I don't think there is a ratio. I think it is apples to oranges, or at least red apple vs. green apple. If your body can handle the pounding of running, running will win out every time if you are jogging vs. riding. If you are genuinely riding, sprints, hills, single track mountain bike, timed long rides, you can do wonders. Look at lance Armstrong who may be the most fittest athlete out there in his prime and he just rode his bike. But it was the way he rode it that gave him the fitness levels he achieved. I think with any type of exercise you get out what you put in, so train and go as hard as you can and push your self past where you want to quit and go a little extra.