Alfine 11; how it works (long)

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Brucey
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Alfine 11; how it works (long)

Postby Brucey » 11 Jan 2016, 3:23pm

The A-11 hub has been with us a few years now, and there is a fair amount of information out there. However unless I'm mistaken no-one has yet put in simple terms how the hub generates the 11 gears, which parts are used in which gears, and collected much of the available information in one place. This is (for good or ill) my stab at it. I've put it separate from the long-running A11 reliability thread mainly so that people can find it. Please let me know of any errors or omissions and I'll correct accordingly.

In a nutshell;

The hub is best thought of as a two speed (reduction or direct) gear which drives a six-speed (direct or increase, 5 options) gear.

The six-speed gear is itself a 3x2 gear, i.e. an intermediate three speed (direct or increase, 2 options) gear which in turn drives a further two speed (direct or increase) gear.

The gear ratios are selected via four selectable clutches (three lockable sun pinions, one sliding clutch) and four (automatically selected, spring preloaded) roller clutches. The eleven available gear ratios all use at least one gear train, and several gears use three gear trains in series.

The gearsets could give twelve ratios (2x6) of which only eleven are used, because one ratio is a near duplicate of another. However, there is no direct drive gear, instead a gear that gives almost the same gear ratio is used, despite the fact that this gear uses three gear trains, and would therefore presumably be less efficient.

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The detail:

The first gear train is similar to that found in an A8 or N8 hub, in that it uses a sliding clutch (C1) to provide direct drive to the planet cage (PC1). C1 is actuated by an axial cam. When C1 isn't locked, a roller clutch (RC1) takes drive from the driver to the ring gear R1 instead. The output is always from the planet cage of this gear stage PC1. The gear ratio is the same as that found in an N8/A8 hub, the tooth counts (including stepped planet gears) are the same also, but the A11 first stage gear teeth are cut helical instead of straight-cut. The rest of the gears in the A11 hub are straight-cut.

There are four sun pinions, of which three are selectably locked. The sun pinion in the first gear train (S1) is permanently locked; the remaining suns (S2,S3,S4) are locked by pawls that pop out of the axle as per N8,A8 ( and the latest N7) hubs.

The intermediate three-speed gear has two suns (S2,S3), stepped planet pinions, and a single ring gear (It works a little like the three high gears in a SA 5s hub). The drive to this stage is input via the planet cage (PC2) from PC1. When neither sun pinion is locked, a roller clutch (RC2) transfers drive from PC2 to the ring gear R2.

R2 in turn drives the planet cage (PC4) of the final two speed gear stage. When sun S4 is locked, the ring gear R4 drives the hubshell via a roller clutch RC4. When S4 is not locked, the R2/PC4 assembly drives the hubshell directly via roller clutch RC3.

Clutch C1 is locked in gears 7-11.
The S2-S4 clutching pattern is the same in gears 2-6 as 7-11
Gear 1 uses a unique S2-S4 clutching pattern that would give direct drive gear when C1 is locked.

In the A11 hub all the planet pinions run on roller bearings (as per Alfine 8, premium Nexus 8 and Rohloff hubs), so as to decrease losses.

Once you know what it is that you are looking at, you can see nearly all the relevant parts in this sectional view

Image

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Gear configuration table:

Clutches___C1___S2___S3___S4___Hubshell Drive__Active Gearsets___Active R-Clutches__Overrun R-Clutches

Gear
11_________L_________L____L___RC4______________-,-,3,4_________RC4_____________RC1, RC2, RC3
10_________L____L_________L___RC4______________-,2,-,4_________RC4_____________RC1, RC2, RC3
9__________L_________L________RC3______________-,-,3,-_________RC3_____________RC1, RC2
8__________L____L_____________RC3______________-,2,-,-_________RC3_____________RC1, RC2
7__________L______________L___RC4______________-,-,-,4_________RC2,RC4_________RC1, RC3

