Rohloff: "Below the 1.9 Threshold"

[ason]

I am currently taking a break from the Panamerica. I’m currently in Ecuador and have an opportunity to take a break and do some maintenance. I’m currently running 32/17 (1.88) combination (since Alaska) and can foresee longer and harder climbs as I go further south. I just bought an 18 tooth cog (1.77) and looking for confirmation or advice against going below the 1.9 threshold that Rohloff suggests.

I’ve been using the Rohloff hub for over five years without any problems buying increasingly easier climbing gear combinations, both belt and chain. The hub has been working great without any problems other than some play (1mm) with the spring clip, and I may go back to the lockring with chain just to tighten that up in the rear. Could be rear cog wear on the 17. I’m looking for success or failure stories from people who use their Rohloff hub with combinations below the 1.9 threshold that Rohloff recommends. What’s the worse that could happen?

Again, I’m looking for success/failure stories from personal experience.

I could use the extra climbing gear, especially for grades over 12% as I’ll see in Peru.

[martinf]

I'm just under the 1.9 threshold at 1.81 with 38/21 on my "touring" Raven Tour, the bike I generally use for cycle-camping.

But :

- I use 150 or 155 mm cranks, which reduce the force applied as compared to 170/175 mm standard sized cranks. Short cranks also help me to "spin" at about 90 rpm rather than "mash" at about 60 rpm. For a given power output, easier on my knees and almost certainly less stress on the drivetrain.
- At age 68, I reckon my power output has dropped fairly significantly over the last five years, by at least 10%, maybe more. So if a 1.9 threshold was OK 5 years ago I believe 10% less (=1.71) should be OK now.

So although I have invalidated the guarantee I am not at all worried about breaking my 13 year old Rohloff hub.

I think it might be an issue if you are a very strong/tall cyclist and tend to "mash" rather than "spin" the cranks.

___________

I don't believe the load carried has much direct influence, I just tend to use lower gears and go slower when cycling uphill with a big load.

But with a very heavy load you sometimes have to push harder on the pedals, which can have an effect. A few years ago I did manage to provoke a gear skip in a Nexus 8 hub while straining to pull my overloaded trailer up the incline to my house. But that was an extreme case with 130 kg of cargo in a 15 kg trailer.

And a Nexus hub is rated for a much lower torque input than a Rohloff, Nexus is quoted at 50 Nm and Rohloff 130 Nm. 

[Andyb1]

Sorry I can not answer your question but as Martin has said other factors come into play such as body weight and crank length which effect how much torque is put into the hub….and Rohloff’s figures are likely to be conservative (they don’t want failures).
Is there a max rider weight / crank length on which they base their lowest final drive ratio?
If so, how does your weight / crank length compare?  If your figures are (say) 20% lower then I would have thought you could safely use a 20% lower final drive ratio.

The hub won’t know if the torque applied to it is from a heavy rider on long cranks at the ‘correct’ final drive ratio or a lighter rider on shorter cranks with a lower final drive ratio.

Edited to add:
Found something on’t net saying that the 1.90 lowest FD ratio is for a rider up to 100kg

[PH]

Sounds like a fantastic trip, please do let us know how it's going.
I think Rohloff's guidelines are conservative, Thorn have been supplying bikes at lower ratios for decades, they point out it's at the owners risk, but I think if there'd been any issues they'd have revised doing so.  Your choice, but I'd be happy to do that on my own hub.

[ason]

Hi PH, I know this might be too intrusive, but I'm interested in those numbers you've seen on Thorns (or personally use).  Thank you for taking the time.  It's just (1) one more gear at the low end.

[UKTony]

If it’s any help, Andy Blance’s (Thorn’s chief designer now retired) own specially built Exxxp S&S Expedition bike ‘Hector’, like a Mk2 Nomad on steroids, was up for sale last year on SJSC website.
I made a note of the gearing - 34x19 (1.78) - close to what have  in mind.

[mickeg]

I find if I fall below about 3.5 mph (~5.6 km/hour) that I start oversteering to maintain balance.  And my gearing with a 2.25 ratio works well for that.  If the hill is so steep that I would want a lower gear to keep my heart rate down, I would not have enough speed to maintain good balance.

Thus, I frequently walk up the steeper hills.

Before I left home, I knew I was going to have to walk my bike up the hill in the photo, at 13 percent grade for a few km, I knew that my heart rate would be way too high if I tried to pedal it.

[PH]

Hi PH, I know this might be too intrusive, but I'm interested in those numbers you've seen on Thorns (or personally use).  Thank you for taking the time.  It's just (1) one more gear at the low end.

