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Bicycles ... or how do I get exercise with a bad back!!!

Gear Inches Calculator

While I was planning my homebuilt recumbent, I did a sizable rewrite of Sheldon Brown's Gear Inches Calculator. I added MPH and KPH for a given cadence and also the ability to calculate using a mix of internal rear-hub gears and derailleur cassettes. I also fixed many bugs and cleaned up the code. I gave the fixed version back to the original web site.

Here is a local copy of the Gear Inches Calculator

Here is the same thing at Sheldon Brown's Web Page. Lots of other good stuff there as well.

My Homebuilt Recumbent Bike

In summer 2001, I built a SWB (short wheel base) recumbent using parts from three bikes. I thought my experiences might be interesting and maybe encouraging to others.

Update 4/14/02 - I have made a number of changes to the bike since last year. My updates in the text below will show up in this color. The main changes are: added front derailleur for 14 speeds, a 35 tooth ring on the boom for granny gears, removed the old cranks from the mid-gear, changed to smoother higher pressure tires, reclined seat and handlebars more, added homemade pedal extenders. Sorry, no new pictures yet.

After test-riding several recumbents, I knew I had to have one. However, before spending almost two grand for a good recumbent, I thought I would test the waters by building one first. Although I thought I wanted a LWB (long wheel base) bike, the easiest plans I found were for a SWB bike. After a summer of riding, I think I prefer the SWB. (Click on image to see it in higher resolution.)

I mostly worked from David's "No-weld Recumbent" plans. The plans are good for getting ideas. They are definitely worth the $6. I did add a number of my own enhancements. In particular, I used a two chain loop approach that allowed me to make fewer modifications to the main bike.

As built, it is a very comfortable bike although somewhat heavy at over 45 pounds. In spite of that weight, it is very easy to ride. I currently have it set up as a 14-speed with a range of 18-60 gear-inches. Since I am more interested in comfort and light climbing than in speed, this is a good compromise in a 14-speed configuration. Shifting and handling are surprisingly good considering the cheap components the main bike came with. It is very easy to balance and has no heel-strike problems.

I have since added a bike computer (an old Avocet that I had on my ten-speed). So now I have a more accurate idea of speeds and distances. Cruising is very easy at 12 mph and a bit of a push at 15 mph. Downhill, I max out at 22 mph - because the gearing only goes up to 60 gear inches. Uphill is usually about 6 mph in low gears. By the time you add stops and hills, most of my long rides have averaged about 10 mph. Not the stuff that people brag about, but very respectable for an out of shape casual rider who is about to turn 50!

I have severe lower back problems and sciatica. Before I discovered recumbents, I thought I would have to give up riding bikes for anything longer than 15 minutes at a time. This bike has been wonderful. My longest ride so far has been a complete round trip on the Olentangy-Scioto bike trail all the way from northern Worthington to well south of downtown Columbus, Ohio (and back). With the jog out to my house that was 37.2 miles. When I was done, my legs were certainly tired, but I had no pain anywhere. (Click on image to see it in higher resolution.)

Here is what I used:

MAIN BIKE: I found a new Y-Frame 26 inch wheel 21-speed mountain bike for $40. Between the Y-shaped frame and smaller frame size, I think it worked out better than the girl's bike the plans called for. The key thing is to have a low enough space in which to mount the recumbent seat. The chain and rear derailleur was left intact (13-28 teeth). The front derailleur was removed and the chain was left on the smaller chain ring (28 teeth). The second chain loop ran from the larger chain ring (48 teeth) to the boom chain ring (35 and 52 teeth). This changed the ratio of the gearing slightly to a low but useful range. The pedals, front wheel, front brake, handle bars and stem were all removed. I also removed the old cranks.

It is amazing how much attention this bike attracts. Especially boys around twelve stare with dropped jaws and then shout out, "Cool Bike!!!" There is something special about seeing the world from a recumbent. You face forward instead of facing down into the road, you recline, and the world rushes by you. (Click on image to see it in higher resolution.)

KID'S 20 INCH STARTER BIKE: This provided the front wheel and brake (and a few lesser parts. I just mounted the wheel on the existing MB fork and used some hardware store brackets to mount the brake a few inches lower.

PEUGEOT 10-SPEED BIKE (30 yr. old): This was the source of the boom. I made the boom by attaching the front fork and a cut section of the frame, which included the bottom bracket. I found David's directions for doing this rather confusing, but once I tried it everything worked well. (The picture below should help clarify this part.) The frame tubing neatly fit around the upper shaft of the front fork (the part which is usually the steering axis). I made a straight cut up the frame tubing about 4 inches and then wrapped that area with 4 hose-clamps to get a tight fit to the shaft of the fork. This also allowed a couple inches of adjustment to the length. The fork part of the boom wrapped around the main bike's steering axis and Y-Tube and was tightly bolted into place. The plans had you cut the long part of the boom from the front-tube, which then requires that you reverse (left-right) the chain and petal assembly in the bottom bracket. I found it much easier to use the up-tube as the boom and thus was able to leave the Peugeot's bottom bracket assembly intact. I left about 6 inches of the front tube in case I ever want to put a front derailleur on the boom. I also used the rear derailleur from the Peugeot as a chain tensioner for the return part of the front chain loop. Although this was illustrated in David's plans, I originally thought I could leave it out since the front chain loop was on fixed gears. However it ended up being necessary in order to keep the chain from jumping out of place.

