sarahale
Über Member
All my longer rides I have found to be more a test of comfort than of stamina. Can you cope with sitting in the same position for 7 or 8 hours? How's your bum? What about your back and neck, shoulders, wrists and so on? In view of this I'd get off your mountain bike immediately and get some serious hours on a road bike before the event. I have no doubt your legs will manage to turn the pedals often enough to do the mileage, but I hope your comfort levels allow you to find out for yourself.
It's a comfy road bike as fits me well but I think you have a very good point here, thanks!