6____________________L____L___RC4______________1,-,3,4_________RC1,RC4________RC2, RC3
5______________L__________L___RC4______________1,2,-,4_________RC1,RC4________RC2, RC3
4____________________L________RC3______________1,-,3,-_________RC1,RC3________RC2
3______________L______________RC3______________1,2,-,-_________RC1,RC3________RC2
2_________________________L___RC4______________1,-,-,4_________RC1,RC2,RC4____RC3
1_____________________________RC3______________1,-,-,-_________RC1,RC2,RC3__________

Notes;
a) Sun pinions are labelled from right to left in the hub
b) if the hub behaves oddly or makes noises in some gears and not others, the table above can help to identify which parts may be responsible.
c) when RC1 and RC2 are not being used to drive, they are overrun, which introduces a small parasitic drag.
d) when S2 or S3 are not locked, they turn (usually backwards) on the axle, which does not introduce an appreciable parasitic drag
e) when S4 is locked RC3 is overrun (giving a small parasitic drag)
f) when S4 is not locked (and RC3 takes drive to the hubshell) RC4 is not overrun; instead S4 turns on the axle with low parasitic drag.
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Tooth counts (thanks to jb for checking these by counting.... and counting again...!)

train 1 S1 =48 Ps1 = 14 Pr1 =22 R1 = 84 (14/22 stepped planets)

train 2 S2 = 36 Ps2 = 20 R2 = 78
train 3 S3 = 39 Ps3 = 15, Pr2 = 20 (15/20 stepped planets)

train 4 S4 =39 Ps4 =24, Pr3 =14, R3 = 78. (24/14 stepped planets)

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Gear Ratios in each stage (from tooth counts)

Stage 1:
1/(1 + (48x22)/(14x84)) = 0.527 or,
1.000 (direct)

Stage 2:
using S2 (1 + (36/78)) = 1.462 or,
using S3 (1 + (39x20/15x78)) = 1.667 or,
1.000 (direct)

Stage 3:
(1 + (39x14/24x78)) = 1.292 or,
1.000 (direct)

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Gear Ratios (as products of gear stages)

Gear: Stage 1 x Stage 2 x Stage3 = total ratio

11: 1.000 x 1.667 x 1.292 = 2.153
10: 1.000 x 1.462 x 1.292 = 1.888
9 : 1.000 x 1.667 x 1.000 = 1.667
8 : 1.000 x 1.462 x 1.000 = 1.462
7 : 1.000 x 1.000 x 1.292 = 1.292
6 : 0.527 x 1.667 x 1.292 = 1.134
5 : 0.527 x 1.462 x 1.292 = 0.995
4 : 0.527 x 1.667 x 1.000 = 0.878
3 : 0.527 x 1.462 x 1.000 = 0.770
2 : 0.527 x 1.000 x 1.292 = 0.681
1 : 0.527 x 1.000 x 1.000 = 0.527

(give or take some rounding errors)
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Percentage intervals

Gear Ratio upshift% downshift % (Total Difference 409%)

Gear 1 0.527 ______ -22.6%
Gear 2 0.681 +29.2% -11.6%
Gear 3 0.770 +13.1% -12.3%
Gear 4 0.878 +14.0% -11.8%
Gear 5 0.995 +13.3% -12.3%
Gear 6 1.134 +14.0% -12.2%
Gear 7 1.292 +13.9% -11.6%
Gear 8 1.462 +13.2% -12.3%
Gear 9 1.667 +14.0% -11.7%
Gear 10 1.888 +13.3% -12.3%
Gear 11 2.153 +14.0% _____

average +15.2% -13.1%

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Cable pulls;
There are some measurements in the A11 reliability thread but in essence all shifts are a nominal 5.0mm except for 6-7 which is longer (around 6.4mm) and 10-11 which is also longer, presumably so that the cable will run full slack in gear 11 even if it is a little draggy. Other than A11-specific shifters ( Shimano, J-tek, Versa), there are no suitable alternatives.
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Comments:

I note with interest that once again (as in Nexus 7) shimano have avoided having a nice efficient direct drive gear 5 (or 6) (which would have been 'L---' clutching pattern). As it is the hub uses a single gear train in gears 1,7,8,9, thus these are likely the most efficient gears. Two gear trains are used in gears 2,3,4,10,11, (medium efficiency) and three are used in gears 5 and 6 (probable lowest efficiency). [NB Under very low loads the parasitic losses from the overrun roller clutches may be more apparent than the gear train (meshing + bearing) losses.]

