Author Topic: Did Rohloff change their approved ratios again?  (Read 6222 times)

mickeg

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Did Rohloff change their approved ratios again?
« on: August 30, 2015, 12:33:57 PM »
From this link:
http://www.rohloff.de/en/technology/workshop/sprocket_ratios/

I pasted the following (I changed font to italics and used bold for emphasis):

Smallest permissible sprocket ratios
The primary sprocket ratio used with the Rohloff SPEEDHUB 500/14 (e.g. 42:16) converts the slow rotational speed at the crank into a fast rotational speed at the rear sprocket and reduces the input torque for the Rohloff SPEEDHUB 500/14 in the same proportion. To prevent overstraining the hub, a minimum factor of 1.9 must be used. This minimum factor equates to a primary transmission ratio of:- 32:17, 30:16, 28:15 and 26:13. These SPEEDHUB 500/14 ratios resemble a derailleur transmission of 20:40.
Larger chainrings can be used without exceptions.

Attention!
If mounted on a tandem or if the rider weighs over 100kg, the minimum factor of 2.50 must not be undercut. This equates to primary transmission ratios of:- 32:13, 38:15, 40:16 and 42:17.
Again, larger chainrings can be used without exceptions.


Is it my imagination or is this is a new approved ratio for solo rider below 100 kg?  I thought that the lowest ratio (solo bike, rider under 100 kg) was two point something, not less than 2.0.

Does not matter to me, the lowest I wanted to go was 36/16 and I weigh about 80kg.
« Last Edit: August 30, 2015, 05:00:51 PM by mickeg »

Danneaux

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Re: Did Rohloff change their approved ratios again?
« Reply #1 on: August 30, 2015, 04:05:06 PM »
Well-spotted, Mickeg!

Looking back at the archives ( http://thorncyclesforum.co.uk/index.php?topic=4412.msg28971#msg28971 ), the last reduction in late 2012 was from 2.35 to 2.1 (for riders who weigh under 100kg). The link at Rohloff's site is broken, but I remember checking at the time and based my own 36x17 selection on it.

1.9 is indeed a reduction, allowing for 32:17, 30:16, 28:15 and 26:13. Idworx has long produced their own gearing to allow 35x17 without incident. They are committed to longer component life offered by odd-odd tooth combinations.

I recall at the time, Andre figured the hub had sufficient safety margins for even lower gearing than that allowed by Rohloff ( http://thorncyclesforum.co.uk/index.php?topic=4412.msg29001#msg29001 ).

Happy days for enthusiasts of stump-puller low gearing.

Best,

Dan.

Danneaux

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Re: Did Rohloff change their approved ratios again?
« Reply #2 on: August 30, 2015, 04:28:20 PM »
Further thoughts...

I'm guessing Rohloff lowered their ratios to allow for the larger rolling stock of "29ers" -- MTBs with 700C rims equipped with fat tires. It has been difficult to get a reasonable low with those, thanks to the larger effective wheel diameter.

I see Rohloff continues to use rider weight as a proxy for power/torque. I suppose it is as good an index as any, but doesn't take into account pedaling style.

I weigh 78kg, but I'm a spinner (high-rev, low-pressure pedaling in round circles), and would guess I put much less torque on the hub than a masher (low-rev pedaling with higher cyclic torque loading). I wouldn't be surprised if the acceptable (but unapproved) ratios might be even lower for spinners, regardless of body mass.

On the other hand, 1.9 is about the practical minimum for staying upright at low speeds, and gives a high of 71 gear-inches and a low of 13.5 gear-inches with 26x1.9 tires. Low, but still very workable if you spin with good technique against a steep slope.

I've modified my past derailleur drivetrains to use freewheel cogs as chainrings and sometimes, chainrings as freewheel cogs, with derailleurs altered to windup and shift it all. I had no problem spinning a (15t/34t, 27" wheels) low of 12 gear-inches that allowed forward speeds of only about 2.5mph/3.9kph, but going even lower made it difficult to stay upright. It can be hard to keep the front wheel weighted with such low gears and very steep slopes, but works nicely if carrying loaded front panniers and a handlebar bag.

Best,

Dan.

mickeg

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Re: Did Rohloff change their approved ratios again?
« Reply #3 on: August 30, 2015, 05:24:49 PM »
Further thoughts...

I'm guessing Rohloff lowered their ratios to allow for the larger rolling stock of "29ers" -- MTBs with 700C rims equipped with fat tires. It has been difficult to get a reasonable low with those, thanks to the larger effective wheel diameter.
...

That would make a lot of sense, those bike wheels probably are a market that Rohloff wants to have.  My Rohloff is on a 26 inch wheel. 

