A series of common questions regarding outdoor rides routinely crop up over the course of each training season, so here are a few answers to some of the more frequent inquiries:
Q: Can I do some of my workouts outdoors?
A: Yes, but the more technical in nature the workouts are, and the more difficult and intense they become, e.g. VO2 Max, Anaerobic; the more likely it is that you'll get much higher workout quality by performing them indoors in a more controlled, distraction-free training environment. The more general and lower in intensity, e.g. Endurance, Tempo; the workouts are, the easier it is to effectively accomplish the work outdoors.
Q: Will the quality of my workout suffer if I choose to do it outdoors?
A: In some ways, yes. The number of distractions thrown at you when you're on the road can have a noticeable impact on the quality of even your easier workouts and you can end up seeing less work, i.e. training stress, thanks to the forced downtime you'll experience at stop signs and traffic lights as well as interruptions that can come at you in many forms and from all directions. So if you're really intent on matching the indoor workout requirements, consider inflating the ride time to 1.3-1.7x the duration of the indoor intervals or overall duration depending on how distraction and interruption riddled your ride becomes. For example, a 1-hour indoor Endurance ride might need to be as long as 80-100 minutes in duration depending on how many times you have to slow or stop your bike.
Q: What if I don't have a power meter but I want to train outdoors?
A: This can actually be an excellent opportunity to start to learning to relate your perception (RPE/Rate of Perceived Exertion) to your power output and grow your ability to ride by feel. As you accumulate more indoor workouts with instantaneous feedback, your knowledge of sensation relative to exertion will grow. Put another way, you'll start to learn how a VO2 Max interval at 120% FTP feels, how it feels to stay under 85% FTP for an entire ride, what it feels like when you're pushing nearer and nearer to your FTP and your legs start to well up. This is the path of the well educated power-based rider, one who can estimate - with increasing accuracy over time - power output based on breathing, effort, and muscle sensations. You can also train by HR, but letting a slippery metric like HR dictate your ride is an iffy proposition and HR should still be coupled with any other available information, e.g. RPE.
Q: Can I count a race as a workout or should I do the workout after the race?
A: A race will almost always suffice as a replacement for a high-intensity workout and there is seldom (never?) a reason to do 2 intense workouts in the same day. Consider your race or truly demanding outdoor group ride as that day's high-intensity intervals. Also, be conscious of the type of stress prescribed by your indoor workout. If the workout calls for 6x3 VO2 Max intervals and you're racing a Tuesday night criterium or road race, make yourself attack the field or group 5 or 6 times for roughly 3 minutes. Not only is this the sort of stress that often results in winning, or at least impactful, moves but it's also a great way to explore your current capabilities in the context of the very thing for which you train - racing! Similarly, if the workout is 3x20 minutes of Tempo at 80% FTP, do your best to sit in and avoid the wind. Instead, practice positioning yourself in order to minimize the work, practice anticipating the movement of the field by watching the riders ahead, and learn to do only the bare minimum amount of work necessary to stay with the field or group.