If the gear ratios are set in a vaguely sensible fashion (i.e. so that the 'flat road, no wind' gear is about 70-80% of top gear) then gears 7,8,9 (which are relatively efficient) are likely to be the most used gears. On a heavily loaded touring bike gear 1 is likely to be heavily used too. This being the case the weighted average efficiency of the gear may not be as bad as the numerical average efficiency might suggest. However there is a question mark against gears 1-6, efficiency-wise, in that when the stage 1 gear is in use, there are axial thrust loads that must be supported by non-rolling element bearings.

Some folk have suggested that there ought to be more gears yet with different clutching (because there are sixteen possible permutations of four clutches) but IMHO this is not the case; S2 and S3 cannot be usefully locked at the same time (so the four '*LL*' clutching permutations are forbidden/ineffective), so the 'L---' clutch pattern is the only allowable and unused permutation.

In theory it should be nigh-on impossible to lose all drive in this hub, provided the gears are not jammed and you can still select C1, and RC2/ RC3 are still working, you should be left with a viable direct drive gear even if you can't lock S2, S3, S4 etc.
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There are some very helpful instructions and photographs (prepared by jb) in the midst of the long running Alfine 11 thread which can be found here

http://forum.ctc.org.uk/viewtopic.php?f=5&t=64432&start=374

[NB; the sun locking pawls are labelled from left to right in jb's notes.]

Below these there are some diagrams which show the drive path through the hub in the various gears.

On subsequent pages there are several other useful photos and posts.

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Known faults;

- the shift control is very sensitive to variations in build tolerance and adjustment. The reason for this is that the cassette joint may (because the RH hub cone is supported on two prongs, leaving gaps that the selector mechanism pokes though) only rotate about 135 degrees total, i.e. about 15 degrees per shift, tops. This makes building the hub accurately very difficult for Shimano and it also makes it sensitive to the exact external setting when in use. Unfortunately with new hubs the cable usually settles and this throws the external adjustment; worse still the build tolerances are such that the 'correct adjustment' (dots lined up in gear 6 http://www.sheldonbrown.com/nexus-mech.html) is not always the 'optimum adjustment'. 'Rofan' (see A11 reliability thread) has reported that the shift control sleeve is lighter built and longer than the equivalent A8/N8 version and this presumably makes it more likely to give trouble through wear or high shift load.

- The helical stage 1 gears were presumably added at a late stage ( the EV techdoc shows straight cut gears), I suppose to make the hub nice and quiet. However this generates an axial thrust load which can cause problems with retention of S1 on the axle (as jb has experienced in the A11 reliability thread). Arguably whoever designed the gear train screwed up here, in that when you pedal hard, the sun pinion S1 is forced rightwards i.e. against the retaining clip, rather than leftwards against a fixed shoulder. Maybe there is a good reason for this, but if they had cut the helical gear the other way (or left it straight cut) this fault may not occur in the same way or perhaps at all. If you routinely give the hub a lot of stick in gears 1-6 this is what is likely to generate this kind of problem.

-numerous users have reported skipping in some gears. This can happen even if the sun locking pawls are fully extended (in new hubs or hubs where there are burrs on the pawls) but it certainly will happen if the sun locking pawls are not fully extended. If the build tolerances of the hub are off a bit, the hub can therefore slip even when 'correctly adjusted'. The same thing is seen in numerous N8/A8 hubs. Many users have found that a little trial and error (with adjustments that are up to about 1.5mm away -in either direction- from the 'correct adjustment') can yield a more reliable setting. However if the axle assembly is examined when out of the hub the pawl lift (and therefore correct adjustment) can be checked directly. [I have seen several N8/A8 hubs where the C1 shift was not synchronised with the pawl lifts in the correct way. I do not know if the same fault occurs with A11 hubs. Note also that the sun locking pawls in a A11 hub are less likely to be overrun than in an N8/A8 hub, which means that any burrs on the pawl tips are unlikely to be knocked off when that pawl is not transferring drive. Hard (i.e. highly loaded) slips can raise burrs on, or even shatter pawls.]

