20” ss to geared conversion. Is this possible?

oaky

I’m looking for some advice. My 7-year-old has a decent Kona 20” wheeled mountain bike. However it’s only a single speed with horizontal dropouts and he now desperately needs/wants gears. For reasons too boring to go into, I don’t want to sell the bike just yet, so am looking to add gears.

I know I can get a Tourney bolt-on derailleur, and the rear hub is both splined and threaded - and currently has a single splined sprocket held on with an external lockring. So my initial thought was that I could simply add a cheap 6-speed screw-on freewheel and it’d be good to go.

However the threaded/splined part of the hub only 20mm wide. So I’m thinking that instead I could break a 6/7/8-speed cassette and use 3 of the sprockets with spacers held on by the external lockring.

Is there any reason why this is a bad idea or wouldn’t work? Is there a better way to do it?

All comments appreciated.

jimothy78

First of all, from what you're describing, it sounds like what you have there is neither a standard freehub wheel, nor a standard screw-on freewheel. Can you take photos, so we can see what you've actually got, plus the name of the bike might help, too? Also, measure the internal spacing between the dropouts so we know what size axle you've got, as this varies a lot on kids bikes.

oaky

The bike is a Kona Shred 2.0 - 2010 I think, the year before they started putting 6-speed gears on them.

Internal spacing is 135mm. I've attached a pic. I know it's a long shot and it's basically just a large single-speed freehub, but even if I can get 3 gears on it, it'd be something.

jimothy78

OK, so it's an unusual freehub designed to take an internally-threaded lockring, instead of the usual externally threaded type.

You're right, you won't be able to fit a whole cassette on, but you can use as many sprockets as you can cram on, assuming that you can fit a mech to suit. (are there any mounting options on the dropouts already?)

This page might be useful - someone doing the same thing to a BMX:
http://faqload.com/faqs/bicycle-compone ... -speed-bmx

oaky

Thanks for the link, it's given me a bit more confidence that I might at least get 3 gears on it.

There's nothing to fix a mech onto, but I've seen some cheap Shimano Tourney mechs with hangers that bolt onto the axel. Just got to find a cheap cassette to split and I'll give it a go.

Thanks for your help.

jimothy78

oaky wrote:

There's nothing to fix a mech onto, but I've seen some cheap Shimano Tourney mechs with hangers that bolt onto the axel.

Do you mean like this?:


You might find it a bit fiddly, as they're designed to be clamped onto dropouts that the axle fits into from 45 degrees below/infront (like the old raleigh and apollo bikes).
In a hortizontal dropout, I think it would rotate the mech too far anticlockwise. You might get away with it, but I think you could do better with chain tugs with a built in derailleur hanger, like this - you'd then be able to fit any standard derailleur:

oaky

That's similar to what I was looking at, didn't realise it wouldn't fit. Thanks. Chain tugs it is then.

jimothy78

Just had a look, and I've got an old 8-sp cassette in garage. Would be happy to split it up and send you some sprockets and spacers for what ever it costs to post them. Available sizes would be: 11,13,15,17,20,23,26,30
Any use to you?
What sizes would you be after?

oaky

Thank you, that's very kind. You've got PM.