How to Build a Downhill Bike

Downhill Mountain Biking

Building your own bike rewards you with a sense of pride. Every time you ride your bike, you will remember that you put the parts together and took the bike for its very first ride. Building a downhill bike adds complexity over standard mountain bike assembly due to the components and suspension design, although the principles remain the same. Using the proper resources, you will accomplish your downhill bike build and enjoy your successes in the rides to come.

Things You'll Need

• Bicycle work stand
• Downhill bicycle frame
• Downhill bicycle forks
• Headset
• Set of wheels, brakes, tubes and tires
• Handlebars, stem, levers, grips and cables
• Crank set, pedals, rear cog set and chain
• Seat, seat post and seat clamp
• Open-end wrenches, hex keys and screwdrivers
• Grease

Instructions

1. Connect your downhill frame to the work stand, and tighten it to hold in an upright position, parallel to the ground. Grease your headset bearings. Place your lower headset on the base of your steer tube, and slide your steer tube through the head tube on your frame. Set the upper bearings from your head set on the top of your head tube, and slide your upper triple clamp over the steer tube and fork stanchions. Tighten the hex head screws to secure your forks.

2. Remove the top of your stem, install your handlebars and tighten your stem onto your handlebars. Slide your brake and shifting levers onto your handlebars and install your grips. Route your brake and shifter cables to place your brakes and rear derailleur in their respective places on your frame. Add the inner portion of your chain guide to the frame.

3. Install the front and rear tire onto your rims. Place your front wheel into your fork dropouts and tighten the hardware. Slide your back wheel into the frame dropouts and tighten hardware. Position your brake units until they properly grip the braking surfaces and secure them in position.

4. Apply grease to your bottom bracket and tighten one side into your frame. Tighten the other side of the bottom bracket into your frame. Rub grease onto the ends of your bottom bracket where your crank arms will connect. Mount the crank arm with the sprockets to face the same side as your rear derailleur. Tighten your other crank arm in the exact opposite position. When one crank arm faces up, the other should face down.

5. Install the single front chain ring by bolting it to your crank arm. Install the outer piece of your chain guide to encase your front chain ring. Slide your seat stem into the seat tube on your frame. Place your seat on top of the seat tube and tighten the rails to the seat stem. Tighten the hardware at the top of the seat tube on your frame to secure your seat in place.

6. Remove a link in your chain and wrap your chain around the cog set on the rear wheel and through your rear derailleur. Wrap the other end of the chain through the chain guide and around your front chain ring. Connect the link you previously removed to make your drive train functional. Add each pedal to the correct side of the bicycle. Remove the complete bike from your stand and make any necessary minor adjustments to position your seat and handlebars. Go for a test ride. For questions on a specific region of your bike, visit the Park Tools Repair Help by Region website.

Tips & Warnings

• Apply grease liberally where necessary, and wipe excess after installation of each piece. Dual crown forks reduce stanchion tube flex, offering a stiffer ride. Adjust your stanchion tubes to increase and decrease your head angle.

• Do not over-tighten screws. Never use parts not intended for downhill bikes. Never attempt to build your own downhill bike frame.

References

• Barnett's Manual Volume 1: Frame, Fork, and Bearings; John Barnett; 2000

Resources

• Park Tools Repair Help by Region