- the clearances in all shimano IGHs are pretty tight; if there is any shrapnel in the hub (particles bigger than ~0.25mm) it will probably cause one or more gear trains to jam and/or be damaged. Stage 2 and stage 3 could jam entirely and you would still have some working gears, but if stage 1 starts to jam you are in trouble because the sun S1 is locked to the axle and those gears must turn at all times when you are pedalling.

- these hubs often leak oil. It isn't clear where the hub is meant to be vented; it seems to me that some leakage (most often on the RHS) is more or less inevitable.

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overall;

The Alfine 11 hub is (internally) only a tiny bit more complicated than a N8/A8 hub, and apart from the helical stage 1 gears there is nothing much new and different inside it per se vs the 8s hubs. So, with one or two caveats the internals ought to be reasonably reliable; an intrinsically 'bad hub' ought to become evident within the warranty period.

However the efficiency is unknown/suspect, the helical gears are probably not the best choice for high torque use in low gears, and a significant proportion of users report skipping or other problems, which can arise for several reasons.

Overall the A8/N8 hubs are both stronger and cheaper, so if they have wide enough ratios for your terrain, they probably make a better choice for any hard use. This is despite the fact that the grease lubrication in these hubs is far from perfect; running them in oil (or highly fluid grease, not shimano's) seems like a good idea to me.

cheers
Last edited by Brucey on 12 Jan 2016, 4:05pm, edited 1 time in total.
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bobc
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Re: Alfine 11; how it works (long)

Postby bobc » 11 Jan 2016, 8:09pm

MEGA thanks for all the hard work brucey

Brucey
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Re: Alfine 11; how it works (long)

Postby Brucey » 16 Jan 2016, 12:30pm

no problem, it took a while but I couldn't have done what little I've done without the input from others.

cheers
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NATURAL ANKLING
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Re: Alfine 11; how it works (long)

Postby NATURAL ANKLING » 19 Jan 2016, 12:05pm

Hi,
Not had time to read the whole post yet and consume.
I find the best way to understand the workings (especially for the non mechanically minded) of gear boxes is in the hand, any chance you have some 3d models / manufactures drawings/ exploded views:?:
Showing path of gear trains etc.
If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
You'll Find Me At The Top Of A Hill...............Somewhere...After Dark..

Brucey
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Re: Alfine 11; how it works (long)

Postby Brucey » 19 Jan 2016, 12:27pm

jb's posts that I linked to contain some diagrams which show the drive path through the hub but not everyone will get it from looking at those either. One reason I wrote this post was that there was little information out there on this topic.

BTW in this case the workings of the hub are somewhat opaque even if you have the internal in your hands; the sun locking clutches cannot be seen working with the hub internal assembled and the roller clutches are automatically selected, so you can't 'see those working' either; all you can do is infer that they are working by seeing how fast some parts of the hub rotate w.r.t. others.

BTW if there is interest in it I was planning to annotate the sectional view.

cheers
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NATURAL ANKLING
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Re: Alfine 11; how it works (long)

Postby NATURAL ANKLING » 19 Jan 2016, 2:45pm

Hi,
Sorry I missed the links :oops:
If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
You'll Find Me At The Top Of A Hill...............Somewhere...After Dark..

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Re: Alfine 11; how it works (long)

Postby Brucey » 20 Jan 2016, 8:34pm

Bigdummysteve sent me a link thusly

.... I found this video, it's a bit of an advert but might be of use to illustrate some of the operation
https://m.youtube.com/watch?v=2k0T2HFQTbI


I've not had a chance to look at it myself yet though

cheers
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Re: Alfine 11; how it works (long)

Postby NATURAL ANKLING » 20 Jan 2016, 9:39pm

Hi,
Smart video.
So how do you rate the oil bath integrity :?:
Electronic shifting, can you rapid change or jump gears with electronic or manual changer, preselector maybe :?:
Can you change under load with confidence :?:
Long time since I had 3 speed sturmy (school days) could you change willy nilly or was there backward pedalling or something.
So theres a torque activated shift :?:
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Re: Alfine 11; how it works (long)

Postby syklist » 21 Jan 2016, 8:52am

Brucey wrote:Overall the A8/N8 hubs are both stronger and cheaper, so if they have wide enough ratios for your terrain, they probably make a better choice for any hard use. This is despite the fact that the grease lubrication in these hubs is far from perfect; running them in oil (or highly fluid grease, not shimano's) seems like a good idea to me.

