Internal-Gear Hubs
Work in progress -- material on each type of
hub is being moved to separate files.
This work is now complete for Sturmey-Archer
hubs and some Shimano hubs.
General remarks | How it works | Lubrication | Chain adjustment | Anti-rotation
Setting gear range with: 3 speeds, 5 through 8 speeds, 9 or more speeds
Hybrid gearing
Information on specific brands and models
General remarks
Since the first decade of the 20th century, internal-gear hubs, usually 3-speeds, have offered a practical, reliable gear-shifting option to the cyclist. With the popularity of derailer gears taking off in the early 1970's bike boom, internal-gear hubs went out of style in most US markets. This is unfortunate, because many casual or utilitarian cyclists are best served by this type of gearing.
Internal-gear hubs are more reliable than derailer systems, and require much less maintenance. The step-up ratios of their top gears make oversize chainrings unnecessary on small-wheel folding bicycles. Unlike derailers, internal hubs shift even at a stop, very nice in stop-and-go urban traffic.
Internal-gear hubs tend to be heavier than derailer systems, and are slightly less efficient in some gears. The direct-drive middle gear can be more efficient, as there is no drag from derailer pulleys. Most internal-gear hubs cannot have a quick-release axle.
If you are interested in old bikes, or the history of this sort of gearing, refer to my page on English Three Speeds.
How an internal-gear hub works
Internal-geared hubs work on the principle of "planetary gearing."
The basic 3-speed hubs have a single "sun" gear solidly attached to the middle of the axle. 3 or 4 identical "planet" gears mesh with and revolve around the "sun" gear. The "planet" gears are surrounded by (and mesh with) a"gear ring" with its teeth on the inside (an inside-out gear).
As the planet gears, attached to a part called a "planet cage" revolve, the gear ring revolves 4 times for every 3 times the planet cage goes around. (Some models have different ratios.)
- Low Gear has the sprocket driving the gear ring, while the planet cage drives the hub. Thus, the wheel turns 3 times for every 4 revolutions of the sprocket, lowering the gear by 25%.
- Middle Gear has the sprocket still driving the gear ring, but has the gear ring drive the hub. Thus, the drive is direct. Although the internal gears are always rotating when the sprocket is in motion, they don't have any effect on the drive in middle gear.
- High Gear shifts the sprocket's drive to the planet cage, while the gear ring continues to drive the hub shell. Thus, the hub turns around 4 times for every 3 sprocket revolutions, giving a 33% gear increase.
There is a more detailed explanation of this on the Sturmey-Archer Web site, from which I lifted the image above.
Hubs with more than three speeds use two or three planetary stages, and/or compound (stepped) planet gears with two or more sets of teeth.
In the late 1990's, internal gears underwent something of a renaissance, with the development of wide-range 7-speed hubs. Progress has continued since. Four different brands are currently available, with as many as 14 speeds. Three-speeds and five-speeds are still currently in production, and they offer an economical, practical alternative.
[Next three sections are by John Allen.]
Lubrication
Most newer internal-gear hubs are grease-lubricated. They require periodic cleaning and replenishment of a special grease that does not make the pawls stick. Some Shimano hubs have roller clutches and are supposed to require an even more special lubricant. Shimano sells an expensive relubrication kit, though bicycle mechanics are reporting success with automatic transmission fluid.
Some hubs with coaster brakes require two different types of grease, a special high-temperature grease for the brake shoes and another grease for the rest of the mechanism.
Older internal-gear hubs have an oil fitting on the shell. Oil lubrication is desirable for an internal-gear hub, because oil generates less drag than grease, and washes wear particles and dirt out of the mechanism. Don't overdo it. Use a light machine oil, not a spray lube or other thin oil. Oil can accumulate on the hub shell, and can become a bit messy. If used to excess, it can run down the spokes onto the rim and make a rim brake squeal and grab. If a drum brake is not well-enough isolated from the gear mechanism, oil could contaminate it too.
When rebuilding an oil-lubricated hub, grease the bearings to help keep dirt and water out and oil in. Tan, soap-based grease is best for this; the oil will wash out petroleum-based grease. Keep grease out of the rest of the mechanism, so it doesn't make the pawls stick.
