Sprocket wear

soundwave

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georgehenry

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I agree Nealh. My Haibike Yamaha was the cheapest entry level bike that Haibike offered back in 2015. There were other Haibikes using the same motor system that were a magnitude of thousands more, probably as much as four times more expensive for the top of the range full suspension Haibike using exactly the same motor but with a much higher level of specification in relation to the parts fitted.

I bought mine to commute on and had no idea at the time that the Yamaha motor was more robust in terms of its bearings than the Bosch and inherently more suitable for commuting . I was lucky to choose it.

However its ability off road meant that I could ride much more demanding and technical routes to work having great fun within the capabilities of the bike rather than hammer my Emate on tracks it just was not designed to cope with.

The trouble was that at the end of a late shift I wanted to get home as fast as possible riding late at night on the road using a 10 mile B road route. The transmission of The Haibike was dirty from the cross country ride to work, and then the power of both me and the motor at first wreaked havoc with the 11 tooth top gear sprocket causing it to wear out prematurely.

I eventually found a simple way to extend the life of The Haibike transmission on the road route home by simply increasing the gearing with a larger chain ring and using a different but cheap 9 speed cassette with a 12 tooth top gear and a 14 tooth gear 8. I learnt only to use the lowest assist level when using the top gear. My bike could assist above the legal limit. Using the same road route each time I learnt exactly what assist levels were required for each section. Impressively the bike could complete the 10 mile journey in 30 minutes. I raised my gearing to the highest point that my bottom 36 tooth sprocket could still get me up the steepest most technical hill on my off road routes into work. I bought my bike in March 2015 and used it until I retired in October 2021.

After retiring I no longer needed that higher gearing or ability to hold cruising speeds on or slightly above 20 mph and simply put a smaller chain ring back on.

Before I bought The Haibike I had already been commuting to work for two years on my rear hub Oxygen, but had begun to experiment with an off road route to work and found that although the Oxygen was much more capable off road than I had expected I was still limited to the easier tracks, the advent of crank drive bikes and their ability off road made me want to get one.

At the beginning I was a boy with a new toy and used The Haibike for all my shifts at work including the early ones when I would ride both to work and back on the road. This just led to me wearing out transmission parts.

When I thought it through I came up with the best way for me to commute to work and back. On any shift that I needed to ride on the road both ways I used one of my rear hub bikes, which were better suited to commuting on the road and nicer to ride in that environment.

On any shift where there was time and daylight to ride on my off road route I used The Haibike.

That became a perfect compromise until I retired. Both styles of bike are brilliant, but it was best to use the bike best suited to the task. Once I started doing this the transmission on my Haibike lasted longer as my 14/16 mile off road route was ridden at a slower speed using the lowest assist level or no assist and generally in gears 1 to 7 rather than the more vulnerable top two gears. As I only used The Haibike when I could use the cross country route to work it was proportionately used much less on the road where the constant higher speeds caused the premature wear to my top two gears.

Andy makes very good points which I mostly agree with but just like life it is not quite as simple as he makes out and there can be very good reasons to favour a crank drive over a rear hub. If you can, have the best of both worlds like me.
 
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georgehenry

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I agree Andy that it would be quite simple to provide a heavier duty chain, chain ring and rear cassette design with perhaps as few as seven widely spaced gears.

After all motor bike chains hardly ever break and suffer the same single point of failure potential that you highlight.

For applications where reliability and longevity are more important than saving weight or outright performance, a so designed crank drive commuter bike or adventure bike would you have thought be highly appealing to many people.

The closest to this I have seen is the extremely expensive Rohloff rear hub gearing system paired with either a chain or a belt.

It does not need to be that complicated, either a derailleur system properly designed to cope with the power of crank drive motors or a similar hub gear system.

But then it would last a very long time with minimal maintenance and manufacturers don't want that!
 
