Gaza

Hopefully I'm posting this in the correct forum.

My son has a Trek Jet 20 single speed bike. After many failed attempts he managed to ride without stabilisers a couple of weeks ago and is now charging about like he has been riding for years.

The only issue he has is tackling inclines. He struggles with all but the smallest. He is a big strong lad (5.5 years old and 125 cm tall) and plays mini rugby and skis so it shouldn't come down to strength.

We were possibly a little shortsighted last year in buying a bike without gears but as it is likely to last him a couple of years more I'm considering retrofitting gears. I'm reasonably technically/mechanically minded so could tackle the job myself if it is not too difficult. The questions I have are:-

1. Is it an easy job for an amatuer?
2. What parts would I need to fit a 7/8/9 speed gears set?
3. Would I only fit a rear derailleur?
4. Is it cost efective?
5. Do I need special tools?

bikemig 

There is a lot to be said for single speed bikes and kids. The bikes are tough and the kid focuses on just riding and having fun.

cny-bikeman

5 1/2 years old is too young for a derailleur equipped bike, primarily due to the issue of hand brakes. Aside from the problem of him trying to brake with his feet, a child of that age does not have the strength, coordination and understanding of how to brake to enable safe usage of hand brakes. The correct solution would be a wheel with internal gear hub and coaster brake, but that will be expensive if you can even find one - perhaps a Dahon dealer. One option would be sourcing a used coaster brake 3 speed hub from which to build a wheel, but again that is not an easy task

HillRider

1. No, not unless you are well versed in bike mechanics. This a major project. the bike wasn't designed for multiple gears and the frame spacing won't accept even 126 mm (7-speed) hubs and it's so small I don't think "cold setting" the dropout spacing is practical.

2. New rear wheel, "claw mount" rear derailleur, shifter, front brake, cassette, chain.

3. Yes, at best and the rear facing dropouts are going to make this even more difficult.

4. No.

5. Yes.

Summary, buy a more suitable, already geared bike. it will be far more cost effective. One possibility is to fit a larger rear cog to replace the current one. You will probably have to get a longer chain too.

Edit: cny-bikeman's suggestion of an IGH (internally geared hub) is a good one but, again, the cost will be more than the bike justifies.

TiBikeGuy

1. Is it an easy job for an amatuer?
No.

2. What parts would I need to fit a 7/8/9 speed gears set?
Shifters, rear hub, rear derailleur, rear derailleur hanger, new chain, cable ties, etc.

3. Would I only fit a rear derailleur?
You can't just fit it on, you have to see if the rear triangle is wide enough to fit the wider hub with the 7 speed freewheel on. You will ahve to rebuild the rear wheel with the new hub, or change to a longer axle to accept the freewheel. If you change the axle, then you will have to dish the wheel. For that you will need a truing stand. A longer chain is needed, and you will have to see if the chainline is able to use all the gears in the freewheel without throwing the chain off the front chainring.

4. Is it cost efective?
NO...it is better off to leave things as they are and buy a bike with gears as he grow older.

5. Do I need special tools?
Yes and it may be beyond the skills of a home mechanic to set everything right.

noglider 

You could fit his bike with a 3-speed wheel. That will probably let him stay on the bike for longer periods. 3-speed hubs are durable and stand up to abuse and neglect. You might find a wheel pretty cheap if you look around, or you could buy a new one. You could even build it from his existing rim and perhaps the spokes, too. That would be a project which would take several hours. If you're eager to try, we can walk you through the whole process.

RubeRad

I will join the others in recommending that the effort required is not worth it.

There are a variety of 20" geared bikes that the big companies have made (Trek, Specialized, ...), you can see one that two of my boys went through (after getting it third-hand, and we passed it on to another family after us) below. Typically they will have a small single chainring in the front, and 6-7s in the back.

My recommendation is, try to sell the single-speed, and get a used geared 20" bike like that. If you are in any major metropolitan area in the US, craigslist will probably have a bike for you locally within a few weeks, for between $50-100.

fietsbob

There is the Sturmey Archer 5 speed internal gear hub option.. make the chainring small the hub cog big,
then cruising gear , 5th will be adequate and have 4 more lower gears ..

noglider 

RubeRad, I don't se enough bikes like yours. I like them. Cantilever and V brakes are better for kids than sidepull brakes, because sidepull brakes require too much force at the lever. These bikes get even better when you replace the knobby tires with smooth or smooth-ish tires.

dsbrantjr

I like HillRider's suggestion of fitting a larger rear cog. Better to get him in the habit of spinning in a lower gear now than to have him risk joint problems from mashing a too-high gear. Fitting a front caliper brake might also be a good idea; he doesn't necessarily need to use it right away but it will be available for him to use when he is ready to learn.

kyselad

I'm currently doing this with both of my boys' 20" bikes, but going with a 3-speed IGH and coaster brake. If you go with a rear derailer, I wholeheartedly agree you're better of buying an already geared bike, if only for the better dropout spacing. The 3-speed coaster is a little spendy -- just over $100 per bike, and that's with free (i.e. my own) labor. But it's pretty slick in my book, and they'll be on 20" bikes for several years ahead, so it's worth the cost to me. Plus, when they do eventually upgrade out of this setup, I'll just steal the hubs for mine and the missus' townies

RubeRad

It was a great little bike; but the front chainring was so small, they spun out at not a very high speed, so it's hard to keep up on a family ride. I didn't know as much about wrenching back then, can't recall what kind of crank/ring setup it was, how hard it would be to slap a larger ring on there.

Another nice thing, that little monster was indestructible (esp. considering it bore virtually no weight). We got ours free from friends, and passed it on free to other friends, but if I had bought it off CL, I could have sold it back for the same price. Free rental, really!

oldbobcat

That's a standard Trek MT60, which will be cheaper and work better than trying to convert a Jet 20. Kid looks like he's having fun.

The chain rings on these are not interchangeable. It would take a new crank, and then the crank arms would be too long. Just teach him to spin and slow down. He'll be there soon enough.

RubeRad

Oh mine is "there already". That pic is over a year old, all three of my boys have graduated to larger bikes; this one's on the red Haro (24" wheels) pictured here.

oldbobcat

Great. Mine's in college and I can't get her to ride enough.

Gaza

Thank's all. It looks as though the best option will be to change the bike for one with gears. Hopefully, I'll be able to sell on his current bike for a reasonable price.

tcs

I've found young riders are all over gears before they're reliable with hand brakes. YMMV. I've set some bikes up with 3-spd coasters and hand brakes for K-3 riders that worked out well.