Among current hubs, the Rohloff Speedhub and the announced Shimano 11-speed are oil-lubricated. Any internal-gear hub with a hollow axle may be oiled by removing the pushrod or indicator spindle and squirting oil into the end of the axle. Convert from grease to oil when rebuilding a hub, so it gets a clean start. If you are a fanatic about oil lubrication, you could even install a Sturmey-Archer oil cap. Tools: #3 (or 5.5 mm) drill and a 1/4 inch 28 TPI tap.
Adjusting the chain
Internal-gear hubs typically use a single sprocket and single chainwheel. The chain is held in place by moving the hub's axle forward or backward in the dropout slots until the chain is just barely slack. A bicycle with vertical dropouts must have an eccentric bottom bracket, or a chain tensioner must be installed.
As the chain wears, it lengthens, and it is more likely to fall off. It must be readjusted periodically. Technique for chain adjustment is described in the article on fixed-gear bicycles.
Anti-rotation
The axle is part of the gear train of an internal-gear hub. You can check this out for yourself. If you hold the hub shell or rim when the hub is not installed on the bicycle and turn the sprocket, the axle also turns -- backwards if the hub's drive ratio is lower than 1:1, forwards if higher.
Special anti-rotation washers keep the axle from turning when the wheel is installed on the bicycle. These washers engage flat surfaces on the axle, and have tabs that fit into the dropout slots. Different washers fit different models of hubs and dropout slot widths. Many newer hubs attach the shifter cable to a pulley that rotates around the hub's axle, between the right dropout and the sprocket. Depending on whether a bicycle has horizontal, vertical or reversed (track) dropouts, different washers are needed so the shift cable can approach from the front of the bicycle. Follow the instructions for each hub.
A hub brake of any kind also must resist rotation. Most brakes on internal-gear hubs use a reaction arm for this purpose. It is usually separate from the anti-rotation washer(s) for the gearing. You must install them too. The Rohloff hub has such a wide gear range that some models use a reaction arm instead of anti-rotation washers.
On a bicycle with rear suspension, the suspension's pivot is usually ahead of the rear hub. Because it tries to rotate the hub's axle, an internal-gear hub lifts the rear end of the bicycle, reducing "pogo sticking" in gears below 1:1; the opposite in gears above 1:1.Pogo-sticking reduces pedaling efficiency, to a degree which depends on the design of the suspension.
Selecting sprockets and chainwheels
By selecting an appropriate-sized sprocket and chainwheel, the overall range of any internal-gear hub can be raised or lowered by any desired amount. Most current internal-gear hubs take 3-splined sprockets, interchangeable among brands. These sprockets are available from various sources from 13-24 teeth, though some hubs can't accept the smallest sprockets.
Many of these sprockets are made for 1/8" chain -- wider than the chain used with derailer gearing. This chain can be used with narrow chainwheels made for use with derailers, though special track chainwheels have taller teeth, and allow the chain to become looser before it could fall off.
The sprocket is held in position by a spring circlip (snap ring). The circlip can be pried off with a thin flat-blade screwdriver, and the sprocket can then be lifted off. Most sprockets made for this system are "dished" so you can adjust the chainline by flipping the sprocket over. The circlip snaps on, also most easily by levering it into position with a flat-blade screwdriver.
After re-installing the sprocket, it is a good idea to seat the circlip by going around it and tapping it lightly with a hammer and punch. This is especially important on coaster brakes, because the brake will fail if the sprocket slips off.
It is also fairly easy to modify any Shimano cassette sprocket that doesn't have a built-in spacer. These are available from 14-34 teeth. Shimano cassette sprockets have the same internal diameter as those used with internal gear hubs, but have 9 splines instead of 3. With a suitable grinder, 6 of the splines need to be removed, and the corners of the remaining three rounded off. A thin spacer washer may also be needed, because the cassette sprockets are a bit thinner than the stock sprockets.
[following sections are by John Allen]
You may also adjust the gear range by changing the chainwheel, though that is usually more expensive than changing the sprocket.
If you install a larger sprocket or chainwheel, you also will need a longer chain.
