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My 4yr old son has a 16in Bikestar and at times he maxes out the gearing on it trying to keep up with his old man. How feasible is it to add either a 2 or 3 speed hub to such a bike? I'm concerned about how much space the hub is going to take up and since I doubt the wheel is a 36h, can one be used with less spokes? I know kids grow out of bikes quickly but he is going to have this bike for a few years for now, and this wheel could be passed down to his sister (right now I'm planning on getting the same brand).

While cruising the flats it seems like his cadence is getting close to the high side while doing 7~8 mph. Any bit of downhill causes him to max out and spin crazy. When he wants to pick up the pace a little will also cause him to spin crazy. We have a few hills along our favorite routes that he struggles on so I can't just swap out the existing gearing. The front chain ring fills the chain guard so that is out of the question as well.

BACKGROUND INFO:

Ok, so I was mostly joking about the keeping up part, I let him lead and set the pace. When he falls behind, I slow down and let him pass, but stubborn kid likes to follow the trailer ...uh princess chariot... too. He also rides this bike daily to daycare and back (2 miles one way).

This bike was picked with commuting in mind. We got him this bike for his 4th birthday and about a few weeks after ditching the training wheels. He just barely fit it then and rides great with it now so we still have some time with it before he gets a new one.

Alternatives won't work as well since who wants to downgrade? He loves having his own bike. A trailer bike would probably not mesh well, he is already trying to attach his sisters trailer to his bike (and I'm tempted to let him). Long distance isn't an issue with him either, his first ride without training wheels on a 12 inch bike was 15 miles and his first ride with this bike was 21 miles. The common "long way" home from daycare is 10 miles itself.

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  • AFAIK it's not feasible, either with an IGH or a derailleur. The IGH would cost the same as the bike, and those wheels look like they have only 20 spokes. A derailleur would not be far off the ground, and would also be $$$. Ride a little slower (up hills?), and find a 20in with gears as the next bike. They do exist!
    – andy256
    Commented Oct 1, 2014 at 4:14
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    A problem with smaller wheels is spoke angle. The large hub causes the spoke to approach the rim at a slant, and the smaller the rim the greater the slant. Unless the rim has angled holes (few do), the spoke nipple will stand straight and the spoke will bend at the nipple. This produces a poor quality wheel that will tend to break spokes quite often.
    – Daniel R Hicks
    Commented Oct 1, 2014 at 11:36
  • According to bicycles.stackexchange.com/questions/21264/… a Sturmey Archer 3sp has a top ratio of 4/3, so it would probably be a lot easier to swap the chainring and/or sprocket to get the same effective ratio.
    – Emyr
    Commented Oct 1, 2014 at 11:47
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    Islabikes produce high-quality bikes in small sizes. They have the Beinn20 which has a Sram drivetrain, 1x7: islabikes.co.uk/bike_pages/beinn20.html Sizechart suggests he might fit a small Beinn20 soon, especially if he's tall, with a minimum 47cm inside leg: islabikes.co.uk/bike_pages/pdfs/sizes/Size_Chart12AW_web-c2.pdf I have a friend who rides a Beinn20 with Brompton bars to suit their Dwarfism.
    – Emyr
    Commented Oct 1, 2014 at 11:52
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    @Criggie, nope, didn't attempt it. I didn't even try it with my second child as well. I have a third that is coming up, so maybe. Anyways, both of my kids so far have only gotten 2 years out of the bike before they outgrew it. When they turned 6, they was able to move to a Islabike Beinn 20L and took to them pretty well.
    – BPugh
    Commented Nov 5, 2018 at 19:06

5 Answers 5

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It's pretty easy if you have a spoke cutter and are willing to run a funny spoke pattern. I suggest buying (ideally second hand) a three speed hub and lacing it into the 16" rim yourself. With a wheel that small and a child on it there's not enough load to make strength an issue, so you can reasonably either lace a 20 spoke rim to a 36 spoke hub using whatever holes are closest, or ignore two spoke holes in the rim and use every second hole in the hub (18/36). It's probably not going to be pretty, but it will work.

However I think you're going about this backwards. Why are you riding faster than he can? Much as you wouldn't suggest stilts so he can keep up when you walk, gears don't address the problem that you can ride faster than him. He doesn't have the power or endurance you do, so without a power assist he's going to be slower.

If you need to cover long distances, perhaps a trailer bike would be a better solution? That way he can "help", and you can go whatever speed you like. That's generally safer for your kids, since you're in control and the only real risk is them jumping off the bike while you're moving.

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  • Yeah, +1 on the trailer bike.
    – Daniel R Hicks
    Commented Oct 2, 2014 at 11:28
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    So the keeping up part was more joke than reality, He leads the way on all the rides, but his cadence is pretty high cruising on flat. Give a little downhill and he maxes out. The main problem is that he burns out quick when he wants to go really fast because he is spinning the hell out of it. Sure he will burn out on a higher gear too but sometimes it is easier to cruise it than maintain a higher RPM in the lower. Trailer bike sounds like a good idea, but he can do 20 miles on this bike, and taking it away and making him ride in the trailer straightens him up right away.
    – BPugh
    Commented Oct 2, 2014 at 14:50
  • Ok, that makes it seem more reasonable. Good luck!
    – Móż
    Commented Oct 2, 2014 at 21:49
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A Brompton uses a 16" wheel size, which means you could get a used Brompton wheel with Sturmey Archer 3-speed hub and swap it out. The only problem is that such wheels are rather expensive even used.

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You could buy a rear wheel from Woom with the Scram automatic 2 speed rear hub. It shifts gears when the hub reaches a certain speed.

I am in the same boat as you trying to modify a 16" bike for my 4 year old

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    Welcome to Bicycles @Chase. We recommend the new members take the tour to make best use of the site. I see some unhelpful person has down voted your answer, without an explanation. Most of us are more friendly than that.
    – andy256
    Commented Nov 3, 2016 at 10:32
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I don't think that its a good idea given that in a few months, you're going to want a 20 inch bicycle for the child. IGH's wouldn't work since the hub width is likely smaller than standard, and mounting a derailleur would be a problem as well. Also, if you were to find a compatible hub or whatever (given the 20 spoke constraint that andy256 mentioned in the comments), you'd be spending quite a bit for building it. You'd also have to run your shifter cables and what not.

What you could do is get something with a 20 inch bike with a low top tube (like a Specialized Hotrock 20) and see if you can get the seat post low enough (possibly by cutting it).

Or, just slow down and let the kid catch up. But I don't think the combination exists out of the box.

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Old thread but why don’t you think the other way and do a “dingle” , put in a double chainring and shift on that rather than the sprocket.... too simple folks.

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  • You've got a good idea there and it is a valid suggestion, and answers OP's underlying need. Welcome to SE! Please do have a browse of the tour to see how things are a wee bit different here.
    – Criggie ♦
    Commented Nov 3, 2018 at 23:47
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    The bike has a full chaincase which is one of the things that attracted myself to it as I bought it for commuting. It uses 1 piece cranks in a child size which I would imagine are not easy to find as a double. Even the better child oriented bike manufactures stick to single rings up front. It also is a step through frame (which was needed) with a oversized downtube so finding a mounting spot for the derailer would be interesting at best.
    – BPugh
    Commented Nov 5, 2018 at 19:22

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