Chainring wear on a fixie

[silva]

I was browsing on a rare historical photos website and came across this:
https://rarehistoricalphotos.com/students-at-smith-colleg-massachusetts/

This is dated 1948, look at how far the chainring teeth are separated, it's like half density, aka every inch instead of every 1/2 inch.
Someone here recently wrote having removed every second tooth, without elaborating why.
Apparently, back then, chainrings were produced like that.

 

[Ian H]

Inch pitch chains were common back in the day (inner link was solid), hence the inch-pitch ring. You can run a half-inch chain on it no problem, but not vise versa.

 

[silva]

How does a "solid" inner link differ from nowadays inner link?
2 outer plates, 2 inner plates, 2 pens, 2 bushings over the pens, 2 rollers spinning over the bushings?
I found this:
http://www.american-vintage-bicycles.com/home/vintage-bicycle-parts/skip-tooth/
"skip tooth" chain it is named.

The inner link plates are longer than the outer so not equal gaps between rollers.
1 gap is big enough to accomodate a tooth, the other isn't.
The rollers are alike in pairs, so between 2 chainring (and then also rear cog I suppose) teeth, instead of 1 roller, 2 rollers.
On the 1950 dated pic I linked, not that detailed to be sure, but it does look like that, you see more white / background every second link.

 

[silva]

Well, it looks like the rear cog now also ceased wearing further.
I had grinded off the teeth tops to nearly points, as to allow the rollers to easily disengage, mounted a new chain, retensioned it now 5 times, and still no teeth broke off, alike happened before.
I have a cog here with 5 such broken teeth, the not broken ones are still quite thick (in the chain direction), but due to the hollowing out like hooks the rollers ripped the teeth off.
All 16 teeth of the current cog became thinner than that used cog, without break offs.
So it looks like it increases the life span alike it happened for the chainring.
How long, will remain to be seen.

 

[Sharky]

If the teeeef look a bit sharky there done.

What are you implying?

 

[silva]

With that mentioned rear cog, 4 months later of which at least 2 with all 16 teeth broken off, yet chain still doesn't skip, when up on a bridge, more force, it occasionally makes a noise and that's it.
Apparently teeth remainder, barely 5 mm, still suffices to not slip, jump over.
I now wonder why they produce these fixed gear application specific - cogs with such high/tall teeth. It's listed as a plus property, but since wear concentrates at the middle of their height, the formed hook shape causes a longer trajectory and opposite to force direction for the rollers to disengage, accelerating wear.
And, since teeth are thicker (plate thickness) at their bottom, the contact surface is bigger so less wear distance radially.
If over again some months (with eventually a replaced chain)

 

[silva]

4 months further - still same 16T cog, all teeth broke off in the middle, which was 3 months ago, but apparently no problem - rollers don't slip over.
I retensioned the chain more frequently, to decrease risk of chain humping off at the slackest point.
The bottom bracket eccentric tensioning module is now turned near to the end of its range, so new chain needed then, wonder what that it will do on that extremely worn cog, since with a worn chain, a set of rollers nearly simultaneously engage and thus spread force, while with a new chain, only one will.

 

[silva]

At now 40 km/day, still the same rear cog, bottom bracked based eccenter tensioner was 3 weeks ago at its end, replaced with new chain.
The circumference of the inbus heads of 1-2 of the 6 mounting bolts showed a flat section due to chain links grinding over.

I unmounted the cog to inspect and clean it, and put specific bolts back in same holes in the hubs IS disc, as to try to have the damaged / flattened sections again closest to the chain path, which succeeded.
Sometimes when pushing hard, I still did hear links grinding over bolt heads, so I decided to try something: allowing 1.5 cm instead of 1 cm vertical movement when tensioning, as to give the links more movement room over the rear cogs teeth - instead of force exerted on the bolt heads, force gets "diverted" by tensioning chain more.
The idea turned out to be working, it's now nearly silent at the rear cog.

The extra risk involved is due to the more slack chain, it may bump aside the rear sprockets teeth which can cause damage.
So I pay more attention to / avoid bumpy road parts.

The chain is a model 420 1/4" motorcycle chain, so it's quite heavier, less easy to bump off.

So, I now have some experience to judge, apparently, as proven, cog teeth for a no derailer use, don't need to be high. Yet they are produced that high, even for dedicated singlespeed/fixed gear alike former Velosolo company did. The "tall teeth" was even listed as a plus.
But the rollers of the chain hollow them out (sharkfin shape), proving that the upper parts of the teeth act more as a resistence to disengage than as a facilitate to engage.

So, couple weeks ago I prepared for a next test: I have with me on the bike a spare Velosolo chainring and a spare cog, brand new.
I took them out, went to the table grinder, grinded down the top of all teeth, then a little rounding in both directions, as to make the curves smooth.
So, whenever I DO replace current 2019 chainring and 1 of 2 cogs that already had have a service life (I replaced them after 3 teeth broke off), and are now living an unimagined next service life), the "new" drivetrain will start with those "adjusted" new ring and cog.
The now lower teeth, and abit wider valley ends, should avoid the increasing wear rate due to the hollowing out.

