Jim’s Tech Talk
By Jim Langley
“Dummy” hubs are used as a place to park the chain when the rear wheel has been removed. Sometimes they’re called “sleeping hubs” or “chain holders.”
They’re usually comprised of a short axle that’s bolted in place in the right rear dropout of the frame with a built in pulley that sits inboard of the dropout to rest the chain on. With the chain on the pulley it can’t get tangled and it’s more likely to remain on the chainring, too.
Great Accessory for Bike Packing and Drivetrain Care
This makes the dummy hub a nice accessory for packing a bicycle in a box for shipping. But, the most common use is for chain and drivetrain maintenance.
Because the chain can turn on the dummy hub’s pulley, you can pedal just like when the rear wheel is in place. And, since the wheel’s not there, you have far better access to both sides of the chain and derailleur pulleys for cleaning, inspection and lubing.
As far as I have been able to determine, dummy hubs have been around since at least the 1960’s. I would imagine even before they existed, mechanics made their own with actual rear hubs with freewheels in place – something you could still do today by removing one from a ruined wheel, for example.
Or you might instead be able to simply use an old, used through axle for the purpose, an axle set with a quick release to clamp it in the dropouts, or slip a long screwdriver blade through the dropouts if they have holes to receive it. All that’s needed is a through rod to catch and hold the chain.
Home made tools like this can work, but if you get to try a modern dummy hub, I think you’ll enjoy their ease-of-use and having a pulley to hold and spin the chain on as you work.
Park Tool & The Robert Axle Project’s Modern Dummy Hubs
The new versions of dummy hubs I’ve tried come from Park Tool and The Robert Axle Project for $19.95 and $35 respectively.
Unlike older designs that usually had a stationary chain holder, both of these new tools feature a spinning pulley that also slides sideways on their axle. This allows shifting the rear derailleur, which opens the body making cleaning and lubing easier.
Along with being able to see better without the rear wheel in place, dummy hubs ensure that solvents and lubes used on the drivetrain don’t drip onto your wheel or even more importantly, the disc brake rotors.
Park’s DH-1 Dummy Hub is a universal design that works on open (quick-release) and through axle frames up to 12mm. The Robert Axle Project’s Drive Thru Dummy Hub is specifically for through-axle frames and available in the 3 common thread pitches 1.0mm, 1.5mm and 1.75mm, or purchase the Value Meal 3 Pack that includes all three sizes. I think whichever one you choose, you’ll be glad you have it in your toolbox.
Here are company videos about both of these new dummy hubs:
Ride total: 9,548
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.