Rohloff SPEEDHUB 500/14 Minimum Sprocket factor

[jrs665]

According to Rohloff , the minmum external sprocket factor for the SPEEDHUB 500/14 is 1.9 (The ratio of the chainring to rear sprocket).
This is to prevent overstraining the hub which can handle a maximum of 130NM input torque.

The ratio is given for riders under 100kg, the minimum ratio jumps to 2.5 for ebikes and riders over 100kg.

With regard to a Rohloff on a TRIKE , what I am confused about is :

1) Is Power not a more accurate estimate of Torque generated than rider weight? Would a rider my weight with double my FTP , but riding at same cadence not generate double my torque?
2) Why would the ratio jump to 2.5 for an ebike as it generates 40-80NM for a 250W motor, well below the 130NM maximum imput.
3) My FTP is only 160W , I do about 250W going up a 15% hill with a 20 inch gear ratio (36 sprocket, 26 chainring). How much torque is this, am I in danger of overloading the 130NM hub if I use a 22 chainring on a TRIKE in conjunction with a 16 rear sprocket ( 1.375 ratio) for lower gears ?

[cycle tramp]

At this point you're over thinking it...

..the bottom line is this - If you use a gearing ratio is below that specified by the manufacturers and you break the hub, you will not get any technical support or refund. That's it, game over, do not pass go and do not collect 200 pounds.

...if you are looking for ratios below that which the rolhoff can provide then you may need to look at derailleur gears..

[JohnR]

What size wheels are on the trike? 22/16 gearing is very low unless you have very big wheels. My Birdy Rohloff with 18" wheels has 52/13 which works out in gear inches similar to 42/16 on 700c wheels. On a good day I can get up a 15% hill at 3mph in 2nd gear with a cadence of 50rpm.

[jrs665]

What size wheels are on the trike? 22/16 gearing is very low unless you have very big wheels. My Birdy Rohloff with 18" wheels has 52/13 which works out in gear inches similar to 42/16 on 700c wheels. On a good day I can get up a 15% hill at 3mph in 2nd gear with a cadence of 50rpm.

I have 26 inch rear wheel. Currently have shimano deore 11-36 sprockets, Sram 44-32-22 chainrings.
Looking at the hub ratios, a rohloff with a 16 rear sprocket and 32 chainring gives a slightlylower gear than my current lowest.
Using a 22 chainring with the rolloff and 16 rear sprocket , I imagine will give me effectively another 2 lower gears,

[geocycle]

Unless there is something about a trike I have missed, 22/16 on a rohloff with 26 inch wheel is very low indeed. On my 26 inch upright I have 40/17 and still get 17 inch bottom gear. I've heard of folk with very high cadences going to 36/17 but not smaller?

[PH]

What others have said, it seems very low gearing, it's one thing to want that bottom gear, but you're then going to have a top gear that will require spinning furiously to get over 10mph!

[Tigerbiten]

I run a 38/55 double 21 sprocket combo on a 20" back wheel and I also have a Schlumpf HSD built into the BB on my bent trike.
On the small chainring this is a 1:1.8 ratio, so below the min recommended but I was after a sub 10" first gear.
Spin-out speed for the 4 gear ranges are 14 mph, 20 mph, 35mph, 50 mph.
I've used that combo at my own risk for 12 years years now.

As for why e-bikes need a higher ratio, it's the shifts.
In theory the power is cut just before the shift, but than may not always be the case.
With a higher ratio the hub is more likely to survive shifts under power.

Luck ........

Edit .....
I'd probably fit a 34/50 compact double with an 18t sprocket and the Rohloff chain tensioner to take up the slack.
This gives you another 3 gears on top of the standard 14.
So more gear down gear while keeping in your top end.

[slowster]

I presume that this is for a recumbent trike. I imagine that maximum torque output at the crank could be less than on an upright, because on an upright a rider can readily apply virtually their whole bodyweight by standing on the pedals, e.g.

100kg rider x 9.81 x 0.175m crank length = 172Nm crank torque.

That would then be geared down depending upon the chainring/sprocket ratio to produce the input torque at the hub.

However, if a ratio of less than 1.9 was something which in practice recumbent trike riders could get away with using without running too high a risk of hub damage (probably the 'sacrificial' plastic parts in the hub shearing), I think it would already be something which had been discussed online by recumbent trike users - probably especially in Germany, so it might be worth doing some google searches in german.