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matthewslack

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Nov 26, 2021
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Thanks for the reply (assuming that you are replying to my question of course), but none of these are specific to a hub bike, as I asked. In fact they are applicable to any bike, electric or not, except the last one......
The very specific "single point of failure" I tend to mention, to fully inform e-bike newbies, on mid motor e-bikes with chain drive systems, is, as far as I can see, specific only to mid motor chain drive systems.....
Though there are a couple of mid motor systems with drive shafts, but tend to be even more expensive than the usual chain drive mid motor bikes......sadly!!!
If an e-bike company managed to produce a drive shaft version, priced below that of the chain drive mid motor systems, and kept nasty firmware away from the design, they really do have the chance to make some big money.....and have happy customers.
With the present mid motor designs with chains, due to the way the torque is transmitted to the rear wheel, I do not see much of a possible improvement in wear characteristic, in the forseeable future.
Now that statement will really get the mid motor "fans" up and shouting again, because they don't want it to be true. But physics, as einstein would say, rarely change as we might wish them to!
A possible "kwik-fix", might be with really heavy duty chains, running on fully hardened sprockets, all at least twice as wide as the present versions, plus instensive cleaning and lubrication as least once a month, or possibly an old fashioned, fully enclosed, chain guard, to prevent dust/mud/water getting on the chain. My first bike had one a great many years ago!!
Or:-
A modern design, in a lightweight material, might reduce the need for chain cleaning and re-lubing!
regards
Andy
I have probably been quite fortunate, as my two most impairing failures happened one within reach of a bike shop, and the other during a work week on my 4km commute, so neither hurt me greatly.

Any failure I can cure on the road is for me no longer a problem, as long as my spares and tools are lighter than a cup of tea and smaller than a good pasty.

As for 'the big one', I recently found a barely used spare motor for my Shimano e5000 for under £200, the original sounds and rides no different to new after 8,500 miles, so not needed for quite some time, but won't be a big deal when it is.

I've no objection at all to hub motors, I just don't see my particular riding and area as compatible with them. I see gradients of MTB severity every time I go out, so mid-drive and low gears is the right horse for my course.

I have a winter project to fit 11 speed to my modest bike and have a go at Bealach na Ba with 38T front 50T rear, which I did not dare attempt with 36T rear in the summer! That's the kind of thing I want to wind my way up slowly and easily, not leave for another day.
 

Andy-Mat

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Oct 26, 2018
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Andy always seems to make his arguments in a combative style.
Its what I am as I have always stood up for myself and for anyone weaker, at all times in my 76 year old life. Its how others treat me, other people with no intelligence and no basic good manners.

Also seen far too often here on pedelec.....

But I have always allowed people who look for a physical fight with me, to have the first punch, not that it did them any good, as my Father, an electrical Engineer, started teaching me boxing when I first started school at age 5, as some other badly brought up little pig, punched me on my first day at school in passing, with no conversation! Just a thump in the stomache....a cowards blow in my book, as we had never even met till he hit me!!!

It was a revelation Iabout bad people that I o_O have never ever forgotten.

Dad afterwards taught me well, as he was a school boxing champion in his youth, he was the one who trained me to never hit anyone first, but I never fought in a ring, as I have a so called "glass nose", which bleeds at the tiniest provocation, and looks far worse than it really is!! I did discover that Bleeding on an opponent, when you are sitting on him and he's getting a red shower, usually stops most school time fights!!

Not Navy ones though!!

Two years later the same little pig picked on me again, and got taken to hospital after about 30 seconds, with a badly damaged nose (that was never right afterwards...), again I allowed him the first punch, but I still got a telling off till I mentioned my first day experience, and he also later admitted it.

A dumb school bully, I still remember his name, Les Cope!!

Its important to remember, that all bullies are dumb (Trump?), as they cannot win verbal fights!

Its the socalled "Dunning Kruger effect"! The Dunning–Kruger effect is a cognitive bias whereby people with low ability, expertise, or experience regarding a certain type of task or area of knowledge tend to overestimate their ability or knowledge. Wikipedia
Trump is used as an example, by a US University Professor, David Dunning, teaching the "Dunning-Kruger effect" to Psychology students!
See here:-
You may like this one too:-
and this:-

In the Royal Navy (1963 to 1973), there are occasional fist fights (sad to say!), around one a year for me, of which I can honestly say, I never lost one, but several times I was (correctly) pulled off someone who was being half murdered (red mist?), but they then tried to get in a punch or two on me as I was being held back and unable to dodge! Now Navy Guys don't like that and I was immediately freed to finish my aggressive attacker as I saw fit.

I was never charged with fighting!

But I always gave them the first punch, as I never ever punched anyone first! Navy rules and regs that whoever starts a fight will get the full blame....NOT ME!!

My last really serious fight, was many years ago, in my own dining room, when a girlfriend of my first wife, brought her drunken boyfriend to our party, who challenged me to go outside IMMEDIATELY (village idiot), who was so drunk he could hardly stand up, but had muscles on places where most people did not, except for his very thin legs! I dodged his first attempt at a hit (I was still sober) and he got the "shoe in the face" treatment, street fighting as learned in Trinidad and similar places, as I could imagine that he was far stronger than me in the upper body.

