Marathon on a bike

i agree when i first started training after only 4 training rides going from 40 to 80 then 20 miles i could ride 100 with out feeling any where near the pain of a marathon. However bristol to london about 140 miles was probs a good equivelent even done slow that is a long ride so i think 150 miles is a bike marathon.

What about fixed? 90-100 would be quite adequate no?