Fitting a Hub Gear to a Frame With Vertical Dropouts

Frames with vertical droputs present a challenge when fitting a hub gear. Without the ability to move the hub fore-and-aft there is no way to tension the chain. Why is that a big deal? The chain is likely to derail, and when worn it will run on the tips of the teeth, quickly trashing the chainring.

There are several ways to run a hub gear in vertical dropouts:

Use a chain tensioner

You'll lose the simplicity and efficiency of the chain part of the transmission and add to the weight, but maybe you don't mind. I would. For an upgrade, it is tempting to use the existing rear derailleur to tension the chain.

Select a chainring and sprocket that are exactly the right size

That might sound crazy, but the FixMeUp pages enable you to find quite a gear combination that is very close to perfect for your chainstay length. The difficulty is that the chain will wear and become slack. Maybe you could keep putting new chains on, or have several bikes that require chains of different states of wear, or have several sets of chainring and sprocket to use as the chain ages or...

Get a framebuilder to fit horizontal dropouts to your frame

Obviously, this is only practical for a steel frame. It shouldn't cost a fortune, particularly if you were getting it enamelled anyway, or don't mind a DIY paint job on the rear end.

Modify the vertical dropouts

This option is for the stout-hearted. I've done this myself and it worked, but that doesn't guarantee that it will work for you. There are risks involved so don't say you weren't warned, and don't blame me if it goes wrong.

The idea is to remove some metal from in front of and/or behind the axle to allow it some horizontal movement, and a channel is cut in each dropout to take Sturmey-Archer type anti-rotation washers.

Before doing anything to the frame do some planning. Work out how much axle movement you need; a worn-out chain is about 1% longer than a brand new one, maybe 1.5% if you are mean, so a typical bike will need 4mm to 6mm of movement. Ideally that wouly be 2mm to 3mm each way from the current position so use FixMeUp to find a chainring/sprocket combination for a chainstay length 2mm-3mm shorter than it is currently. In a less ideal world you may need to allow more movement in one direction if tyre clearance is tight or if you are determined to use particular chainring/sprocket sizes.

If the hub has anti-rotation washers that engage on one side of the axle, they have to be changed to the both-sides type. You can buy Sturmey-Archer ones as spares, but the hole might not be the right size and will require some filing to make it a snug fit. Make sure you achieve this before attacking the frame!

Mark out the shape of the finished slots, making sure that the slots on the two dropouts are parallel with the other.

The best way to cut the metal would be a milling machine; a Dremel tool could also be used to good effect for the anti-turn channel, but I found simple hand tools were adequate.

Good luck