He had very long hair, I always have very short hair even as a boy (today about 6mm, my COVID CUT!), as long hair puts you at a huge disadvantage in any sort of a fight, as he found out!
He actually apologised to me (suddenly sober) when the Police arrived (called by my ex wife, the Police wanted to cart him off!), and the next day he was all the colours of the rainbow!! I sometimes wonder if he ever found out why.......he was SO drunk, he may have thought that I used my fists!!!

A subject that I have as good as forgotten today, only an old man's memories......So sorry to take up so much of your e-bike time on Pedelec.....

I liked the rest of your comments below, they showed good common sense....
There are pros and cons to both systems. I own both, and really like both and appreciate their different attributes.

The can bus systems built into mostly the purpose built crank drive bikes serve nobody else but the manufacturer and are a right pita. They are effecting a lot of goods now.

I spoke to a mechanic of a very large crank drive selling bike shop recently and he said that the latest crank drive motors are built for performance and have got lighter and more powerful as a result. In his words they are brilliant to ride but not designed for a commuting role. This was born out when I chatted to Peter at Performance line bearings who told me the bearings on my 2015 Yamaha motor were much more robust than the latest motors. To make the motors lighter the bearings are now less robust than they were and the motors put out more power. If you are competent enough to take full advantage of their performance a high spec full suspension crank drive bike will offer an exhilarating ride. However like any high spec performance machine you need to understand the cost of maintaining such a bike and how long it will last.

I think that the problem is that crank drive bikes are now dominating the market place and someone new to electric bikes without a great deal of knowledge may buy one for a role that a simple geared hub motor bike would be more suitable, cheaper to buy, much cheaper to run, and much cheaper to keep running.

I don,t clean the drive trains of any of my bikes as often as I should. However I keep my chains oiled and keep an eye on chain wear and like soundwave tend to change chains around .5 wear point.

Interestingly, since I started measuring the wear of the chains on my bikes, I have found that although my geared rear hub bikes do take longer to reach this wear point than my crank drive bike, they reach it quicker than I had realised before I started measuring. I think before I measured the wear rate I just kept riding my bikes and the rear hub bikes can be ridden for thousands of miles further and sometimes years longer with a worn chain that a crank drive bike.

The Cassette on my crank drive Yamaha ridden mostly off road has completed 2,393 miles, 3,851km . I have swapped chains at wear limits but as my rear cassette must be getting pretty worn now have put back on a chain I previously took off when it just hit the .5 wear limit and will ride that chain until it is completely worn out. I expect it to get me through the winter. Then with the beginning of nicer weather I will put a new transmission on. This will involve a deep clean of the rear derailleur and replacement of the jockey wheels as well as a new chain, cassette and chain ring.

I like all my bikes to earn their keep but am not fastidious about their appearance. Change the brake pads, oil and change the chains at wear points, and change the tyres.

My Haibike Yamaha that I bought new in March 2015 for £1,750 is seven years old and has completed 16,732 miles.

My Befang rear hub Oxygen Emate that I bought new in June 2011 for £1,399 is eleven years old. The mileage is not recorded on that bike but it will be a lot as it gets used a lot. It did 6,000 miles by the end of its second year.

Note that my Haibike Yamaha was £350 more than my Oxygen which I thought good as it had hydraulic disc brakes rather than mechanical, 9 gears rather than 7, and an air adjustable front fork, all of which are really essential for serious off road riding.

My Yamaha crank drive is an infinitely better climber than my geared rear hub bikes. The rear hubs climb well up to a point, but beyond a certain gradient will bog down and drop out of their efficient power range.
 

Zlatan

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Nov 26, 2016
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Yo
Its what I am as I have always stood up for myself and for anyone weaker, at all times in my 76 year old life. Its how others treat me, other people with no intelligence and no basic good manners.

Also seen far too often here on pedelec.....

But I have always allowed people who look for a physical fight with me, to have the first punch, not that it did them any good, as my Father, an electrical Engineer, started teaching me boxing when I first started school at age 5, as some other badly brought up little pig, punched me on my first day at school in passing, with no conversation! Just a thump in the stomache....a cowards blow in my book, as we had never even met till he hit me!!!

It was a revelation Iabout bad people that I o_O have never ever forgotten.

Dad afterwards taught me well, as he was a school boxing champion in his youth, he was the one who trained me to never hit anyone first, but I never fought in a ring, as I have a so called "glass nose", which bleeds at the tiniest provocation, and looks far worse than it really is!! I did discover that Bleeding on an opponent, when you are sitting on him and he's getting a red shower, usually stops most school time fights!!

