My current furthest ride in a day was 190 miles, i achieved this on a mountain bike set up for road, although it did have a heavy front suspension fork. I hope to break 200 miles in august, my bike has had some good upgrades since the last (lightweight rigid forks, 11-21 dura ace cassette and a few other bits) and im feeling a lot fitter so im confident i can achieve this. I do these ride solo so there no drafting involved. As many others have said though you don't need to ride that far for training, just push yourself harder over shorter distances. I only do the long rides now and again, more for the sense of achievement than fitness beneficial. Happy riding mate!!!