How Do Bike Trainers Generate Resistance?

Bike Noob took a look at trainers at about this time last year, and is revisiting the topic with a guest post from Ron Fritzke.  Ron describes himself as a “cycling product reviewer with a passion for ‘all things cycling’.”  A former 2:17 marathoner, he now directs his competitive efforts toward racing his bike…and looking for good cycling products.

It doesn’t take too much time wading through the bike trainer world to get a good feel for the various features and benefits that a perspective buyer should keep their eye open for.  I’ve spent hours and hours writing indoor bike trainer reviews and have come to conclude that several factors are on most cyclist’s minds when they’re looking for a bike trainer.

Is It Quiet Enough?

Although the level of sound coming from the trainer doesn’t directly effect the workout, it sure effects the riders enthusiasm for getting onto it to begin with.  And that’s saying nothing about the lack of enthusiasm, or even open hostility the rider will face from members of the family who are subjected to a howling wind trainer.  It can get so loud that even residents living in the same apartment complex stop saying ‘Hello’ in the hallway, replacing the greeting with a scowl.

In general terms, the fluid trainers are the quietest, the magnetic (mag) trainers come in second place, and the wind trainers can create a sound similar to a living room hurricane.

Where’s The Resistance Coming From?

It’s not too hard to figure out where the resistance comes from in each of the three main trainer types.  The wind trainer creates resistance by spinning an impeller through the air, the fluid trainer does something similar by spinning an impeller through fluid (typically silicone), and the mag trainer creates resistance by spinning repelling magnets past each other as the flywheel spins.

Moving Air

Starting with the simplistic wind trainers, there isn’t too much mystery as to what’s going on with this type.  After all, everything’s exposed.  In case the word impeller isn’t in your knowledge base, it’s nothing more than a propeller with the blades safely inside the flywheel rather than pointing outward.  A true propeller might be interesting except for the possibility of the manufacturer’s legal department  having to  field a lot of ‘missing fingers and toes’ complaints.

An interesting version of wind trainer design is CycleOps’ vortex shaped impeller.  The claim is that it increases resistance while reducing noise.  That sounds like the best of both worlds in the wind trainer world.

Magnets That Hate Each Other

Heralding back to the days of primitive elementary school science experiments, mag trainers use the repelling force of similar poles of magnets to create resistance.  These trainers work by spinning the magnets on one part of the trainer past the magnets on another part of the mag trainer.  The repulsion as they get close to each other creates the resistance.

The big issue with mag trainers centers around how they increase or decrease the resistance levels.  On the least sophisticated models, the rider dismounts (getting a welcome relief from the tyranny of the workout) and changes the setting directly on the trainer.  The next level of complexity requires the rider  to merely change the setting using a lever that’s been attached to the handlebars.

A recent development in mag trainers is the system on the CycleOps Magneto.  It’s called progressive resistance and uses the power of centrifugal force to spin the magnets further and further away from center as the rider increases their intensity.  The engineering in this model is such that there’s more resistance the further the magnets move outward.

Fluid Trainers And Leakage

Fluid trainers have long been at the top of the heap when it comes to resistance.  On these trainers the harder you pedal, the more the trainer resists.  While that may seem obvious, what I mean is that the resistance increases exponentially.  If you were to look at the level of resistance as it relates to the speed of the turning wheel you wouldn’t see a straight line.  Instead you’d see an intimidating upward swooping line that almost approaches vertical at the upper end.  This type of resistance is particularly valuable for strength type workouts and may not be as necessary for trainer riding at a steady state.

In the past, it was almost certain that fluid trainers would begin leaking due to the friction and extreme heat generated during a workout.  The whole leakage problem was confronted head-on when the Kurt Kinetic company developed a design that is today featured in all of their fluid trainers, with the Kurt Kinetic Road Machine being the foundation of the line.

Kinetic trainers have a sealed chamber housing the impeller and the silicone.  Outside of the chamber is a flywheel with six strong magnets imbedded into it.  These are matched to six magnets in the impeller.  In this case, rather than repelling each other, these magnets are configured to form a magnetic bond to each other.  The result is a magnetic coupling with the impeller and the flywheel spinning in tandem without the sanctity of the fluid chamber being breached.

Not to be left behind by this design, the Cycleops Fluid 2 Trainer is the result of efforts on the part of CycleOps to beef up their fluid trainer products.  It’s not clear how they accomplished the improvement, but it’s very evident that something’s been done since customer dissatisfaction is markedly reduced among the ever present complainers on the internet.

Summing It Up

It’s been my intention to expose the reader to the implications of how each of the trainers generates resistance.  Each of the styles has its strengths and weakness…no one type suits every rider.  Casual riders may do well with the relative simplicity of a wind trainer, while more intense riders would be best suited to a fluid bike trainer.  There’s plenty of information on the internet, and my intention is that this short article will get you asking the right questions in your quest for a good bicycle trainer.


  1. says

    I bought a trainer a few months back (magnetic) and planned on using it heaps. I didn’t of course, because of the noise. I’m happy enough to some earphones in, but I’m as much worried about disturbing the old lady across the back fence.

    Just glad it’s not only me.

  2. Barbara says

    I’ve got an inertial trainer, which I didn’t see mentioned in the review….pretty quiet overall and has a couple settings to increase the resistance if needed. Been pleased with it over the past three years….but never happy about having to get it out cause it means I’m not on the road pedaling.

  3. Simon says

    Purchase a fluid trainer 2 weeks ago, as fed up being sidelined with all the snow and ice we had here in VA. Returned it earlier this week after one session, to noise and not realistic enough. Have to love Performance Bikes return policy.

Leave a Reply

Your email address will not be published. Required fields are marked *