Not Navy ones though!!

Two years later the same little pig picked on me again, and got taken to hospital after about 30 seconds, with a badly damaged nose (that was never right afterwards...), again I allowed him the first punch, but I still got a telling off till I mentioned my first day experience, and he also later admitted it.

A dumb school bully, I still remember his name, Les Cope!!

Its important to remember, that all bullies are dumb (Trump?), as they cannot win verbal fights!

Its the socalled "Dunning Kruger effect"! The Dunning–Kruger effect is a cognitive bias whereby people with low ability, expertise, or experience regarding a certain type of task or area of knowledge tend to overestimate their ability or knowledge. Wikipedia
Trump is used as an example, by a US University Professor, David Dunning, teaching the "Dunning-Kruger effect" to Psychology students!
See here:-
You may like this one too:-
and this:-

In the Royal Navy (1963 to 1973), there are occasional fist fights (sad to say!), around one a year for me, of which I can honestly say, I never lost one, but several times I was (correctly) pulled off someone who was being half murdered (red mist?), but they then tried to get in a punch or two on me as I was being held back and unable to dodge! Now Navy Guys don't like that and I was immediately freed to finish my aggressive attacker as I saw fit.

I was never charged with fighting!

But I always gave them the first punch, as I never ever punched anyone first! Navy rules and regs that whoever starts a fight will get the full blame....NOT ME!!

My last really serious fight, was many years ago, in my own dining room, when a girlfriend of my first wife, brought her drunken boyfriend to our party, who challenged me to go outside IMMEDIATELY (village idiot), who was so drunk he could hardly stand up, but had muscles on places where most people did not, except for his very thin legs! I dodged his first attempt at a hit (I was still sober) and he got the "shoe in the face" treatment, street fighting as learned in Trinidad and similar places, as I could imagine that he was far stronger than me in the upper body.

He had very long hair, I always have very short hair even as a boy (today about 6mm, my COVID CUT!), as long hair puts you at a huge disadvantage in any sort of a fight, as he found out!
He actually apologised to me (suddenly sober) when the Police arrived (called by my ex wife, the Police wanted to cart him off!), and the next day he was all the colours of the rainbow!! I sometimes wonder if he ever found out why.......he was SO drunk, he may have thought that I used my fists!!!

A subject that I have as good as forgotten today, only an old man's memories......So sorry to take up so much of your e-bike time on Pedelec.....

I liked the rest of your comments below, they showed good common sense....
Mmm. We might get somewhere if you took as much trouble reading other poster's opinions as you do expressing your own. Not sure what your dad's occupation has to do with topic or why it's in slightest helpful aliking discussions about chain wear etc to fist fights in navy I have no idea.
You stick to educating us all. Meanwhile I, ll stick with crank drives. Thanks for help.
 

Andy-Mat

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Oct 26, 2018
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Yo
Mmm. We might get somewhere if you took as much trouble reading other poster's opinions as you do expressing your own. Not sure what your dad's occupation has to do with topic or why it's in slightest helpful aliking discussions about chain wear etc to fist fights in navy I have no idea.
You stick to educating us all. Meanwhile I, ll stick with crank drives. Thanks for help.
Yo
Mmm. We might get somewhere if you took as much trouble reading other poster's opinions as you do expressing your own. Not sure what your dad's occupation has to do with topic or why it's in slightest helpful aliking discussions about chain wear etc to fist fights in navy I have no idea.
You stick to educating us all. Meanwhile I, ll stick with crank drives. Thanks for help.
Great post!
I was fairly sure that someone here would show the Dunning Kruger effect in action!
-and they did!
Many thanks
Andy
 

Sturmey

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I ride with a mid-drive Bafang 750w kit. I have to replace the rear sprocket at least three times a year which gets expensive. Does anyone else have this problem?
If your chains have quick links and you can replace the chain yourself, then you could try 'chain rotation'. I keep all my old chains and refit them again as the sprockets wear down as you cant put a new chain on an old sprocket. Better explained below. e.g.
 

WheezyRider

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Apr 20, 2020
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I'm sure it's been said before, but I'd like to see a mid drive with the motor running it's own strong chain and sprocket on the left side of the wheel, leaving the right side for human input. Obviously it would cost more so probably won't be done.
 