Note that a lower ratio will correspondingly increase the reaction torque in all the gears bar gear 11, e.g. see this post of Brucey's - viewtopic.php?p=841318#p841318. In gear 1 the reaction torque is 357% of input torque. If the plastic components in the hub did not fail using a ratio of 1.375, I suspect some frames/dropouts might nevertheless be damaged by the reaction torque.

[JohnR]

Note that a lower ratio will correspondingly increase the reaction torque in all the gears bar gear 11, e.g. see this post of Brucey's - viewtopic.php?p=841318#p841318. In gear 1 the reaction torque is 357% of input torque. If the plastic components in the hub did not fail using a ratio of 1.375, I suspect some frames/dropouts might nevertheless be damaged by the reaction torque.

In reality the reaction torque isn't difficult to manage given that one Rohloff solution is an M6 bolt through a hole in the dropout 40mm from the axle
https://www.rohloff.de/fileadmin/_proce ... 92125d.png

For calculations of Rohloff gearing it's useful to remember that 11th gear is direct drive.

[jb]

The force at the wheel for any given gradient is the same for all systems. Its more likely that damage would happen if you tried to climb a steep hill in too high a gear. thus putting a huge force on the input shaft. The limit on the sprocket chainwheel ratio by Rohloff or any other manufacturer is to prevent shock load caused by standing and stomping on the pedals. As most recumbents force the rider to be seated this won't happen.
Having said that the low gear is more than enough for most things when used with the recommended ratio.

[jrs665]

What others have said, it seems very low gearing, it's one thing to want that bottom gear, but you're then going to have a top gear that will require spinning furiously to get over 10mph!

Will be using the current 44-32-22 chainrings. Unlike a bicycle, a trike is not limited to 1 chainring due to chainlength

[jrs665]

The limit on the sprocket chainwheel ratio by Rohloff or any other manufacturer is to prevent shock load caused by standing and stomping on the pedals. As most recumbents force the rider to be seated this won't happen.

That exlains they use rider weight as a criteria.

[plancashire]

...
However, if a ratio of less than 1.9 was something which in practice recumbent trike riders could get away with using without running too high a risk of hub damage (probably the 'sacrificial' plastic parts in the hub shearing), I think it would already be something which had been discussed online by recumbent trike users - probably especially in Germany, so it might be worth doing some searches in German.
...

In this thread https://www.rad-forum.de/topics/1266951 there is a comment from a trike rider Landradler.

Die Übersetzungsangaben werden aber erst interessant wenn ihr auch die verwendete Reifengröße angebt! Ich fahre am Trike 39/14 das macht mit 20" Laufrad 1,23m - 6,46m Entfaltung. Das reicht mit Gepäck bisher für jeden Berg und bergab kann ich bis 35kmh noch mit treten.

Translated:
The gearing information is only useful when the tyre size is given! I ride a trike 39/14 with 20" wheels that makes 1.23m - 6.46m per crank revolution. That is enough so far with luggage for every hill and downhill I can pedal up to 35km/h.

Zweiradmeister writes that he recommends to his customers that they have their main gear ratio set for gear 11, which is direct drive in a Rohloff. That gives three higher gears and ten lower. All are happy. I have set mine up that way too, lowering from the original setup.

There may be relevant information here: https://www.rohloff.de/de/service/handb ... len#c25720. There are a lot of tables, including for 20" wheels. The heavier cargo bikes and recumbents (one or two tracks = trikes included) have higher allowed chain ratios to keep the torque at the hub below 130Nm. You could calculate the torque on your setup from max pedal pressure, crank length, chain ratio, trike weight and hill slope.

Rohloff gives the gear ratio unit as "entfaltung", which is distance travelled per crank rotation. This makes much more sense than the British "inch" unit.

[PH]

What others have said, it seems very low gearing///

Will be using the current 44-32-22 chainrings. Unlike a bicycle, a trike is not limited to 1 chainring due to chainlength

Ahh, outside my experience so hadn't even occurred to me

[steelframe]

Unless there is something about a trike I have missed, 22/16 on a rohloff with 26 inch wheel is very low indeed.

Possibly you missed a thing or two:
- a trike cannot tip over. With a two-wheeler you have to balance the bike which in practice limits the lowest speed possible uphill and thus also the lowest useful gear. No issue on a trike.
- at the same time you cannot stand up on a trike while pedaling - you have to pedal while seated even on the steepest hill. Therefor you need lower gears than on a conventional bicycle
- pushing a trike uphill is, depending from the trike, a PITA in most cases. Even worse with luggage. You cannot grab the bars while walking thus keeping the thing in a straigt line or turning where you want it to is a challenge. You'll rather pedal, if that's very slow - so be it.