Author Topic: What's your Rohloff combo (chainring, cog)?  (Read 63889 times)

Peter_K

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #270 on: January 30, 2017, 03:58:03 PM »
I run into the problem that I might have to shorten my chain during wear, which I do not like.

So I made this calculation to determine the sprockets so that they have the required gear ratio, and I also can wear the chain out without shorting it. (I added a second sheet with gear inches for you inch lovers.  :P)

Does anybody know a calculation on the internet that does something similar, so I can check my calculation?

Matt2matt2002

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #271 on: January 30, 2017, 05:57:24 PM »
This look interesting.
Can you talk me through how I can use it please?
I don't like shortening chains either.
Matt
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JimK

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #272 on: January 30, 2017, 06:15:28 PM »
Wow that is very cool! I thought a bit about chain stay length and how that sets up the initial position of the EBB. Very nice to see this spread sheet!

Peter_K

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #273 on: January 30, 2017, 06:53:23 PM »
@Matt2matt2002

The yellow figures are dimensions of your bicycle and can be measured, or looked up in the Thorn documentation.

The blue figures are what you chose to ride under most strenuous conditions: so probably climbing a mountain.
Climbing the cadence can be lower (for instance 70 tpm) than on flat (about 100 tpm). The speed is the lowest you see during climbs, the margin is added and subtracted to give a bandwidth in which the available gears are acceptable. So for all gears shown and with a cadence  of 70, the speed will be between 5.1 km/hr and 6.1 km/hr (the higher the gear the higher the speed).
The blue figures for the gear inches work similar.

The results are given in three tables:
  • the first table is a combination of the next two: giving only the chain wear parameters for the acceptable speeds
  • the second table gives all chain wears that can be obtained
  • the third table the speeds, and the speeds that match the choice are coloured orange

Chain replacement at:
  • 0.5% = very early
  • 0.75% = normal, suitable for aluminium cogs/sprockets
  • 1% = late, suitable for steel cogs/sprockets

Chain wear can naturally be measured with devices like this one or this one.
« Last Edit: January 30, 2017, 08:39:16 PM by Peter_K »

Javier

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #274 on: January 30, 2017, 10:57:23 PM »
I have noticed a subtle grinding noise when pedaling off the saddle in very steep slopes (>15%) when the sprocket looked like had to be replaced. Once I replaced it the noise was gone. I sent a picture of the replaced sprocket to SJS mechanics and they told me that I did the change at the correct time (i.e. not too early not too late). So from now on I will keep my ears sharp for a similar grinding sound, which might be an indication that replacement is needed.

Peter_K

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #275 on: January 31, 2017, 09:07:03 AM »
@Javier
On my weekend/holiday bikes I replace my sprockets because of the noise too, because I like things quiet.

But mechanically it is not required. If you don't have a chain tensioner you could ride on till there is hardly anything left of the teeth, because the chain has no room to skip. (Unlike with derailleur sprocket)
Most city bikes here in the Netherlands, also mine, are used in that way. When changing the chain, one changes also the sprocket since they are not that expensive for city bikes.

Javier

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #276 on: January 31, 2017, 03:32:44 PM »
Thanks Peter_K
j

John L

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #277 on: April 30, 2017, 02:58:11 PM »
17t  x 32t  8)

Pavel

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #278 on: April 30, 2017, 11:32:38 PM »
17t  x 32t  8)

Is that a typo?  That would give a low of 13.7 gear inches, and a high of only 71.8 gear inches.  Useful if one travels only through bogs or up 27% grades and does not mind not voiding Rohloff's warranty. I can't go fast enough at a cadence of 120 rpm with a low of 17.9 to keep my ballance - you must be a trapeze artist with amazing balance. Or ... it's a typo?  :)

Danneaux

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #279 on: April 30, 2017, 11:42:36 PM »
Quote
you must be a trapeze artist with amazing balance.
When I was building my own low-gear drivetrains (chainrings as cogs, cogs as chainrings, custom long rear derailleur cages with outsized tension pulleys, brazed-together front derailleur cage,s 4 chainrings, etc) for myself and my late father, I found 12.5 gear-inches 16t or 17t chainring with 36t cog and 700C wheels) was the practical lowest I could handle. Jack (Dad) managed okay with 15.5 gear-inches. Even then, it required a pretty steep hill to balance -- ~24% with a load. We had hoped for a low enough to manage the 31% grades we often encountered on roads and cat-tracks to timber sales. Nope. We couldn't get traction and when we did, the bike kept wanting to "wheelie over". Managed it once to the detriment of my knee on gravel and Jack's elbow on same.  :(

Riding *really* low gears is an acquired skill. Rather than spin-out it is more like a track-stand, where you let the tension of the hill load the drivetrain and work against that with counter-steering to keep balance. Forward speed was about 2-2.5mph/~3-4kmh, tops. Walking might have been faster but not in the pre-SPD plastic-soled racing cleats I wore at the time.

Best,

Dan.
« Last Edit: April 30, 2017, 11:49:00 PM by Danneaux »

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #280 on: April 30, 2017, 11:58:45 PM »
I run a cadence of 72 to about 80 most of the time.  I estimated that the slowest I could balance a bike on an uphill with a load was 3.5 mph (~5.6 km/hr).  I calculated that the chainring I would want for touring was 36 to pair with my sprocket of 16, that gives me a cadence of 72 at 3.5 mph in first gear with a 559X57 Marathon Extreme tire.   But that gearing means I spin out on the long shallow downhills because I don't run my cadence much over 80.  Gearing is 16.5 to 86.5 gear inches.

For around home use, I run a 44T chainring (and 16T sprocket) instead, the hills near home are not steep enough with an unloaded bike to need my 36T touring chainring.  I find the 44T is perfect for around home, as I don't need a gear lower than 1 or higher than 14.  Gear inches is about 20.1 to 105.8.