That is, to be experienced in a future, if I survive it...

 

[silva]

8 months further test with the 2nd life cog with all its teeth been broken off: it STILL does the job of transmitting power to the rear wheel.
So it became a proof of concept.

Leading to the question why they fabricate sprockets with such high teeth?
It's not needed since it's proved that a quarter of a circle circumference suffices.
And the important: further cog wear nearly ceased, simply because nothing sits in the way for the rollers to disengage, during the entire life of the chain (the cause of the self-accelerated sharkfinning).
Maybe they like accelerating wear because it leads to replacement need which means sales?
Because, the chainring and cog are both dedicated for singlespeed (thicker plate>teeth to accommodate 1/8" chain), so any possible derailer gearing problem is ruled out).
Nothing sits in the way to design rings and cogs teeth profile directly in such "end of wear" shape.

In the past, not knowing better, I replaced cogs as soon as I judged the teeth too thin to hold thus prone to breakage and misery along the road.
Later I decided to risk a break, and even waited until 3 broke off.
Again later, I risked the very last breaking off.
I expected chain then rattling over teeth remainders and transmission failure (slow riding or walk further).
But none of this happened.

Also the chain must wear less, because in orde to disengage (almost "escape") rollers have to roll with higher resistence (backwards) along the steadily longer trajectory of a sharkfin shapes inner curve.

Also proved for the chainring. A quarter of the 47 teeth were broken off (due to lack of insight back then I even filed them down completely because I feared skipping leading to further breakages). It was mounted begin 2019, now 6 years in service.

Out of interest, upon a next disassembly, I'm gonna weight this cog, to know how much of its material (chromoly) was lost (by subtracting the measured from the weight of a new).
Same for chain ring. That's all wear that could have been avoided by simply fabricating them like that, even cheaper since less material due to smaller diameter of required plate)

 

[fossyant]

You are doing something wrong, I've never snapped teeth off sprockets or chainrings, and I ran a fixed gear commuter for years.

 

[silva]

You are doing something wrong, I've never snapped teeth off sprockets or chainrings, and I ran a fixed gear commuter for years.

... because you replaced before breaking?
I ceased doing that.
And they continued doing the transmission job, despite now and then teeth broke off in the middle until all did.
After becoming too short/thin (in the chain running direction) metal.

So, both ring and cog stay, I only replace the chain, when the oval shaped bottom bracket tensioning mechanism reached its end position.
So (2) I hope to be able to say over 10 years that I've never replaced a sprocket.
But then you will be saying that I never used the bike, no?

There is one problem: the chain link plates slightly void the 6 bolts of the cogs mount.
Because wear also happens (but way less) in the depth.
Those have now a flattened section on their circumference. I keep an eye on it.
Just bad luck due to 16T, with 17T it wouldn't have happened. But I didn't know then, I bought 1 or 2 cogs in the testing phase of the avatar bike when new. Velosolo is now gone.
Also, it would reduce my gear from 2.94 to 2.76, which means quite more spinning legs which I don't like.

 

[fossyant]

I replaced when worn. No way would I run a set of gears into the ground like that - I value my teeth.

It's the reason the teeth are longer on single speed bikes, to stop them ever coming off. Unshipping a chain on a fixed gear can be a disaster, especially if you are riding quickly and spinning quickly.

Each to our own, but I'd rather have guaranteed reliable equipment.

 

[silva]

I replaced when worn. No way would I run a set of gears into the ground like that - I value my teeth.

It's the reason the teeth are longer on single speed bikes, to stop them ever coming off. Unshipping a chain on a fixed gear can be a disaster, especially if you are riding quickly and spinning quickly.

Each to our own, but I'd rather have guaranteed reliable equipment.

As described: the reliability of the cog is proven.
I decided to risk continuing its usage.
In case the transmission failed somehow (I expected skipping), I've spares with me.
But it didn't fail. Even not after 4 months with ALL teeth broke off in the middle.
That's how guarantee, reliability is proved, no?

A chain coming off, is usually due to not retensioned for too long.
With my avatar bike, 2017 acquired, I never had a chain jumping off.
Just because I bothered to retension.
With the all-teeth-broke cog I initially kept close eye on it, retensioned more.
But as proved later on, it wasn't needed.

Why I bother all this testing?
Because there are major benefits to keep using the cog in such a wear state.
- I don't have to replace it = no cost / work
- I don't have to flip it regularly (to maintain a minimal sharkfinning) = no work
- The rollers travel less distance on the teeth = less wear = longer lasting chain = less cost/work

Same for the 2019 chainring.
Instead of 6 times cost of chainring, and above described work.
No cost and no work.

