dan_x saidPretty sure riding an actual bike and a spin bike are the same thing.
As a spin instructor (Well ex-instructor anyway) this isn't true at all. It is like comparing a treadmill to running outdoors...not the same. An instructor can create a ride that is more geared towards actual riders, but in the end it isn't the same nor is it meant to be.
As for taking an actual spin class 7famark, I would give spinning a few shots. Reason being, the first class may not be the most enjoyable one because like any new work out, it can be exhausting and painful, and you have to find a instructor that you like. Not all instructors are the same whether it be music, teaching style, etc. If you have the right instructor, spinning is just awesome and can be quite addicting.
Spinning is also excellent cross training and you will notice a different in your running and biking if you incorporate spin classes in your work outs.
And...just some warnings/advice.
Unless you use a cushion, your ass is going to hurt for the first week or two you start spinning. For your first few classes i would advice against using the full resistance an instructor may ask for, reason being, you need to get used to the motions and different positions on the bike. NEVER go out of the seat, positions "2" and "3", with no/light resistance...it is dangerous and you could fall off. I would also advise to avoid doing sprints on the bike for at least a week or two. Generally i would advise more but since you are young and fit you are more likely to adjust to the fluctuations of your heart rate faster than most beginners.
Hope this helps.
Just ease into it if you are serious about taking the classes.