This left-side view gives a better idea of how the boom is fit together and attached. Notice how it is bolted through the main frame in two places. I also added a U-bolt at the very end for extra security although it might not have been needed. I wanted a relatively low bottom-bracket (They still call it that even though it is in front!) I was able to keep it a few inches lower than the seat. You could certainly place it higher if you wanted. There is now a smaller second chain ring (35 teeth) and a front derailleur on the boom. In the high-resolution image, you can also get a better idea of how the two chain loops are run. (Click on image to see it in higher resolution.)

Back on the right-side view. This shows the old rear derailleur serving as a chain tensioner. The plans suggested a small clamp on a bit of cable to hold it at the correct angle. I found that the stop-screws that are intended to limit the normal extent of travel could be tightened all the way down to hold the position I needed.

SCAVENGED FROM A FRIENDLY LBS (Local Bike Shop): The nice folks gave me the two wheel cage from a rear derailleur (without the levers or springs). The wheels on it were about 2 inches in diameter. I mounted this in a fixed position to provide a bend-point for running the front chain loop over the top of the front fork of the main bike. The plans had a chain running to the side of the fork, but that geometry would not work in my case, since the front fork was a suspension fork and thus too wide.

I was a little concerned about excess drag caused by having a "bend-point" wheel on the power side of the chain (all derailleurs have two of them on the return side with little ill effect.) I kept the angle as flat as I could. As far as I can tell this has not been a problem. Sometimes my heel hits the chain and it comes off the (red) wheel, but I can just reach down and put it back. (Click on image to see it in higher resolution.)

PURCHASED NEW: an extra chain (to combine with the Peugeot chain to get enough length for the front loop), extra cables and sheathes for the re-cabling, an extra long front post for the handle bars and a highly curved "easy-rider" style handle bar. I extended the grips on the handle bars with about three inches of wooden doweling (broom handle!) Getting enough space for my bent legs under the handle bars took some adjusting. I found the mountain bike tires too inefficient for riding paved paths, so I switched to Primo Comets. They are rated at 100psi, but I keep them at 75-80psi for a good balance of speed and comfort.

BUILT FROM SCRATCH: A padded recumbent seat - using plywood, foam, and vinyl. Even the firmest 4-inch seat foam I could find in a fabric store was still too soft for the bottom of the seat (although I used it in the back section). So for the bottom section I started with two layers of 5/8 inch closed-cell foam cut from a camping mat. On top of that I put the 4-inch foam compressed down to about 2 inches. The cushion seems good. I spent a very long time experimenting with different seat positions and angles before I mounted it in place. That seems to have paid off, because I find the riding position better than any test-bike-ride of any bent at my LBS. What this tells me is that adjustment is extremely important and that test-rides can be misleading about comfort.

Finally, I tried to move the petals outward with commercial extenders only to discover they didn't quite fit. (It turns out the old Peugeots used 14mm threads instead of the usual 9/16inch - they differ by about a hundredth of an inch!) So I built out the petals themselves using some heavy duty one-inch strapping metal. If you look at the placement of my feet on the petals before I extended them (in the last picture below), you will see why I wanted extenders. They really helped my comfort - especially my knees.

The hinged plywood frame and quick-release seat post allow me to adjust the angle of the seat back. I like the back at about 135 degrees. The seat portion is cut into a wide wedge which makes it easy for me to put both feet on the ground while I am reclined in the riding position. This shows the fill material I used. The block of white "foam" is actually polyester fiber that is sold for padded deck furniture. The green material is sold as camping mats. (Click on image to see it in higher resolution.)

The bent quarter inch metal rod that the seat back rests against is actually the supporting portion of the seat from the 20 inch kids bike. Of course that made it super easy to attach to the seat post. Also notice the lumbar support I built into the padding.

Conclusion: It only took about 30-40 hours to build (and about an equal amount in preplanning). I had some difficulties with the chain routing and with the handle bar stem slipping (I have always hated that cinch post design), but in the end everything worked well. I have been riding it for over six months without any problems.

I love riding it now. It saves my aching back (and neck and shoulders and wrists and forearms and butt). On flat roads, it rides almost as nice as the Vision R44 and Tour Easy I test rode (and still want). But it only cost $175 verses $1800!!!

Now here is the strange thing. In the fall I went back to my LBS and test rode a few recumbents, including some that I loved before and also a Longbikes Slipstream that I had been waiting six months for the store to get in. All in all I didn't think the rides were as good as on my homebuilt. To be fair, the bikes were a lot lighter than mine and were a lot easier to lift in and out of the store. There were no significant hills on my test rides and they probably would have done better on that. Also, the components were a lot smoother shifting and certainly more reliable than mine. Clearly, I have spent a lot of time adjusting my bike to me. (And probably, all the riding meant that I spent a lot of time adjusting me to my bike!) Perhaps with more time doing that on the commercial bikes, I would have better appreciated some of their subtle qualities. But for simple straight forward flat riding, I am happy with what I built.

Hope this description is helpful to other would be homebuilders. Let me know if you do take the plunge.

Timothy Lipetz