Chain slipping in hardest cog on rear

[Aaron R]

Hi

On my wife's 2018 Trek Powerfly 7 Bosch ebike the chain seems to slip (and make a crunching noise) only when on the smallest cog on the rear wheel. It doesn't seem to jump to another gear, but it seems to just slip.

It only does it on the smallest cog on rear wheel only.

Took it the the bike shop a few days ago and he replaced the smallest cog on the rear wheel with a new one.

The chain didn't slip anymore. But this only lasted for a day. On the second ride of the bike today, it started to slip again.

It does it every couple of hundred meters. Goes crunch, crunch, crunch. Seems to do it when you peddle really hard.

Bike has done 1143 km since new.

Thanks
Aaron

 

[soundwave]

chain is to loose or it is toast given the mileage id also change the hole cassette if it is cheap enough. where did you take it tesco pmsl

 

[vfr400]

The chain has worn a bit so that it doesn’t have enough tension in top gear. You can probably solve it by adjusting the B-screw on the back ofthe derailleur.

 

[Aaron R]

Im in Australia, I took it to the bike shop who sells mainly Trek bikes (shop we bought the bike from)

I’ll try to adjust the B Screw.

Thanks
Aaron

 

[Gadfly]

Check the chain wear with a suitable gauge. If it is worn then it will soon cream cracker the new sprocket.

 

[vfr400]

Check the chain wear with a suitable gauge. If it is worn then it will soon cream cracker the new sprocket.

Please explain that to me because I can't see how it can happen. The chain rollers sit in the same position in the sprocket and drive it the same way regardless of the state of chain-wear. If anything, there should be less wear because the approaching rollers won't be dragged down the leading edges of the teeth.

 

[Gadfly]

That's just it. With a worn chain the rollers move slightly further apart under tension because the pins on which the roller rotate become worn. When the rollers then contact the sprocket teeth they do not locate exactly between the teeth, but rather slide down the tooth edges, thus producing accelerated wear to the tooth profiles. In addition, this sliding action tends to lift the chain from the sprcket causing slip. It happens more on small sprockets.

Hope this helps.

 

[vfr400]

...but the wear only happens on the leading edge, and when the chain wears, the increase in pitch moves the following rollers away from it, so wouldn't wear be less? Surely, the reason small sprockets wear faster is because they have fewer teeth to spread the wear over?

 

[mike killay]

If it is an 11 tooth sprocket on a crank driver, well they all wear.
I don't know how many times I have replaced mine. so now I don't use it but only use the adjacent 12 tooth sprocket.
In my case I tried new chains, adjustments etc. All to no avail.
As far as I can see, there is no visible wear on the teeth or the chain which still works perfectly on the other sprockets.

 

[vfr400]

Yes, I know they wear, but the question is whether they wear more or less with a slightly worn chain. My logic and understanding seems to indicate to me that the wear should be the same or less. If that's not true, I'd like someone to explain to me why or how without drawing conclusions from disconnected facts like, " My chain was worn . My sprocket wore out quickly. Ergo, a worn chain wears a sprocket more quickly".

 

[Gadfly]

OK. Here is a technical article from the master of cycle mechanics. This will explain better than I (although I spent forty years as an engineer).

https://www.sheldonbrown.com/chain-wear.html

also

https://www.bikeradar.com/road/gear/article/bicycle-chain-wear-explained-46015/

 

[soundwave]

with sram eagle 12spd the chain fits the teeth so tight you cant even pull it of a sprocket the fit is so tight this also means less wear and noise.

https://www.sram.com/sram/mountain/products/xx1-eagle-chain

 

[Andy-Mat]

Hi

On my wife's 2018 Trek Powerfly 7 Bosch ebike the chain seems to slip (and make a crunching noise) only when on the smallest cog on the rear wheel. It doesn't seem to jump to another gear, but it seems to just slip.

It only does it on the smallest cog on rear wheel only.

Took it the the bike shop a few days ago and he replaced the smallest cog on the rear wheel with a new one.

The chain didn't slip anymore. But this only lasted for a day. On the second ride of the bike today, it started to slip again.

It does it every couple of hundred meters. Goes crunch, crunch, crunch. Seems to do it when you peddle really hard.

Bike has done 1143 km since new.

Thanks
Aaron

The problem is usually the spring on the gear change arm, that "takes up the slack". It needs to be adjusted to make it stronger.....to keep more tension on the chain when using the smallest sprocket.
As you did not put a photo here, I am unable to tell you exactly how yours is adjusted.....but a quick look on the web should help. Here is the same gear type as you apparently have.
https://www.livestrong.com/article/477246-how-to-adjust-the-chain-tension-on-a-mountain-bike/
The guy in the shop is an idiot, by the way.....demonstrating poor knowledge of how a bike works!!
Regards
Andy