Author Topic: What's your Rohloff combo (chainring, cog)?  (Read 170824 times)

gearoidmuar

  • Jr. Member
  • **
  • Posts: 95
Re: What's your Rohloff combo (chainring, cog)?
« Reply #45 on: July 25, 2012, 08:49:18 pm »
When I bought my TRT it had 40x16. I found this a little bit too low at the upper end and I found having to keep the chain/cog in sync when I changed the wheel a nuisance.
When they were worn I changed to 42x15. For me this is perfect. I'm 62 and 15st and tour a lot but not with a huge amount of luggage. Usually 30lb max. I would go for a 42x17 except that the high gear would be too low for a bit of fast stuff.
I think that the TRT with Rohloff hub is just the best thing ever. I've had maybe 3 dozen or more bikes in my time and this is the most satisfactory.

swc7916

  • Jr. Member
  • **
  • Posts: 52
Re: What's your Rohloff combo (chainring, cog)?
« Reply #46 on: July 26, 2012, 05:50:50 pm »
Most of the people here sure gear their bikes low!  I can't imagine needing gearing in the 'teens and losing my top end.  The gearing on our tandem is 50x15; with 26x1.25 tires this is equivalent to a gear range of 23 to 122 gear-inches.  This is an improvement over our derailleur tandem which has a range of 25 to 120 gear-inches.  When we need gear 1 for climbing, our speed is about 4-5 mph; it would be hard to stay upright if we were going any slower than that.  On downhills we frequently exceed 30 mph and occasionally reach 45+ (mid-40's is my stoker's limit.)

On the subject of chaincases:  As a cyclist and resident of the Pacific Northwest, you would think that these would be particularly beneficial here, but I've never seen one.  Besides, they look like a PITA.  Chains are cheap and tandems go through them so fast that I can't see that a chaincase would be worth the trouble.

Danneaux

  • Administrator
  • Hero Member
  • *****
  • Posts: 8232
  • reisen statt rasen
Re: What's your Rohloff combo (chainring, cog)?
« Reply #47 on: July 26, 2012, 06:49:30 pm »
Quote
Most of the people here sure gear their bikes low!  I can't imagine needing gearing in the 'teens and losing my top end.
Well, yes! But...
1) You are able to pull high gears without injury (like Jawine, who does this regularly as well).
2) You have great knees (also like Jawine and unlike me, who donated mine to a car accident while in high school).
3) I greatly admire you, Jawine, and Jobst Brandt for 1) and 2) above. Perhaps in my next life, I'll do it too.  :D

Meanwhile, it is "gear low and pedal like a hummingbird" with a light, fast cadence for me, never dropping below 80RPM under load, 60RPM at worst. If I do that, I'm fine with no complaints.

You make a very good point about diminishing balance returns at low speed. For years, I did trackstands at traffic lights while commuting (till a police officer issued me a USD$50 ticket, arguing a single-track vehicle could not truly be balanced at rest without toppling; therefore, I must be moving and had run the stop sign though I was well behind it at the time he collared me), and that may have helped with the low gear-balance thing. I find I can manage okay fully loaded on 16-24% hills down to 2.5mph/4kph before dabbing a toe, but that's it. I've got the tandem geared with a 46x13 high (92") and a 22x28 low (21"). Yes, we spin-out pretty quickly, but the last time I had my father on the back (age 87 at the time) we still managed 63mph down a local hill with the Arai drag brake lightly on. Would have been more if the light at the bottom of the hill had stayed green; Dad was disappointed, as he wanted to go for 65 or even 70 (former motorcyclist who also donated his knees to a youthful car accident in which he broke his cervical vertebrae. We bounce well).

Quote
On downhills we frequently exceed 30 mph and occasionally reach 45+ (mid-40's is my stoker's limit.)
Above 45, does your stoker do the kidney-pinch thing? I've had some that did...! Not Dad or Sis, but Others.

Quote
On the subject of chaincases...I've never seen one [in the PNW]
They're pretty rare down here in Eugene, too. I recall seeing a couple on bikes brought by Dutch students at the local uni, but that's about it. They just don't seem to be on anyone's radar.  I think there may be a perceptual barrier to overcome. Be ideal for commuting, so that's where we might see them first, introduced by a company like Civia, whose offerings already sport top-run covers.

