Changing hub to derailleur system.

[Andy in Germany]

I've mentioned before that I'm working on a new bike for Beautiful Daughter, seen here:

You will notice that this bike, apart from being as pink as a pink bike could possibly be, currently has a hub gear system, also has a dropper for a derailleur system.

We live in a hilly area, and our 3 boys went off cycling when they used a hub gear bike; the three gears don't help much with our hills, and anyway the friction from the hub rather cancelled the advantages in any case. I have been wondering what is required to change to a derailleur geared bike.. As far as I can tell I'd need:

New rear wheel
Rear Derailleur
Shifter of some kind
New chain
New chainwheel (?)

Bear in mind I work in a shop refurbishing used bikes the parts shouldn't be too much trouble, except possibly the chain wheel, so I've got a few questions:

How feasible is this conversion generally? I never converted hub-derailleur before. Has anyone else tried?
Is there something I'm not thinking of; bikes throw up nasty surprises; would a normal rear mech really fit on such a small wheel?
Do I need to change the chain wheel? I suspect so because single speed chains are wider than derailleur gears chains.
How many gears? Eight would be simple because it's easy to get parts, but is there a good reason for using seven or even six?

 

[Ian H]

New hub. Etcetera. Measure the drop-out width first, to determine what width of cassette will fit (might be narrower being a small bike).

I wonder whether it would be possible to fit a screw-on freewheel block of, say, 6-speed to the current hub (you'd have to dish the wheel), to give 3x6 gears. Just an idea.

 

[Cycleops]

If you're feeling brave you could lace a freewheel hub onto that rim. As Ian says you need to measure the drop out width. Given the free availability of rear wheels available to you might not be worth the trouble. The frame has a hanger so was obviously an option on some models so should be fine.
24" wheels?

 

[chriswoody]

Seems like a lot of work to me and with those small wheels the Derailleur will be hanging close to the ground and quite susceptible to damage. You'll need a new hub/wheel with the conversion and I don't know how much trouble you'd have fitting one in between the dropouts, measuring the space you have between them would be high on my list of first jobs.

I would be more tempted to have a hunt through your scrap pile and look into swapping the 3 speed hub for a 7 speed, maybe the increased range would be more suitable? I know Puky fahrräder have Shimano Nexus 7 hubs for example, that might well be the same OLD as the 3 speed hub you have?

 

[MichaelW2]

Hub gears run on wide singlespeed chains and normal width 8spd chains. I have used both on my hub gear and cant tell the difference.

 

[Andy in Germany]

Many thanks for the replies...

I'm not brave enough to put a block on that hub, and from experience the hubs are generally not suitable for what we as a family need: they're fine for playing and riding 1k to friends, but Beautiful Daughter has ambitions of riding 40k+. She's managed 35k with some assistance on her current 18" wheeled single speed so it's far from impossible, but it means a complete swap would be the goal.

I can get a new rear wheel with a freewheel or freehub attachment for about 35 €. For that price I think it's worth it for the time saved lacing the existing wheel anyway. Freehub feels a bit like overkill though.

As you say, measuring the rear forks will be the first step. If this looks feasible, I may leave it for now so Beautiful Daughter has a bike ASAP, then get the parts together and replace the rear wheel etc later...

 

[chris667]

Yes, wrong time of year for that job! Get this one dirty in the bad weather then replace with a derraileur when the weather gets nicer.

IIRC that Nexus 3spd hub is 127mm oln, so a 6 speed freewheel hub.

Might need to get rid of the chainguard though? Will need measuring.

 

[Andy in Germany]

Yes, wrong time of year for that job! Get this one dirty in the bad weather then replace with a derraileur when the weather gets nicer.

IIRC that Nexus 3spd hub is 127mm oln, so a 6 speed freewheel hub.

Might need to get rid of the chainguard though? Will need measuring.

Useful information there, thanks.

And the point about the time of year is taken; it also spreads the cost a bit.

 

[Dogtrousers]

As an aside I wonder whether the reason why there is a derailleur attachment on that frame is because it was made with a standard dropout that was cheaply available, rather than because the manufacturer intended it to be used that way.

 

[Andy in Germany]

As an aside I wonder whether the reason why there is a derailleur attachment on that frame is because it was made with a standard dropout that was cheaply available, rather than because the manufacturer intended it to be used that way.

Its an interesting thought. I just looked on the manufacturers website and their current model (600 €, thank goodness I work in a bike shop) doesn't have this, neither does a near identical model in my storeroom from either a year before or after. The bike in the storeroom doesn't have rear V-Brakes either which is one reason this one is getting restored for Beautiful Daughter.

 

[Reynard]

Mmmm, if that bike's got 24 inch wheels, then the clearance for derailleur should be OK tbh, especially if the bike isn't being taken on anything terribly gnarly.

 

[Andy in Germany]

Mmmm, if that bike's got 24 inch wheels, then the clearance for derailleur should be OK tbh, especially if the bike isn't being taken on anything terribly gnarly.

They're 20"

 

[Reynard]

They're 20"

Ah, ok...

I got decent clearance on my 24" wheeled bike. Guess with 20", it'll probably be a "stick it on and see how it fits" kind of thing...

 

[chriswoody]

Andy, another thought, have you got any folding bikes in your pile? Plenty of 20 inch folders have 6 or 7 speed derailleur setup's. I see a few cheap and cheerful folders set up like this on my train each morning, so there must be some knocking around unwanted.

I don't know the width of the drop outs on a 7 speed folder, but if your lucky maybe the wheel and parts would be a direct transplant.