Step 1: Materials and Tools
- One whole kid's BMX-style bike with 16" wheels
- The steering tube and steering components from another bike (or some ingenuity)
- One length of 1" EMT electrical conduit (around $7 for 10')
- One length of 3/4" EMT electrical conduit (around $5 for 10')
- A couple of feet of 1" x 3/32" mild steel or some other stout steel for brackets
- Enough 1/2" - 3/4" plywood to fit your kid's back and posterior
- Miscellaneous nuts, bolts and screws
- Optional: An old 3-speed bike for the rear hub, front sprocket, and chain guard
- Flux core welder, welding gloves, tip dip, wire brush, chipping hammer
- Various clamps
- Angle grinder with cutoff/grit/wire wheels
- Bench grinder with cutoff/grit/wire wheels
- Hack saw
- Bike assembly tools
- Woodworking tools (to cut out and shape the seat)
Step 2: Disassemble and Cut Frame
Strip your donor bike down.
If you are careful with the source bike you select, you should only have to cut the frame in three places.
*where the top-tube hits the seat tube
*where the bottom bracket and chain stays intersect
*where the seat tube and the bottom bracket intersect
If your donor bike top tube doesn't match up with the 3/4" conduit well, you will just want to remove the top tube entirely and replace it. Try to avoid this as it makes things trickier.
Step 3: Extend Top Tube and Chain Stay
Measurements are tough on this one, but you will need to add conduit to stretch the bike out. Base the measurement on the length of the rider sitting down with legs stretched out. The new tubes should allow for the measured length from the seat back (with padding, etc.) to the pedals when they are as far as they get from the rider.
I was able to jam the new top tube piece into the old top tube and weld. If I had more time, I would have smoothed this transition a little more with body filler. Weld the top tube about halfway down the seat tube.
The new chain stay piece will attach centered up where the old one did on the bottom bracket. you will have to make a little bracket for it to attach to both the bottom of the seat tube and the chain stays. If you attach the new tube to the bottom of the seat tube, it will be too high to weld to the old chain stays, so I cut the tube so that I can weld a piece of 1/8" stock to both the new and old chain stays. That bracket is shown below.
I do my best to keep everything straight and have had pretty good luck with eyeballing it. These long bike frames are long enough that you can see if something is off. If you aren't confident in your eyeballing abilities, clamp the frame to something you know to be straight when you weld to form a temporary jig.
Step 4: Steering
Now to create the remote steering. This is where a second head tube assembly from a junker bike is handy. If you are clever, you could fabricate something and just use one bike for the project.
The measurements are iffy on this one. You will want to measure it to the passenger. The easiest way is to assemble the head tube together with handlebars and have your rider hold it somewhere comfortable. Measure up for a riser tube to mount the head tube to, cut, fit, and weld. Try to make sure that the remote head tube is close to the same angle as the donor bike's head tube. Its also good to make sure that you can make the tie rods for steering fairly level.
My tie rod ends were from Wick's Aircraft Supply and are really nice, but probably the most expensive part of the bike. I've heard of people buying them cheaper at Summit Racing Systems (which is only a few miles from me - d'oh!). The images below illustrate how the tie rod ends are connected. The tie rod itself is made from 1/4' scavanged round stock. I cut threads to match the tie rod ends.
To make sure things were secure, I created a gusset for the remote steering tube out of and old crappy kid's bike gear.
Step 5: Seat
The seat is simply plywood with a few brackets holding it together. I covered it with foam and some leftover denim fabric I had. The seat is attached at the bottom with brackets made from tubing split down the middle with wings attached. See the photos for details. The rear bracket is bolted to the old seat adjustment bolt holes. In theory, you can re-drill the bracket and scooch the seat back as the rider grows.
Step 6: Prep and Paint
Go over all your welds again and fill with body filler. Sand the body filler smooth, prime, sand, and prime again.
The paint my son chose was fluorescent yellow and was a flat finish. To make it shiny, I added a clear coat.
The front fork was painted gloss white with a coat of 3M retro-reflective clear. You can really see this bike coming. It's hard to look at in the sunlight!
Painting all the little brackets was time consuming, but worth the effort. I even ended up painting the old Raleigh emblem white and refitting it.
Step 7: Assemble and Ride!
I let the paint dry several days in the sun. It still is soft (a year later!), so I have to be careful with it on the bike rack - I usually wrap and contact points in a plastic bag. I ended up cutting out small grommets and washers out of a 2-liter soda bottle so that the nuts and bolts wouldn't mar up the finish.
I gave everything a good dose of quality bike grease and cleaned up and lubricated the chain. After mounting and adjusting the brakes and the shifting mechanism, we were ready for a test drive. It was a little twitchy at first, but he got the hang of it quick.
I added a few photos with measurements so you can get an idea of seat size, etc.
This bike turns heads everywhere we go with it. My son likes the ride and loves the attention he gets. Because it's a 3 speed and comfortable, I can take him with me on rides that I couldn't before.