Author Topic: What's your Rohloff combo (chainring, cog)?  (Read 180329 times)

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #225 on: May 24, 2016, 05:23:43 pm »
Hi all, sorry for dredging up an old thread, but as I'm soon to be purchasing a new Rohloff, I'd appreciate some advice regarding the approved gear ratios for those of us over 100kg: 112, to be precise and slowly becoming lighter, although at 6'7" not likely to get far below 100kg.

The Rohloff is destined to live on my 29er mtb. I've been running it as a dedicated singlespeed for the past three years and have now decided that it's limiting the amount of riding I use the bike for. I'd like the equivalent of a 24x36 lowest gear ( 19.4gi with 56mm tyres ) and have found that using the supplied 16t sprocket with a 40t chainring, my lowest gear will be 20.3gi. I could achieve 19.3gi with a 38x16 combo, or 19.8gi with 39x16. These work out at a factor of 2.375 & 2.437 respectively. Are they really far enough below the recommended 2.5 to be of concern?

I'm not sure how much difference this makes in the real world. I'd like to think the lowest gear I have available on the Rohloff will be suitable for steep climbing on bridalways and forest tracks, especially after a few hours of riding.

The gear ratios shown on the Rohloff site are 32:13, 38:15, 40:16 and 42:17, so factors of 2.461, 2.533, 2.5 and 2.470. Difficult to see much difference between 2.437 and 2.461, but I'm very wary of causing any damage to such an expensive component.

Cheers,

Pete

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #226 on: May 24, 2016, 06:07:58 pm »
Hi all, sorry for dredging up an old thread, but as I'm soon to be purchasing a new Rohloff, I'd appreciate some advice regarding the approved gear ratios ...

This is a timeless topic, resurrecting something that is timeless is just fine.

... I'd appreciate some advice regarding the approved gear ratios for those of us over 100kg: 112, to be precise and slowly becoming lighter, although at 6'7" not likely to get far below 100kg.
...

I never recommend to anyone that they take any action that could void a warranty.  But it sounds like you are in the range of round off error for your ranges.  So, I think you will have to decide for yourself.  If you start out with a chainring that meets the criteria and find out that you want a smaller ring, you could decide at that time.

It is not clear to me if you are putting this on a new frame or a frame you already have, but if you went with a 26 inch wheel that would give you slightly lower gearing and it may make it possible to stay with an approved ratio for your desired gearing.

I never stand on a pedal to accelerate up a hill or start out from a stop, my knees are too fragile for that.  For that reason if I was over 100kg I might be tempted to use an unapproved ratio because I know with certainty that I would never put all 100 kg of weight on a pedal when I stay in the saddle.  And it would be a lot easier to stay in the saddle if I had the lower gearing that allows me to avoid too much stress on my knees.

Good luck.

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #227 on: May 24, 2016, 07:21:02 pm »
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It is not clear to me if you are putting this on a new frame or a frame you already have, but if you went with a 26 inch wheel that would give you slightly lower gearing and it may make it possible to stay with an approved ratio for your desired gearing.

It's definitely for a 29er, so that limits my options slightly.

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I never stand on a pedal to accelerate up a hill or start out from a stop

This is a very good point. While I like the idea of plenty of bail-out gears, I think my singlespeed habits will take a while to go away, and with the hub being on a mountain bike, I expect some stomping of pedals will be involved, despite my 'stomp' not being what it once was...

Thanks for the input! Better to play it safe, I think  :)

Andre Jute

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #228 on: May 24, 2016, 10:44:32 pm »
The gear ratios shown on the Rohloff site are 32:13, 38:15, 40:16 and 42:17, so factors of 2.461, 2.533, 2.5 and 2.470. Difficult to see much difference between 2.437 and 2.461, but I'm very wary of causing any damage to such an expensive component.

Pete, I ride a 29er as my everyday bike, and in my street clothes, which I wear for cycling, I weigh near enough 100kg.