But from a mechanical integrity perspective, the torque on the cog is the only thing that really matters and that is determined by (1) how much force the rider puts on the pedal, (2) crank arm length, and (3) on the chainring to rear cog ratio - and wheel size is independent of that.  Crank arm length varies so little (usually in between 165 and 175mm), I can see why Rohloff left that out of the criteria.  So if they changed the ratio for the 29r market or the fat bike market, they did it to protect or gain market share, not because those wheels allow a lower ratio.

...
On the other hand, 1.9 is about the practical minimum for staying upright at low speeds, and gives a high of 71 gear-inches and a low of 13.5 gear-inches with 26x1.9 tires. Low, but still very workable if you spin with good technique against a steep slope.
...

I use a 44/16 ratio for around home riding.  For touring in steep hill country I calculated the size chainring I wanted based on an estimated 3.5 mph minimum speed to retain balance and based on cadence of 72, which I consider a minimum for my knee health, that gives me a 36/16 ratio.  You have commented before on your hummingbird cadence, but I am content with roughly 72 to 78 on my derailleur bikes, I have a slightly wider cadence range on the Rohloff bike of 72 to about 80 due to the wide 13 percent gear spacing.

In preparation for a trip in a bit over a week, I recently switched over to the 36T chainring.  I find myself coasting down hills that I used to pedal down.  And virtually never go lower than about gear 5.  So, I am looking forward to switching back to my big chainring of 44T after my trip.

I really think that there is no better solution than a weight based criteria that Rohloff could use.

A side note on cadence.  I recently fixed up and put a few new parts on a bike that is over 50 years old, I had not ridden that bike in over a decade.  Getting used to friction down tube shifting again.  I find that I use a much wider range of cadence on that bike because it is so inconvenient to shift for short distances, like starting out after stopping for a stop sign or stop light.  But on the Rohloff bike it is so simple to down shift two or three gears for starting out from a stop, then re-shift after about three or four crank revolutions.


Danneaux

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Re: Did Rohloff change their approved ratios again?
« Reply #4 on: August 30, 2015, 06:49:02 PM »
Quote
I really think that there is no better solution than a weight based criteria that Rohloff could use.
I agree; it is as a good an index as any, given the whole spectrum of variables.
Quote
A side note on cadence...on the Rohloff bike it is so simple to down shift two or three gears for starting out from a stop, then re-shift after about three or four crank revolutions.
Absolutely! One of the great joys of the drivetrain.

My hummingbird cadence has its roots in the same injuries that started me cycling with intent. At 17, I was in a car wreck that caused me to remove the left window crank, bend the shift knob, and crack the steering column cover with my knees. I started cycling as physiotherapy, but found my knees could not stand much pressure on the pedals and technique made a big difference to my endurance, so pedaling fast, light, and developing really good form made longer rides possible and less painful. I guess it became a habit. I'm 55 now and my knees are long since healed, but remain sensitive to high stresses, so I still gear low and pedal light to avoid problems. I secretly admire the mashers, but couldn't do so to save my life.
Quote
Getting used to friction down tube shifting again.  I find that I use a much wider range of cadence on that bike because it is so inconvenient to shift for short distances, like starting out after stopping for a stop sign or stop light.
After exclusively riding the RavenTour AndyBG so kindly loaned me last summer, I became lazy on my return and found I'd forgotten the old maxim to shift down before stopping on my loaded derailleur bikes. Oof! Urgggggh!  :P I soon remembered the need and got with the plan again quickly.

Sure fun to bring an older bike back to riding form again. Best wishes for some happy journeys together.

All the best,

Dan.

mickeg

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Re: Did Rohloff change their approved ratios again?
« Reply #5 on: August 30, 2015, 09:01:26 PM »
...
I've modified my past derailleur drivetrains to use freewheel cogs as chainrings and sometimes, chainrings as freewheel cogs, ...

You described a Mountain Tamer.  Mounts on a 74mm BCD five arm crank.  Uses a vintage Suntour cog off of their splined freewheels.

http://www.abundantadventures.com/quads.html

I bought one so I could go lower than 24T granny gear, tried it, did not keep it on the bike.  The 52/42/20 as a triple really did not work as well as I hoped, went back to 52/42/24.


Danneaux

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Re: Did Rohloff change their approved ratios again?
« Reply #6 on: August 30, 2015, 09:27:34 PM »
Quote
You described a Mountain Tamer.
Yep, and the version before that used Maillard threaded cogs and Avid Microdapter 1 and 2, but I made my own years before they were introduced, milling my own custom adapter plates and drilling and tapping my crankarms or adjacent chainrings.

Worked best with compact half-steps of 38/34/15 or so, with a shortened front derailleur so the cage plates would clear the top of the chainstays. I have a 38/34/24 on my father's bike now, with a 13-24 6-sp freewheel. A de-toothed 44t chainrings is the bash guard.