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flecc

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Oct 25, 2006
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I'm sure it's been said before, but I'd like to see a mid drive with the motor running it's own strong chain and sprocket on the left side of the wheel, leaving the right side for human input. Obviously it would cost more so probably won't be done.
The Swizzbee that Nealh owns has an in frame Heinzmann motor driving the left side of the rear wheel via a belt and pulley, deraileur gears on the right for the rider.
.
 
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Andy-Mat

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If your chains have quick links and you can replace the chain yourself, then you could try 'chain rotation'. I keep all my old chains and refit them again as the sprockets wear down as you cant put a new chain on an old sprocket. Better explained below. e.g.
Clever.
I really don't feel that I need it, but when I need to repace the chain/Cassette, I may well try it out, as old Scots try anything to save a few Bob!!
Many thanks.
Andy
 

Andy-Mat

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The Swizzbee that Nealh owns has an in frame Heinzmann motor driving the left side of the rear wheel via a belt and pulley, deraileur gears on the right for the rider.
.
Someone has a switched on brain! That appears to me to be an excellent way to "fix the problem!"
I wonder if the chain wear is seriously reduced or not, does anyone have some facts? Theoretically, chain wear should be about the same as a hub bike.....
regards
Andy
 

Zlatan

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Nov 26, 2016
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Someone has a switched on brain! That appears to me to be an excellent way to "fix the problem!"
I wonder if the chain wear is seriously reduced or not, does anyone have some facts? Theoretically, chain wear should be about the same as a hub bike.....
regards
Andy
Fixing a problem that doesn't exist. Millions of ways to do that.
 

guerney

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Sep 7, 2021
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If your chains have quick links and you can replace the chain yourself, then you could try 'chain rotation'. I keep all my old chains and refit them again as the sprockets wear down as you cant put a new chain on an old sprocket. Better explained below. e.g.
Thank you, that's a fantastic idea - my rear cassette may be too old for that by now, but I may try swapping my new-ish chain for a new one, to see if it also wears in after 70 miles or so...
 

guerney

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Sep 7, 2021
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All mid motor e-bikes with a chain drive will ALWAYS suffer more chain and sprocket wear, simply because all the motor AND the human developed torque travel via the relatively weak, chain drive.
Furthermore, certain failures of the mid motor unit on some designs, can also stop any torque from the motor or the rider, actually turning the rear wheel.
I call it "the single point of failure", which of course the mid motor brigade hate, because its 100% true, and for them, simply very annoying.
But any good engineer, taken as an average, will simply not buy a mid motor chain drive e-bike, just because they see and understand immediately, why this unfair strain on certain drive components, components originally designed for the level of torque that a human can produce, as being very obvious!
Of course there are also engineers that miss that problem completely, though I myself have yet to meet one!
And as someone else here, fully and correctly mentioned, the 750 Watt motor you have, just makes the chain drive wear problems even worse....a motor, assuming that you live in the UK, is of course totally illegal there. And as someone else here mentioned, apparently his 250 Watt motor, allows these components to have a longer life. If you are every stopped by the Police, or are involved in an accident, that motor may count against you legally.....
The chain component wear problems are only (very) simply physics, nothing more, nothing less.
So you either have to accept the wear effects as "running costs", or change to a hub motor system e-bike, where the torque of the motor actually tends to "reduce" the wear and tear to chain drive components, and they generally, provided they are of reasonable quality, which makes them last even longer than the same components on a traditional non e-bike system, due to the much lower torque being passed through these chain components, on a hub e-bike system.
A further problem with the "Single point of failure", is that if damage occurrs on the chain components, it will usually mean a walk home, or a pickup by a car, as the bike may not have any power drive, human or motor, to the rear wheel.
Whereas the hub e-bike owners, simply remove say the broken chain, get on the bike and simply do "air pedaling", to activate the motor, or simply twist the throttle, to drive home on any remaining battery power.
My first e-bike got me home with the "air pedaling", and the second can be got home with both "air pedaling" and/or "throttle", its a great system.

This same subject gets regularly addressed on Pedelec, with the mid motor e-bike owners, doing the job of being the "nay sayers", because they simply neither understand nor accept simple physics wear and tear, in a system that (in my opinion) was not properly designed for problem free long term riding.....!!
The mid motor owners, appear to be under the impression that as they paid many times the average price of most hub (because of far simpler hub drive mechanics = cheaper) e-bikes, that they bought something "BETTER"! But they really didn't, and they find this MOST galling.
They actually have bought something with many different possibly "built in" failures.....at a far higher cost. Not forgetting that some manufacturers actually install firmware that precludes an informed owner, from maintaining his own e-bike himself, like even replacing a battery,which I find totally appalling!
My second e-bike new, complete with two batteries, cost only a tad more than a replacement motor (may not even be new, just repaired!) for a Bosch e-bike, and where the owner is precluded from installing it himself, and if the guarantee is gone, even has to pay the bike shop to do the work, as well as the price of the motor, around 800 UK pounds plus work at an hourly rate!!!

