Shimano Alfine 11 - Longer term reliability

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Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimano Alfine 11 - Longer term reliability

Postby Brucey » 11 Feb 2020, 7:27pm

the 'squashy feeling', especially in the lower gears is 'normal' for this type of hub, and is (mostly, I think) caused by the presence of roller clutches.

In a post above , Meandros seems to claim that the direct driving pawls inside Rohloff hubs are less efficient when climbing. I beg to differ! On the same hills, I find myself using lower gear ratios when using hubs with roller clutches (Nexus8, Alfine8, Alfine 11 etc) and I also find myself going very much more slowly. I agree you are best off pedalling swiftly at low torque with these hubs, but this is making the best of a bad job; I think the roller clutches have a strong negative effect on pedalling efficiency.

I suspect (but cannot prove) two further things

1) that the flexing is worse if the roller clutch is in poor condition, i.e. there are not very many rollers engaged and sharing the load. This would be expected to cause the drive rings to flex more, into various odd-sided polygonal shapes, under load. Brand-new hubs, badly lubricated hubs and hubs where the bearings are not correctly adjusted are all likely to be worse in this respect.

2) that the measured efficiencies that you read of are measured under constant torque conditions, where the flex (which normally occurs with every pedal stroke) doesn't affect the efficiency readings.

So overall I have concluded that, for my riding, anytime where efficiency is important, hubs without roller clutches suit me better that those with.

Hubs with pawl drives include

Most SA 2s, 3s 5s, 7s, 8s (*) hubs,
most Sachs/SRAM 2s,3s,5s,7s (**) hubs
Shimano Nexus 7 (***)
Rohloff 14.

But note the following

(*) SA 5s 7s and 8s hubs have a patchy reliability record
(**) SRAM hubs are no longer made and the 5s/7s hubs seem internally reliable, but have pretty lousy shifting arrangements.
(***) No roller clutches in Nexus 7 hubs but no roller bearings either. It is not a super-efficient hub, partly because there is no direct drive gear ratio.

cheers
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jb
Posts: 909
Joined: 6 Jan 2007, 12:17pm
Location: Clitheroe

Re: Shimano Alfine 11 - Longer term reliability

Postby jb » 11 Feb 2020, 8:13pm

Brucey
Did you not think that in the vidio it seemed a little excessive, he did say it was present in all gears which I certainly never noticed, only in tenth & seventh I think.
Cheers
J Bro

Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimano Alfine 11 - Longer term reliability

Postby Brucey » 11 Feb 2020, 9:03pm

It might be, but I'm not entirely sure which gears he is in when he is doing the demonstration.

FWIW on a MTB the tyre often makes any transmission feel a bit squodgy, but on a more road-oriented machine I'd say that -to an aggressive rider especially- the A11 hub especially feels very squodgy in many of the lower gears.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

meandros
Posts: 58
Joined: 1 Jan 2018, 7:34pm

Re: Shimano Alfine 11 - Longer term reliability

Postby meandros » 12 Feb 2020, 12:49pm

It felt to me, whenever I was using a regular pawl clutch IGH that _when shifting gears_ it seems especially less efficient than a roller clutch IGH as I can better maintain cadence (put more pressure on pedal stroke at precise moment of shifting) on account of the roller clutch mechanism aiding with shifting; that is to say, no need to stop pedalling or slow down which, to me, seems an issue especially in lower gears when going steep slopes: in that scenario, I know for a fact, pawl clutch IGHs don't cut the mustard.
Btw, isn't it that, by design, the Alfine 11 is more efficient in higher gears than lower ones and the roughloff is the exact opposite? I'm sure I saw a graph once somewhere. Overall, the roughloff is more efficient on paper by about 5-6%, but my claim is that in real world use, the roller clutch is just a more evolved design, as far away from a "bad job" as you can be, actually making shifting easier. Even acclaimed hub makers like CK and I9 state the only reason they didn't use roller clutches is the public being in favor of clicks in their rear hubs and preferring loud hubs over silent ones. It can be argued as to how tight the roller clutch spring in the A11 actually is or needs to be however precise and silent engagement was never an issue with roller clutch freewheel hubs.

Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimano Alfine 11 - Longer term reliability

Postby Brucey » 12 Feb 2020, 1:38pm

Both Rohloff and Alfine hubs are less efficient in the lower gears because both use one additional gear train in the lower half of the gear range; in essence the Rohloff is a 2x7 gear, the Alfine 8 is a 2x4 gear and the Alfine 11 is a 2x6 gear (with one unused ratio). The alfine 11 (like the Nexus 7) has an additional handicap in that the one ratio they have chosen not to use is the direct drive ratio, which means that the average efficiency of the hub is worse than it could be.

It is a bad idea to always shift under load with any IGH because there are always some shifts where there is a sliding clutch which may object. In N8/A8 hubs this is shift 4-5 , N7 hubs 5-6 and A11 hubs it is 6-7. In the shimano hubs the other shifts can usually be made under some load rather than none and this is nothing to do with the roller clutches, rather more to do with the unidirectional loading in each gear train and the way the sun pinions are locked. Indeed the N7 hub has no roller clutches and can be shifted under load as well as a N8 more or less. The N8 hub originally had just one roller clutch, but the current N8/A8 hubs have no less than three, with either one or two in use in any one gear, always two in the lower half of the gear range. In the A11 hub it is worse than that, IIRC you can have three roller clutches in some gears, each contributing its bit of sponge.

In any event the amount of time you spend not pedalling hard during shifting is a tiny fraction of the whole with any hub (or any gearing system cone to that). You need to be travelling extremely slowly for this to genuinely impede your progress in any real way.

If you attach an electric motor drive through the hubs you may measure a certain difference in the efficiency of various hubs but this is pretty much completely bogus; real pedalling is variable torque, not constant, and anything which feels spongy when you pedal (which can include fat tyres, belt drives, certain IGHs, Nu Vinci drives, some framesets etc) is almost certainly soaking up your effort in a bad way. My butt-dyno is pretty sensitive to these things and when climbing or into a strong headwind it feels horribly slow on some hubs and not on others. I think Andrew S may have first raised the issue with me some years ago re roller clutches and since then I have done a lot more miles on various hubs and I have pretty well come round to his way of thinking. [NB I never liked shimano 'silent clutch' freehubs because they also use a similar type of clutch which also feels spongy under high torque. ]

FWIW the Rohloff ain't perfect either; there are signs of sponginess in some (mostly lower) gears. However this arises (I think) mainly through the various parts inside the hub flexing slightly under load, and is nowhere near the sponginess often felt in A11 hubs.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~