The chainrings-as-cogs were repurposed steel 'rings indented originally for Ashtabula one-piece cranks. I just milled out the centers, leaving pegs to engage the freewheel spline notches.

Ran some quads for awhile. Surprisingly, the chainlines weren't bad when used with the bottom one or two cogs at the rear. Had to mill new links for the parallelogram links on the front derailleur and extend the cage.

Best,

Dan.

Andre Jute

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Re: Did Rohloff change their approved ratios again?
« Reply #7 on: August 31, 2015, 01:27:35 AM »
Well spotted, Mickeg.

Looking back at the archives ( http://thorncyclesforum.co.uk/index.php?topic=4412.msg28971#msg28971 ), the last reduction in late 2012 was from 2.35 to 2.1 (for riders who weigh under 100kg). The link at Rohloff's site is broken, but I remember checking at the time and based my own 36x17 selection on it.

I recall at the time, Andre figured the hub had sufficient safety margins for even lower gearing than that allowed by Rohloff ( http://thorncyclesforum.co.uk/index.php?topic=4412.msg29001#msg29001 ).

I suspect the link is broken to avoid the embarrassment of the remark in the removed advice that it was positively the last lowering of chainring/sprocket ratio -- and here we have another lowering permission. I forecast at the time that it wasn't the end, and in the correspondence started by my post that Dan references in the URL above, I and others agreed a ratio of about 1.7 as possibly understressed enough even for the cautious Herr Rohloff.

***

It is ironic then that after I spent the time to work out what Herr Rohloff knows and wasn't telling us, the circumstance of going over to a midmotor forced  me to fit the same 44x16 gearing that Mickeg uses for everyday work. I was a bit worried that I might have to learn a higher cadence than my 45-60rpm mashing, something I've tried and failed to do before, but it turned out I'm stronger now than when I had to go down to 38x16 (and tried to go to 38x17 but the Germans who supplied my bike on Herr Rohloff's orders wouldn't fit the "illegal" components!), the motor is not only torquier but has better software, and I have learned to use both the Rohloff gearbox and the pedelec software better, so that my problem with learning a faster cadence in practice didn't arise. In fact, i'm doing so well on the current 44x16 (remember, gentlemen of experience, though I ride in very hilly country, I have a motor to help on the steepest hills), which is a cheap trial with an optional pressed steel Bafang chainring, that I have decided not to order the projected, very beautifull, billet-machined 42T aftermarket chainring (the smallest that will fit) for the time being.

All the same, when last weekend a lady came by arrangement from upcountry to look at my Kranich and ride it around the supermarket parking lot, and asked which of the offered cranksets she should order, without hesitation I said she should order the 38x16. This is on 29er wheels but applies pretty much to 26in wheels too, especially for tourers. 38x16 still seems to me such a no-brainer for easy everyday work, utility cycling, recreational cycling, weekend camping, and aftermarket component availability, that unless you're an experienced big overload tourer, or you're really decrepit but still have mountains to conquer, it is an automatic choice.

***

Dan's put his finger on the decisive factor in determining how low you can gear: balance. I've found on the steepest piece of road I ride on that 5kph/3mph is about the limiting speed for my best cadence of 60rpm because it is not possible to keep balance below that. If I lose the cadence, or slow it, I have to put a foot down, and on a hill steep enough to gear down that low, that means you can't start again. Perhaps the butterflies can use the centrifugal gyro force of their spinning legs keep their balance at a slower speed in unchallenging riding conditions, and thus gear lower, but even for them there must be a natural limit, and by common sense it can't be too far below 5kph.

***

I conclude from this that, whatever the reliability limit of the Rohloff may be, it is below the limit rider balance imposes on a practical bicycle. A spot of quick mental arithmetic tells me Herr Rohloff won't ever have to lower the permitted ratio on his gearbox to the 1.7 that Martin and I and others agreed (back in 2012) would still be reliable. I think there might possibly be one more permission relaxation, which even the stumppullers will consider a ratio too low, and that will be it; or perhaps 1.9 will be so obviously far enough, the ball stops rolling.


Danneaux

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Re: Did Rohloff change their approved ratios again?
« Reply #8 on: August 31, 2015, 01:45:55 AM »
Quote
I suspect the link is broken to avoid the embarrassment of the remark in the removed advice that it was positively the last lowering of chainring/sprocket ratio...
Nope. All the old internal post references are "broken" because they refer to thorncycles.co.uk. They can be revived by replacing that prepend with thorncyclesforum.co.uk/

I'm in the process of updating the links during my off moments, but there are several thousand of them....

Best,

Dan.

