49erRider wrote on 07/30/13 at 2:51pm:
... should a trail mile just count as one mile or more?
As a rider of both MTB and roads, I think you ought to use at least a 2:1, if not 3:1 ratio - depending on what sort of MTB riding you do. Beatty & Sherman probably closer to 2:1, DuPont, Whitewater black sections, Steve's Place are probably more like 3:1.
As another response said, maybe gear more towards time on the bike. If you have the budget or inclination, time coupled with heart-rate (level of exertion) would be even better.
If I were focused only on miles, and I was coming up short for the week, my brain would tell me to go get 30 or 40 miles quickly on the road bike to fill the gap, probably circumventing what you're trying to accomplish if you're just looking to get mileage only.
Then you should consider what your overall objective is - fitness? weight loss? max fun? For example, if weight loss were the goal, you'd be better off doing 3 longer (time-wise) rides per week, than doing the same time/distance in 6 sessions due to the time spent in the aerobic fat-burning heart-rate zone.