Introduction: Transforming Bicycle! Tall Bike to Chopper Bike
This bike transforms from a tall bike to a chopper/low rider (and back) while you ride it! It is made with a full suspension mountain bike and a set of gas shocks. The spring on the mountain bike is removed to allow the bike to pivot, the fork and rear triangle of the bike are extended. The gas shocks are extended when the bike in the tall position and compressed in the chopper position.
In this instructable, I will describe the general steps for building this type of bike. Specific materials and sizes used will vary depending on what materials you have access to, the specific bike used, and the rider’s size.
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Step 1: Materials and Tools Used
The main parts needed to make this bike are:
full suspension mountain bike - one with a spring and pivot point (like this), the spring will be removed to allow the bike to pivot
two pieces of steel tube to extend the front fork - I used two pieces of two foot long steel, sized to fit my existing fork
a piece of steel to extend the rear triangle - I used a 10.5 inch piece of scrap rectangular steel tube
gas shocks - I bought mine from LS Technologies, they included end fittings and mounting hardware
a way to mount the springs to the bike - I used 1/4 inch steel plate, coupling nuts, and the hardware that came with my gas shocks
a way to cut the bike - I used a reciprocating saw, you could maybe use a hand saw or a cut off wheel on a grinder
welder - or someone to weld it for you
grinder - for cleaning up pieces before welding
longer brake cables - I used 78 inch cables from ebay
two bike chains - you will need a longer chain made from two chains joined together
basic tools to take apart the bike and reassemble it - adjustable wrench, hex keys, screwdriver, wire cutters, hammer, grease
"bike specific" tools:
crank puller tool - I used Park Tool Compact Crank Puller, $13.46 on amazon
chain breaker tool - I used Park Tool Mini Chain Tool , $15.26 on amazon
Step 2: Remove Components From Bike
The components of the bike were removed before cutting and welding. The shocks were removed from the fork as well (no photo of them apart, but photo shows where they come apart).
The cranks were removed with a crank puller tool. Here's a video showing how to remove bike cranks. Also clean the bottom bracket before welding so that the grease won't get gummed up from the heat.
More common tools were used on the other parts of the bike (wire cutters, an adjustable wrench, allen/hex keys).
Step 3: Chop It Up
The bike was cut behind the bottom bracket, and a grinder was used to clean up the cuts before welding the extension piece.
Step 4: Extend the Rear Triangle
A scrap piece of rectangular steel 10.5 inches long was welded in place to extend the rear triangle.
Step 5: Extend the Front Fork
Two pieces of two foot long steel pipe were used to extend the fork.
Step 6: Which Gas Shocks to Use?
Now you need to figure out where to mount the gas shocks to the bike. Distances between potential mounting points on the bike were measured to find possible extended and compressed lengths for gas shocks. The wheels and seat were reinstalled to make this process easier, the cranks and pedals were reinstalled to make sure they would not hit the shocks in either position. You can see my measurements in the photo, I ended up using shocks with 37 inch extended length and 20 inch compressed length, purchased from LS Technologies.
The force of shocks will depend on the mounting angle and the weight of the rider. I just guessed on what force to use, if anyone can help with the math of determining the force please share in the comments!
First I bought two 120 lb shocks, and I (120 lbs) could not get the bike to go down. My dad tried it and got it to go down and come back up! He weighs 160 lbs, so 66% of the force of the two shocks.
Then I bought two 90 lb shocks, so that my weight is 66% of the force of the shocks. They worked well for riding slowly, but riding faster over small bumps and cracks in the road made the bike slowly compress. I tried one 120 lb and one 90 lb shock (so my weight is 57% the force of the shocks) and I could not get the bike to go down. I even tried wearing a backpack with a 10 lb weight in it (61%) and still couldn't get them to compress. So I stuck with the two 90 lb shocks.
Step 7: Mount Gas Shocks
The top end of the gas shocks were mounted in the center of the triangular part of the bike frame near the seat. A 1/4 inch piece of steel was cut to fit the triangle and welded to it for reinforcement. The gas shocks came with metal socket end fittings and 5/16 inch threaded ball studs. A 5/16 inch coupling nut was welded to the 1/4 inch steel.
The bottom end of the gas shocks were mounted to a similar steel plate that is attached to the bike's rear rack mounting holes with screws. The coupling nuts are attached to the plate with a bolt rather than welding which allows you to easily try different mounting positions for the end of the shocks. You can see a hole in the corner of my plate that I used to try a different angle.
Step 8: Putting It Together
I chose to not reinstall the shifter, and made the bike single speed. The rear derailleur was used as a chain tensioner, a small piece of wire was used to lock it in position.
Two new chains were combined to make a single large chain.
I ditched the old flat handlebars and put on more comfortable upright cruiser type handlebars.
New 78 inch brake cables were used, the back cable used the existing cable standoffs and zipties to hold it in place, the front brake cable used a single zip tie to hold it in place.
I added a bmx bike peg on the left side as a step to get on the bike.
Step 9: Finishing Touches and Wait, How Do You Get on That Thing?
Once I had it put back together and knew it worked, I took it apart again and stripped the paint and painted it. I used JB Weld to smooth out the edge of the gas shock mounting triangle. I did not want to grind down the edge of triangle too much because the bike metal was thin.
I added a rubbery gasket to act as a bumper when the bike is in chopper position.
How do you ride it??
I put the left pedal down, hold on to the handle bars with both hands, put my right foot on the bmx peg and push the bike like a scooter to get it going. Then I step onto the peg with my right foot, step onto the left pedal with my left foot and take my right foot off the peg and over onto the right pedal.
Shifting my weight back just a little is enough to compress the gas shocks and transform the bike to chopper. To go back to tall bike, I just stand up on the pedals which takes my weight off the shocks, allowing them to expand.
It's best to get off when the gas shocks are extended (tall bike position). When the bike is in chopper position, the only thing keeping it there is your weight. If you stop in chopper, once you put your feet on the ground, weight is taken off the bike, the shocks expand and the bike goes up and knocks you off. You have to learn to hop off pretty quickly to avoid being knocked off and falling. In order to take the photo of the bike in chopper, I had to lock it in place with another person's help.
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