In the current Thorn Bible (Downloadable from the link below) it says "You’re welcome to be pro-active and to choose forbidden gears, as long as you take personal responsibility for your decision." page 49 if you want to read it for context.
https://www.thorncycles.co.uk/bikes

[Andre Jute]

Seems to me that well before you arrive at Rohloff's CYA lowest permissable transmission ratios, never mind transgressing them, your choice will be logically determined by the best cadence you can maintain on a hill such as the one George walked up, photo above in this thread, and consequently by the lowest velocity at which you can maintain your balance and a relatively straight line of progress.

Transmission Tooth Tables at http://coolmainpress.com/BICYCLINGHebieChainglider.html illustrate the point. The first one is for me -- and demonstrated that for my best cadence of 60rpm, even on the flat, my choices (of Chainglider-capable transmission couples) was limited by my balance to  about 3.5mph/5.6kph. It wasn't even necessary to recalculate for my best maintainable cadence on a long steep uphill, of which there are plenty where I live in a town called "the Rome of West Cork". Mental arithmetic told me an ultraconservative 38x16 would suit my best high-stress cadence of 40rpm. (Note that the calculation is for a 622mm wheel with a 60mm wide tyre.)

If you want a similar table to help you determine the right choice, post or send me in a PM your wheel and preferred tyre sizes, your all-day cadence on the flat, plus your maintainable cadence on a long steep hill, and I'll create two tables.

Andre Jute

[martinf]

With 38x21, my lowest gear is just under 13 inches.

That corresponds to about 5.5 kph at 90 rpm.

If I am very tired I may drop pedalling rate to 60 rpm, which is 3.7 kph, about my lower limit for keeping balance.

That works on the loaded bike. With no front panniers, the front wheel lifts on very steep climbs.

[Dunroving]

With 38x21, my lowest gear is just under 13 inches.

That corresponds to about 5.5 kph at 90 rpm.

If I am very tired I may drop pedalling rate to 60 rpm, which is 3.7 kph, about my lower limit for keeping balance.

That works on the loaded bike. With no front panniers, the front wheel lifts on very steep climbs.

Exactly, this happens on my bike also. That plus the "keeping balance at slow speeds" issue mentioned by Mickeg means that below a certain gear ratio, there's no point reducing further. We just have to figure out what that point is for each of us.

[mickeg]

With 38x21, my lowest gear is just under 13 inches.

That corresponds to about 5.5 kph at 90 rpm.

If I am very tired I may drop pedalling rate to 60 rpm, which is 3.7 kph, about my lower limit for keeping balance.

That works on the loaded bike. With no front panniers, the front wheel lifts on very steep climbs.

Exactly, this happens on my bike also. That plus the "keeping balance at slow speeds" issue mentioned by Mickeg means that below a certain gear ratio, there's no point reducing further. We just have to figure out what that point is for each of us.

Yup.

[Tigerbiten]

With 38x21, my lowest gear is just under 13 inches.

That corresponds to about 5.5 kph at 90 rpm.

If I am very tired I may drop pedalling rate to 60 rpm, which is 3.7 kph, about my lower limit for keeping balance.

That works on the loaded bike. With no front panniers, the front wheel lifts on very steep climbs.

Exactly, this happens on my bike also. That plus the "keeping balance at slow speeds" issue mentioned by Mickeg means that below a certain gear ratio, there's no point reducing further. We just have to figure out what that point is for each of us.

Another 38/21 gear setup with the hub built into a 20" wheel for a sub 10" gear.
But I'm also on a recumbent trike so no real minimum speed for hill climbing as long as I keep traction and don't just wheel spin.

[mickeg]

In first gear on loose gravel, I have had wheel spin problems with my Nomad Mk II, both unladen and with a heavy load.  When your gear ratio is low enough and your hill is steep enough, loose gravel can be a problem because that low gear gives you a lot of wheel torque.

First photo, if you look down, you can see some switchback gravel road, I had a lot of trouble with wheel spin there.  But, I needed that low enough of a gear to climb the hill.  Each time it spun and I lost momentum, I would have to push the bike to the next turn where it would be flat enough for me to start out pedaling on the bike again.  I had a 57mm wide Schwalbe Marathon Extreme on the bike, that might have not had enough grip on gravel because of the tread design, the knobs are big and the grooves are small.  Bike was unladen.  There were several other mountain bikers (derailleur bikes) in the group I was in, they all pushed their bikes to the top, but I managed to pedal parts of that hill.