I want to get deep on VirtualPower®! Okay, I used the trademark there because TrainerRoad has trademarked the combined word. I think I’m okay using the word Virtual Power as a separate and not combined entity. I’m sure someone will let me know if I am doing it wrong. I looked it up online, and yes, TrainerRoad has trademarked this word combo. I wonder if anyone has trademarked ShitSandwich yet? Anyways, without getting too far off topic. Why do we want to understand some of the basics when it comes to virtual power curves? Well, it will help you make a more informed decision when buying a standard indoor trainer. It won’t answer all of your questions, but it will give you a little more insight. Now, if you want to know how to create your own powercurve for you standard trainer using Google Sheets, you can take a look at the quick video I put together on Building Your Own Virtual Power Curve.
Not every trainer is created equal. We have Mag Trainers, Fluid Trainers, Wind Trainers, and various rollers. Each one comes with a unique virtual power curve. There are other things to consider when purchasing a trainer. I’m not going to cover that here. The main consideration being noise that the trainer makes and flywheel weight. Rollers can be the quietest with wind trainers being amongst the loudest. In this article, we are only looking at Power Curves.
Mag trainers provide a linear amount of resistance over speed. There is no “curve” in a Mag trainer’s power profile. The Mag Trainer just gets progressively harder. The primary resistance being the distance the magnet is away from the flywheel. The closer the magnet, the harder the resistance. If you are a steady state rider and are not worried about the upper limits of the power curve, then a mag trainer is a great option. Also, some Mag trainers can be very quiet.
However, don’t expect to hit wattage numbers above 700 to 1000 watts on a mag trainer. They are not designed to support that type of training. As you can see, the picture of the Blue Twist is very typical of a magnetic trainer and its linear resistance curve. It never reaches those big power numbers even at the 7th resistance level.
Fluid Trainers use a magnetic resistance in combination with a chambered liquid substance to provide added resistance at the top end of the curve. Think of stirring something in liquid. The faster you stir, the harder it gets. The advantage of a fluid trainer is the ability to hit higher resistance levels at higher speeds. The fluid adds some additional resistance that the magnetic resistance cannot achieve. For riders that would want to hit higher resistance levels, the fluid trainer is not a bad option. The days of leaking trainers is probably long gone by now. Manufacturers have figured out how to make sealed fluid chambers that never leak. Well, so I heard.
As you can see from the fluid resistance image, the fluid resistance curve starts heading north on the wattage scale pretty quickly as you start putting on some significant wheel speed and force. Not a bad trainer if you want to see higher numbers during your training session.
Wind trainers are also a great option if you really want to hit higher power numbers. That is, if you can get comfortable with the sound of a high speed whirling fan box behind you. I’ve never ridden one myself, but I’ve heard they can be loud.
I have attached a picture of RevBox. RevBox is a wind resistance trainer out of New Zealand and it’s not cheap. You can look at the power curve below and see how much more resistance that large fan puts out. At 25mph, you are already at 900+ watts on your bike. That’s plenty of power for a short 20 second burst of power.
Rollers can also be very quiet. However, there are many rollers out there on the market today. You can buy standard rollers, rollers with magnetic resistance settings, or rollers with a fan attachment like Kreitler puts out. Standard rollers by themselves will have a power curve similar to a magnetic trainer; very linear. To the right, is an example of the Elite Arion Roller’s power curve (power curve provided by Elite). As you can see, it is very similar to a mag trainer.
However, some rollers can have some pretty extreme virtual power curves. Kreitler is one such company that makes an indoor roller that can have a very strong power curve. They attach a fan to the function of the rollers and the resistance can be tremendous. However, the fall you experience coming off your rollers in a sweat induced sprint may also be tremendous.
I’ll show you a crazy power curve with the Kreitler rollers to the right. We will use an 80kg bike+rider with the fan only 1/2 open on the 4.5 rollers. Looking at the power curve, you can see how much resistance the fan adds to those rollers. Much higher than the Elite Arion Rollers. Don’t attempt to sprint at full fan though, i’ve heard the hurricane force winds may blow you completely off your bike. Just kidding, I have no idea how strong it is. However, my mind is going crazy with thoughts of pulling 1300 watt sprints on Kreitler rollers as the fan blows gale force winds at your face.
So, those are your choices out there folks. I hope this article helped you understand that each trainer has it’s own virtual power curve. How the trainer is built will effect the type of virtual power curve you will experience. The Sufferfest App, Zwift, and TrainerRoad all have virtual power curves with their training Apps. You don’t really need to buy a fancy electronic trainer if you don’t want to. Some of these trainers can provide plenty of resistance for you to train with over the winter months. You can set reasonable and reliable targets for your indoor cycling workouts and track progression as you proceed through your training plans.
If you want to learn more about figuring out your own virtual power curve for your trainer, I have provided this video below. It will show you how to create a spreadsheet in google spreadsheets that will show you the power curve for your individual trainer. This is mostly for us geeks who just like to do things like this for fun. I would love to get a bunch of trainers and just validate virtual power curves against what the manufacturer is putting out. I’ve seen a few that seem to be more reliable than others. It would also be cool to validate trainers that are older and see how well they have held their power over time and use. However, unless the trainer is in my hands, there is no way I can know for sure. Talk to everyone later.