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?
15 thoughts on “Lose The Spoke Magnet Before You Lose Your Spoke Magnet”
Great post Karl! Sometimes it’s the little things. Depending on the bike (or trike) I sometimes epoxy them to the disk brake rotor. For cadence sensors I have epoxied them to the inside of the crank. Works great.
We have a Zyao City Coco scooter for family shopping trips into our village, school runs etc. All within a Km or so from home so it’s very useful machine, and with a dual seat and FS, it’s more practical for this use than our electric Fat bikes.
The standard twist grip throttle, and combined Speedo and battery meter is useless though, and reads double the real speed and therefore distance..No wonder the manufacturer claims 80 kph top speed, and 160km range on the double 60v 20ah battery packs..about twice the True figures, and it appears impossible to programme in any way..😂😂
Anyway, I soon ordered and fitted a Luna Batt Man meter, which is a great piece of kit and easy to install and set up. As the scooter has solid and high polished alloy wheels, the supplied spoke magnetic was clearly no use, so I did exactly what you suggest. I have epoxied 1 cheap but powerful Neodymium magnet to the edge of the wheel rim, and popped an extra one on top for more magnetic field strength, and it works perfectly with the sensor about 15mm away on the scooter rear swing arm. It’s been in place and has worked perfectly for over 6 months so far..😉😊
except the fact that you’ll never be able to true your wheels again…
Heat up the epoxy to 250* with a heat gun. The epoxy will get soft and peel off. No damage to the rim.
Seems with a little precision and counter balancing it wouldn’t be too difficult.
Karl, As you mentioned above….”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.”
By chance do you know if this adapter will be available as a “part”? I’m working on a custom bike project that doesn’t require a “boat anchor” chainwheel spider. & I do need the smaller front sprocket as this bike won’t be breaking any speed records.
I don’t know, contact email@example.com . He’s a great guy, super busy.
Barge All-Purpose cement is a great alternative to epoxy for bonding little bitty magnets. It has much better toughness and won’t shatter under sharp impact like epoxy and its much easier to apply because it is a contact cement. It outperformed the epoxy I tried to bond neodymium magnets to my brake levers. I bet a magnet will shatter before it breaks loose – and if that somehow happened there’s a chance enough material will remain to activate the reed switch on the speedo.
Sweet, thanks for the tip.
Hey Karl, I’ve been very interested in your ebuilds lately….can we get together and do some sort of a newbie build. I love the wheel barrow and think a double tire model could be cool for something utilitarian……or even some kind of 4 wheel model to really create some weight. I also have an antique tandem bike and a 3 wheeler that could be fun. I do have mowers that could be converted too, if you’ve had any interest, nice paint job btw very inspired.
Thanks, hope to hear from you.
On Tue, Dec 11, 2018, 9:20 AM ElectricBike-Blog.com Karl Gesslein posted: “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) ” >
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I don’t trust the speedometer reading on my ebike. That’s why I use GPS. As long as I have battery volt reading. Most important.
I bought a 100 48v hub kit for 150.then bu
ilt a battery it wont go because pedle assist , how to bypass? [PLEASE]\
This is good info. How did you get the sensor mounted at an angle to read the magnet. Not much room on my bike to mount the sensor without tire rub.
Adhering the magnet to the rim is definitely the way to go. I just spent a good 30 min fiddling with the stock setup trying to find a position that provided enough clearance, and while I could’ve gotten it to work eventually, I just busted out the JB Kwik Weld and and epoxied it to the rim. Much lower profile than that gigantic spoke magnet.