Top Banana Bike




About: Long time bicyclist, bike commuter, bike tourer, recent bike builder/experimenter. I'm an energy consultant for hydro electric, solar and other renewable energy generation.

Convert a small kid bike into a fun sporty looking silly riding adult bike.

Kids outgrow their bikes so fast but here is a way to put even the smallest 12" wheel kid bike back into action as a cool-goofy adult bike.

Re-uses/repurposes old items from the dumpster:
small kid bike,
old steel tube,
wood mop handle.

Visit a good primer on Dumpster Dipping

Only had to buy the banana seat and a 5" long 1/4" bolt.

Step 1: Parts Needed

12" or 16" kid bike
Banana seat
Steel tube to fit in steering tube and support seat nose.
Steel tube that accepts kid bike stem
caster wheel from cart, furniture etc to form swiveling seat nose bracket
1" or 7/8" wood dowel (about 8" long) to connect caster threaded post to steel seat nose support tube.
Crutch to support back end of seat
3/8" bolt to bolt seat nose to caster bracket
1/4" by about 5" long bolt and 5-6 nuts to bolt seat back to crutch

Step 2: Pull Stem From Kid Bike and Make a New Tall Seat Support Tube Instead

Take stem from kid bike and measure tubing diameter needed to replace the stem and slip snugly into the fork's steering tube.

Slip it into steerer and determine length needed to get eat to right height for you.
Cut to length remembering to subtract height of caster frame that goes between tube and seat nose bracket.

Shave dowel down to fit snugly in top of stem tube. Pound it in at least 5 inches. Cut off protruding excess dowel. Drill snug whole to let you force thread the caster bolt into the dowel.

Attach stem tube to bike either slipping it directly in fork's steerer tube or using an intermediate tube in the steerer and slipping the stem over the intermediate tube. fit with aluminum can strip shims if needed for snugness.

Step 3: Miter and Weld Stem

Cut and miter (mitering means to cut or grind joint to fit together snuggly for welding) stem extension onto stem upright.

I used a tube with an inside diameter that the bike's stem fit inside (just like the fork's steerer tube).

Weld in place with goopy weld. I use a MIG (Metal Inert Gas) welder with flux core wire and no shielding gas. This really helps me avoid pretty welds.

Step 4: Gently Squash Crutch Arms

Cut armpit brace off of upper crutch arms.
Gently semi-squash aluminum crutch arms into ovals so the bike's rear wheel bolts can reach through after proper sized axle whole is drilled in each arm.

Step 5: Assemble the Seat Nose

With caster screwed tightly into wood dowel in stem, now you can assemble (bolt) the seat nose bracket to the caster bracket.

Step 6: Proto Type Testing

Take rear wheel axle nuts off and put drilled crutch arms on axle and re-tighten nuts (gently so as not to crack the aluminum).

For testing purposes the rear of the banana seat can be suspended by rope from the crutch while you finalize seat height desired.

Yes, it's already fun to ride.

Step 7: Cut Crutch and Assemble Seat Rear Mount

Cut crutch to length.
Drill hole for bolt (1/4" or largest bolt that seat eyelets accept.)

Assemble with nuts to keep parts in desired locations.

Step 8: Enjoy the Finished Product

Rides slow because of very low gearing on 12" bikes. (helps parents keep up with the little rascals)

The feeling alternates between:

Recaptured youth and your first bike ride or

It feels like the circus is in town or

you need to be wearing a Shriners' hat.

This bike was a proof of concept experiment for building a successor to my compact triangle bike



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    35 Discussions


    7 years ago on Introduction

    This thing rocks. I place this right up there with the Barfly. A bar stool with a small gas engine and a steering wheel with the gas and brake controlers on it.


    8 years ago on Introduction

    This is pretty brilliant. If the parts are on hand, I might have to try this next time there's down-time in the shop I work in.


    8 years ago on Step 2

    This "Seat Support Tube" fits in the fork's steerer tube (I welded it in there instead of using an expansion bolt) just like the stem would on a normal bike. So the Seat Support Tube is conceptually a modified overgrown handlebar stem that now holds the handlebars (by holding their stem) and supports the nose of the seat.


    8 years ago on Step 2

    I know your pretty spacific but I don't quite understand. Does the tube go inside the same spot the fork is or does it get welded to the top.


    9 years ago on Step 5

    I think this is a really neat idea....this use of a caster. It did worry me how you would keep the seat from slewing when you turn the handlebars. I can't help wondering how stable the seat will be, however. How did you find it, in practice?

    2 replies

    Reply 9 years ago on Introduction

    The seat is fairly stable and only wiggles because some hardware is loose after hundreds of riders at Maker Faire(s). In practice the bike rides funny with the very short cranks. and long tiller dimension (~stem length). When you ride the bike it feels like you are getting in touch with your inner circus clown. From bringing my wide variety of bikes to Maker Faire I notice most people test several and find one that hooks them somehow more than the others. People who enjoyed silliness, enjoyed this bike. See others at


    Reply 9 years ago on Introduction

    well, I really like the idea...and you'd have to have something of the clown about you to even consider building one (as I am). I think I might be tempted to raise the crank centre and have longer pedals or even put a cog further forward, just beneath the word "speed".


    11 years ago on Introduction

    Thats amazing!!! I'm a big fan of wacky bikes. One question though. Where were you able to find a banana seat? It seems like they are pretty hard to come by.

    2 replies

    10 years ago on Introduction

    This is so kool, I had to build one! Thanx for posting another of your unique creations, Tom! :)


    Reply 10 years ago on Introduction

    I'm glad you like it. to keep up with Critcal mass ride speed >3 MPH, you may want to put a larger chainwheel on the front and/or a smaller rear cog to give you a higher gear ratio driving the 12" rear wheel. The store bought bike is designed with a low gear so your little kid can't outrun you. Happy Trails!


    10 years ago on Introduction

    does it turn easily? with the weight of the rider... wont it affect the turnability??

    1 reply

    Reply 10 years ago on Introduction

    The handle bars and stem turn easily because the rider weight is supported on the top ball bearing race that is part of of a shopping cart caster wheel fork assembly, (You normally see this piece other end up on a shopping cart.) The bike handle funny ( like the circus is in town) because of the tiny cranks.


    Is it though? Many people make a decent living finding scrap metal and things other people didnt want at dumps, and can keep the good stuff for themselves if they need to.


    Reply 10 years ago on Introduction

    Davethescubarock uses the word "find" in terms of discovering something and acquiring it at no financial cost. You are using the word to describe your discover of a purchase opportunity. This makes you sound like a 13 year old Mall Rat. Additionally, you might want to consider the hundreds of thousands of people that own a PC only because they found one scavenging through the trash. In many third world countries, this is the case. So....scavenging is for hobos and civilized people with PC's.