Technical > Transmission
How do my teeth look?
steve216c:
@PH- when I purchased bike 2nd hand the previous owner had no idea how far it had been ridden. But the sprocket was visibly sharktoothed. So when I flipped it it was already well worn in one direction and it was only a 3-4000km on the flip side before I noticed that sprocket teeth began to lose their ends. I can only warrant the km I have ridden, of which the first 5000km was fully exposed, ridden in all weathers on daily commute including approx 10km of unpacked forest paths which threw up a lot of crud onto exposed chain. I suspect accelerated wear occurred during this time. I am hopeful that new running gear all round with fitted Chainglider will see slower decay of new chain/cog.
I have a black touch up stick for car paint which I will try to cover blemish to help identify if it starts rubbing again. But nail varnish would probably have done the trick too. Not sure how shocking pink or ruby red from Max Factor would look adorned on my hub. Good talking point though if I had gone that direction 😜
& Mickeg - I was not aware of that part existing. I will keep an eye on further wear and certainly consider such a fitting if I notice this happening again.
PH:
--- Quote from: steve216c on May 07, 2022, 09:34:51 am ---@PH- when I purchased bike 2nd hand the previous owner had no idea how far it had been ridden. But the sprocket was visibly sharktoothed. So when I flipped it it was already well worn in one direction and it was only a 3-4000km on the flip side before I noticed that sprocket teeth began to lose their ends.
--- End quote ---
That might explain it. I've wondered if there's an optimal time to flip a sprocket, in theory the chain should only be wearing a previously unused surface, though if it's been left long enough there might not be much left to wear away.
Likewise with chains, I've never used one to destruction, neither brave or stupid enough to try, I have a feeling it'd always be the sprocket that gave up first. I suspect it's another advantage of a larger chainring and sprocket, having more teeth and links engaged at all times can't be a bad thing.
JohnR:
I've just noticed that titanium Rohloff sprockets are available. Do they last better or are they for those people who want to shave another ounce off the weight of their bike after weighing it down with a Rohloff hub?
PH:
--- Quote from: JohnR on May 07, 2022, 10:39:23 am ---I've just noticed that titanium Rohloff sprockets are available.
--- End quote ---
Doesn't make much sense - At the same thickness titanium will wear faster than steel, though of course there's different alloys of each and steel's hardness (Brinell) is also dependent on it's manufacture. On the Brinell index it's usually quoted as 70 ti - 120 steel .
Designing from scratch and having all the wearing parts made in ti, dimensions could be increased to have something longer lasting for less weight, but no one has done that.
EDIT - I wrote the Brinell numbers the wrong way round :-[
EDIT, EDIT - of course hardness isn't everything, checking the numbers I notice glass is 1,500 but I wouldn't recommend it as a sprocket material. Which reminds me, when I worked in a tool place, diamond tipped circular saw blades were around twice the price of any other (Carbide?) and were reputed to last four times longer, diamond tipped sprocket anyone?
mickeg:
I have replaced chains several times on my Nomad Mk II without reversing the sprocket, which might have been a mistake. But when I finally flipped my sprocket, it was so worn that a new chain would catch on the hooked part of the worn teeth as the chain lifted off of the teeth as I pedaled. It took a while to figure out exactly why I could feel something odd in the feel of it and the odd noise. I run an even number of teeth (16) on my sprockets, not the Thorn norm of odd (17) number of teeth. So every other sprocket tooth wears differently as only the chain links with outer plates elongate as a chain wears.
I used to replace my chains at 0.75 percent elongation (or stretch), but now only do that on my derailleur bikes, I run my chains much longer on my Rohloff bike.
I do not recall if anyone on this forum was going to experiment with KMC sprockets, but if my memory is correct, KMC makes a Rohloff sprocket that is thicker than the Rohloff sprocket, instead of an 8 speed chain it uses the wider single speed chain. If they were both the same steel, I suspect that the wider sprocket would give longer life simply because more metal would have to wear off before it wears out.
--- Quote from: PH on May 07, 2022, 11:27:27 am ---
--- Quote from: JohnR on May 07, 2022, 10:39:23 am ---I've just noticed that titanium Rohloff sprockets are available.
--- End quote ---
Doesn't make much sense - At the same thickness titanium will wear faster than steel, ...
...
Which reminds me, when I worked in a tool place, diamond tipped circular saw blades were around twice the price of any other (Carbide?) and were reputed to last four times longer, diamond tipped sprocket anyone?
--- End quote ---
Fully agree that titanium is softer, I suspect in all alloys would be softer than any steel that anyone chose to use for a sprocket.
I am a geological engineer by training. Geologists think in terms of hardness on the Mohs scale, diamond has a hardness of 10. The mineral corrundum is aluminum oxide with a hardness of 9. Quart has a hardness of 7, tool steel further down the list. But that is says nothing about brittleness, you hit a diamond with a hammer, the hammer won't break, instead the diamond will.
But marketing departments love to use the word titanium. I have even seen clothing listed as titanium even though there was no titanium added to the clothing. And some razor blade manufacturers have added a titanium coating to the razor for reasons that I am clueless on.
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