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The Shimano Nexus System

by Sheldon "Totally Enclosed" Brown

Planetary Gears Are Back!

Did You Ever Have A Three-Speed?

Do you remember how easily it shifted, even when you were stopped for a traffic light?

Do you remember how trouble-free it was?

Do you remember how the chain never fell off?

Do you remember how weather-proof the gear system was?

Do you remember how comfortable it was?

But...

You also probably remember the narrow range of gears, and the big jumps in between.

You probably remember the gap between gears, where your feet would spin freely, with no result.

You probably also remember how heavy your old "all steel" bicycle was,

and how badly the brakes worked in the rain...

The Good Without The Bad!

The Shimano Nexus group combines the best features of your old 3 speed, and eliminates the worst, thanks to modern materials and technology.

Nexus is a family of parts, but the most exciting part is the Nexus Inter 7 seven speed hub.

Shimano Nexus 7-speed hub

New! On-line Gear Calculator for Internally-Geared Hubs

The overall range is 244%, in jumps of:

For comparison, your old 3-speed had a range of 177%, in jumps of:

A typical 1970's "10 speed" had 8 usable gears, a range of 247%:

Other features of the Nexus system:

Nexus 7-speed internal gear systems also incorporate all-weather braking systems. They are available in two forms:

• Coaster (back-pedaling) brake

  or

• Hand operated "Rollerbrake ®" at the rear hub.

Both of these systems provide quite a good rear brake, which works as well in rain and snow as it does on a sunny spring afternoon.

There is also a front roller brake available, but, in my opinion, a conventional cantilever brake is better for the front. I would not particularly recommend the Nexus front brake.

Nexus Technical Page

Gear Adjustment:

The adjustment is made witht the shifter in 4th (middle) gear. On the right side of the hub, just outboard of the sprocket, there is a "cassette joint pulley" which the cable moves back and forth as the gears are changed. Next to this is the "cassette joint bracket" which is stationary. Both the pulley and the bracket have red index marks, and gear adjustment is correct when the marks on the two parts align with the shifter in 4th gear.

There are two sets of these red marks, one on top, the other on the bottom. This lets you see one set of marks whether the bike is right side up or upside down.

Click here for more technical info on the Nexus hubs.

Converting an Existing Bicycle:

In some cases, it is possible to convert an existing bicycle to the use of a Nexus hub. I have a very nice 1970's Raleight Competition racin frame which I have converted into a Nexus 7-speed.

Sheldon Brown's Nexus Raleigh Competition

Ideally, frames for use with the Nexus system should have horizontal drop outs. Bikes with vertical drop outs don't provide any way to adjust the chain tension, so you would need to install a chain tensioner (or a rear derailer) to regulate the chain tension.

If your bike has vertical dropouts, you need to order a special set of anti-rotation washers designed for vertical dropouts, or the cable routing will be incorrect.

Ideally, the frame should to have a drop-out spacing of 130 mm. Older bicycles are typically narrower than that. In the case of steel (Cromoly) frames, it is usually possible to spread the rear triangle to the needed 130 mm width. Any good bicycle mechanic will be able to do this, or you can do it yourself. If you leave off the Rollerbrake and use a thinner cone lockwasher on the left side, you can re-space a Nexus 7- or 8-speed hub to about 126 mm. Similarly, if your frame is made for 135 mm spacing, you can add spacers to the axle to fill in the gap.