I had already bought the hubs for my Brompton Nexus 8 conversion when the A11 was announced. At first I wondered if I shouldn't just go for the A11 instead. However, when the first reports of unreliability started appearing I decided to stick with my 2 chain ring/front derailleur and Nexus 8 solution. Besides the A11 appearing to be much less robust than the N8 (there are plenty of MTB riders who seem to have severely abused their N8 hubs without managing to break them) I discovered that the A11 hubs were much more sensitive to cable stretch than the N8 which was not good on a bike you fold up several times a day. The overall gear range of an N8 with a 34/50 chain ring is similar to the A11 but with a more robust hub. Plus a N8 with a double chain ring costs about half the price of an A11.
So long and thanks for all the fish...

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Re: Alfine 11; how it works (long)

Postby Brucey » 21 Jan 2016, 10:13am

NATURAL ANKLING wrote:Hi,Smart video.So how do you rate the oil bath integrity :?: Electronic shifting, can you rapid change or jump gears with electronic or manual changer, preselector maybe :?: Can you change under load with confidence :?: Long time since I had 3 speed sturmy (school days) could you change willy nilly or was there backward pedalling or something.So theres a torque activated shift :?:


Often an A11 will lose most of its oil between services, and only a dribble comes out. However only a dribble is required to keep the hub working too, so maybe that is OK. A 'near total loss' system (as per SA hubs of old) worked quite well; arguably the worst thing about it was the mess it made.

I didn't mention the shift control mechanism; it is not the defining feature of this hub (electronic or otherwise) and may well only serve to confuse the issue.

In general terms it isn't a good idea to change gear under full load in an IGH and indeed most shifts won't go under full load anyway. The A8/A11 shift control has springs in it that so that if you pull the cable so as to move the shift control (ie downshift in an A11/newer A8, or upshift on an older A8/N8) when the hub cannot shift, a shift control spring inside the hub is preloaded. The shift will then occur under spring force as soon as the pedalling torque is reduced enough to let the shift happen. This does not always make the shift 100% reliable. You can store up a couple of shifts or so like this, not as many as you like. Going the other way, the cable goes slack if you try this, and that invariably causes trouble of one kind or another sooner or later.

Similarly if you move the shifter when the hub is stationary (and there is no pedalling torque applied) the shift control inside the hub will move, but the gear won't necessarily be fully in; in some cases it will only fully engage once the hub starts to rotate; if this is under high torque then damage can result.

Not all shifts are equal; obviously any shift that involves engaging C1 (6 to 7 in an A11, 4 to 5 in an A8) may not go smoothly under high torque; repeated slippage of this clutch -which is only pushed fully home by a relatively weak spring in most cases- will eventually damage it. Other shifts involve swapping locked sun pinions; in some cases the new sun can become locked whilst there is still torque being applied (eg upshifts 1-4 and 5-8 in A8/N8 hubs) but in many others (see the table in the first post) a shift requires that a sun pinion will become unlocked in a given gear stage before the shift will occur.

In an A11 hub if a given gear stage reverts to 1.000 ratio then the relevant sun(s) must be unlocked and this won't happen under continuous high load.

In practice the pedalling action has dead spots in it and these are often long enough for the shift to go in. But if the shift is only part complete and the highest pedalling torque is applied, slippage/damage is always possible. This means that the best shift technique is to reduce the pedalling torque until you are sure that the shift has gone in.

