What would be a similar distance on a road bike in terms of toughness to achieve, a marathon....... or how many miles on a road bike? I can't really phrase this question very well, but have thought about doing a marathon with some guys from work in a few months. I can run a bit, say 20km or so if pushed, but don't enjoy it that much so only run occasionally.
Just wandering for those that do both, how far on a road bike giving it similar effort would you say you'd have to ride to be as tough (given average gradient, conditions, not riding over the Alps in a hail storm etc)

