Author Topic: What's your Rohloff combo (chainring, cog)?  (Read 115594 times)

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #345 on: September 06, 2021, 04:04:36 PM »
Hello All, thanks for accepting me onto this forum. I am not a Rohloff owner at the moment, BUT my retirement bike is in the making and I'm at the point of choosing a chainring/sprocket combo for the Rohloff.

Being new to the Rohloff world, it's been a steep learning curve, and I've found this thread fascinating (yes, I have read all 23 pages!). I wonder if somebody would kindly answer a few questions.
...

Q1 - Yes.  For example, a 34 chainring and 17 sprocket has a ratio of 2.0.  And a chainring of 36 and sprocket of 18 would also have a ratio of 2.0.

Q2 - Correct.  Bigger chainring means you have less tension on the chain.  And bigger chainring and bigger sprocket will have a smaller articulation angle as the chain unwraps off of the sprocket and wraps onto the chainring.  Both tension and articulation angle are a function in chain wear.

Q3 - Smaller crank arm length means you will want your gearing to be a bit lower, otherwise it would increase how hard you have to push on the pedals in your first gear.  I think it would not change anything in other gears, as you would likely just automatically use the gear that you want to use.  In other words, if you pedaled that bike with 175mm cranks in gear 11, with 165mm cranks you might choose to use gear 10, without even thinking about it.  But your first gear remains your first gear.

I have a 170mm crankset on one bike, the rest of my bikes are 175mm crank arm lengths.  I notice no difference, but I would expect that my cadence might be a bit higher with the shorter crankarms.  I however have not attempted to measure that.

Where you say the lower end is where you are matching to, I think that is the right plan.  If you need a higher gear, unless you are racing you do not REALLY need a higher gear.  But if you need a lower gear, you do REALLY need a lower gear.  That is why for my touring chainring size, I set it based on the cadence that I wanted at a specific speed that I felt was my minimum speed to maintain balance in my lowest gear.

If your new bike will be heavier than the Litespeed, which most certainly is the case, you might want a lower gear than you have on the Litespeed as you will be lifting more weight up the hill.  You probably noted when reading previous posts that I use a 44T chainring with an unladen bike around home, but when I load it down for a bike tour with my camping gear, I use a 36T chainring instead to get lower gearing.  The 44T chainring needs four more chain links, I use a second quick link for one of those four.  If you want to change gearing later, with chain drive that is easy to do with a different chainring and adjusting number of links in the chain.  Belts, not so easy.

That said, I think the Thorn Mercury has specific chainring and sprocket combinations that are needed for a small bottom bracket eccentric.  But I do not own a Mercury, I could be wrong on that.

There are lots of things you will notice when you get a Rohloff bike after using derailleur bikes.  The thing that I noticed most was that the Rohloff which uses two shifter cables must have some slack in the cables.  If I am in gear 10, my shifter will easily move 9.5 to 10.5 with cable slack.  But a derailleur bike, as you know you always have tension in the cables. If you do not have enough slack in a Rohloff shifter cable, when you shift you might land somewhere between the gears within the hub, which does not work so good.
« Last Edit: September 06, 2021, 04:08:21 PM by mickeg »

Dunroving

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #346 on: September 06, 2021, 06:18:14 PM »
Hello All, thanks for accepting me onto this forum. I am not a Rohloff owner at the moment, BUT my retirement bike is in the making and I'm at the point of choosing a chainring/sprocket combo for the Rohloff.

Being new to the Rohloff world, it's been a steep learning curve, and I've found this thread fascinating (yes, I have read all 23 pages!). I wonder if somebody would kindly answer a few questions.
...

Q1 - Yes.  For example, a 34 chainring and 17 sprocket has a ratio of 2.0.  And a chainring of 36 and sprocket of 18 would also have a ratio of 2.0.

Q2 - Correct.  Bigger chainring means you have less tension on the chain.  And bigger chainring and bigger sprocket will have a smaller articulation angle as the chain unwraps off of the sprocket and wraps onto the chainring.  Both tension and articulation angle are a function in chain wear.

Q3 - Smaller crank arm length means you will want your gearing to be a bit lower, otherwise it would increase how hard you have to push on the pedals in your first gear.  I think it would not change anything in other gears, as you would likely just automatically use the gear that you want to use.  In other words, if you pedaled that bike with 175mm cranks in gear 11, with 165mm cranks you might choose to use gear 10, without even thinking about it.  But your first gear remains your first gear.

