For me it is exactly the opposite. I can ride all day at 17 mph. But, I have my doubts whether I would even survive a 5 mile run. Okay, I am not a runner. Perhaps natural preferences and differences in physiology play too much of a role for any ratio to make sense for a broad group of folks.

I've read everyone's points on wear and tear on the joints, mechanical advantages on the bike, wind resistance and all. But, I still want to know how the TdF riders can possibly be doing the equivalent of a marathon-a-day 20 days in a row. Perhaps elite marathoners could do this if their knees would hold out.

Cheers,
Jamie