chimpanzee

I want to convert below Cannondale 20" kids bike to a commuter, so it looks like a folding bike. Can this be done?

I would need to extend the steerer tube, plus need longer seat post. Would this be safe?

tornado60

There are tall seat post you can buy. Or a piece of pipe might work. Seat might need new clamp to connect it. It has rails so any LBS should have what you would need. Handlebars might be trickier. I have not had luck finding extremely tall thread less stems. I know Amazon used to carry tall quill stems cheap.

Skipjacks

Unless you're really short that'll make an uncomfortable commuter.

I mean technically you could put a longer seat post on and raise the handlebars so your legs fit. But you can't put bigger wheels on it. So you're going to be peddling an awfully lot harder than you'd probably want to. It's just not geared for an adult commuting purpose. And the small wheels will have you working overtime.

If you're in the Baltimore area I'll buy that bike off you though. I'm in the market for a 20" for my kid. To put that in perspective my kid is turning 7. The 20 inch bike is a good size for her. Trying to convert that into an adult bike is just not going to work well.

If it's a space saving issue that you need a small bike when you get to work to be able to store it you might be better off removing the wheels from a big bike. I'd guess that 20" bike is roughly the length of my full size bike from axle to axle. So if it's a space saving issue the adult bike with no wheels would fit in the same small space.

If you're thinking of this as just a side project just to say you can do it though....I'm down with that and more power to you!! Doing it because you shouldn't is always a valid reason!!! haha

Khb

Small wheels aren't really an issue (try a folding bike sometime; Brompton, Downtube, Dahon). But the gearing for a kids bike is quite different than an adult bike. A used Dahon Speed d7 or Mariner can often be had for $200 or so. Not nearly as good as . Brompton or a Downtube, but a reasonable way to get a feel for small wheels with long seat post and bars....

mcours2006

How tall are you? My nine year old son rides a 20" bike and he's outgrown it already. I could see using a 24" perhaps, but unless you're well under five feet tall a 20" kids bike is going to be pretty small, even with longer stem and seat post.

HardyWeinberg

You might want a setback seatpost to keep your knees from hitting the handlebars.

BobbyG

That is basically the whole "mini-velo" thing (google it)...an adult, non-folding frame with 20" wheels and geared to compensate. Granted, a true mini-velo's frame is taller so that the seat and stem don't have to extend as far, but many 20" wheel folding bikes do have low frames with extended posts and stems.

So as to why a mini-velo? At just a few inches shorter than full-size wheel bikes, they may fit certain storage requirements or transit rules, and the smaller wheels can provide quicker acceleration, and be relatively sturdier than "full-size" wheels.
@chimpanzee says he wants to commute on it, but how far and in what environment? For a couple, three miles at a slower pace it would work just fine. For a longer commute where more speed may be adventageous, higher gearing would be needed. If there's a desire for carrying clothes or supplies, whatever the 20" low-frame folding bike people use should work.

I have thought about doing this myself, out of curiosity.

Leisesturm

I have to think that there is more difference between a 20" wheel Dahon folder, a 20" wheel mini-velo, and a 20" kids bike! Simply having 20" wheels does not, I suspect, qualify a juvenile market bicycle as a safe or efficient option for the commuting adult.

prathmann

Comparing this to my Bike Friday with 20" wheels there are some obvious differences. The handlebars on my bike are way higher with a super long stem. Even if you could put such a stem on this bike it would add extra stresses to the frame which it may not be designed to handle. Similarly with adding an extra long seatpost plus an adult weight might be more than intended for a children's bike. Then there's the gearing. Highest gear on my Bike Friday is with a 60 tooth chain ring in front driving an 11 tooth cog whereas this bike looks more like a 36 tooth chain ring and 14 tooth cog. So you'd have to pedal at twice the cadence for the same speed.