I have a 170mm crankset on one bike, the rest of my bikes are 175mm crank arm lengths.  I notice no difference, but I would expect that my cadence might be a bit higher with the shorter crankarms.  I however have not attempted to measure that.

Where you say the lower end is where you are matching to, I think that is the right plan.  If you need a higher gear, unless you are racing you do not REALLY need a higher gear.  But if you need a lower gear, you do REALLY need a lower gear.  That is why for my touring chainring size, I set it based on the cadence that I wanted at a specific speed that I felt was my minimum speed to maintain balance in my lowest gear.

If your new bike will be heavier than the Litespeed, which most certainly is the case, you might want a lower gear than you have on the Litespeed as you will be lifting more weight up the hill.  You probably noted when reading previous posts that I use a 44T chainring with an unladen bike around home, but when I load it down for a bike tour with my camping gear, I use a 36T chainring instead to get lower gearing.  The 44T chainring needs four more chain links, I use a second quick link for one of those four.  If you want to change gearing later, with chain drive that is easy to do with a different chainring and adjusting number of links in the chain.  Belts, not so easy.

That said, I think the Thorn Mercury has specific chainring and sprocket combinations that are needed for a small bottom bracket eccentric.  But I do not own a Mercury, I could be wrong on that.

There are lots of things you will notice when you get a Rohloff bike after using derailleur bikes.  The thing that I noticed most was that the Rohloff which uses two shifter cables must have some slack in the cables.  If I am in gear 10, my shifter will easily move 9.5 to 10.5 with cable slack.  But a derailleur bike, as you know you always have tension in the cables. If you do not have enough slack in a Rohloff shifter cable, when you shift you might land somewhere between the gears within the hub, which does not work so good.

Thanks for the quick reply. I'm glad that I am at least on the right track! I'm really looking forward to this bike build (I'm not building it, but it's nice to have some autonomy on the component selection, etc.), and especially for the Rohloff hub part of the decision, I want to make sure I get the gear selection right, or approximately so.

I hear what you are saying re: the belt option. I was originally attracted to the simplicity of it, especially the part about not having to clean it - but after much research, and especially after reading this thread, I realised (a) cleaning an IGH chain is nowhere near the faff of cleaning chain, derailleurs, jockey wheels, etc., and (b) if you get the gear ratios wrong with a belt, it's an expensive mistake to correct!

Your comment about getting the bottom gear right has really made me think more about that subject. I definitely agree with your comments about top end speed - these days, if I can go at 30 mph on the flat it would be a miracle, and going downhill I'm not that bothered if I exceed 30 mph due to pedalling harder, or due to gravity. Regarding bottom end, I'm not 100% sure I should be aiming for lower gears than the Litespeed, though it seems logical. Here's my reasoning:

On the Litespeed, unloaded, I run out of gears, and steam, and balancing ability, around the 20% gradient mark (I need to check this, but I think it's about right). In the 22 (front) x 33 (rear) combination, on 26 inch rims and 2.2 inch tyres, pedalling at 60 rpm, I'm doing 3.1 mph. Generally, when it gets really steep (approaching 20%), I do drop from 60 rpm and pound the pedals a bit, but this is where I usually stop. I'm not actually sure what is the primary cause of me stopping - lack of leg strength or lack of balance (the front wheel rises from the floor, and I never was good on a unicycle).

Assuming balance is my limiting factor, and I can't balance below 3.1 mph, would a lower gear really help me? (thinking aloud here)? Is it that, with a lower gear, I'd be able to maintain 3.1 mph with a higher cadence (bearing in mind that, as you said, shorter cranks usually mean higher cadence)?


martinf

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #347 on: September 06, 2021, 07:18:30 PM »
Q2: If I'm correct in the above, from reading this thread it seems that a "big-big" combination has the advantage of less chain wear, but greater likelihood of chainring strikes on lumpy terrain? And that conversely, a "small-small" combination raises the chainring (less chance of chainring strikes), but causes faster wear on the chain?

If you are considering fitting a Chainglider (for even less maintenance under most conditions), another thing to take into account is Chainglider compatibility. I generally agree with Mickeg that it is best to fit a fairly big chainring and sprocket to minimise wear, but as I wanted a Chainglider, for my first Rohloff bike I chose a small chainring and sprocket (38x16), which is compatible.

