Tuesday, May 17, 2011

How Internally Geared Hubs Work

Ever wonder just what was going on inside your internally geared hub?

Here are some photos of some the hubs we have recently had the pleasure to tear apart, clean up, overhaul and reassemble.

For starters, here is very quick summary of the function of planetary gearing (that's the magic inside your internally geared hub). For the sake of simplicity, there are three main components to gearing of 3 speed hubs: the driver, which is attached to the sprocket, the planet cage, which houses the planet gears, they use the stationary sun gear fixed to the axle the increase their rotational rate and interact with the third main part, the gear ring. This all just means that the sun gear is held stationary in relation to the bike and as the planet gears revolve around they rotate faster individually than the planet cage does as a whole which in turn causes the gear ring to rotate faster than the planet cage. Both the planet cage and the gear ring have pawls which can drive the hub body and allow for coasting.

So, if you want your hub to spin slower than the sprocket (low gear) you have the sprocket drive the gear ring while the planet cage drives the hub. If you want your hub to spin at the same rate as the sprocket (middle gear, or direct drive) you have the sprocket drive the gear ring which then also drives the hub. If you want your hub to spin faster than the sprocket (high gear) you have the sprocket drive the planet cage while the gear ring drives the hub. Simple! Want more speeds? Add more sun gears and/or planet gears in a similar manner and you get more than 3 gears. These changes inside the hub occur when you use your shifter to position the clutch which sets up whether the driver interacts with the planet cage or the gear ring and you never even need to think about it. On to the photos...

We begin with the classic. The Sturmey Archer AW for use with rim brakes. This one happens to be from 1959 and it still runs smooth.
These hubs are fairly easy to disassemble completely for servicing. replacement parts are available.

Now for one of Sturmey's current offerings. The new X-RD5(W). Its a 5 speed hub with a drum brake.

You may notice how many fewer parts there are in the X-RD5(w) than in the AW. This is representative of the new standard for internally geared hubs; modular design where many of the main components are meant to be broken down only so far (that, and we didn't photograph the drum brake, sprocket, axle nuts, etc.). This makes servicing simpler and eliminates the possibility of installing parts in incorrect positions. On the flip side, you also need to replace entire components groups, and often the entire internal assembly, if one small part wears out or gets damaged.

Shimano has been making internally geared hubs for decades and this is one of their newer models. The SG-3D55. It's a 3 speed hub with a disc brake.As in the newer Sturmey Archer hubs, Shimano has simplified things with modular design. If you look closely you can see that some of these parts are rusted out from a harsh Minnesota winter. Though these hubs are relatively low maintenance, if ridden in extreme conditions, moisture can work its way into the hub where it will wreak havoc on the assembly. A new internal assembly and now it's ready for many more miles of happy riding.

Another of Shimano's internally geared hub offerings is the very popular Nexus 7 speed. This one is the SG-7R40, set up for use with a roller brake (not pictured).

As with most internally geared hubs, very little is recommended in the way of maintenance. Get your hub cones adjusted well and properly set up your cassette joint and shift cable, then ride. That being said, don't ignore your hub. You can have the internal assembly removed, cleaned and re-lubed to keep things running smoothly and to avoid unnecessary wear to the expensive parts inside.

Last, but not least, we've got another new hub, this one from Sram. It's the S7, this one has a coaster brake, and it is by far the most complicated hub out of this bunch...

The operation of this hub is just as smooth and simple as the Shimano offerings. Sram uses a modular design as well, but many of the sub assemblies can be broken down to their smallest parts. In practice there is no need to ever take one of these apart to such a degree.

If you are interested in learning more about internally geared hubs, and the bikes they are available on, then stop into our Minnehaha shop. You can test ride bikes with different types of hubs or talk to our service staff about one that you are already riding.

Monday, May 9, 2011

Look for The Hub at this years North-side Bike Fests

The Hub will again be providing mechanical support for the 2011 North side bike festival events. The events will be packed with bicycle-fun for both kids and adults. Below are the times and dates. Hope to see you there!

Saturday May 21 is the big kick-off to the summer; this event will take place at the Special Operations Center on 41st and Dupont in North Minneapolis. We will be staged across the street at the Salem Lutheran Church Parking Lot from 10am - 2pm.

Other event dates include:

Thursday, May 26 Harrison Park 503 Irving Ave. N 4 - 7pm
Thursday, June 2 Creekview Park 5001 Humboldt Ave. N 4 - 7pm
Thursday, June 16 North Commons Park 1801 James Ave. N 4 - 7pm
Thursday, June 23 Farview Park 621 29th Ave. N 4 - 7pm
Thursday, June 30 Glen Gale 2448 Ilion Ave. N 4 - 7pm

The Hub at Last years Festival