And what's the point? It still wouldn't be or look like a folder since it doesn't fold. Most transit rules that make special allowance for folding bikes insist that they have frames that fold, not just have smaller wheels.

hermanchauw

1. You can change anything on any bike.

2. I have seen uncles and aunties using children's bikes for marketing, but i doubt they use it for commuting.

3. Gearing can be changed, but the limitation is crank length. They are designed with lower bb and shorter cranks.

4. Another possible limitation would be the rear axle width. Not sure what is the width. If the frame is steel, you can easily respace the rear width to fit any wheel. If it is alu, you are stuck with one width.

5. If you are smaller size, why not. Stem/bar i suggest using bmx ones. So that you have more reach/rise adjustment. Seat post can use stainless steel ones to limit flex.

Viich

I'm familiar with the cannondale kids bike you show, my niece and nephew have them. They are quality bikes. You'll want to look for a stem extender - clamps to the steer tube and let's you tension, then attach your stem to the extender. To my recollection, the seat tube is slacker than the head tube by a bit, you may end up with a reasonable fit from a super long seatpost, stem extender and some tall BMX handlebars.

I expect you may want to change the front chainring to up the gearing, or it may be fine for you. Post pics if you do it!

dabac

I wouldn't worry about frame strenght(much).


Kid's bikes are often fairly cheap.
A very helpful trick to make a cheap frame is to use thick tubes, which are easy/fast to join.
Downsisde for the kids is that the bikes get heavy.
An advantage for a tinkerer is that it is likely to be plenty of safety margin that can be used for other purposes.
A similar reasoning applies to wheels and hubs. they often use (near) the same parts as adult bikes, which makes them over-heavy for their original intent, and strong enough to hold up to plenty of improvisation.


Stem and seat post are concerns though.
Either from the access perspective, but also strength.


Gearing is a practical concern.


I built a folder once using a 12" kid's bike as a parts donor.
Stretched the frame to match the axle spacing of a BMX. Swapped in a 50-something tooth crank.
Wheels, fork, rear stays held up fine.
The coaster brake didn't like it much.
Pretty much an "operation succesful, patient died" scenario.
I managed to do what I intended, only it didn't turn out as useful as I'd hoped.

fietsbob

I would have to inspect your completed job in order to pass it on safety,,

So I will not say .. since I have no clue as to your mechanical competence...

you have a local bike shop to consult?


how much do you need in raising the saddle and bars? Answer with measured numbers..








....

rodteague

a set of ape hanger handle bars and a longer seat post; shouldn't be a problem. Larger tooth front chainring should be simple enough. I don't see any issues in making the conversion. good luck!

Link

Ape Hangers

Extra Long Seat Post

Regards

Rod

RubeRad

Check this out:

Sheldon Brown's Thorn Raven Bicycle

You don't need to have two handlebars, but you can put a quill stem inside the (extended) steerer tube, as long as a threadless stem (perhaps sawed off) is holding the headset together.

The question of how to buy or fab a long enough extension is another question...

hermanchauw

Saw this in the internet.

rodteague

OMG I would have died to have fat tires like that on a schwinn stingray back in the sixties. I would have been the coolest kid on the block

Darth Lefty 

I'm sure it's possible but between the reach and the crank length, I can't see how it will be comfortable.

55murray

Here is my 20" commuter, 1984 junkyard build from a '55 Murray frame. I must have 20,000 miles on this thing. I'm 6'1":



Here it is next to a modern 20" I found at a rack. All the contact points line up perfectly, weird. I have compared it to folders as well with the same results.



The front fork is from a 24" cruiser, that lifts the bike just enough to be able to use longer cranks than the original kiddie size (they are not full size however, they are pretty much right between the small and full). 48/16 drivetrain, hills are a challenge, but it can cruise pretty fast.

You can see the saddle is toast, I have a B17 on it now, it has earned it.

RubeRad

Looks like your seatpost is a little bent at the collar. Or maybe it's just the photo.

SloButWide 

and the slowest
Imagine the skid marks we could have made.