Thorn Cycles Forum
Community => Thorn General => Topic started by: Manuel on October 04, 2019, 12:23:53 pm
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Is there any obvious reason why no one seems to be using the now readily available 50 x 21 tooth combination with the Rohloff? With 26" x 2 tyres this would give a very useful touring ratio of 90.8 to 17.3, along with longer wearing cogs and chain. Am I missing anything?
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The Thorn chainring is very long-lasting. The Rohloff sprocket is very long-lasting but often on a different time-schedule than the chainring. A common replacement for the Thorn chainring is the Surly stainless steel chainring -- you guessed it -- which lasts forever. So the likelihood is that someone going to 50x21 might have to throw out part-worn components. In addition, the Chainglider is pretty popular among members of the forum, and that only works with particular tooth counts in both the sprocket and the chainring, and it is virtually indestructable. Furthermore, you might consider that a large chainring on a touring bike makes your transmission more vulnerable to damage when you go off the tarmac -- or even ride through a pothole on the tarmac.
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I want to use even numbers of teeth on my chainring and sprocket.
https://www.sheldonbrown.com/chain-life.html
I bought my Rohloff separately from my Nomad, SJS as a default supplies bikes with a 17T sprocket, but from other sources the default sprocket was 16T when I bought mine.
If I could have bought a 20T (threaded) sprocket when I built up my Nomad, I would have.
It will be years before I need to buy a new sprocket, I have a spare threaded 16T sprocket that is unused. Now that there is an 18T splined one available I would probably switch to 18 from 16 when I need another.
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Now that there is an 18T splined one available
Thanks for that info, George.
Happily, Hebie's chainglider is designed to fit 15-18T sprockets.
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I have the 38x16 combo which gives almost exactly the same ratios - which indeed work great!
The ratio ranges are 0.25% different - fun math!
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Now that there is an 18T splined one available
Thanks for that info, George.
Happily, Hebie's chainglider is designed to fit 15-18T sprockets.
Unfortunately not John, https://www.sjscycles.co.uk/chainsets/hebie-chainglider-chainguard-for-rohloff-1517t-rear-black/ Hebie Chainglider Chainguard for Rohloff 15-17T - Rear - Black.
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Thanks, Mac, interesting item...
On the back of my 'glider (bought in early 2014), the sizing reads "15T - 18T".
Downsizing? ;)
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I do not use a chain glider, so I am quite ignorant of size issues, but could the sizing have changed when then went from threaded sprockets to splined?
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I do not use a chain glider, so I am quite ignorant of size issues, but could the sizing have changed when then went from threaded sprockets to splined?
Interesting point. My concern is that the new splined cog sits further 'out' and does not allow the Chain glider to fit for that reason.
Anyone made the change of sprocket with a 'glider?
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Anyone made the change of sprocket with a 'glider?
Not me not yet, Matt, and as I have a regular spare 17T sprocket, I doubt I ever will.
OTOH, I understand that the slimline splined sprocket (try saying that quickly!) keeps the chainline at 54 mm, so it shd be OK with the 'glider.
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Slim version changes chainring by 1 mm, the regular version by 3mm.
https://www.rohloff.de/en/products/speedhub/accessories/
If you click on:
Conversion from threaded, to splined carrier. Which model to choose
you get a table of data.
I had bought a spare threaded sprocket when I learned that the new carrier would be several mm change in chainline, but that was before I learned that a slim version would come out later. My chainline is about 5mm off of optimum on my Nomad (intentional, my choice) because I wanted the Q factor (pedal width) on my Rohloff bike to be about the same as my derailleur bikes. Thus my bottom bracket spindle is about 10mm shorter than I should have bought for an ideal chainline.
But if I had known that a slim version would come out that only added 1mm, I would not have bought the spare threaded version.
But I have no clue if there are any other aspects of the splined system that would conflict with the chainglider.
The link above is also where I learned that there is an 18T sprocket.
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The larger chainring and sprocket also add a few extra grams to drag uphill!
Mike
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You're right, Mike. Probably best used in the Netherlands, 'cept for the "Dutch Alps" region, down near Maastricht ;)
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If a 21T sprocket had been available when I got my 1st Raven Tour, AND if the Chainglider didn't exist I would have gone for it, but not with a 50T ring, because I like lower gears than 17 to 91 on a loaded tourer.
I do have a 50x19 combo on my Raven Sport Tour.
50 because I have some NOS TA rings in that size.
19 because it was the biggest available (screw-fit) sprocket at the time.
No chainglider because it is difficult to fit with the geometry of the Raven Sport Tour, so not limited to the 38x17 ratio.
18 to 94 inch range is OK at the moment on a bike I use for unloaded day rides. But I have some smaller NOS TA rings available for when I will need lower gears as I get older.
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Is there any obvious reason why no one seems to be using the now readily available 50 x 21 tooth combination with the Rohloff? With 26" x 2 tyres this would give a very useful touring ratio of 90.8 to 17.3, along with longer wearing cogs and chain. Am I missing anything?
That'd probably work for me - on a 700C x 35mm tyre that's be around 18 - 95" which is about what I use. if ever the chainring/sprocket/chain need replacing at the same time I'd be tempted to give it a go, though I'd also need a new bash/outer guard/.
Isn't there an efficiency advantage with bigger rings? I'm pretty sure there is, though I can't remember why. I know on my derailleur bike those ratios that are duplicated on the middle and outer ring feel easier on the larger one, and the chainline isn't much different.
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Is there any obvious reason why no one seems to be using the now readily available 50 x 21 tooth combination with the Rohloff? With 26" x 2 tyres this would give a very useful touring ratio of 90.8 to 17.3, along with longer wearing cogs and chain. Am I missing anything?
I think the consensus is that there is an obvious reason. We all started out with a different smaller sprocket and chainring. And we all plan to use what we already own until a sprocket or chainring or both wear out. Once they wear out, maybe make a change at that time.
But those that use the chainglider are more likely to not make any changes since they have something that they are content with.
The advantage of the bigger sprocket and chainring for longer chain life and possibly longer sprocket and chainring life is not in question for those of us that do not use a chainglider.
I plan to stay with even numbered sprocket and chainrings, but it will be years before I run out of the old threaded sprockets.
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Isn't there an efficiency advantage with bigger rings?
Yes. But I don't know if going from 38x16 to 50x21 makes much difference to efficiency, my experience would suggest not.
Very small sprockets are significantly less efficient, here I am thinking 11T as used on a Moulton versus the 14T top gear sprocket on my derailleur lightweight. Found a summary here that gives an idea of the efficiency gain going from 13T to 24T:
https://www.cyclingpowerlab.com/DrivetrainEfficiency.aspx
For me, the most noticeable difference in going for larger rings/sprockets is durability.
Past experience with derailleur bike half-step triples suggests that 44/50 lasts significantly longer than 40/36, both these were with small inner rings (26 to 30), wear on the latter is fast if used often, which wasn't the case as mountain touring only accounted for a fraction of my riding.
On utility bikes with hub gears, 44x22 was slightly more durable than 38x19 before I discovered the Chainglider.
I suspect that the main effect as far as durability is concerned is faster chain wear on a small sprocket leading to faster wear on the chainring(s).