chagzuki

I've been trying to figure out why the 3 5 speed SA hubs I've owned all seem to be much less efficient than 3 speed hubs, often feeling very grindy in certain gears or across all gears when pedaling hard. The one's I've used have all been of the ball locking type so I've wondered whether other designs have performed similarly.

All the fine-tuning I've attempted when servicing the hubs hasn't done much to improve upon what seems to be a flaw intrinsic to the design. . . but given that there's not much more in the 5 speeds than there is in the 3 it's hard to see where the inefficiency comes from.

It crossed my mind today that the obvious difference lies in the number of teeth on the planet pinions and the fact that there are smaller sizes. I wish I was more adept with the language of engineering, I can only try to explain this in layman's terms but clearly cogs with a low number of teeth are less efficient due to the exaggerated change of tooth angle through the rotational path. This wouldn't matter so much if the teeth were rounded but SA pinions use non-rounded teeth. So as the small pinions turn the force exerted by the contact areas of teeth are very irregular due to the angular shape. This would seem to account for the fact that the grinding feeling tends to increase in line with pedaling force.

Are are there other reasons/explanations that I'm not seeing?

brokencase

The 3 speeds can be done with a single planetary gear set. As the speeds increase they have to add more planetary gear sets.
The grindyness comes from the fact that the power is going through more gear meshings.

However, Maybe I'm just lucky but I don't notice much grindyness when I am in the higher gears (4-7) on my nexus 7 speed hub.
It's only in the lower gears when I'm climbing a steep grade, so what little efficiency loss there is does not bother me very much since I'm probably standing on the pedals anyway.

The HPVA did a very careful test on derailuers vs. hubs and the efficiency difference is very small, like 1 or 2 percent.
This might mean something to racers, but for casual touring and commuting it is no big deal.

FBinNY 

This is true for hubs with more than 5 speeds, but not true of the classic SA 5 speed hubs made in England. Those used planets where 2 gears shared a pinion, and the range was changed by sliding a stepped sun back and forth, so it is basically a standard 3 speed design, with 2 ranges built into one. In all fairness, I don't know if current hubs from Taiwan share this design.


Internal gear hubs are most efficient at higher rpms and lose efficiency as torque increases. But the overall power loss is amazingly small, and shouldn't be a factor. I can understand that they might feel a bit grindy in your hands, but I've never felt anything like that through the pedals, and that's what counts. Use of a decent machine or gear oil keeps friction reasonable and protects the internals.

All in all, when you consider the long service life of these hubs, you have to conclude that there can't be all that much friction. In my many years of using and servicing SA (UK) hubs I've yet to see one with the sun, pinions or ring gear worn out.

LWaB

The Shimano Nexus 7 hub is a compound epicyclic hub, you are always driving through two epicyclics and there is no direct drive. You can't compare that to the SA hub, where you are only driving through a simple epicyclic or in direct drive, as noted previously.

Wider range epicyclics are slightly less efficient than narrower range. Earlier SA5 hubs didn't use optimal epicyclic tooth profiles for the wider range epicyclic, so they felt much more 'grindy' and were less efficient than could have been the case. The latest model Sunrace SA 5 speeds have good tooth profiles though. The Brompton BWR 3sp hub is effectively the wide range epicyclic of the SA 5sp hub.

Dan Burkhart 

I have 2 ball lock type 5 speeds, one that I've been using for 5 years, and one I've had laying around in a box and just put into service yesterday. I don't notice any grindiness with either of them.
FBinNY, I'm not familiar with any design you describe. These hubs have 2 sun gears that are alternately locked to the axle to give selectable ratios. This is accomplished by means of grooves and ramps in the pin that passes through the axle that pushes ball bearings out to couple the selected sun gear to the shaft, and simultaneously retract the balls from the other sun gear to allow it to free wheel. This is what ball lock refers to.

chagzuki

Strange. . . seems to be just me. One of my hubs is extremely grindy only in 5th gear (irrespective of cable adjustment). I don't understand why that would be given that first gear is fine.

Would it be fair to assume that performance will improve as tooth edges round off slightly? I've been riding one of these hubs for nearly 4 years, it's probably due a servicing in a few months so I'll check the state of the pinions then.

tcs

The SRAM S7 and iMotion9 use single stage gears for every ratio.

The S-A 5(W)s, yes. The Sturmey 8-speed is a very different and unique design.

tcs

The Simano Nexus 7 is single stage in gears 1, 2, 6 and 7 and dual stage compound in gears 3, 4 and 5.

tcs

Well, they actually conclude that...oh, here's the report (beginning on page 3). Anyone interested can read it for themselves.

fietsbob

Have you opened it up? see any worn gears? . grease might just not be getting lube distribution right.

I run Phil Tenacious into my UK AW3, [down the hollow axle hole],
and use [boat trailer bearing] grease on the ball bearings on the axles.