In addition to the above, some N8/A8 hub versions certainly (and others I would assume) have what is effectively a shift control servo action; if a shift that turns the cassette joint CW (downshift in an older N8/A8, upshift in newer A8/N8, A11) doesn't go, a pair of pawls in the shift control mechanism pop out and briefly lock the shift control mechanism to the driver. This forces the shift control mechanism, regardless of the applied torque. I am not convinced that this always happens without any risk of damage.

Note also that a high applied load to the hub can baulk the shift control directly, i.e. hinder it from rotating. This can happen in belt-drive hubs if the belt preload is too high, for example. I've not heard of this happening through a dead-weight load on the wheel but I suppose it could do. A slack bearing adjustment may make such problems more likely.

So anyway the simple answer is to back off the power when shifting in either direction; it is OK (preferable even) to keep pedalling forwards, just with no power. As a rule this works for most shifts and most IGHs.

cheers
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Re: Alfine 11; how it works (long)

Postby Brucey » 21 Jan 2016, 10:45am

syklist wrote: .... Besides the A11 appearing to be much less robust than the N8 (there are plenty of MTB riders who seem to have severely abused their N8 hubs without managing to break them) I discovered that the A11 hubs were much more sensitive to cable stretch than the N8 which was not good on a bike you fold up several times a day. The overall gear range of an N8 with a 34/50 chain ring is similar to the A11 but with a more robust hub. Plus a N8 with a double chain ring costs about half the price of an A11.


I agree. Hybrid gearing has its attractions for sure. It is just that in practice such systems usually lack the (apparent) elegance and simplicity of an 'all IGH solution'.

Maybe I'm alone in this but one thing that annoys me with a hybrid system is the tensioning pulley; this (sooner or later) seems always to cause problems of one kind or another.

cheers
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Re: Alfine 11; how it works (long)

Postby simonineaston » 21 Jan 2016, 11:57am

A super post, which reflects oodles of work and thought - thnx, Brucey. Another pint is in the post... ;-)
The info is invaluable, 'cos I'm (still) trying to work out whether to risk an Alfine, or splash for a Rohloff.
ttfn, Simon in Easton
(currently enjoying a Moulton TSR & a nano Brompton...)

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Re: Alfine 11; how it works (long)

Postby syklist » 21 Jan 2016, 12:49pm

Brucey wrote:I agree. Hybrid gearing has its attractions for sure. It is just that in practice such systems usually lack the (apparent) elegance and simplicity of an 'all IGH solution'.

Maybe I'm alone in this but one thing that annoys me with a hybrid system is the tensioning pulley; this (sooner or later) seems always to cause problems of one kind or another.

A hybrid system is a compromise, in my case it was because fitting a Rohloff to a Brompton requires a lot of extra engineering and a big chain ring. The N8x2 system is much better than the old 6 speed system it replaced. Of the hybrid systems I have used I prefer the one where the the gears that get changed most often are in the hub. I have never been able to get on with the SRAM DualDrives in our Dahons for this reason. The chain tensioner is not a problem with a folder like a Brompton
So long and thanks for all the fish...

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Re: Alfine 11; how it works (long)

Postby syklist » 21 Jan 2016, 12:58pm

simonineaston wrote:The info is invaluable, 'cos I'm (still) trying to work out whether to risk an Alfine, or splash for a Rohloff.

I did some research a few years ago when trying to decide whether to upgrade our old tourers from derailleur to IHG or chuck them away. We'd bought new VSF bikes with Rohloffs and realised quickly that we were never going to use the old bikes again if they didn't have an IHG in the back wheel. I discovered that the multi speed hubs (N8, SRAM i9, N11, SA 8, Rohloff) weighed about the same despite having different numbers of gears. From my research only the Rohloff and the N8 seemed to be robust enough for touring. Of these two, only the Rohloff could be used in a large wheeled bike and give very low gears whilst staying within manufacturers recommendations for chain ring to sprocket ratios. So I chose the Rohloff over the N8 for our old tourers. We used them in the summer of 2014 on our cycle tour with 16.something" 1st gear and towing 30kg of child and trailer in the hills of Norway without any problems.
So long and thanks for all the fish...