I check the belt once a year and failed to notice any cracks or such. My bike and belt is five years old. Do the teeth sheer off like this frequently or is this a freak incident?
Thanks for looking!
EDIT: I’m also wondering whether teeth sheering is evidence of some other problem such as the belt tension being to low or high.
https://www.instagram.com/p/Cg2SvoAvhYF/?utm_source=ig_web_copy_link
Thanks for showing!
I can’t remember any similar damage 
Twisted and torn belts I’ve seen already, but not this “tooth decay”.
Hope you have a supplier near you (?)
Edit: Personally, I’d suspect an issue during fabricaton of this belt.
Edit 2: If possible, please post an image of your freewheel (teeth closeup), too.
So I’ve been talking to Bill at Strida Canada – super helpful gentleman and a reasonable source for another belt – and I should add more context.
I was riding to work when the belt slipped off. It was a close call but I managed to avoid a crash but the belt was all mangled with the rear wheel and brake. Bill’s surprise and now yours makes me consider the alternative idea that the belt slipped and the teeth were cut off by something. My first guess would be the rear disk brake. My thought earlier in the day was the the teeth sheered off and that caused the belt to slip.
I still had to get to work, so I worked the belt back on. I could only do so when using the sheered portion of the belt. That led me to believe that the teeth came off first. But now I’m not so sure. To give you an idea of how mangled the belt was, there is something rubbing when I roll the bike now. I bet the rear brake needs to be adjusted.
I’m not working on the bike now, so it’s hard to get a good profile view of the freewheel. Nonetheless, I’ve taken two more photos that view the freewheel teeth. I’ve also included a video of me pushing against the belt to give an idea of tension.
https://www.instagram.com/p/Cg2hgJDvtf4/?utm_source=ig_web_copy_link
My theory for how that happened:
I guess you stopped pedaling at some point in time.
Your belt became a bit loose because the freewheel is worn already (but not that much).
Anyway, the diameter of the freewheel decreased (a little bit) and that generates more play, that was the reason for the belt to start skipping teeth.
At the moment when the first tooth got stuck between the snubber and the freewheel - while the rear wheel was still turning - the tooth was ripped off immediately.
(Possibly you felt some kind of kickback at the pedals?)
So, I think that the belt’s teeth were sheared off by the freewheel’s teeth.
To mount a new belt properly you must open the big groove nut at the left side of the bottom bracket, too! Opening only the bolt 274, at the underside of the bottom bracket, is not sufficient.
You need a Ø 60 mm hook key.
Treating the belt with a screwdriver, as the Strida manual suggests, is nothing but wrong btw!
There is no maintenance-free bike existent in this world - but dubious marketing claims are present everywhere!
The belt itself is maintenance-free, but belt tension has to be observed according to mileage.
(I guess you never increased it within five years?)
Next, you should figure out what’s rubbing 
That’s correct. I was at a stoplight and had started to pedal. There was certainly something funky going on down there at some point but it’s hard for me to give details since I was so surprised at the moment.
I don’t have a tension meter for the belt. How do you judge the correct amount of tension without one? Is there a rule of thumb for the STRIDA? The belt is much looser now than before the accident. But I had been doing it be feel and noting how much effort it took to push the belt against the crank tube.
Oh yes 
I’ve overlooked totally the function of the freewheel, actually the process was the opposite as above mentioned…however.
I do have a (mechanical) tension meter for belts - but it does not at all help!
I’ve tested also frequency belt apps but they did not work, I believe that is because the tension is too low to measure for them; these apps are likely made for industrial purpose.
There is no correct amount of tension known for a Strida!
(In the manual, Ming cycle is giving us just one dimension - that is not sufficent! We need two dimensions; deflected distance AND the required force to achieve this deflection. We’ve told Ming cycle several times…)
You can adjust the belt only by feeling, sorry to say that.
Mark Sanders said somewhere: “Keep belt tension as low as you can tolerate!”
I’d add this: “But keep tension as high as required.” (To avoid tooth skipping.)
For my meaning; if you can touch the frame with the belt - then, tension is too low.
To get a feeling for this procedure I’d recommend that you try too much tension intentionally.
Without riding the bike, pedaling with your hands, you can feel that the whole drive train developes drag. Now, adjust the excenter a bit below and feel the difference.
For a better orientation, to see how much rotation of the excenter has which effect on the belt, you could make a few marks (on adhesive tape) at the excenter and corresponding on the frame.
I’ll repeat here also once again that the belt tensioning method, shown at the Strida manual - without using a hook key - is wrong!!!
Only a tight groove nut AND a tight bottom bracket bolt TOGETHER are able to withstand the high forces at the bottom bracket!
Hey … thanks so much for sharing your expertise and experience. I find it very helpful.
Do you think that the tension of the belt is related to the speed of the bicycle when pedaling?
No.
(Except you’d pedal so hard that the belt becomes hot - in that case would the tension increase.)
Reading your question again and again I must confess not to understand it completely, did you perhaps mean:
And were you thinking about the two parts of the belt which are called usually tight strand and slack strand 
What I mean was if by tightening the belt, we will be able to go faster. that is, being able to exert more force to run more.
I feel the strida too soft, and when I want to go faster, I can’t because my feet are spinning in the air, without any resistance. So my question is if we could resolve it by tightening the belt
Thanks, that’s better now, I believe to understand.
Let me repeat your wish with my words (and forget about belt tension, that won’t help you at all).
You want to pedal harder while increasing your speed and decreasing your pedaling frequency (called commonly cadence).
There is only one logical way to achieve this, you must increase the gear ratio.
And to do that, there is just one chance - a gear drive.
Your Strida has 16" or 18" wheels?
It has 16" wheels.
I understand what you mean. I will keep the bike as it is and I will use it only for relaxed rides. I’m not going to spend any more money on it at the moment.
Ah I see 
Here’s a short summary of your options:
2a. Installing a speed drive at 16" bikes would increase for about 30%.
2b. Speed drive plus 18" wheels would mean around 45%.
3a. The efneo drive has the “hardest” gear ratio, with 16" wheels you get ~ 40% increase.
3b. 18" wheels plus efneo drive will produce about 55% increase - over 6,2 m per crank revolution!
Those speed drives you propose are for changing to metal chain, right? Is there one with a belt?
No, above I’m referring to belt drive (kits) only.
efneo GTRO:
https://www.efneo.com/shop/gtro-for-folding/
Both kits include a belt, a 80 t beltwheel and the excenter.
The ATS has to be shifted by heel and the efneo by wire.