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My belt failed

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My belt failed

Postby invisiblehand on Thu Aug 04, 2022 6:55 pm

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
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Re: My belt failed

Postby Blackstridaaustria on Thu Aug 04, 2022 7:34 pm

Thanks for showing!
I can't remember any similar damage :shock:
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.
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Re: My belt failed

Postby invisiblehand on Thu Aug 04, 2022 9:15 pm

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
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Re: My belt failed

Postby Blackstridaaustria on Fri Aug 05, 2022 5:55 am

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 :wink:
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Re: My belt failed

Postby invisiblehand on Fri Aug 05, 2022 12:53 pm

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.
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Re: My belt failed

Postby Blackstridaaustria on Fri Aug 05, 2022 1:48 pm

Oh yes :oops: 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!
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Re: My belt failed

Postby invisiblehand on Fri Aug 05, 2022 6:23 pm

Blackstridaaustria wrote: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.
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