Converting a dead smart trainer into a dumb trainer?

For reasons, I’m going to have a dead smart trainer on hand. I wonder if there isn’t a way to modify it to work like an old-school magnetic trainer with some fixed level of resistance?

Paging @GPLama and any engineers!

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which trainer? there is always some resistance, even when powered off/broken.
probably could rig up some sort of array of magnets to provide eddy current braking, depending on which trainer is in question.


rhymes with smicker door

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Unlikely with a Smickr Door trainer. :wink:

Elite trainers can do this as they still rely on physically moving a magnet in/out for resistance.

I figured maybe I could attach some powerful permanent magnets to it somewhere…

It seems like some industrious folks have been repairing Kickr circuit boards, but this is a bit above my paygrade. It would be nice if there was someone I could send my control unit to and have it fixed… I could handle replacing the board, at least.

Also, I got the impression that maybe the brake on these trainers is mechanically adjustable to some extent, given the fact that the factory spindown exists (I had to do one once, due to the trainer reading too high).

Some local shop over here says that they are able to fix the circuit board and such

the braking/resistance is supplied by an electromagnet, iirc.
no functional electronics = no control.

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  • Yup, I think the Kickr/Core flywheel is aluminum and could be modified with external magnets to make a higher level of resistance. See the DIY roller vids below for the concept & results. I did my own resistance using the one from CycleOps and added manual adjust which works well (1st vid). I could see this being a fine hack for a dead Kickr.

  • DIY Motion Rollers - YouTube

  • DIY Motion roller trainer with resistance - YouTube

  • DIY Free Motion Cycle Roller with Magnetic Resistance - YouTube

  • If you find a good combo of external magnets, I suspect it might be reasonable to remove the flywheel, gut the internals, and add your magnets inside the housing (fixed in the same location as the electromagnets. But this would be best done after experimenting with the best size, count and location of the magnets externally.

  • The issue here is that it could be lots more work, and may eliminate the option for manual adjustment that is shown in 2 examples above. And considering that the basic resistance profile of a mag unit is more linear than progressive, having some amount of adjustment (beyond bike gearing) is a nice option.

  • In short, strong magnets, closely placed (just short of touching) give the greatest resistance. Just a matter of mounting them firmly and determining how many to use.

The gears provide some modicum of resistance control.

If I could get it provide 70-120 watts of resistance, my wife could use it. Just need to get her a bike first…

Ideally I would like to replace the Gem2 module and get it working again.

I’ve got a dead Hammer Gen1. Needs a new circuit board, could see some hotspots and tried replacing some components but it didn’t fix it. It’s Electro magnetic so could easily setup some variable resistance to alter voltage. Project for another day as my current hammer working well.

Approached company to purchase a new circuit board, they aren’t interested… believe it’s not customer repairable, it’s no harder to do then a belt change. Anyway due to a ‘£20’ circuit board, it makes this a £500 piece of junk. Do wish I hadn’t brought another Hammer and supported this company as they have no interest in sustainability, next time it’ll be something more planet friendly with right to repair.

Wahoo also thinks the Core belt isn’t user replaceable, which is ludicrous. Any shade tree mechanic could replace it with their eyes closed,

They should be required to sell us wear parts.


does the belt have any numbers on it ? could try matching up if you know an auto parts guy worht his salt.

  • Yes, they all do. I recorded the one from my Kickr V6 for future reference.

  • The electro-mag coils are visible at the outside circular shape.
  • That is how the Elite trainers work, but all the other major brands use electromagnets like the example above.

I think It’s a 370J, which isn’t a car belt size, but rather more like something used in washing machines, I think.
I tried to order one from Ali Express, but it never showed up. My belt never broke, it just frayed a bit on one side, so the trainer still worked until the board died.

370J6 a 6 groove 37" serpentine belt
known at Advance Auto Parts as a
_ I spent 15 years behind a counter finding numbers that don’t exist and finding parts to fit in place of older parts they didn’t make anymore_ loved my small but dedicated hot rodder customer base
Circuit boards,…not much help there though…
Wheel bearings and seals for trailers were also a fun afternoon as those lack any possible standards along with mid-year changes I have gone on enough…


So, if I was going to 3D print some holders for six rare earth magnets, how big would they need to be (flux rating?..) to get a respectable amount of resistance (say, 700 watts?) at a wheel speed equivalent to say 50 km/h?

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buy and try if you want to take this project on, noone is going to have the exact specs spoon fed for you


Right, not sure I can make anything more than a guess at best. I’d have to crawl into my attic to measure the CycleOps ones, but 5 or 6 of them around 1" to 1.5" diameter are a quick guess from memory.

But the ratio of the flywheel, material thickness are all different here, so that may not even be a useful reference. So some experiments are in order.


I was just hoping someone could do the ballpark math so I could know if it’s even feasible.

Basically magnets half as strong as the stock electromagnets would work, in theory.