Steering the ship of discourse back toward Rohloff gearing, I have decided to go with 40x17 (and a pie-plate/bash-guard protector) on the Nomad. I had planned to go with 38x16 to allow for a Hebie Chainglider, but I think it best to go with the Thorn default spec for now to allow the hub to break in at the usual rate. I can always adjust gearing at some point in future, but this will give a great, standardized start for this Rohloff newbie, and the low will be low enough for my loaded touring at 17.1". The high is 89.8, which is the stuff of my dreams on the flats but might see occasional use screaming downhill. One of the really nice things about this choice is it puts Gear Eleven at 61.2, and either 58 or 62 gear-inches are my favorites for cruising on flats, so will see lots of use. I figure with time and familiarity, I will gain a better idea if the Rohloff needs further adjustment.

Oh! Nix on the Chainglider for desert touring for the very reasons Andre cited -- the sifting, silting talc would get inside and wreak havoc, and I have great concerns about the possibility for wear on the hub by the chaincase especially in those conditions. I'm going to let Pete (Il Padrone) try his first! ;) Lookin' forward to full reports on using it in your red clay and bulldust, Pete.

Best,

Dan. (who thinks good knees may be a Super Power akin to x-ray vision)
« Last Edit: July 26, 2012, 07:06:46 pm by Danneaux »

swc7916

  • Jr. Member
  • **
  • Posts: 52
Re: What's your Rohloff combo (chainring, cog)?
« Reply #48 on: July 27, 2012, 04:52:49 am »
In regard to your question about gear 11:  I didn't plan my gearing around 11th gear, I just chose the chainring/cog combination that gave me the range I wanted.  Gear 11 is about 87 gear-inches on our tandem.

Further, regarding the pie-plate bash ring:  We have something like that on our tandem.  Since the bike was built with two single-bike double cranksets, the front had an empty position.  The builder put the chainring on the inner position and for the outer position installed a chainring which, with its' teeth ground off, is the same size as the inner chainring.  it is evident in this photo:

http://www.rodbikes.com/catalog/makeshift/images/makeshift6-5.jpg
« Last Edit: July 27, 2012, 04:58:30 am by swc7916 »

Danneaux

  • Administrator
  • Hero Member
  • *****
  • Posts: 8232
  • reisen statt rasen
Re: What's your Rohloff combo (chainring, cog)?
« Reply #49 on: July 27, 2012, 06:20:44 am »
Hi swc7916,

My! That tandem of yours is something else again -- more gorgeous with each viewing. And...such an elegantly simple drivetrain. That single-side drive with the single 'rings (double on the stoker's crank) with Rohloff is just.so.sanitary.

Wow.

By any chance, is that R&E's wall in the background? It looks a bit familiar from my last visit up there.

Quote
I didn't plan my gearing around 11th gear, I just chose the chainring/cog combination that gave me the range I wanted.  Gear 11 is about 87 gear-inches on our tandem.
swc, do you notice any less effort in direct-drive 11th compared to the adjacent gearing? I figure if a difference is really noticeable, it would be even moreso under a heavy tandem load.

Thanks for the insights.

Best,

Dan.

fleur

  • Newbie
  • *
  • Posts: 30
Re: What's your Rohloff combo (chainring, cog)?
« Reply #50 on: July 27, 2012, 06:49:11 am »
On our tandem, we have 48x15 with 26x2 tires rear, so very close to what swc7916 has (the recumbent stoker has an even bigger ratio 38x34 x 48x15, so something like 53.6x15 with IPS).

We don't feel any efficiency nor noise difference between the highest gears (8-14).  

The lowest group 1-7 is more noisy but its almost impossible to subjectively evaluate if there is any efficiency difference since those gears are only used going uphill and of course riding much slower.

