From Sheldon Brown's web site:
The four- and five-speed versions have two sun gears, which can slide back and forth, so that one of them is locked to the axle, while the other freewheels. The planet gears are stepped gears, with different numbers of teeth at each end. The large end of the planet gears engages the small sun gear, and the small end of the planet gears engages the large sun gear and the gear ring.
Depending on which sun gear is locked to the axle, these hubs are, effectively 3-speeds with a choice of wide or narrow range.
Per the SRAM parts manual this is also how the SRAM 5 speed hub appears to work judging from parts drawings. The 7 speed is the same except that it uses 3 step planet gears and 3 sun gears that can each be locked to the axle via the control shaft.
--- In Geared_hub_bikes@yahoogroups.com, "astronut1001" <astronut1001@...> wrote:
> Warren brings up a interesting question here about cascading of IGH Planetary gear sets in hubs with more than 3 speeds. Per reading I know this is done in the Rohloff and, I presume in other >7 speed hubs. Also I believe that it is done in the Shimano 7 speed which has no direct drive gear.
> Per my understanding though at least in SRAM 5 and 7 speed hubs, and presumably SA 5 speeds, only one planetary gear set is actually used at a time. The 5 or 7 speeds are obtained by choosing which of the two (5 speed) or three (7 speed) planetary gear sets is used and the direction of drive through each. This is the reason why it is the middle gear on these hubs which is the direct drive ratio. Any difference in efficiency during indirect drive use using the planetary gear sets should then be dependent more on the size and rotation rate of the planet gears being used in a given selected ratio rather than the use of multiple sets simultaneously.
> Also worry about additional losses in high gear count IGH hubs seems to me to be a minor point as the increased rider efficiency allowed by having the "right" gear selected should more than make up for any minor hub losses.
> OK true experts out there lets have your thoughts. Do I have it right or am I mistaken about SA and SRAM 5 and 7 speed hubs operation principles.
> Rich Wood
> --- In Geared_hub_bikes@yahoogroups.com, Rich Wood <astronut1001@> wrote:
> > I received this as an email and am forwarding it to the group for some ideas and thoughts for Warren.
> > Rich Wood
> > --- On Fri, 9/4/09, Electrify Me <electrifyme321@> wrote:
> > > From: Electrify Me <electrifyme321@>
> > > Subject: Re: File - Member Welcome
> > > To: "Geared_hub_bikes Moderator" <Geared_hub_bikesfirstname.lastname@example.org>
> > > Date: Friday, September 4, 2009, 10:13 AM
> > > I
> > > understand that Sturmy Archer is considered a quality hub
> > > manufacturer.
> > > I have never had problems with my Shimano 333. I only
> > > weigh 137lbs so
> > > I am not allot of dead weight on a bike. I
> > > wish to buy a modern-day multi-
> > > speed hub that internally runs only one planetary gear
> > > set at a time. It is my
> > > understanding that once you go beyond 3 speeds, they
> > > run one planetary
> > > gear with another resulting in reduced efficiency in
> > > some of the gear ratios.
> > > I have caliper brakes on front and rear. Shimano made
> > > their 8 speed hub
> > > quiet by changing how they transfer
> > > the power I believe. Which 3 speed is
> > > the most efficient? I plan to strip my Shimano of
> > > the grease and will try to use
> > > oil instead to reduce friction.
> > >
> > > Additionally for a 26 1x 3/8" tire I have a
> > > choice so far of a Sun Rim or a
> > > Weigman 440grams (looking at Sheldon Brown's
> > > Harris Cyclery) site. Can
> > > you recommend a lightweight 36 spoke rim that is
> > > inexpensive but is well built?
> > > I prefer not to go over $50 per rim.
> > >
> > > Could you recommend an inexpensive 36 spoke front
> > > hub to go with the
> > > multi-speed hub you recommend and do you have any
> > > thoughts on lightweight
> > > but strong/sturdy spokes?
> > >
> > > Regards,
> > > Warren
> > >