One of the most annoying problems that I’ve had with a bunch of my ebikes is the cheap & craptastic spoke magnets.
- The magnets fall off in the middle of the woods never to be found again (I’ve lost 2 of them before I started using blue loctite)
- The spoke magnet detector gets knocked out of position from hard riding
- The magnets get knocked sideways halfway spinning around the spoke and stop working at all
- When removing the rear wheelset with a fat tire, you can hit the detector and it breaks off or gets knocked out of alignment (I’ve destroyed at least 4 of them)
The setup with the BBSxx and the Ultramax spoke magnets is one of the worst ideas ever, luckily there is a fix. This article is about how you can throw out the spoke magnet that comes with your kit and instead use tiny neodymium magnets epoxied to your bike rim which is lighter, more reliable and allows for a much-improved magnet detector position that does not get bumped when removing the rear tire for service.
I’m sure there are other people gluing magnets to the rims of their bikes, but the first bike I’ve seen from a factory with it done was the AWD Christini ebike I tested last winter (review here). I was so impressed with their AWD system that I’ve ordered an AWD steel geared Ultra Max setup with an obscenely large frame (25″) that will fit Snowshoe 2XLs in the front and the rear (review is coming). They have to make significant changes to the front fork to fit the 2XL, but the end result should be awesome. They are also in the process of custom machining a 104 BCD 4 hole chainring adapter to replace the stock 130 BCD 5 hole adapter that comes with the Ultra max (312g), which is one of my bigger complaints about that setup. The Ultra Max prototype had a 4 hole 104 BCD, but the production version had the 5 hole 130 BCD. If you want to grind through a foot of powder in low gear, you just can’t do it with at 130 BCD chainring with a 42T Raceface chainring you are much better off with a 32T chainring on a 104 BCD adapter.
A magnet is a magnet, but they’re not all created equal
The stock spoke magnet that comes with the BBSxx and Ultra Max is not very powerful. With a BBSxx it must be mounted within 5mm or so of the detector, with the Ultra Max it’s more like 10mm. You can buy tiny high power neodymium magnets from ebay or amazon for almost nothing. I bought 100 magnets from ebay for only $7 shipped here (thats about 7 cents each). These magnets are pretty handy and are surprisingly powerful. I found that a single neodymium magnet would cause the BBSxx sensor to trigger while it was still about 10mm away and for the Ultra Max it was about 15mm. If you want more range you can just easily stack them on top of each other. They work well enough that even with the forces of aggressive trail riding the magnets won’t fall off.
Almost every ebike on the market has some kind of spoke magnet if it has any kind of speedometer on it. Almost any speedo can be mounted differently and the spoke magnet replaced with neodymium magnets. To get the neodymium magnets to stick to the rim you can either jb weld a small piece of steel to the rim to stick a magnet to it, or you can do what I do which is just JB weld the magnet directly onto the rim. Make sure the surface is clean and lightly sand it with some 200 grit sandpaper and clean it with rubbing alcohol before you glue the magnet to it. When using epoxy you can usually use a tiny fraction of the amount that you think you should use (too much is never enough). Since you’re trying to hold a tiny amount of weight to a wheel that is moving pretty slowly you need only a couple pinheads worth of epoxy.
7 cents for a high power magnet and a tiny dollop of JB weld might be able to end your speedo woes forever. What’s not to like?