Back in early 2019, I replaced the then new chainrings default mounting bolts (annoyant small bicycle chainring dedicated things with one side sleeve ends around big hole, other side an internal hex for allen key, easy to damage head, easy to lose, with M10 bolts with nuts. To allow to do the job with no risk of damage / loss, with a couple 17 keys. That made flipping also alot easier and faster.
Well, it became even more easier, because once worn to the degree an end of life chain inflicts, no work at all.

After that succesful chainring test, now also rear cog test succes.
The chainring is now 7 years and has had an equal number chains.
Not a single occurrence of chain jumping/dancing/whatever off.
Despite 12/47 chainring teeth and 16/16 cog teeth broke off
So that risk you say you see, if something didn't happen in 7 years, what's left of it?

Initially the chain was UK brand Gusset model "tank", basically a 1/8" internal width chain with 3/16" style link plates.
Later on I moved to a motorcycle type 420 chain brand Regina, full 1/4".
I bought 1 to test - clearance chain to rear wheels dropout might have been a problem - but it didn't void it, upon which I bought a lifetime stock of these chains.
I also had bought a stock Gusset Tank's but I decided to keep these for last.
It stayed that Regina 420 OROY since mid 2020.

I DID have a single occasion of losing the chain.
Not due to jumping from teeth, but due to the closing plate of the quicklink breaking in the middle, causing the chain to roll off to the street.
Something I never expected to happen. But I had spare chain and extra spare quicklink with me, I managed to get the bend-wide-open quicklink off, put the spare in it, and continued riding home.
But the bike felt so weird that something clearly was wrong.
Also, the days before and that day, I discovered like 4-5 teeth broke, in such a short time.
I decided to stop to take a good look.
It took me like 10 minutes to finally discover that the frames tube bottom bracket to rear wheel dropout / driveside was half cracked, on the verge of disaster.
Thus all aside the discussion topic here, since the cause was not sprocket wear.

 

[classic33]

As described: the reliability of the cog is proven.
I decided to risk continuing its usage.
In case the transmission failed somehow (I expected skipping), I've spares with me.
But it didn't fail. Even not after 4 months with ALL teeth broke off in the middle.
That's how guarantee, reliability is proved, no?

A chain coming off, is usually due to not retensioned for too long.
With my avatar bike, 2017 acquired, I never had a chain jumping off.
Just because I bothered to retension.
With the all-teeth-broke cog I initially kept close eye on it, retensioned more.
But as proved later on, it wasn't needed.

Why I bother all this testing?
Because there are major benefits to keep using the cog in such a wear state.
- I don't have to replace it = no cost / work
- I don't have to flip it regularly (to maintain a minimal sharkfinning) = no work
- The rollers travel less distance on the teeth = less wear = longer lasting chain = less cost/work

Same for the 2019 chainring.
Instead of 6 times cost of chainring, and above described work.
No cost and no work.

Back in early 2019, I replaced the then new chainrings default mounting bolts (annoyant small bicycle chainring dedicated things with one side sleeve ends around big hole, other side an internal hex for allen key, easy to damage head, easy to lose, with M10 bolts with nuts. To allow to do the job with no risk of damage / loss, with a couple 17 keys. That made flipping also alot easier and faster.
Well, it became even more easier, because once worn to the degree an end of life chain inflicts, no work at all.

After that succesful chainring test, now also rear cog test succes.
The chainring is now 7 years and has had an equal number chains.
Not a single occurrence of chain jumping/dancing/whatever off.
Despite 12/47 chainring teeth and 16/16 cog teeth broke off
So that risk you say you see, if something didn't happen in 7 years, what's left of it?

Initially the chain was UK brand Gusset model "tank", basically a 1/8" internal width chain with 3/16" style link plates.
Later on I moved to a motorcycle type 420 chain brand Regina, full 1/4".
I bought 1 to test - clearance chain to rear wheels dropout might have been a problem - but it didn't void it, upon which I bought a lifetime stock of these chains.
I also had bought a stock Gusset Tank's but I decided to keep these for last.
It stayed that Regina 420 OROY since mid 2020.

I DID have a single occasion of losing the chain.
Not due to jumping from teeth, but due to the closing plate of the quicklink breaking in the middle, causing the chain to roll off to the street.
Something I never expected to happen. But I had spare chain and extra spare quicklink with me, I managed to get the bend-wide-open quicklink off, put the spare in it, and continued riding home.
But the bike felt so weird that something clearly was wrong.
Also, the days before and that day, I discovered like 4-5 teeth broke, in such a short time.
I decided to stop to take a good look.
It took me like 10 minutes to finally discover that the frames tube bottom bracket to rear wheel dropout / driveside was half cracked, on the verge of disaster.
Thus all aside the discussion topic here, since the cause was not sprocket wear.

Which is easier and cheaper replace?
The frame(Isn't this the second frame that's failed/cracked on you?) or the drivetrain parts.

You're putting safety, not just yours, at risk to try and save a few pounds.

 

[fossyant]

And too much time analysing things. Never had a frame break or chainrings or sprockets.