There are three things you have to understand about Bernd Rohloff, the designer of the gearbox you want to buy. The first is that he is German manufacturer, and that even among German manufacturers he is a master of CYA, covering his ass (more politely, protecting his brand's reputation for longevity) with extremely conservative usage ratings and service intervals; there are remarks in threads here and there on this forum about precisely how conservative these ratings and service schedules are, and it makes remarkable reading; in any event, Rohloff's permitted chainring/sprocket ratio that determines the torque fed into the box has been reduced twice in the last decade, i.e. Rohloff admitted each time that it could handle more power than previously stated as the unalterable maximum for the ages; I, for one, don't believe we've seen the last relaxation of these still-conservative ratings. The second is that he is a designer of German agricultural machinery intended to serve your great-grandchildren as faithfully as it serves you; a Rohloff is a heavy box not because Herr Rohloff is an incompetent engineer, or not a cyclist (he's very competent indeed, and a cylist as well) but because it is deliberately the antithesis of the "cheap, light and reliable, choose any two" Lotus paradigm. The third is that the Rohloff gearbox is designed to shrug off the abuse of being ridden on sand-dunes and wet beaches because its design was quite literally inspired by derailleur bikes on his honeymoon self-destructing in protest at being ridden on a beach. It was never intended as a refined touring box, but instead is a mudplugger's box; touring installations happened by accident.

While, like George (Mickeg), I would never advise anyone positively to breach the warranty conditions on such an expensive component, I'll tell you what I would do, in consideration of the above: First, I'd keep the supplied sprocket of 16T and run it with a cheap, probably steel, but permitted chainring until after the box is proven. By this I don't mean run in; as the great Chalo Colina said, a Rohloff box runs in at the kind of mileage where a Shimano hub gearbox lies down and dies (I trashed a couple before 5000m). What I mean is that you have to understand that there's quite a bit of hand-fitting in a Rohloff, so it rubs in the gears in the first couple of thousand miles (you'll see quite a bit of ground steel come out in the first oil change -- use a magnet in the dirty oil to see it, or rub the dirty oil between your fingers to feel it). This is also the time when, if it will break, it will break, so you may want it replaced under warranty. After a couple of thousand miles or after the first service at three thousand miles I'd buy the chainring I really wanted and fit it regardless because the chances are that, unless one abuses the box grotesquely, one won't ever require warranty service.

The first table at http://coolmainpress.com/BICYCLINGHebieChainglider.html contains all the gear-inch and speed combinations for each of the Rohloff gears for selected torque transmission (Chainring/Sprocket) sets for a 29er. Ask if you want another ratio calculated and I'll feed it into my spreadsheet.

Good luck.

PS: Better to reopen a relevant old thread than to spray pieces of the same discussion all over the forum. Anyway, this is one of those perennial ever-fresh threads.
« Last Edit: May 25, 2016, 11:38:11 pm by Andre Jute »

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #229 on: May 25, 2016, 11:33:37 am »
Thanks for all the the information, Andre. I have a 42t chainring that can be used initially, so will see how I get on with that.

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It was never intended as a refined touring box, but instead is a mudplugger's box; touring installations happened by accident.

This is certainly good to know, as it will see its fair share of mud.

My current concern is that my usual mtb range will fall between the 30-70gi range, which will see a lot of switching from gear 7 to gear 8. Something I believe is best done more carefully than switching between 1-7 and 8-14?

geocycle

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #230 on: May 25, 2016, 12:09:41 pm »

My current concern is that my usual mtb range will fall between the 30-70gi range, which will see a lot of switching from gear 7 to gear 8. Something I believe is best done more carefully than switching between 1-7 and 8-14?

To be honest I don't even think about changes now but I suppose you do have to back off slightly across 7 and 8.  If you mess it up you end up in 7 or 14 which is quickly remedied. IME the difference between a 19" or 20" first gear is hardly detectable and I use these gears very rarely compared to the mid range ones -but that's for touring of course.  Personally I'd make sure 8-12 are in the range you use most of the time and be less concerned about the extremes.
 

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #231 on: May 25, 2016, 03:54:32 pm »
...
My current concern is that my usual mtb range will fall between the 30-70gi range, which will see a lot of switching from gear 7 to gear 8. Something I believe is best done more carefully than switching between 1-7 and 8-14?