So, I think that it is more important to choose your ratio to be remain as much as possible in the highest gear group than using as much as possible gear 11.
« Last Edit: July 27, 2012, 06:53:27 am by fleur »

Danneaux

  • Administrator
  • Hero Member
  • *****
  • Posts: 8232
  • reisen statt rasen
Re: What's your Rohloff combo (chainring, cog)?
« Reply #51 on: July 27, 2012, 07:19:45 am »
Quote
...I think that it is more important to choose your ratio to be remain as much as possible in the highest gear group than using as much as possible gear 11...
Thank you Fleur; this helps tremendously, and confirms I have made a correct "initial choice" in gearing the Nomad for my needs with the 40 x 17 combination. My goal was to be conservative and make a selection that will work for my requirements, place my most-used gearing in the upper-tier, and meet Rohloff's recommendations to remain in warranty while still giving the low gear I needed. I realize the hub will go through a break-in period, and it seems worthwhile to give it every opportunity to achieve a good meshing between gears using one of the "legal" combinations.

For me, it isn't just about warranty coverage; I really do want to maximize lifespan and minimize any chance for breakage when I'm away from civilization. With that in mind, anything that ensures a good outcome is worthwhile. That's why I ordered an oil change kit, Oil of Rohloff, and a sprocket remover right away, so I can be prepared to do maintenance on-schedule. It is to my advantage to give it the best chance for success, especially during this early break-in period.

I thought strongly of going for the 38x16 because of the even-numbered tooth combination, but I think wear with the larger 40x17 will give much the same end result, thanks to the larger diameters in play. I plan to keep a close eye on wear by distance traveled to see how things are going. It would be wonderful to do an "A-B" comparison, but there are too many variables to draw any conclusions between different riders. Maybe my next cog and chainring will be a 38x16 so I can compare!

By happy coincidence, the 40x17 combination also places gear 11 to perfectly match my favorite derailleur flat-terrain crusing gear at ~62 gear-inches. 38 x16 would have been nearly identical, so it was largely a matter of going with Thorn's recommendation of a 17T cog and matching the chainring I needed.

I appreciate the input, everyone. Gathering this collective experience is painting a much fuller picture for those of us who have never owned a Rohloff previously and wish to learn as much as possible from afar so we can consider or plan a purchase or just to better understand this IGH. A real service to anyone contemplating this drivetrain. Thanks!

Best,

Dan.

Andre Jute

  • Hero Member
  • *****
  • Posts: 4069
Re: What's your Rohloff combo (chainring, cog)?
« Reply #52 on: July 27, 2012, 01:27:08 pm »
Oh! Nix on the Chainglider for desert touring for the very reasons Andre cited -- the sifting, silting talc would get inside and wreak havoc, and I have great concerns about the possibility for wear on the hub by the chaincase especially in those conditions. I'm going to let Pete (Il Padrone) try his first! ;) Lookin' forward to full reports on using it in your red clay and bulldust, Pete.

After close inspection of the Rohloff-specific rear end of the Hebie Chainglider on hand of the discussion here, I would have ZERO concern about damage to the outside of the Rohloff box even in the playa. My concerns were about that fine grinding dust getting inside the Chainglider with the oil, and having no way of escaping, but that would damage the chain and sprockets, not the casing.

As described further up the thread, I had more concern about the possibility of the dust getting into the Rohloff box itself were it operated by an innocent/inexperienced/thoughtless/careless/ignorant rider, which isn't you, Dan.

Anyway, I'm one of those people who abhor the practice of collecting things and not using them. I have no objection to the signs of fair wear and even honourable scars  of war on implements meant for hard use. You're not buying a Rohloff gearbox to polish and put in a glass case, you're buying it to use, and a few honourable scars you can point to as you tell the story of traversing a dangerous desert adds to its value for the initiated. (Still, smart to order it anodised in black rather than merely polished plain aluminium.)

Andre Jute

swc7916

  • Jr. Member
  • **
  • Posts: 52
Re: What's your Rohloff combo (chainring, cog)?
« Reply #53 on: July 27, 2012, 07:21:26 pm »
By any chance, is that R&E's wall in the background? It looks a bit familiar from my last visit up there.

It's in the alley behind the shop.

do you notice any less effort in direct-drive 11th compared to the adjacent gearing?

