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My daughter has a hand-me-down 16" wheel bike, and she finds the pedals very difficult to turn. The bike currently has a single-speed coaster hub on the back. Is there any way to replace the rear hub/wheel with something that has an easier gearing?

I'm aware this could cost more than the bike is worth, but other kid's bikes seem to share this problem. Could it be an issue with chain tension, or are there other ways I could fix this?

side view of bike rear hub driveside view rear hub other side view

  • Great pictures! – David D May 6 '19 at 15:00
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    How old is your daughter? If she's three it may be reasonable that it's difficult, if she's six...less so. – J... May 6 '19 at 15:51
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    First and foremost, make sure the seat height is "correct". It should be lowered to where her feet can touch the ground only long enough for her to gain a "feel" for biking, then the seat should slowly raised to where she can barely touch her toes on the ground. Then, after she gets used to that, raise the seat further, to where her legs are ALMOST all the way extended at the bottom of the pedal stroke (without "rocking" on the seat). – Daniel R Hicks May 6 '19 at 16:03
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    Partly off-topic remark, however I found it useful (tried on my kids) - get rid of the cranks, the chain and the training wheels, lower the saddle a bit, add front caliper brake converting the thing into a balance bike. Your daughter will not experience the difficulty with pedalling and will learn to balance in no time. Then either restore the removed parts (except for the training wheels) or get her a bigger bike. – Mike May 6 '19 at 16:03
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    From the pictures I'd say that the chain is quite taut. Check the middle of the chain and move it up and down in several positions of the crank.. If it moves less than 1 to 1.5cm at the tightest position you'll need to slide the wheel forward. Re-tighten the nuts after correct alignment of the wheel, of course. – Carel May 6 '19 at 19:43
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Children's bikes are usually designed with easy gearing appropriate to children.
As Chris H said - they are not usually assembled by people who care that a bike is assembled correctly. From the factory it seems like everything is always too tight.

My guess is that there is something that can be adjusted to make things better.
Flip the bike over so it's sitting on it's seat and handlebars.
Pedal the bike and see how it feels. This will give you a baseline to know if you've made improvements as you adjust things.

Things that make a bike hard to pedal:

  • You are right to ask about chain tension. If the chain is tight it will be hard to pedal. You may be able to loosen the chain a little and feel an improvement immediately.
  • Rear wheel hub adjustment. With the brake disengaged the wheel should spin freely. If it does not you'll need to loosen the bearings on the hub.
  • Crank bearings. If the chain tension is OK slip the chain off the chain ring and feel how easy the crank is to move. If the crank is stiff you'll need to loosen the crank bearings.

Edit: Adjusting Chain Tension
(When I started writing this I thought it would be a few steps - but it kept getting longer...)

There is the easier way and the slightly harder way to adjust chain tension.

The Easy Way

  1. Remove the nut on the chain side of the wheel that holds the training wheel.
  2. With the training wheel off loosen the nut that holds the wheel on.
  3. At this point you may be able to squeeze the chain and get a little slack in the chain . Since you are only shifting one side of the wheel adjusting this way can put the wheel off center in the frame. That's OK as long as the tire does not rub on the frame. If you are able to get enough slack in the chain to smooth out pedaling without having a tire rubbing on the frame you are done - go to step 4.
    If the tire is rubbing skip step 4 and to "The Slightly Harder Way" step 1.
    Note: if you wanted to tighten the chain pull the right side (right side of the wheel looking at the wheel from the chain side) of the wheel toward you.
  4. Re-assemble in reverse order.

If the tire is too far off center
The Slightly Harder Way (continuing from the previous steps)

  1. Get the chain tension where you want it and tighten the nut that holds the wheel. This will set your chain tension.
  2. Remove the nut that holds the training wheel on the non-chain side.
  3. With the training wheel off loosen the nut that holds the wheel.
  4. At this point you may be able to center the wheel and re-tighten the nut. If the wheel won't center - step 5

Non-Chain Side and Brake Strap
Picture of the non-chain side and the brake strap after the training wheel is removed. 1. Loosen the screw that holds the brake strap (you may need a wrench to hold the nut on the other side of the screw). 2. Center the wheel
3. Tighten the nut that holds the wheel
4. Tighten the screw that holds the brake strap 5. Put the training wheels back on

  • Great advice. I bought a bike like this from Target or wherever, and the handle bar bearings were too loose, crank bearings were too tight and the rear wheel wasn't straight. Fixed all those and added some good lubrication and it was ready to go. – JPhi1618 May 6 '19 at 18:18
  • Sorry for such a basic question but how does one loosen the chain, on a coaster- or hub-geared bike like this. – trr May 7 '19 at 5:42
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    @trr It looks like it might be possible to move the back wheel forwards a bit. If not, then I think the only option would be to add an extra link to the chain! – joeytwiddle May 7 '19 at 5:46
  • @trr I think that's a new question and needs a new post but I'm going to take a stab at putting the instructions in this post. – David D May 7 '19 at 13:54
  • Thanks David actually joeytwiddle's comment pointed me in the right direction but your new image does illustrate it well too – trr May 8 '19 at 2:14
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Easing the chain tension may help, but a coaster brake itself is a good thing - it stops the kid simply back pedalling because it's easy, but doesn't propel the bike. It should be possible to change the cog to get a lower gear ratio, but it tends to be quite low anyway - keep the old cog to restore it later.

I've found the chain case on kids bikes sometimes needs a little adjustment with a file or knife to stop it rubbing on the chainring or chain.

These bikes aren't necessarily assembled by people who know what they're doing (even if you or a previous owner paid for the service). It's possible the hub is too tight, or poorly locked off so that when the axle nuts are done up it gets too tight.

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At least some coaster brake hubs have removable sprockets, so you may be able to replace the sprocket with a larger one. This Park Tool page includes instructions for removing the sprocket.

Find the size of the current sprocket and see if it's possible to buy a larger one before proceeding of course.

With a larger sprocket you will need to move the wheel forward in the horizontal slot dropouts to achieve proper chain tension. If the wheel ends up all the way forward in the dropouts but is still to tight you will need a new chain cut with one extra link. Single speed chain sizing and tensioning can be found in this Park Tool video.

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