My head is huge. It goes off most scales, measuring at 63 - 64 cm (depending on air pressure / tidal motion).

Hence the need to try before I buy, as even XXL sizes that claim to be big enough, seldom are big enough.