I hope that you now have a far better understanding of "why", but if you have any further questions, please just ask us all here on Pedelec, as the massive amount of experience here, can help a fellow rider almost always.
regards
Andy
Sometimes a mid-drive is the right tool for the job, and for hauling heavy bike trailers up steep hills with my 20" wheeled folding bike, I don't think any legal hub motor would be capable - glad I bought a mid-drive. (A hub motor wasn't available for my bike at the time anyway, turns out I'm glad one wasn't).

But I have always allowed people who look for a physical fight with me, to have the first punch
That's a great way to lose teeth! Attack first if there are no witnesses! Leave no witness alive! (joking)

Not sure what your dad's occupation has to do with topic or why it's in slightest helpful aliking discussions about chain wear etc to fist fights in navy I have no idea.
Objects in contact under pressure damaging each other?
 
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Sturmey

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Clever.
I really don't feel that I need it, but when I need to repace the chain/Cassette, I may well try it out, as old Scots try anything to save a few Bob!!
Many thanks.
Andy
If your new chain skips after replacement and you can separate the individual worn sprocket, its also possible to 'dress' or reshape the 'U' of a worn cog with a round file rather than replacing the sprockets. (e.g chainsaw sharpening file). I have done this and it works if the cog is not too badly worn. Explained below.

 
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flecc

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Someone has a switched on brain! That appears to me to be an excellent way to "fix the problem!"
I wonder if the chain wear is seriously reduced or not, does anyone have some facts? Theoretically, chain wear should be about the same as a hub bike.....
regards
Andy
On the Swizzbee that wouldn't be possible to assess Andy, since the drive is a balanced one between the motor and belt drive on the left and the deraileur on the right.

To achieve this the rear hub is a differential. The electric motor and belt drives a sun wheel, the crown gear is driven by muscle power through the r/h derailleur, and the power take-off is provided by a planetary-gear carrier on the driven wheel of the bicycle.

Hence both share the drive need, according to what each, rider and motor, puts in.

Information Link

Information Link 2 (Alternative version)
.
 
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Zlatan

Esteemed Pedelecer
Nov 26, 2016
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Just to offer perspective.
There is a common misconception that power transmission is the culprit for chain wear. It isn't. As I mentioned earlier the major influence is actually torque, which with chain drives exhibits itself with a difference in tension between the driven side and the slack. Folk then hit an issue with misunderstanding of torque and power. (Andy had it in his head since average riders can only churn out 100w they can not be responsible for chain wear. That is utterly wrong)
Somebody standing on a static pedal is putting extreme amounts of torque into the system (simply their weight in lbs x length of crank in feet to arrive at foot pounds) but with no movement is actually producing zero work.!(ie no watts at all)
So that person even only producing 100 w can still inflict damage to teeth etc which then goes onto show itself as wear, but because a motor is also involved we blame that.
The motor, for want of a better description, gives gentle, smooth assistance with fairly constant low figures of torque. The rider supplies pulses of extreme torque,especially at low cadence. (with result of much damaging torque and low power)
The motor produces its power by delivering relatively little torque but at high rpm..
Invariably, damage sustained even on crank drives, is initiated by rider, not the motor. The motor simply exacerbates the inherent weakness in lightweight chain drives. The riders do all the damage. High mileage is put on crank drives by simply riding, pedaling and changing gear as we really should.
 

Sturmey

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Sheldon Brown has nice picture below shown the wear on the chains pins and bushes that causes the chain stretch. This wear takes place as the chain bends when wrapping itself around the sprockets under tension. I would say there are many factors that increase chain wear. For example, the smaller the sprockets, the more the chain bends/wears at pins. Those small 11 tooth sprockets cause a lot of wear. Also more torque puts more tension on chain when bending at small sprocket and increases wear. Also other factors e.g Chainline......dirt in links.....lubrication........milage........
Of course, wear takes place in other areas e.g rollers. But I think chain elongation due to pin and bush wear is the major culprit. This elongation/change of chain pitch causes extra friction between the chain and sprockets as they no longer match up.

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