Which is better for fitness?
The sticking point with many spin bikes is that it’s easy to look (and feel) as though you’re clocking a calorie-burning, cardio-boosting pace without actually working out, as the wheels keep spinning once you’ve stopped applying force.
Spin bikes tend to have a weighted flywheel that, once in motion, has its own momentum that makes it seem like you’re logging a higher cadence than you would with the same effort on the road.
On a road bike (or cyclo-cross or mountain bike, for that matter), you need to use your hip flexors and quadriceps to overcome the friction of the road and wind resistance. If you slack off, you stop – there’s nowhere to hide!