Originally Posted by
Kopsis
OP description is a little confusing because it compares speed on the rollers to speed on a "stationary bike". Unless "stationary bike" actually means riding the same bike on the same rollers, any comparison is pretty meaningless.
This is where I figured it was going. Since indicated speeds on stationary bike at gym were more consistent with on-the-road (i.e., hard efforts and sprints hovering in the 20s, peaking just over 30 maybe in both cases, it seems the bad fit and position takes away any gains enjoyed by a lack of wind resistance, whereas on well-fitting bike on rollers, nothing takes away from the advantage gained. Still, it's hard to believe fit and position could make the difference between being able to "sprint" inside at 40 vs 30 mph.