Thorn Cycles Forum

Technical => Transmission => Topic started by: KDean on October 12, 2021, 03:54:52 PM

Title: Nomad Rohloff gearing
Post by: KDean on October 12, 2021, 03:54:52 PM
What's the smallest gearing ratio  you can have a a Nomad MK2   38---19?
Title: Re: Nomad Rohloff gearing
Post by: mickeg on October 12, 2021, 05:07:35 PM
If for a solo bike and if your weight is less than 100 kg, the ratio of 1.9 of chainring to sprocket.


For touring, I am running a 36T chainring and 16T sprocket, ratio of 2.25. 

But if you are a spinner and want a high cadence, you could certainly go down towards the 1.9.

If you weigh more than 100 kg, ratio is higher.
Title: Re: Nomad Rohloff gearing
Post by: KDean on October 12, 2021, 05:56:52 PM
I'm under 92kg  , What the best for steep hills , Sorry I switched off looking at all these charts .
Title: Re: Nomad Rohloff gearing
Post by: martinf on October 12, 2021, 08:10:10 PM
For me, the best gear on hills is the lowest possible that still gives me a "reasonable" top gear.

I currently have 38 x 16 on my tourer, because that was the lowest permitted ratio when I bought the bike in 2012. I very rarely use the highest gear, so I will probably go to 38 x 19 at some stage.

38 x 19 gives a range of 14" to 74" with the 26" by 2" tyres I run. Top gear 74" at my preferred pedalling cadence of 90 rpm is 33 km/h, that speed will be OK for me on a loaded tourer, as I can only go that fast for any significant length of time on downhills or with a substantial tail wind.

I can still get the speed up to 43 km/h for a short period by increasing cadence to 120 rpm, for example if I need to integrate traffic on a big roundabout.

I have a 71" top gear on my 8-speed utility bike, and don't miss not having a higher gear on that.

As Mickeg says, it also depends on your pedalling style.

Title: Re: Nomad Rohloff gearing
Post by: mickeg on October 12, 2021, 09:16:31 PM
I'm under 92kg  , What the best for steep hills , Sorry I switched off looking at all these charts .

I can't tell you what the best is for steep hills for you.  Everyone is different.

I find the slowest I can ride and maintain horizontal and vertical stability is about 3.5 mph.  And the slowest cadence I can run with it being smooth and not a pulsating slog is about 72 rpm. 

So, after some calculations, with my 559X57mm tires I find that I need a 36T chainring and 16T sprocket to have a first gear that is about 3.5 mph with a cadence of 72.  That is what I use for touring.  I spin out on some shallow downhills but the steep uphill gearing is more important than shallow downhill gears.

But that is touring, with a heavy load of camping gear on the bike.  When near home with an unladen bike, I switch to a 44T chainring instead, add four chain links.  That way I have the lowest gears I need on an unladen bike and I have better downhill gearing for shallow downhills.

You likely will want something different, everyone is different.
Title: Re: Nomad Rohloff gearing
Post by: Danneaux on October 12, 2021, 11:03:30 PM
Another data point to consider:

I use 36x17t on my Nomad Mk2, which weighs 20kg (dry and bare) and sometimes carries 37kg beyond that, mostly in water (26.5l/kg) and food for self-supported back-of-beyond solo expeditions. I myself weigh 78kg in summer cycling kit. I often encounter steep hills (briefly up to about 22% on gravel logging roads and going cross-country, more commonly around 8-10%) and at those times I am very grateful for the low gearing, especially when fully loaded. I am a spinner (110-120rpm) with a fast-light cadence.

I would not want to gear any higher at the low or high end for this bike and how I use it.

That said, everyone is different and will have -- or develop -- their own preferences. Fortunately, chainrings and slide-on Rohloff sprockets are relatively cheap so you can try a variety of options before settling on what works best for you.  :)


Title: Re: Nomad Rohloff gearing
Post by: Andre Jute on October 13, 2021, 10:52:26 AM
Couple of generic notes about The Ratio:

1. Underlying wide adherence to whatever the current Ratio is, lies the widespread, implicit belief that a) the Rohloff guarantee hangs on observance, and b) that Rohloff goodwill (fixing your gearbox without charge if anything goes wrong even beyond the warranty period as long as you aren't at fault) depends on it, in both instances as much as observing the oil service intervals.

2. The Ratio has been Relaxed twice in the last few years, that is, a greater amount of torque has been permitted, and The Ratio has become a lower number. Many, probably most of us, believe the Rohloff box is immensely strong, certainly in no danger of breakages under even stringent use at the present Ratio. The consideration of keeping faith with Herr Rohloff isn't that we aren't scofflaws but that we'd rather he kept faith with us, as above.

3. Anyone's desirable Ratio is limited at the bottom end by how slowly he can keep his balance (as Mickeg says above) and at the top end by his short-spurt  cadence for instance for blending with faster traffic, pointed out in this thread already by Martin.