Q3: (most important question!)I'm wondering what will be the effect of shorter crank arms (165mm on new-build vs. 175mm on Litespeed) on the actual riding experience?

My own experience from going from 170mm/175mm to 150mm/155mm cranks (about 13% difference) is that I increased pedalling cadence and so needed to lower ALL my gears.

I don't really notice 5mm difference (it's about 3% between 170 and 175). I think I would notice a 10mm difference (about 6%).

My reason for going to short cranks was knee problems due to pushing high gears too slowly. Quite by accident I found out that short cranks solved the problem for me, without slowing me down. I don't know why short cranks are better for my knees, maybe less force on each pedal stroke, maybe a smaller bending angle at the knee joint.

PH

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #348 on: September 06, 2021, 09:10:32 PM »
greater likelihood of chainring strikes on lumpy terrain? And that conversely, a "small-small" combination raises the chainring (less chance of chainring strikes),
There's various charts that sow chainring diameter by the number of teeth, this is the first google found
https://www.wolftoothcomponents.com/pages/chainring-diameter-by-tooth-count

On my small wheel folder that might be an issue, on all my other bikes I'd have all sorts of other problems before chainring strikes would be a concern. maybe that would be different if I did a lot of serious rough stuff, but if I did I'd probably look for a bike with a higher BB.
Quote
Q3: (most important question!)I'm wondering what will be the effect of shorter crank arms (165mm on new-build vs. 175mm on Litespeed) on the actual riding experience?
I'm interested in your motivation for this?  the right length for your biomechanical efficiency will have more of an effect than any gearing changes, is there something makes you think your 175's are wrong?  It's correct of course that a shorter lever requires more force, it's how your body best provides that which is complicated, otherwise we'd all be riding 190's.


PH

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #349 on: September 06, 2021, 09:20:08 PM »
lack of balance (the front wheel rises from the floor, and I never was good on a unicycle).
I used to struggle a bit with this, a tip I picked up (Possibly from this forum) is to bend your elbows 90 degrees, really it is that simple! I was sceptical, but haven't lifted a front wheel since.

Matt2matt2002

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #350 on: September 06, 2021, 10:06:03 PM »
lack of balance (the front wheel rises from the floor, and I never was good on a unicycle).
I used to struggle a bit with this, a tip I picked up (Possibly from this forum) is to bend your elbows 90 degrees, really it is that simple! I was sceptical, but haven't lifted a front wheel since.

Hope I'm not deviating too much from the script but I saw the reference to unicycling and as a retired semi professional juggler thought I could contribute a constructive comment re balance.

Unicycling and indeed balancing a stick on your hand is best achieved by purposefully creating off balance and 'on ' balance.
Whatever you do, dont try to remain upright without movement fore and aft. Or side to side.

Re bike balance; I suggest the same principle.
Never drink and drive. You may hit a bump  and spill your drink

Dunroving

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #351 on: September 06, 2021, 10:08:26 PM »
Q2: If I'm correct in the above, from reading this thread it seems that a "big-big" combination has the advantage of less chain wear, but greater likelihood of chainring strikes on lumpy terrain? And that conversely, a "small-small" combination raises the chainring (less chance of chainring strikes), but causes faster wear on the chain?

If you are considering fitting a Chainglider (for even less maintenance under most conditions), another thing to take into account is Chainglider compatibility. I generally agree with Mickeg that it is best to fit a fairly big chainring and sprocket to minimise wear, but as I wanted a Chainglider, for my first Rohloff bike I chose a small chainring and sprocket (38x16), which is compatible.

Q3: (most important question!)I'm wondering what will be the effect of shorter crank arms (165mm on new-build vs. 175mm on Litespeed) on the actual riding experience?

My own experience from going from 170mm/175mm to 150mm/155mm cranks (about 13% difference) is that I increased pedalling cadence and so needed to lower ALL my gears.

I don't really notice 5mm difference (it's about 3% between 170 and 175). I think I would notice a 10mm difference (about 6%).

My reason for going to short cranks was knee problems due to pushing high gears too slowly. Quite by accident I found out that short cranks solved the problem for me, without slowing me down. I don't know why short cranks are better for my knees, maybe less force on each pedal stroke, maybe a smaller bending angle at the knee joint.