My impressions are the same as fleurs'.

swc7916

  • Jr. Member
  • **
  • Posts: 52
Re: What's your Rohloff combo (chainring, cog)?
« Reply #54 on: July 27, 2012, 07:32:27 pm »
such an elegantly simple drivetrain. That single-side drive with the single 'rings (double on the stoker's crank) with Rohloff is just.so.sanitary.

Thank you.  Most tandemists are confused by the drivetrain until I explain it to them.  First of all they expect a cross-over drive and secondly they expect a derailleur system.  They will look at the stoker's crankset, see two chainrings, and ask if I have a double.  What they don't notice is that there is no front derailleur and two chains, one of them going forward.

fleur

  • Newbie
  • *
  • Posts: 30
Re: What's your Rohloff combo (chainring, cog)?
« Reply #55 on: July 27, 2012, 08:17:51 pm »
Thank you.  Most tandemists are confused by the drivetrain until I explain it to them.  First of all they expect a cross-over drive and secondly they expect a derailleur system.  They will look at the stoker's crankset, see two chainrings, and ask if I have a double.  What they don't notice is that there is no front derailleur and two chains, one of them going forward.

The very clean system of your tandem with both chains on the right side is becomming common in Germany where there are many tandems factory equipped with a Rohloff.  I guess there are much less in the States ?

Danneaux

  • Administrator
  • Hero Member
  • *****
  • Posts: 8232
  • reisen statt rasen
Re: What's your Rohloff combo (chainring, cog)?
« Reply #56 on: July 27, 2012, 08:36:09 pm »
Quote
I guess there are much less in the States ?
Yes, fleur, very much so. Crossover drive is the norm with derailleur-geared tandems here in the 'States. It is, however, twice as efficient at making one's legs oily from the chain.  :D

Best,

Dan (who is thinking a crossover chain-case would make a lot of sense)

JimK

  • Hero Member
  • *****
  • Posts: 1652
    • Interdependent Science
Re: What's your Rohloff combo (chainring, cog)?
« Reply #57 on: July 27, 2012, 10:30:39 pm »
OK, now this discussion about tandems has got me thinking - which is always a dangerous thing!

The idea behind a minimum gear ratio on the Rohloff is to insure some maximum torque is not exceeded at the sprocket. Some maximum pedal pressure (and crank length) is assumed.

But with a tandem, there are two feet pushing on two pedals... the torque at the sprocket would be double! Shouldn't the minimum gear ratio be doubled to respect that torque limit?

But two riders weigh twice as much... to get up the same hill at the same speed, they'll need that doubled torque at the sprocket!

I seem to have proved that a tandem with a Rohloff needs wheels that are twice as small!

What have I got scrambled???

Danneaux

  • Administrator
  • Hero Member
  • *****
  • Posts: 8232
  • reisen statt rasen
Re: What's your Rohloff combo (chainring, cog)?
« Reply #58 on: July 27, 2012, 10:37:19 pm »
Quote
...has got me thinking - which is always a dangerous thing!
Not at all!
Quote
I seem to have proved that a tandem with a Rohloff needs wheels that are twice as small!
Correct, by all my calculations as well.
Quote
What have I got scrambled?
It's not you, Jim, but I think your/our analysis fails to take into account the healthy safety margin Rohloff engineers into their hubs. (others will hasten to correct -- as they should -- if my assumption is incorrect).

I believe this is why so many people (after a suitable break-in period) are able to get by using "illegally low" gearing without consequence or bad outcome.

Dan. (...think I've got that right...the Dan part is okay; I mean right about the Rohloff safety margin)

JimK

  • Hero Member
  • *****
  • Posts: 1652
    • Interdependent Science
Re: What's your Rohloff combo (chainring, cog)?
« Reply #59 on: July 27, 2012, 11:09:44 pm »
"illegally low" gearing

I do get tempted. But I find my lower speed limit is much like what you mentioned recently, 2.5 mph, because of balance difficulty The 38x16 is probably about a 40 or 50 rpm cadence or thereabouts at that speed. Plus I spin-out downhill at maybe 33 mph or so.

I just need a few years to work on my physiology.

(We skipped the New Paltz book buying trip, or rather, we went by automobile. Family life gets complicated!)