For shifting, I grew up shifting Sturmey Archer 3 speeds and later switched to the old "ten speeds" that had a 5 sprocket cluster and a cotter pinned double up front.  Those non-indexed derailleur bikes with friction downtube shifters always required care in shifting.  Thus, I learned that you anticipate your shifts and always back off on your pedal pressure when shifting, regardless of what your drive train was.  That has served me well when shifting the Rohloff.

If you regularly shift under load, yes the shift from 7 to 8 or 8 to 7 could be a bit difficult.  That said, when I have been mountain biking, if I was going slow and needed to downshift, it did not really matter much what gear I was in, I always wanted to back off on the pedal pressure which forced me to anticipate my downshifts a little bit more.

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #232 on: May 25, 2016, 08:08:54 pm »
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IME the difference between a 19" or 20" first gear is hardly detectable

I expect you're right. I'm probably just over thinking things :)

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #233 on: May 25, 2016, 08:13:15 pm »
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when I have been mountain biking, if I was going slow and needed to downshift, it did not really matter much what gear I was in, I always wanted to back off on the pedal pressure which forced me to anticipate my downshifts a little bit more.

I seem to remember the only real annoyance would be with the front derailleur occasionally refusing to shift*. Apart from that, I was never one to force a shift when riding, so there should be no issues.


*Last time I used gears was before the 1x11 'revolution'.
« Last Edit: May 25, 2016, 08:14:58 pm by PeteG »

Andre Jute

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #234 on: May 26, 2016, 12:07:08 am »
My current concern is that my usual mtb range will fall between the 30-70gi range, which will see a lot of switching from gear 7 to gear 8. Something I believe is best done more carefully than switching between 1-7 and 8-14?

7 snf 8 are also the noisiest gears in the box for the first few thousand miles, though that is likely to be of more concern to tourers than to you.

Gear 11, direct drive, is the most attractive gear in the box. It would do well for you to consider the gears 12-14 as overdrives, for fast riding on the road, and to plan your offroad gearing back from gear 11 at 70 sprocket inches for your regular cadence.

For instance, for a cadence of 60 rpm at the pedals, with 60x622 tyres (the full 29er katootie), reading straight off the table I referenced yesterday, your best bet is 42x17, for a ratio of 2.471 (a wee bit safer than Rohloff's own 32:13 ratio of 2.461!), which will give you 29.8 to 72.8 sprocket inches between gears 4 and 11, reserving 12-14 as overdrives for tarmac road work and 1-3 for the steepest bits offroad, presuming you can keep your balance at 5.8kph or a fraction over 3mph in gear 1.

42x16 is close enough to be getting on with.

This is looking up for you already. We need a specific tyre size and cadence to come any closer.

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #235 on: May 26, 2016, 11:08:05 am »
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your best bet is 42x17, for a ratio of 2.471

Coincidentally, while assaulting my credit card with the purchase of the hub this morning, I also ordered a 17t sprocket and a removal tool.

Just checked my tyres and they're 62mm casing width and 56mm casing height/60mm knob height. (76/80mm - 20mm rim height ), so should work alongside your table.

Andre Jute

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #236 on: May 26, 2016, 02:04:29 pm »
Congratulations. You'll be a lot happier with a Rohloff.

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #237 on: May 26, 2016, 11:39:51 pm »
...
Coincidentally, while assaulting my credit card with the purchase of the hub this morning, I also ordered a 17t sprocket and a removal tool.
...

I hope you get stuff that matches if you are getting two different sprockets, they are transitioning to the new splined sprockets.

PeteG

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #238 on: May 27, 2016, 08:21:53 pm »
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I hope you get stuff that matches if you are getting two different sprockets, they are transitioning to the new splined sprockets.

Ah yes, I was looking at those. Good to see that they have a simple adaptor for the present hub.

mickeg

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Re: What's your Rohloff combo (chainring, cog)?
« Reply #239 on: May 27, 2016, 11:40:02 pm »
I should have mentioned earlier but did not think of it, the new splined sprockets have a different chainline than the old thread on sprockets.  So, if you are calculating a spindle length for your bottom bracket, you might want to make sure you use the right data for your type of sprocket.

For chainline reasons, I am sticking with the old thread on sprockets.  Sprocket removal on a bike tour would not be very convenient, I find removal at home is quite easy with the proper tools.  I bought a spare thread on sprocket a few weeks ago while I can still get them.