JimK

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #281 on: May 01, 2017, 05:17:10 AM »
One of my goals right from our start in Utah last summer is to ride up to Francis Peak, elevation 9540 feet. The start of the climb is at 4300 feet. I just got up the first little paved part today, building back up from the winter's laziness. That was about 1000 feet of climbing. Last summer the highest I got was about 7200 feet, so about 3000 feet of climbing. Looks like the steepest sections today were about 13%. I glanced a few times at my speedometer and saw maybe 2.3 mph. I know that I will get down around 1.9 or 1.8 mph sometimes. My combo is 38x16. I could use lower gears but I could use higher gears too. What I have, gear-wise, is good enough. Legs and lungs, that's the project!

https://ridewithgps.com/routes/20761751

martinf

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #282 on: May 01, 2017, 09:21:45 AM »
17t  x 32t  8)

Is that a typo?  That would give a low of 13.7 gear inches, and a high of only 71.8 gear inches.  Useful if one travels only through bogs or up 27% grades and does not mind not voiding Rohloff's warranty. I can't go fast enough at a cadence of 120 rpm with a low of 17.9 to keep my ballance - you must be a trapeze artist with amazing balance. Or ... it's a typo?  :)

Depends how you ride.

My average speed for long distance riding with full touring load in flattish terrain was between 22 and 24 kph in 2011, and much lower in mountain areas. 24 kph corresponds to a 54 inch gear at my target cadence of 90 rpm.

My current lowest gear is 17 inches, on my Raven Tour. I'm fairly sure I could gear lower, but I chose the gear ratios before Rohloff lowered their lowest gear recommendations.
With full front panniers to keep the front wheel down I can ride my 17 inch lowest gear on very steep hills at about 4kph slowest (= about 2.5 mph, so slow walking speed), dropping my cadence to about 50 rpm.
My Raven Tour top gear of 89 inches I only use on downhills, so I could quite well do without it on a luggage-carrying touring bike.

I have higher gearing (18 to 95) on my Raven Sport Tour, but again I probably don't need the 95 inch top.

On my old 5-speed hub gear bike I recently dropped the gearing from 44x21 (36 to 82 inches) to 38x22 (30 to 67 inches).
Both these ring/sprocket combinations are Chainglider compatible, particularly important for me because I currently use that bike in often mucky conditions for survey work, riding on paths, across grass fields, etc. I don't want to risk a Rohloff bike because I often lock and leave the bike and continue on foot, so I put up with the fairly high low gear of 30 inches.
I don't notice much handicap with the very low highest gear of 67 inches on the tarmac stretches. At 90 rpm I do about 30 kph and can increase to about 120 rpm and 40 kph for short periods (negotiating roundabouts in traffic or similar).

Pavel

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #283 on: May 01, 2017, 04:30:59 PM »
Very interesting insights to be gleaned here, reading all of these varied approaches to the problem of how best to get up and down hills.  To add a bit more wood to the fire, I've found that I tend to cycle at a high cadence when going uphill, and a much lower cadence when on flats or downhill. It tends to be about 90-110 when on a climb as I find it less fatiguing as lactic acid does not build up in my legs (turning them into jelly) and on downhills since I don't need or like to go fast (I put the brakes on at about 30 mph - it's hard to enjoy the scenery when one needs to concentrate at higher speeds) I slow to about 60-70 and the change ups seems to let me last longer in a riding day. I break this of course, regularly, if the situation calls for shooting up a small hill and then use the last few seconds of the bottom of a slope to gain momentum with a frenzied spin.

Any comments on that? Might I be doing some of this upside down and backwards?

On a side note, I find small hills, whether gentle or steep, to be fun. It's the long mile long or longer gentle slopes that I find hard and when those long, long stretches turn steep - I find myself justified in appealing to the gods to place a miracle pub every mile.  In fact, if you ask me, that is the problem with cycling in the US of A. Not enough pub density to call this a civilized country.  But never mind, that's another topic.

with my 41 and 17 combo  the lowest ratio is  17.5 gear inches. On longer steep hills I'd start out spinning and then as I tired, I found that as my cadence dropped I would hit about 4 miles per hour and find it not worth the taxation on my body to keep grinding up the hill on the bike.  I was near where I'd find myself moving back and forth two or three feet on the road at those slow speeds and that's just not worth it with traffic.  Getting off and pushing had me going at 2 to 2.5 miles per hour, so I felt that there was no real loss, and it would change up the muscles used and I felt that I could go all day that way longer.

So when I got back I bought a nice steel Surly ring, meaning to raise my lowest gearing up a bit.  Looking at Sheldon Brown's calculator (http://www.sheldonbrown.com/gear-calc.html) it seems that the 17/43 gives a low of 18.3 to a high of 96.5.  I've not been able to cycle for several years, so I have not yet bothered to install this ... but looking at those numbers, right away I think, I don't need that high a top end, and the bottom seems a very small change.  Seeing how some of you approach this, I wonder if maybe I should not have a stab at the opposite direction? Maybe my problem was that the ratio was not low enough and I could not keep my cadence up.  Hmmm.  I wonder now.

Funny how so much effort, time and money is required for the much critical "ultimate" setup, eh?  Wives just don't understand. Mine has even made the mistake of wondering out loud "why not just go ride it, as is?"  Now that was hilarious. :D

David Simpson

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #284 on: May 01, 2017, 05:27:03 PM »
I've found that I tend to cycle at a high cadence when going uphill, and a much lower cadence when on flats or downhill.

Any comments on that? Might I be doing some of this upside down and backwards?

I ride the same way.

- DaveS