Go to Sheldon's Gear Calculator to scope out the possibilities. John Allen's table of internal-gear hub ratios allows you compare ratios of the different hubs.
Three-speeds
All current three-speeds except for the Sturmey-Archer S3X fixed-gear hub have a wide range, with big steps between all of the gears. The way bicycle manufacturers commonly set up three-speeds, the top gear is not so high as to be completely useless, but then the middle gear is too low for level-ground riding. A 3-speed hub will serve you much better if you install a larger rear sprocket or smaller chainwheel, so the top gear is optimized for level terrain. The low and middle gears are then better for acceleration and climbing.
If you spin out on downhills, then you can coast. Sheldon disparaged coasting, but really, occasional coasting is better than struggling up hills and having no level-ground gear! The top gear with a 3-speed should be in the range between 70 and 80 gear inches (5.6 and 6.4 meters development, 5.0 to 6.0 gain ratio), depending on your strength and pedaling style -- say, a 46-tooth chainring and 22-tooth sprocket with a 26-inch rear wheel. If the terrain where you ride is all up and down, with little or no level ground, you may want even lower gears than that. Clip-in pedals or toeclips and straps (practical only without a coaster brake) help you pedal at a higher cadence, so your power range is wider -- an advantage on any bicycle but more so on one with big steps between gears.
5 through 8 speeds
An internal-gear hub with 5 through 8 speeds generally works best if your level-ground gear is the second-highest gear is, around 70 gear inches (5.6 meters development, 5.0 gain ratio, more or less depending on your strength and pedaling style). You will then have one higher gear for downhill riding or tailwinds. If you ride where there are no steep climbs, you may want the third-highest gear of a 7 or 8-speed hub to be the level-ground gear, so you don't spin out when you have a strong tailwind. All current 5-speed hubs have enough range for smart acceleration in urban riding. Hubs with 7 or 8 speeds also offer lower gears for climbing, and generally, smaller steps between gears.
9 or more speeds
If a hub has 9 or more speeds, you generally want to the level-ground gear to be the third-highest. Again, as with the hubs with fewer speeds, this depends on terrain.
Hybrid gearing
Hybrid gearing uses an internal-gear hub along with derailer gearing. With any freewheeling internal-gear hub, you can have hybrid gearing using double or triple chainwheels You must then also use a spring-loaded chain tensioner, or a rear derailer without a cable. In this way, you get to enjoy the quick shifting of the internal-gear hub in a city such as San Francisco, and also have "bail-out" gears. Some hubs have splines wide enough that you could install two modified cassette sprockets and shift them with a rear derailer. 13 and 15 teeth or 18 and 21 teeth split the wide steps of a three-speed nicely in half. Use narrow chain, and sprockets made for it.
Sturmey-Archer and SRAM make 3-speed hubs with splines for an 8- or 9-sprocket cassette. These are especially useful on bicycles which can't take a front derailer and on small-wheel bicycles, where the step-up top gear of the 3-speed hub avoids the need for an oversized chainwheel.
The stock cassettes sold with SRAM hybrid-gearing systems work OK, but I like other combinations better. The 8-speed progression 11-13-15-17-19-21-24-28 works particularly well with a small wheel, and is achievable using the Shimano M 7-speed cassette by adding an 11-tooth sprocket at the outside. The Shimano H 7-speed cassette, 13-15-17-19-21-23-26, with a 30-tooth cog added at the inside, allows a more normal-sized chainwheel on a bicycle with larger wheels, and gives a smoother progression with the Sturmey-Archer hubs, which have slightly narrower steps. In either case, you should replace the 7-speed spacers with 8-speed spacers, for better indexing. You need an 8-speed chain -- and an 8-speed shifter and/or alternate cable routing. You may have to grind off the rivets that hold some of the cassette sprockets together to replace the cassette's spacers. With either of these combinations, you use all 8 cogs with the hub in its most efficient, direct-drive middle gear.
