Firecracker - Section 1

Section 1 | Section 2

* Featured on Makezine.com and Instructables .com *

A typical kids' bike with extended frame and some long front forks give a cool chopper look.

Choppers aren't just for grownups, dude! In fact, with the abundance of kids' bikes at yard sales, scrap yards and dumpsters, it only makes sense that this had to be done. Even brand new, a 12-inch wheel kids bike will only set you back a little more than 50 bucks. As for learning to ride a chopper, kids just don't seem to know the difference - they wobble around on the bike without a care in the world. Most kids who tried the small choppers that I made could ride them on the first try. I guess if you're not used to a standard bicycle yet it may even be easier to master a chopper. Old dogs, new tricks, you get the idea.

Because of the size of the tubing on these bikes, and the fact that the rider will not weigh very much, a single tube can be used to extend the frame into a chopper. Notice the oversized down tube on this bike (Photo 1). It will be easy to lengthen this to create a stretched frame chopper.

Photo 1 - A typical kid's bike as found at the local dump.

It sure doesn't take long to break a small bike like this down to the individual bolts (Photo 2). Overall, the entire bike was in good shape, even though it was found under the scrap pile at the dump. I guess these bikes only see a year or two of life due to the speed at which a kid will outgrow a frame this size. For the record, there are seven common bicycle wheel sizes - 12", 14", 16", 20", 24", 26", and 28". Do you think they did this so a kid would need a new bike every year until they stop growing?! Hmmm.

Photo 2 - Ripping it all apart

The down tube and head tube are separated from the frame (Photo 3), and a length of muffler tubing is inserted into the mix. Any thin tubing of 1.25 to 2 inch diameter would work, but this muffler tube was handy in my scrap bin at the time. The head tube will end up almost twice as far away from the seat as it used to be, but some of that distance will be taken up by the extra rake angle forcing the handlebars towards the rider.

Photo 3 - Muffler tubing stretches the frame.

Once the ends of the tubing are ground to fit properly, the extension tubing is welded in place (Photo 4). It should be very easy to ensure alignment, since the end of the top tube and the bottom bracket are both in their original positions. All of the joints are fully welded and ground at this point.

Photo 4 - Welding the extension tubing into the frame.

Fork length and bottom bracket height are the determining factors in head tube angle, so the bike is mocked up at its proper height, and the front wheel is positioned where it is desired in the final build (Photo 5). The goal is to ensure that the pedals will not scrape the ground when the bike is finished.

Photo 5 - Testing for proper head tube angle.

Once the correct head tube angle is determined, the end of the new top tube can be ground out to form a good joint for welding (Photo 6). It is best to tack weld the head tube in place first only at the sides so that you can check it visually for alignment; or hit it slightly with hammer to readjust before welding again if necessary. On my design, the head tube was actually 90 degrees to the top tube, so alignment was easy.

Photo 6 - Welding the head tube in place.

The original forks will be extended by cutting them off near the top and inserting whatever length of 1-inch thin walled electrical conduit tubing you like. This conduit is the same diameter as the fork tubing, so welding it end-to-end with the original fork tubing will work out nicely. Cut the original dropouts from the forks as clean as you can, keeping their original shape (Photo 7). Once cut, it's a good idea to grind the dropouts in a vice clamped side-by-side so that they end up exactly the same size.

Photo 7 - Cut the dropouts from the original front forks.

The two lengths of conduit will be inserted into the forks as shown in Photo 8. Put everything in place, and ensure that both fork leg extension tubes end up the same length, or your front wheel will not center easily.

Photo 8 - Extending the forks.

To ease the entire fork building process, bolt the front dropouts to the front wheel as shown in Photo 9, and then the dropouts can be welded to the fork extension tubes in the correct position. If you lay both fork tubes on a flat board and do this, the front wheel and dropouts will be centered and aligned on the fork extension tubes. Of course, tack welding everything in place first is always a good idea, then you can give it the visual inspection before welding the entire joint.

Photo 9 - Start with the fork dropouts.

Once the forks are tack welded and appear straight, weld the entire joint, and grind it as smooth as possible (Photo 10). Because of the similarity in outer diameters of the original fork tubing and 1 inch conduit, the final product should look like one continuous length of tubing after paint is applied.

Photo 10 - Extended forks completed.

Section 1 | Section 2