Magnetic exercise bikes: how the resistance actually works

What is a magnetic exercise bike?

A magnetic exercise bike uses magnets to slow a spinning metal flywheel, without ever touching it. As the flywheel passes through the magnetic field it induces small circular currents in the metal, called eddy currents, and those currents drag against the wheel. Move the magnets closer and the drag increases, so pedalling gets harder. Move them away and it eases off.

That is not marketing language, it is the engineering. The patent literature for magnetic ergometers describes it plainly: the magnets and the rotating member together generate eddy currents which slow the rotating member down^[1] (European patent EP1040852A2). The important word in all of that is "without touching". Everything people like about these bikes follows from it.

Magnetic or friction: what is the real difference?

Friction resistance presses a pad or a band against the flywheel. Magnetic resistance never makes contact. That one difference explains the noise, the wear and the servicing, and it is why magnetic has taken over the home market.

The same patent is blunt about the comparison: an eddy-current brake functions very smoothly and silently compared with a braking band^[1], while a friction arrangement is "relatively loud". Worth knowing what magnetic gives up in exchange: a friction knob changes the moment you turn it, whereas magnetic resistance moves in fixed steps and can feel a beat behind your hand.

Magnetic or flywheel: the question is a bit of a trick

These are not two options you pick between, which is why the comparison never quite makes sense. The flywheel is the spinning mass. Magnetic resistance is how you slow that mass down. Most magnetic bikes have a flywheel as well.

Our own range proves it. The CityRide U2 is magnetic and has a 3 kg flywheel. The Studio Pro S3 has an 11 kg flywheel. So there are really two separate questions: how is the resistance applied (magnets, or a pad), and how much mass is spinning (which decides how smooth and road-like the pedal stroke feels, not how hard the bike can get).

Now the awkward part, and we would rather say it than quietly skip the question on a page with "flywheel" in the heading. The FoldFit X1 is magnetic with 16 levels, but its manufacturer does not publish a flywheel weight. The manual gives the resistance type and no mass. We are not going to invent one, and we are not going to imply we know. The Studio Pro S3's 11 kg is published, so we print it. For the same reason we do not describe the Studio Pro S3 as magnetic or as friction: its maker does not state the resistance type, so neither do we.

Are magnetic exercise bikes actually quiet?

Yes, and this is the one claim on this page we did not take on trust. Quiet is the whole selling point of magnetic resistance, and every listing repeats it, so our owner Asif rode all five of ours and wrote down what he heard. These are his own first-hand notes, not a lab measurement.

On the FoldFit X1: no noise at all. On the ComfortGlide R500: none at all. On the CityRide U2: surprisingly quiet even at high speed, which is the point at which a friction bike would be making itself known. So the claim holds up on our bikes. You can ride any of the three with the television on and win the argument about it.

One honest complication, because it would be easy to leave out. The Studio Pro S3, which is our weighted-flywheel bike rather than one of the magnetic three, was also quiet. Quiet is not magnetic's private property. What magnetic reliably gives you is quiet with nothing rubbing, which is also why there is no pad to replace.

Does magnetic resistance get hard enough?

That depends on the bike, not on the mechanism. This is the most useful thing we can tell you, and it came out of riding two magnetic bikes back to back.

On the FoldFit X1, Asif found that up to about level 10 he could not feel much, and at level 16 he nearly died. It genuinely bites at the top. On the CityRide U2, which runs 1 to 15, he found it smoother and said that even at level 15 you will not feel the pain: he was expecting a slap in the face at the top of the range and did not get one.

Same mechanism, two different bikes, two genuinely different ceilings. So do not buy on the word "magnetic", and do not buy on the number of levels either, because level 15 on one bike is not level 15 on another. If you want resistance that fights back, the FoldFit X1 is the magnetic one that does it, and a studio bike with a heavy flywheel is the other route. If you want steady, comfortable cardio you can do daily, the CityRide U2's gentler top end is a feature rather than a fault.

Which of our exercise bikes are magnetic?

Three of the five: the FoldFit X1 (16 levels), the CityRide U2 (1 to 15) and the ComfortGlide R500. The DeskFit Mini uses a manual resistance knob, and the Studio Pro S3 is the weighted-flywheel bike whose resistance type its maker does not state.

Resistance is only one axis, though. It does not tell you what shape of bike you want. If the room is the constraint, look at foldable exercise bikes. If you want a plain, familiar riding position, look at classic upright bikes. Or see all five bikes together and compare them properly.

Magnetic and friction, side by side

Compare the whole range

Every bike we stock, side by side. All prices include VAT.

Magnetic resistance questions, answered

Keep reading

• Foldable bikes for smaller rooms
• Upright bikes for steady cardio
• Compare all five bikes
• How free UK delivery works
• What the 2 year warranty covers