A good 9-speed combination is 13-15-17-19-21-23-25-28-32. With any of these cassettes, choose the chainwheel so the highest gear with the hub in its 1:1 direct drive ratio is around 75 inches (6.0 meters development, 5.5 gain ratio), or a bit higher if you ride in flatlands with strong tailwinds. Shifting the hub to the low or high gear gives you two additional gears at the top and bottom of the range.
Some internal-gear hubs are not rated for the stresses from extremely-steep climbs and a heavy load, a potential problem with do-it-yourself hybrid gearing. Usually, manufacturers rate hubs in terms of the acceptable chainwheel/sprocket ratio, but this rating really amounts only to "we will make it so hard to pedal that you will get off and walk." Pushing a lower gear up the same hill actually stresses the hub less. A small rear wheel and smooth pedaling reduce stress on the hub.
Shimano Nexus 4-speed hub (discontinued)
The overall range is 184%, in jumps of:
| 1st | 24.0% | 2nd | 21.0% | 3rd | 22.7% | 4th |
|---|
This hub only gears up. The lowest gear is 1:1, direct drive.
For that reason, this hub is especially suitable for a small-wheel bicycle.
As this hub is discontinued, rebuilding may require cannibalizing another hub.
For specific gear info, use my Online Internal Gear Calculator
See also Shimano user instructions
New! Shimano Nexus (and Alfine) 8-speed hub
The overall range is 307%, in jumps of:
| 1st | 22.2% | 2nd | 16.1% | 3rd | 13.8% | 4th | 17.5% | 5th | 22.3% | 6th | 16.0% | 7th | 13.8% | 8th
|
|---|
For specific gear info, use my Online Internal Gear Calculator or see the Harris Cyclery page on this model
See also the Online Nexus 8 Service Manual
Eagerly anticipated, but not yet available
SRAM Spectro 7-speed Hub (Current version)
The current version has an overall range is 303% in jumps of:
| 1st | 19.3% | 2nd | 20.2% | 3rd | 22.9% | 4th | 22.7% | 5th | 20.3% | 6th | 17.5% | 7th
|
|---|
This chart shows "fractional" sprocket sizes corresponding to different hub gears.
For specific gear info, use my Online Internal Gear Calculator
See also SRAM online manuals
SRAM/Sachs 7-speed Hub (Old version, discontinued)
The overall range is 284% in jumps of:
| 1st | 14.0% | 2nd | 20.2% | 3rd | 22.9% | 4th | 22.7% | 5th | 20.3% | 6th | 14.1% | 7th
|
|---|
For specific gear info, use my Online Internal Gear Calculator
SRAM i-Motion 9-speed Hub
[Sheldon did not get around to writing a page about the SRAM 9-speed , but he
installed it on one of his bikes and wrote about it here,
You may look up the gear ratios in his Online Internal Gear Calculator- John Allen]
See also SRAM online manuals, which provide good information on installation and rebuilding.
SRAM/Sachs Elan 12-speed Hub
Note: This hub has been discontinued
and is no longer supported by the manufacturer.
The overall range is 345% in jumps of:
| 1st | 23.1% | 2nd | 17.7% | 3rd | 18% | 4th | 12.7% | 5th | 12.0% | 6th | 8.0% | 7th
|
|---|
| 6th | 8.0% | 7th | 8.7% | 8th | 9.7% | 9th | 8.3% | 10th | 6.7% | 11th | 7.2% | 12th
|
|---|
This chart shows "fractional" sprocket sizes corresponding to different hub gears.
For specific gear info, use my Online Internal Gear Calculator
Rohloff Speedhub 14 Speed
The current "state of the art" in internal-gear hubs is the astonishing 14 speed Rohloff Speedhub. This is truly a triumph of Teutonic technology!
This hub has even 13.6% steps between each of the
14 gears - the ratios are, according to the handbook:-
0.279, 0.316, 0.36, 0.409, 0.464, 0.528, 0.6, 0.682,
0.774, 0.881, 1, 1.135, 1.292, 1.467.
It comes with a 16t cog, but 15 and 17 are available.
Thanks to Matt Dekker for providing the data on the Sturmey-Archer Sprinter.
If you would like to make a link or bookmark to this page, the URL is:
http://sheldonbrown.com/internal-gears.html
Last Updated:
by John Allen