Sure, many athletes use spinning and train indoors during the cold winter months. Others (like me) do it because they have kids and it's the only way to fit in a workout. You can try spinning videos or 10 - 20 minutes warm up, 2 mins hard, 2 mins rest, 2 hard, 2 easy, etc. Then cool down for 10 - 20. It is a great way to be efficient with your time due to life commitments.

Stationary bikes have radically different geometry than road bikes. You're still getting a cardio workout, but I really wouldnt subsitute it for bike time. Its more like cross training.

A trainer is much better. Youre not gonna hurt your bike, cover it with a towel so you dont drip salt all over it. I like the trainer, cause I can be home with the girl and the dogs, and watch a movie or two. Not to say its not boring, and there are many distractions trying to temp you away from your ride, but riding in the pitch black on the bike trail isnt exactly stimulating.

You really need a specifically designed spin bike for that... regular stationary bikes don't have the resistance necessary to do the spinning type stuff, like sprinting, getting out of the saddle, etc.

I bet if you talk to your gym though, they can probably pull out one of their spinning bikes for you to use on your regular workout.

I've heard most folks here recommend Cyclops or Kurt Kinetic brand trainers with confidence

The trainer is your best bet, but you can supplement it with a spinning bike or stationary bike (I personally feel like killing myself if I spend more than one hour on a trainer). The spinning bikes have a weighted front wheel that makes it easier to maintain a high cadence and harder (impossible) to coast, so the cardio training is really extreme. That's why they're so popular in gyms; it's a much better way to burn a ton of calories than most people could get on a regular bicycle.

That being said, the spinning training won't equate exactly to time on your bike. Because the wheel is weighted, your hamstrings contract eccentrically at the top of your pedal stroke to slow the speed of the flywheel. You'll feel the difference in your pedal stroke when you get back on a regular bike. But as a way to build aerobic base in these cold months, it's okay; like I said, you're going to have to work a lot harder on your indoor trainer than on a spinning bike to get your heart rate up.

Thanks. That's all good advice. It sounds like a combination of spinning, using the trainer and getting out on the road when possible is probably the best bet.