Indoor cycling is becoming more and more popular. But why would anyone choose to ride inside over having fun outdoors? Or maybe... why go outside if you can stay inside? Let's try to answer these questions by finding advantages and disadvantages of both types of cycling.
The case for indoor cycling
Safety
Undoubtedly indoor cycling is safer. There are no cars, cyclists, pedestrians, dogs, potholes, oil spills, ... The risk can be alleviated to some degree by riding a gravel bike or MTB in a forest. However, if something happens, the chance of someone helping you is much lower. The number of dangerous situations grows as we spend more time on our bikes. That's why I believe that cyclists that train a lot should do most of their workouts indoors.
Productivity
When we ride outside, we may be able to use bone conduction headphones to listen to podcasts. However, we still need to pay attention to the situation on the road. When riding inside, we can focus on the podcast. We can even use our computers to do some work or learn something new. What I've found out is that I'm actually more productive when I'm programming while doing my zone 2 rides. That's why these long, easy rides are a perfect match for work.
No route planning
We can either ride our well-known routes all the time or plan new routes. The first option is boring. The latter option is actually quite time-consuming. Using route planners may help, but we still need to verify these tracks - Garmin on multiple occasions decided to include dirt roads on my road bike rides. Don't trust any software.
No interruptions
When we ride outdoors, we often have to stop because of traffic lights or other road users. It's annoying and it wastes our time. It also causes interval training to be less effective. Unfortunately, finding a 20-minute stretch of uninterrupted road for a threshold interval is nearly impossible in my neighbourhood.
Simulating climbs or flats
Many people (including me) live in flat areas. It's possible to simulate climbs to some degree... However, I find "indoor climbing" to be more realistic. Zwift's "Alpe du Zwift" is a great hill to train on and it looks like Climb portals are going to be useful too. On the other hand, people that live in mountainous areas might find it difficult to do easy outside rides. Indoors we can choose exactly how hard we want to ride.
There is no rain
Have you ever ridden for four hours in a cold rain? I have. And I'm not looking forward to doing it again. This problem does not exist inside. Although it can be really annoying when there is a bad weather outside and Zwift chooses to put us in a torrential rain in Watopia...
Handling equipment failures
Flat tire, broken chain... sometimes these failures result in a crash and/or a long walk back home. If your chain snaps indoors, you won't crash and you already are at home!
Easy fueling
A lot of water and food is needed to fuel long rides. You either have to take all that stuff with you or pause your ride to buy it. Indoors you can just put your water bottles and food within your reach.
The case against indoor cycling
Not practicing other bike-related skills
When training indoors it's impossible to practice skills such as cornering, handling difficult terrain or riding in a group. And these skills are neccessary for both performance and safety when racing outdoors.
Probably less power
Most people can't output as much power indoors as they do outdoors. This is caused by less efficient cooling, lower motivation, insufficient bike movement and a few other factors. However, this doesn't mean that indoor training is less effective - a couple of watts won't make a big difference.
For or against - "it depends"
Enjoyment
Some people can't stand indoor rides, because they find them boring. Some people love indoor cycling, because it gives them an opportunity to watch the next episode of their favourite show. Enjoyment depends on personal preferences and choice of entertainment. I can do 6 hour indoor rides and I don't get bored, because I can do both cycling and programming at the same time.
Cost, time
Maintaining an outdoor bike and it's drivetrain in a good condition takes time and costs money. On the other hand, a regular bike paired with an indoor trainer can be seriously damaged by sweat. That's why it's best to use an old, cheap bike indoors and keep the nice bike for outdoor riding. There are also dedicated indoor bikes such as Wahoo Kickr and Tacx Neo Bike. Indoor riding may also become expensive if you use AC. Which one is cheaper - riding indoors or outdoors? It depends on your setup.
Social aspect
Group rides give an opportunity to talk with your friends and meet like-minded people. Can this benefit be replicated in virtual world? To a certain extent, yes. It's possible to ride with other people and chat. There are also virtual cycling clubs - a group of people can arrange a ride. In some cases indoor group rides are better - people that live far from each other can cycle together. Even if they live in different countries.
Which one is healthier?
If air quality in your area is bad and you don't have an air purifier, indoor cycling may not be the healthiest solution. On the other hand, road cyclist breathe harmful car fumes... unless roads are almost empty. Another thing to consider is sun. A short exposure to sun is beneficial - it increases vitamin D levels. However, riding 20 hours per week in the summer can cause skin cancer. Even if we use sunscreen.
So... which one to choose?
It's clear that both indoor and outdoor cycling have advantages and disadvantages. So why should we choose one? Why not do both? For example if weather is bad or you want to do long uninterrupted intervals - go indoors. If you haven't practiced cornering for a while - go outside. Ultimately it's up to you how much indoor vs outdoor riding you want to do.