JimK

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Re: Did Rohloff change their approved ratios again?
« Reply #9 on: August 31, 2015, 02:37:42 AM »
I speculate from time to time whether a lower ratio than the 38x16 would be worth my while. At least the 38x17 since that should still work with the chainglider! My speedometer wouldn't read speeds below 2 mph... now it just won't sense the wheel movement at all! The bike tipped over when I was loading it up with groceries & apparently something got knocked somehow. For the moment I will just ride unmeasured! But from prior experience, I can certainly balance decently well a bit below 2 mph, and I am riding down in that zone about about a 15% grade. If I were confronting grades steeper than 20% on any regular basis, I'd probably gear a bit lower. As it is, I will also spin out gear 14 sometimes. So a lower gear would carry a small price there.

Andre Jute

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Re: Did Rohloff change their approved ratios again?
« Reply #10 on: August 31, 2015, 07:19:55 AM »
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I suspect the link is broken to avoid the embarrassment of the remark in the removed advice that it was positively the last lowering of chainring/sprocket ratio...
Nope. All the old internal post references are "broken" because they refer to thorncycles.co.uk. They can be revived by replacing that prepend with thorncyclesforum.co.uk/

I'm in the process of updating the links during my off moments, but there are several thousand of them....

Best,

Dan.

I'm talking about a broken link at Rohloff, Dan, nothing to do with the Thorn server.

Andre Jute

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Re: Did Rohloff change their approved ratios again?
« Reply #11 on: August 31, 2015, 07:33:00 AM »
Jim, I'd rather spin out downhill than push uphill. Maybe forum members who live on gently rolling countryside are never faced with the choice but I spun out on my first ride on my new Rohloff bike. I calculated in advance that it would happen and so wasn't disappointed. With my hills you can't have it both ways. I considered fitting a Schlumpf two speed bottom bracket gearbox to broaden the Rohloff's range but that gets you less than at first appears, in part because back then the permitted ratio was only 2.35.

mickeg

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Re: Did Rohloff change their approved ratios again?
« Reply #12 on: August 31, 2015, 12:34:18 PM »
Jim, I'd rather spin out downhill than push uphill. Maybe forum members who live on gently rolling countryside are never faced with the choice but I spun out on my first ride on my new Rohloff bike. I calculated in advance that it would happen and so wasn't disappointed. With my hills you can't have it both ways. I considered fitting a Schlumpf two speed bottom bracket gearbox to broaden the Rohloff's range but that gets you less than at first appears, in part because back then the permitted ratio was only 2.35.

My derailleur touring bikes have a range of 630 percent.  Thus, I was a bit hesitant to buy the Nomad MkII which did not have a derailleur hanger, since a Rohloff by itself has a range of 526 percent.  The reason for my concern about the lack of hanger was that I considered putting on a front derailleur and two chainrings for one and a half step gearing (36 & 44) which would give me a range of 643 percent.  The derailleur hanger would have allowed a way to install a something to maintain chain tension with two chainrings.

I weighed the difference between buying  the Co-Motion Pangea which would have allowed more customization and the Nomad MkII, but since I liked the handling of my Sherpa, I decided to stay with the Thorn brand although it lacked the hanger.  (I find the brake bosses on the back side of the fork on the Nomad to be confounding too, but that is off topic.)

I have gotten used to having the 526 percent range of the Rohloff and the times I feel that the range limits me is very rare, so the lack of a hanger is something I no longer think about.

On my derailleur touring bikes I have six gears between the range of 60 to 85 gear inches which is where I spend 80 to 90 percent of my time when touring and over 95 percent of my time around home.  But with the Rohloff nearly uniform spacing of 13.5 percent, I only have three gears in that range.  In that regard I find the 13.5 percent spacing to be more limiting than the total range of 526 percent. While a front derailleur and a double would have fixed this too, over time it has become less important to me.
« Last Edit: August 31, 2015, 12:38:12 PM by mickeg »

onrbikes

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Re: Did Rohloff change their approved ratios again?
« Reply #13 on: September 01, 2015, 11:08:59 AM »
So what if you weigh 85kg and carry 30kg's?

We have a 42t and 17t selection and when we climb hills will always end on the lowest gear, number 1, for hours.

Have often thought of going for a 39t or 40t but am too lazy

mickeg

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Re: Did Rohloff change their approved ratios again?
« Reply #14 on: September 01, 2015, 12:03:02 PM »
So what if you weigh 85kg and carry 30kg's?
...

I do not work for Rohloff, so I am not in a position to interpret their criteria. 

But I suspect that if the 30kg that you carry is on a rack, not any problem.  That weight will not contribute to additional force on the pedal, which in turn causes torque on the hub cog.

But if that weight is carried on your body (such as a backpack), then that is additional weight that can be transmitted to the pedals which (if you are strong enough) could exceed their 100kg criteria for force on the pedals.