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Belt drive, "clunk" when starting to pedal

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Belt drive, "clunk" when starting to pedal

Old 02-18-24, 10:26 AM
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Belt drive, "clunk" when starting to pedal

Hey folks,

I have an ebike with mid motor (Bosch Gen4), Gates Belt and Enviolo hub.

Often when starting to pedal from zero, there is a *clunk* that is felt on the pedal at the early stroke. Afterwards the bike pedals normal This happens more often on higher assist levels and less with the motor off.

I brought it to the shop and the mechanic adjusted the alignment at the rear wheel/hub. That seemed to have removed most of the clunk, but not all. Upon further inquiry, the mechanic told me that it's because I've ridden the bike crooked, and it should fix itself after a while.

Is that something you guys have seen before? Does it make sense to wait for it to settle?
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Old 02-18-24, 10:37 AM
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The mechanic saw it and we don't, so I'd defer to his judgement. Doubly so since was able to partly resolve it.

In your shoes, I'd let the bike and time prove it either way.

OTOH you might ask at the E-bike subforum, where you're more likely to find someone with first hand experience.
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Old 02-18-24, 12:17 PM
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The first thing I think of is the build up of wear in the various parts in the drive system. Clutches, gear meshing clearances, shaft end plays, linkage pivots all will wear and loosen up with use. When the bike is new we usually call this "the break in period". After lots of miles are had this is called "wear and tear". But it's the same process happening. Some of this can be serviced via adjustable designs, chain tensions, angular contact bearing preloads, spoke tensions, key fastener torque levels as examples. Some of it can't be adjusted, again dependent of how the bike was made.

Is the shop that looked at it an ebike dealer of any brand? Of a brand that also uses the same assist system? Of any brand? I've watched a fellow wrench spend many hours on the diagnosis and fix of a few ebikes over the last few years. These on bikes we sold, one of the big three brands, bikes with a both a bike brand dealer service department and the drive system brand's own dealer support dept. We also decline service on ebikes we didn't sell largely because the lack of this after the sale service support of many brands (that are often sold on line...). My best suggestion is trying to find a shop or person who has both the experience with the drive system you have as well as access to parts if needed.

Just like with ecars wearing out their tires at a far faster rate then drivers were expecting and those cars' accident repair costs being so high the ebike market is slowly becoming aware of the issues and challenges that these early generation ebikes have, especially at the lower cost levels and non brick and mortor sourcing. Andy
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Old 02-19-24, 01:37 AM
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Just FYI, Enviolo is a renaming of the NuVinci ball-style CVT. I've never used one, looks briliantly simple, but like metal-band on metal-pulley CVTs on cars, I worried about slippage of hard, smooth, small-contact-area, steel parts, submerged in lube. I also don't know if they are rated for the higher torque of e-bikes. Though all functioning similar, they make different models, slightly different ratios, and possibly torque ratings. I don't know if the hub is part of the problem, but look for threads about NuVinci.

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Old 02-19-24, 12:05 PM
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Originally Posted by Duragrouch
Just FYI, Enviolo is a renaming of the NuVinci ball-style CVT. I've never used one, looks briliantly simple, but like metal-band on metal-pulley CVTs on cars, I worried about slippage of hard, smooth, small-contact-area, steel parts, submerged in lube. I also don't know if they are rated for the higher torque of e-bikes. Though all functioning similar, they make different models, slightly different ratios, and possibly torque ratings. I don't know if the hub is part of the problem, but look for threads about NuVinci.
They do make stuff for e-cargo and heavier duty applications. Generally what most e-bike manufacturers are spec'ing from Enviolo are pretty suitable for e-bikes. Some people are rougher users and could use a heavier duty hub (Extreme or Heavy Duty) but having sold a large bunch of them over the years it is a very infrequent problem. Usually the biggest issue is people shifting them hard at a standstill.

In terms of Fandomii's question. My best guess is belt tension maybe being off or maybe belt line but I have to imagine the shop checked that from the get go. I would also have made sure everything is properly torqued and shifter is set up properly but I have a feeling that was also checked. Hopefully it has gotten better. Without having in the stand it is tough to tell but if nothing else reach out to the OEM and maybe Enviolo and see what they say. Good luck!
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Old 02-19-24, 12:08 PM
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Originally Posted by veganbikes
They do make stuff for e-cargo and heavier duty applications. Generally what most e-bike manufacturers are spec'ing from Enviolo are pretty suitable for e-bikes. Some people are rougher users and could use a heavier duty hub (Extreme or Heavy Duty) but having sold a large bunch of them over the years it is a very infrequent problem. Usually the biggest issue is people shifting them hard at a standstill.

In terms of Fandomii's question. My best guess is belt tension maybe being off or maybe belt line but I have to imagine the shop checked that from the get go. I would also have made sure everything is properly torqued and shifter is set up properly but I have a feeling that was also checked. Hopefully it has gotten better. Without having in the stand it is tough to tell but if nothing else reach out to the OEM and maybe Enviolo and see what they say. Good luck!
Thank you! Can you say a bit more on what is "hard shift at standstill"? Forcibly shifting too hard beyond the natural stop of the hub?
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Old 02-19-24, 12:32 PM
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Originally Posted by Fandomii
Thank you! Can you say a bit more on what is "hard shift at standstill"? Forcibly shifting too hard beyond the natural stop of the hub?
Basically people just cranking on the shifter to the limits not gently.
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Old 02-19-24, 08:28 PM
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Does an Enviolo/NuVinci need to be rolling to shift? Or do they shift fine when stopped?
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Old 02-20-24, 01:38 AM
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Originally Posted by Duragrouch
Does an Enviolo/NuVinci need to be rolling to shift? Or do they shift fine when stopped?
They shift fine when stopped, but up to a point. The last 20-25% of the gear range can be accessed after rolling a bit, half a pedal stroke.
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