4. I don't know what the present practice is, but for many years Rohloff gearboxes came from the factory with a 16T sprocket fitted. By far the most common Rohloff transmission arrangement from Continental bike makers was 38T x 16T. Thorn danced to a different tune, perhaps because its designer, Andy Blance, and his wife toured the toughest roads. I seem to remember from 12 or 13 years ago that he made such a good case for a 17T sprocket that he probably convinced quite a few cyclists who didn't in the end buy a Thorn to start with a 17T sprocket. Thorn also had their own 19T Rohloff sprocket made.

4. The problem with the Rohloff sprocket is that it lasts forever. It's actually the cheapest part of a Rohloff transmission (excluding, obviously, the box itself), but who wants to throw away such excellent engineering half-worn? So you need to choose your sprocket right in the first instance, but you needn't weep if you decide later to change it before it is worn out.

5. There is considerable enthusiasm for a chain cover called a Hebie Chainglider, inside which I've proven that you can run a medium-range KMC chain for its whole service life on its factory lube without harm to any other component. This instantly reduces routine service on your bike to once a year. That's an immense boon to older cyclists growing a bit too stiff to bend over the bike often or long to clean the chain. But, while the Chainglider has a custom Rohloff rear end which fits all the available Rohloff sprockets, its chainring covers, plural, one per chainring tooth count, fit only a selection of tooth counts, and Frank Revelo demonstrated on this forum some years ago that if you choose the wrong tooth count for the Chainglider cover you can get, the result is ineffective and ugly. If you intend fitting a Chainglider -- and I recommend it very highly -- you must choose a compatible tooth count at the front. The chainring inside a Chainglider needs to be thinner than most aluminum rings, so that steel or stainless steel is often chosen, again reducing service because steel and stainless chainrings last forever, just like the sprocket.

6. There's an odd Rohloff Effect, contrary to perfectly reasonable expectations, which a few of us have commented on. You get a Rolloff-equipped bike and you ride it happily on Easy Ratio, perhaps for years. And then you notice that you're stronger, even if older, and can bring your end of a more demanding transmission. After two heart operations, instead of going down easy street as expected, when I was forced to go from a 38T chainring to 42 or 44 or even 46 because a central electric motor I wanted to try needed a dished chainring, I thought that would put me off cycling. Not a bit of it. I took to it like a duck to water.

7. In consideration of all this, I'd advise you to leave your options of different ratios and a service-reducing chain cover open by settling on a chainring of a particular tooth count, and buying it in stainless steel (I was happy with Surly's version but there were complaints on this forum of out-of-round, etc) or even cheap steel (I liked an Indian-made Amar, which after some thousands of kilometers inside a Chainglider had not even marked the paint it came in), and then taking Dan's suggestion of swapping Rohloff sprocket tooth counts. This is the cheapest trial and error method of arriving at an arrangement that suits you perfectly which also leaves all your other options open. You can always later sell the Rohloff sprockets you don't use on, though my bet is you won't have more than one extra, which you will want to keep, as I did.

8. If you want to tell me the rolling diameter of the tyre you have in mind, obtainable from the maker, and your normal cadence in RPM, I'll make you a decision table like those at
with only components directly relevant to you to reduce the confusion.
Title: Re: Nomad Rohloff gearing
Post by: KDean on October 13, 2021, 02:52:04 PM
My rims are 26" with 2" tires  & my average cadence is 65rpm .
Title: Re: Nomad Rohloff gearing
Post by: Andre Jute on October 13, 2021, 05:55:49 PM
My rims are 26" with 2" tires  & my average cadence is 65rpm .

You're leading me on to believe that the rolling diameter of your tyres are 26in plus twice 2in equals 30in. My 60mm Big Apples have a rolling diameter on 622mm rims of 29.45in, with my measurement and the manufacturer's tables matching, so clearly your tyres don't have a rolling diameter of 30in.

You need to look up a specific number for a specific brand, model and size of tyre on the manufacturer's netsite. Anything else is speculation with a large built-in error. If you haven't chosen your tyre yet, we can take this up again when you have.
Title: Re: Nomad Rohloff gearing
Post by: mickeg on October 13, 2021, 08:34:45 PM
My rims are 26" with 2" tires  & my average cadence is 65rpm .

My 26 inch 50mm Dureme tires have a circumference of 2057mm, diameter of 655mm.
Title: Re: Nomad Rohloff gearing
Post by: Andre Jute on October 13, 2021, 09:15:55 PM
Thanks, George. That's something to work with. I have other commitments now and will get to it tomorrow.
Title: Re: Nomad Rohloff gearing
Post by: Andre Jute on October 14, 2021, 04:19:42 PM
At I've posted  a table, right at the bottom of the page, showing all the likely Chaingliderable transmission ratio choices in detail, gear by gear, for a cadence of 65rpm plus a couple around the currently highest permissible torque ratio of 1.9 which won't take a Chainglider but in which the bigger sprocket might deliver a bit better chain wear than a smaller bare sprocket.

The input data was for a 50mm x 26in Dureme, kindly supplied by Mickeg; thanks, George.

If anyone wants to see a table for a different size tyre, different gear combination, different cadence not already covered in the tables above the one I'm discussing here, let me know. I need to know the rolling diameter of the tyre and your everyday cadence.