I've read the copious amounts of information n the Chainglider and although it seems like manna from heaven, it's not on my radar, so choice of chainring/sprocket don't need to take this into account.

Crank length - my reasons for going short are similar to yours - I have a total knee replacement (right) and advanced arthritis (left). Also, hip flexor tightness. Shorter cranks help all around - mainly due to the more open hip angle at the top of the stroke (for a 10mm shorter crank, saddle goes up by 10mm, plus at the top of the stroke, pedal is 10mm lower, so effectively a 20mm difference). Also, because of this, the knee has a mechanical advantage - you can half-squat a lot more weight than a full squat (obviously the magnitude of difference is a lot less, but the biomechanics is the same). On reflection, the greater force needed to turn shorter cranks may not actually be as big a deal as it seems.

Dunroving

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #352 on: September 06, 2021, 10:12:24 PM »
greater likelihood of chainring strikes on lumpy terrain? And that conversely, a "small-small" combination raises the chainring (less chance of chainring strikes),
There's various charts that sow chainring diameter by the number of teeth, this is the first google found
https://www.wolftoothcomponents.com/pages/chainring-diameter-by-tooth-count

On my small wheel folder that might be an issue, on all my other bikes I'd have all sorts of other problems before chainring strikes would be a concern. maybe that would be different if I did a lot of serious rough stuff, but if I did I'd probably look for a bike with a higher BB.
Quote
Q3: (most important question!)I'm wondering what will be the effect of shorter crank arms (165mm on new-build vs. 175mm on Litespeed) on the actual riding experience?
I'm interested in your motivation for this?  the right length for your biomechanical efficiency will have more of an effect than any gearing changes, is there something makes you think your 175's are wrong?  It's correct of course that a shorter lever requires more force, it's how your body best provides that which is complicated, otherwise we'd all be riding 190's.

Yes, I'm not really concerned with chainring strike, but have seen it raised in some other forums.

Regarding crank length, my reasons are explained in the response I just posted, plus the fact that all of the common formulas for estimating appropriate crank length from height, inside leg, femur length, etc., all say 165mm (I'm a shade over 5ft 7in). I have to take care of my knees as they're the only ones I have. I do get soreness from my 175mm cranks on the Litespeed, especially the patellar tendon.

Dunroving

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #353 on: September 06, 2021, 10:14:11 PM »
lack of balance (the front wheel rises from the floor, and I never was good on a unicycle).
I used to struggle a bit with this, a tip I picked up (Possibly from this forum) is to bend your elbows 90 degrees, really it is that simple! I was sceptical, but haven't lifted a front wheel since.

I think it's due to the geometry of the bike (short chainstays, short wheelbase, designed to be a twitchy trail bike). I've tried bending my elbows until my nose is almost touching the bars. ;-)

My new bike is being designed to not have this problem.

Dunroving

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #354 on: September 06, 2021, 10:19:05 PM »
lack of balance (the front wheel rises from the floor, and I never was good on a unicycle).
I used to struggle a bit with this, a tip I picked up (Possibly from this forum) is to bend your elbows 90 degrees, really it is that simple! I was sceptical, but haven't lifted a front wheel since.

Hope I'm not deviating too much from the script but I saw the reference to unicycling and as a retired semi professional juggler thought I could contribute a constructive comment re balance.

Unicycling and indeed balancing a stick on your hand is best achieved by purposefully creating off balance and 'on ' balance.
Whatever you do, dont try to remain upright without movement fore and aft. Or side to side.

Re bike balance; I suggest the same principle.

Are you suggesting I should balance a stick on my head while going uphill? ;-)

I'm sure if I went out on a hill and practised enough, I'd get better at it. I find I do some of the things you mentioned almost automatically, but clearly not well enough. I could also practise wheelies, I suppose, as I presume that's a similar principle, but I'm too lazy to put the time in.

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #355 on: September 06, 2021, 10:55:29 PM »
One thing I found helpful to slow-speed uphill climbing in very low gears was to learn to do trackstands back in the day.

