Mutant High Racer Plans

With high racers being all the rage these days, I started thinking that I might enjoy one too. Since I have always liked the performance of my old Trek racer, the idea having it’s performance in a comfortable and aerodynamic recumbent platform was exciting. Could this be the best of both worlds? Many people agree. It may not have the lower air drag of a low racer, but the lower rolling resistance wheels may make more sense to someone like me who’s goal is to have a 20 mph cruise.

I set out to create a very simple design that would keep the geometry of a diamond frame (DF) road bike. Since I am a firm believer in the K.I.S.S. (keep it simple stupid) system I went for the minimum number of critical alignment joints. This design has only one where the boom is brazed to the head tube. After a study of my old Trek and many design iterations I decided to keep as much of the donor, bike including the 700c wheels, and mutate it into a high racer. That's how the Mutant High Racer was born. This aint no clone! A scratch built mono tube design might turn out a little lighter, but would be more difficult to build well requiring jigs, and it forces a shorter rider to sit even higher. In this design one lowers the seat by making easy step by step modifications. Still due to the large wheels and limitations of the DF frame, people outside of an estimated 5’-4” to 6’-2” range may not fit. It should be no harder to build than an EZ clone.

Before Building

You will need two DF donor frames. The first will be the basis of the final product. It should be from a light high performance chrome-moly road bike. The size of the frame should be approximately sized for yourself.. Measure these frames and make sure you have the necessary tubes for the whole job.

If you are new to homebuilding, you should check out the following links for details on recumbent construction. You will need to know how to braze, miter tubes, build a seat, pulleys, etc..

WISIL projects
My first recumbent bike page
Tim Smith's building links
EZ clone
Tube mitering
BMX to recumbent conversion

Construction Steps

Do the following frame modification steps in this order to assure that the original alignment is maintained.

1. New Top Tube

Fit and braze a section of top tube from the second DF as shown. This will establish your seat height. The height should be in the 22”-24” range. Keep in mind that the bottom bracket will be approximately 32 inches high, so don't make it too low. It can be horizontal or tilted slightly up at the front. It may be easier to get the height and tilt correct if the wheels are installed while fitting. A higher height could also make routing of the chain easier.

2. Reposition the Seat Stays

Rotate the stays and braze them to the new seat tube/top tube intersection. First cut the seat stays at seat tube end. The preferred method is to unbraze the drop out ends and rotate the stays together to the new position. An optional method is to bend the stays which is harder to do both side evenly. Then cut the stays to the new length required, bend, miter and braze the ends to the seat tube. Depending upon your frame geometry, you may need to remove the brake bridge. The brake can be moved to below the chain stays. This may require the addition of a tube or flat plate to mount the brake.

3. Remove Old Tubes

Cut off the old DF top tube at the head tube and the top portion of the seat tube as pictured.

4. Second Down Tube

Fit and braze a new second parallel down tube from the head tube to the top tube as shown. Use the top tube you just cut off in step 3.

5. The Boom

This is the hardest step. Be careful to get the length correct; to avoid crank interference with the wheel and to braze it to the head tube aligned with the frame. Cut the seat tube of the second DF at the top. Cut off the chain stays at the bottom bracket. Cut the down tube 7 inches from the bottom bracket to make a front derailleur tube. Be sure to leave plenty of down tube left as it will be used to strengthen the boom. Do not use the down tube as the boom as the bottom bracket threads will be on the wrong sides.

This is going to be a fixed length boom. There will be some seat adjustment, but it is important to get the boom length close. There are various methods to do this such as laying it all out in cad, but here is a simple one. First measure your x-seam as described here. Subtract 6.5 inches for the crank arm, call this “Y”. The next step will be easier if you install the wheels and have the help of a friend. From a position near the back of top tube measure out a distance “Y”. This is the bottom bracket position. Hold the boom in place, it might be easier if the bike is laying on the floor, and mark the cut off length on the boom, leaving room for your miter. To avoid crank-wheel interference make sure that the bottom of the bottom bracket shell clears the front tire by at least 6.75 inches, assuming 170mm cranks and 1.6 inch O.D. bottom bracket shell.

After mitering, check the fit of the boom carefully before brazing. Also, it’s important to have the correct angle of the front derailleur tube to insure proper shifting. To check this estimate the position of the drive side chain pulley and run a string from the pulley location to the center of the bottom bracket. Now measure the angle between derailleur tube and the string. The angle should be close to 65 degrees. If its way off try locating the pulley higher and check again. If it’s still not close you’ll need to reposition the derailleur tube. One simple way would be to make a partial cut 90% through the tube near the bottom bracket, bend into position and braze.

To strengthen the boom add a second parallel tube above it attaching to the derailleur tube in a position that does not to interfere with proper derailleur position. The addition of the vertical tube in between should add further stiffening.

An option for more advanced builders would be to fabricate a mono tube boom from 1.75-2.00 inch chrome-moly or muffler tubing. Built properly it could be lighter and stiffer and even adjustable.

Completing the Bike

The frame is now 95% completed, but there is still lots of details such as the seat, handlebars, chain path, etc. to complete the bike. All these part can be purchased for a price or fabricated if desired.

The Seat

Many options exist for a seat. It can be made from composites, wood and foam, or tubing and mesh. Purchase prices can run $200 for a Rans type seat to over $300 for a carbon fiber hard shell design. There are many seat plans available on the internet for the home builder, see above references. Here’s another example. Keep in mind that since this bike has a high bottom bracket that you will need the seat to be quite reclined to get a comfortable open riding position. Some seat designs may not be suitable.

The Handlebars

Handlebar choice can be very personnel. You may be happy with a bar made for a mountain bike or an old upright. You may want to bend your own from chrome-moly or conduit, or you can buy a recumbent specific bar.

To keep your knees from striking the bars you’ll need a stem riser which may require a quill. These can be purchased or fabricated as per my page.

The Chain

The chain consists of 2+ regular length ones. The top drive side will need a pulley to direct it under the seat and through the rear triangle. This can made from an inline skate wheel, bought from McMaster Carr (www.mcmaster.com part #6234K3) or recumbent specific. To mount the pulley fabricate a bracket from 1/8 inch steel plate and braze it to the frame as pictured. If you want a more moveable solution, you can mount it to a clamp such as found on the WISIL site. You will also need a chain tube on the bottom to avoid rubbing against the fork and frame. You may want or need one on top too as the chain may slap against the frame or get your leg dirty. These can be cut from 1/2 inch water pipe or teflon tubes. Hang them off the frame with zip ties.

Note, the chainline as outlined here may contact the front tire, or front brake during very low speed sharp turns. This should not be cause for alarm as it will rarely happen and then only be a nuisance. The lower chain tube may also contact the fork depending on it’s the width. If this should interfere with the function of the chain you can reroute the chain over the fork with an additional pulley.

Notes:

To date I have yet to build my high racer. I'm stiill looking for the right donor bikes and not about to chop up my Trek. Therefore, this is an unproven design and the success of a bike made to these plans is unknown. The questions to be answered when the bike is completed are: Will it have the desired strength and stiffness?; How convoluted will the chainline be?; and Will I be able to ride it at all due to the high bottom bracket?

The plans are posted for the free use to the homebuilding community. In setting out to build your own bike you do so fully knowing that there are risks involved with building and riding your own bike. Please follow all safe building and riding practices. If you want to use these plans, or think that this site is helpful, please send me an e-mail (coppola1962@yahoo.com) as I’d love to hear from you.

Copyright Nick Coppola 2004 All Rights Reserved