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Why does the Shimano Nexus-7 has such a great friction?

Published: 09 June 2019
Last updated: 26 October 2024

The huge friction problem of Shimano hub gears

What many people don't know is that the Shimano Nexus 7 hub gear require a lot of extra pedaling energy, I have personally experienced this with my Gazelle city bike. On my old city bike with an 3 gear hub, I easily cycle 25kmh, but with the same effort I can't drive faster than 20kmh with my city bike. This is very frustrating. The cause of the high friction is the poor quality of the inside planetary gear. I explain the reason for this in this article.

The Nexus 7 is most notorious for its poor efficiency, so, avoid this hub. The Shimano Nexus 8 and the Alfine 8 also have serious friction but in the most used gears this is less bad than the Nexus 7.

Why does the Shimano Nexus-7 has such a great friction?Why does the Shimano Nexus-7 has such a great friction?

Huge drag Shimano Nexus-7 caused by poor quality casted gear wheelsHuge drag Shimano Nexus-7 caused by poor quality casted gear wheels

Why do you have to pedal so hard?

The power delivered during cycling is often no more than 75 Watt and therefore not much energy should be lost. Everything has to be as efficient as possible. You have to pedal harder if the tires are not inflated hard enough.

Racing bicycles are much more efficient than city bikes, you can easily drive 20 km/h on a racing bicycle without any effort.

To be able to cycle more easily uphill or against the wind, you need a gear. A hub gear has the advantage over a derailleur that it requires less maintenance. But the gear has to run smoothly, otherwise the extra pedaling resistance may be greater than the benefit of the extra gears. The hub gear should therefore be of high quality.

The Nexus-7 planetary low quality gear wheels

To save the manufacturing costs, the gear wheels are cheaply made by casting instead of milling, which is much more accurate. The rough gear wheels are the cause of the great friction. The friction is also force-dependent, if you lift the rear wheel off the ground and turn the pedal by hand, you hardly feel any resistance.

The Shimano Nexus-7 planetary gears have no bearings:

The Shimano Nexus-7 planetary gears have no bearings:The Shimano Nexus-7 planetary gears have no bearings:

Can you reduce the friction of the Shimano Nexus 7 / 8?

In this article I describe how I have tried to reduce the huge friction of the Shimano Nexus 7 hub gear. However it turns out that it doesn't work.
I thought that the thick grease was the cause of the enormous friction, but that doesn't appear to be the main cause. The cause of the friction is the poor quality of the planetary gear stages. That also explains the fact that the friction is very force-dependent, the faster you ride, the higher the friction of the hub.

Lubricating with thin oil doesn't reduce the friction

The Shimano Nexus gears cannot be maintained by lubricating with oil as gears with oil drain plugs such as the Shimano Alfine 8. I have tested whether lubrication with thin oil helps. For this purpose, I drilled a 5 mm lubrication hole, which makes it easy to lubricate the hub from the outside. A piece of good duct tape appears to be sufficient for sealing. However, Lubricating with thin oil doesn't reduce the friction.

Lubricating with thin oil doesn't reduce the friction of the Shimano Nexus 7 / 8Lubricating with thin oil doesn't reduce the friction of the Shimano Nexus 7 / 8

The Shimano Nexus 7 turns your bicycle into a moving home trainer

I call my bicycle a home trainer because the Shimano Nexus 7 absorbs so much energy that you will lose weight twice as fast.

With the Shimano Nexus 7 hub gear you will lose weight twice as fast.With the Shimano Nexus 7 hub gear you will lose weight twice as fast.

The Shimano Nexus gears are lubricated with grease instead of oil.

By the factory, the Shimano Nexus gears are lubricated for life with grease. It is not the intention to be lubricated periodically otherwise they would have an oil drain plug. The grease is syrupy and this may be one of the reasons of the high friction.

I put special Rohloff oil in the gear with the hope that the gear would run smoother, but unfortunately that didn't work in my case.

Drilling the oil drain hole in the Shimano Nexus

Keep the gear clean when drillingKeep the gear clean when drilling

Drilling the oil drain hole in Shimano Nexus 7Drilling the oil drain hole in Shimano Nexus 7

Drilling the oil drain hole in Shimano Nexus 7Drilling the oil drain hole in Shimano Nexus 7

Duct tape is sufficient for sealing.Duct tape is sufficient for sealing

Shimano Nexus-7 internal shifting mechanism how does it work

I thought it was super interesting to know how switching between gears actually works. So, I bought an old Shimano Nexus-7 gear hub and took it apart and filmed how the shifting works. In brief, switching between the gears works by locking or unlocking the one-way clutches of the sun gears.

Hub gears are very complicated and to understand it I found some excellent articles:

Shimano Nexus-7 one way clutch pawls of the sun gearShimano Nexus-7 one way clutch pawls of the sun gearShimano Nexus 7 Rotating shifter sleeveShimano Nexus 7 Rotating shifter sleeve

Shimano Nexus how it works

Mid Drive Kits, Dump the Derailleur and get an IGH
How to Convert a Shimano Alfine 8 Speed Internal Gear Hub to Oil Bath
Shimano Nabenschaltungen im Vergleich
Shimano Nexus/Alfine 3, 4, 7, 8, 11 Speed Hub Technical Information