See: https://www.youtube.com/watch?v=nFtS4KYxz9k

Learning to balance at rest had the happy dividend of making it easier to ride and balance at nearly stationary speeds. It has the effect of "buying" me more time before I need to worry about the pedals coming 'round.. I find it easiest on my Fixie (fixed-gear bike that doesn't coast...the cranks are always in motion if the bike is moving) but it translated well to my bikes with freewheels so now I sometimes start from rest and then hold a track position till I get the second cleat into my other pedal before going on. In fact, it is easiest to learn how to do a trackstand if there is a hill.

A useful skill at traffic signals, but once earned me a ticket for running a stop sign though I was effectively stationary. It was issued by a newly minted police officer who firmly believed a single-track vehicle could not remain stationary or nearly so unless the rider put a foot down -- this despite acknowledging I had not moved even half a foot in the full minute he'd observed me. Ah, well.  ;)

Best,

Dan.

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #356 on: September 07, 2021, 01:46:39 AM »
...
Assuming balance is my limiting factor, and I can't balance below 3.1 mph, would a lower gear really help me? (thinking aloud here)? Is it that, with a lower gear, I'd be able to maintain 3.1 mph with a higher cadence (bearing in mind that, as you said, shorter cranks usually mean higher cadence)?

That is exactly what I was thinking, I decided that 3.5 mph was my lowest speed without excessive over-steering to maintain directional and vertical stability, and I wanted to have a cadence of about 72 at my lowest speed of 3.5 mph.  So I spent some time with a calculator to figure out what chainring size I needed to match the 16T sprocket that came on the hub in first gear.

My thinking was a lower gear would not do me any good.  When hills get steep enough that I can't keep my heart rate in a desired range at that minimum speed needed for balance, I get off the bike and walk.

When you are trying to assess gearing, this website may be of assistance to you:
https://gear-calculator.com/

Here is my gearing with a 44T chainring for riding unladen near home:
https://gear-calculator.com/?GR=RLSH&KB=44&RZ=16&UF=2120&TF=90&SL=2.6&UN=MPH&DV=teeth

With that you could do trial and error options to play with different sprockets and chainrings to see how that compares to your Litespeed gearing.

martinf

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #357 on: September 07, 2021, 07:08:10 AM »
Crank length - my reasons for going short are similar to yours - I have a total knee replacement (right) and advanced arthritis (left).

In your case it might be worth trying 150 mm.

The trouble is finding them. It was easy for me because I had already sourced them for my wife, who is much smaller than me. 

In the UK, Spa Cycles do the reasonably-priced Stronglight Impact Kid chainset in a variety of short lengths:

https://www.spacycles.co.uk/m8b0s109p1927/STRONGLIGHT-Impact-Kid-Chainset.

SJS used to have a good range of short cranks, they still have the Origin8 Alloy Single / Double Crankset in 155 mm.

Aleman

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #358 on: September 07, 2021, 08:24:58 AM »
Crank length - my reasons for going short are similar to yours - I have a total knee replacement (right) and advanced arthritis (left).

In your case it might be worth trying 150 mm.

The trouble is finding them.
SJSC have some 150mm cranks and also "Kiddie Cranks" that are double drilled at 115 / 140mm so possibly a bit small

Moronic

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #359 on: September 07, 2021, 10:30:07 AM »
Assuming balance is my limiting factor, and I can't balance below 3.1 mph, would a lower gear really help me? (thinking aloud here)? Is it that, with a lower gear, I'd be able to maintain 3.1 mph with a higher cadence (bearing in mind that, as you said, shorter cranks usually mean higher cadence)?

This might be a less general question than it seems. As in, it could depend on your likely use of the bike. Will it be a mountain bike and mainly ridden off-road? Will you be just doing day rides or loading it up for multi-day bikepacking trips? For example.

Whether you want a lower first gear isn't necessarily just about whether you could use it to pedal steadily up an extremely steep hill. For example, one reason why I like the extremely low first gear that I have (15-in) is that it allows me to negotiate very steep, very tight turns with more comfort. I might be travelling so slowly mid-turn that balancing requires a fair bit of skill and attention, but that is just for a few seconds and it's helpful that I can adjust that very low speed very easily even on a steep gradient.

That's just one example. And against gearing lower in first than your Litespeed is that the narrower Rohloff range means your top will be markedly lower even with the same first.

BTW, have you ordered a Thorn, or are you speccing a custom build from elsewhere? You might get better information if we knew more about its application. (Apologies if you explained and I missed it.)