A perimeter weighted flywheel is when the inner weight of an exercise bicycle has most of its weight loaded along the outside or perimeter of the disk.
The other type of flywheel is uniform in size and weight. It’s just a flat disk that rotates. Some call that a center weighted flywheel.
With a regular bicycle you ride outside, the resistance comes from your weight on the bicycle and the resistance of the rubber tires on the road. And, of course, a lot depends on the angle of the road. It’s a lot harder work to ride a bicycle uphill than on a flat surface.
But with a recumbent indoor exercise bike, none of that applies. You make the front wheel turn by pedaling with your feet. The resistance comes from the bike somehow exerting force inside that wheel, which your leg muscles then have to overcome. These days, that force is usually magnetic.
The flywheel is the metal disk set inside the front wheel section of the bicycle. It rotates around the middle as your feet pedal.
However, the designers of these bikes want to duplicate as much as possible the experience of riding a bicycle outside.
A Perimeter Weighted Flywheel Rides More Like an Ordinary Bicycle
That’s because, by having more weight located along the outer edge, the flywheel generates more inertia.
Inertia is the tendency of matter to keep doing whatever it’s doing until acted upon by an outside force.
That sounds complicated, but it’s intuitive. Isaac Newton laid it out in his First and Second Laws of Motion hundreds of years ago.
If something is moving, inertia keeps it moving until friction, or running into a large object, stops it.
And if it an object is at rest, it stays at rest until you hit or throw it.
And the more mass (weight) that object has, the greater the inertia.
That’s why, in general, experts advise you to buy the exercise bicycle with the heaviest flywheel.
And by putting more weight along the perimeter than in the center of the disk, those manufacturers have more weight going around full-circle.
That Affects the Motion of Your Pedaling Feet
The flywheel goes around no matter what, obviously, because it can’t move anywhere else.
But perimeter weighted flywheels, because they have more weight along the perimeter than in the center, exert more force to keep your feet on the pedals moving around.
Instead of a more up/down movement.
This Puts Less Stress on Your Ankles, Knees and Hips – and Leg Muscles
One of the major reason people ride bicycles, either outside or indoors, is to reduce stress on their joints.
Otherwise, it’d be simpler to run or walk.
Therefore, by encouraging you to pedal more circularly than up-and-down, the stationary exercise bike gives you a smoother ride that’s easier on your joints.
Indoor cyclists, especially those using a recumbent model rather than an upright, are more likely to be older or to have tendon, ligament and joint issues.
All stationary indoor bikes are less stressful on your joints than running or even walking. By eliminating the jerky pedaling, models with perimeter weighted flywheels are even less stressful on your joints than models with uniform weighted flywheels.
Schwinn is one brand that has many perimeter weighted flywheels. Many spinning bikes also have them. However, many brands don’t have them.
Therefore, make sure you check before you buy.
Of course, if a bike’s flywheel is too heavy for you, that’s additional stress, so you must make sure you get one that suits your level of strength and fitness.