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John Tetz: Trike Foamshell Velomobile p3
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John Tetz: Trike Foamshell Velomobile, p.3

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Horizontal bottom bracket: To accommodate different size riders, I built a BB that can be adjusted horizontally. With a standard BB mounted on the end of an angled boom, any adjustment affects toe or heel clearances in the nose of the shell, where the clearances are closing in fast.

The BB consists of a square aluminum tube that slides inside a U-shaped clamp. The adjustment can be reached by the rider leaning forward on the seat. This adds another pound to the vehicle.

The best method of storing the shell when using the trike unfaired is to suspend it as it was hung while building it. That way the shell will take on a normal shape without distortion. If left on the floor, it will expand in width and eventually take on a set. The tail and turtledeck are stored inside the shell. The dimensions for storage and shipping are 80 inches/203 cm long, 28 inches/71 cm high, and 27 inches/27 cm wide.

Future projects: Forward/back seat adjustability (presently the shell is attached to the seat back, which makes moving the seat for different size riders essentially impractical), cooling vents, a night lighting system, and a lightweight (10 pound) 100-watt electric uphill assist for local use.

Construction time line of the overall project: Drawings made in the winter/spring 2004. Started to build the trike in 5/04; this is my first trike and I had lots to learn (much more than a bike). The first version was on the road in 8/04. Trike version changes 2, 3 and 4 up to 1/05. Started the mold construction in 1/05; shell on the road in 3/05. Continued trike version changes 5 and 6 up to 9/05.

Comments: I live in a suburban area, so I have open roads which are good for cruising. I often use a streamliner to run errands to neighboring towns and use the trike VM for local runs in town. The following comments are based on this type of riding.

Noise: The foamshell is very quiet, a non-issue. The trike itself makes more noise.

Size of vehicle: I find this vehicle to be huge and fat: 94"/239 cm long, 30"/76 cm high in front of the windshield, and 26.8"/68 cm wide. When I was carving the mold, I couldn’t get over how big it was. I’m used to narrow and trim bike streamliners. I find when lifting the vehicle I have to lean over much further than with a streamliner, therefore placing a strain on my back. So with this fatness and extra weight, the ability to lift this machine is becoming somewhat limited. However this fatness does give a bit more rider room inside.

Slower speed or more rider effort than on a bike streamliner, due to poorer CdA. The A of CdA is part of the problem, and the disturbance from the wheel cutouts also messes up the CdA. Higher Crrs (0.008 vs 0.004 for a bike at summertime temperatures).

Slower acceleration due to both the total weight of the vehicle and the extra rotating weight of 3 wheels.

The trike uses more room on narrow roads, so slinking between cars and the curb at intersections is much more difficult. This slows forward progress a bit, having to wait in line with cars at traffic lights (and breathing exhaust fumes).

But a trike VM is wonderful at busy intersections when running errands in town. Much more relaxing. Safer because I’m not taking chances at intersections - I can come to a complete stop and look carefully. No energy used to balance. In a streamliner you need to maintain balance while coming into an intersection at slow speeds, while checking for cross traffic, and preparing to get at least one foot down. This can make you quite tense. Also, struggling to hold up a streamliner at a stoplight in a crosswind can be a real chore. Remember, your feet are closer together in a streamliner, so this adds to the stress on the leg holding the vehicle up. Even without wind there is leg muscle power being consumed to maintain balance.

The trike VM can go slower when climbing, resulting in less power required. Climbing power changes more rapidly with speed than with weight.

But the trike VM is more nerve-wracking on hard cornering, even at low speeds. A streamliner can fly smoothly and quietly through a corner with neutral forces (feels sooo good). If you go down, the fall will be from a seat 7 inches from the ground with the shell taking the brunt of the slide. But in a trike this could mean rollover and this would mean going over the high side and possibly rolling it completely over. Yuck. Many of the European VMs have a high turtledeck behind the rider, which is used as a roll bar to protect the head, the highest part sticking out.

One good thing is that the lightness of the shell does not raise the CG of the vehicle, so cornering with and without the shell is the same.

At high speeds, crosswinds push the VM nose left and right. Lots of wander. The rider’s body rocks left and right, adding to the sensation of instability. Again, it's nerve-wracking because of the chance of a high side rollover. In a streamliner, a crosswind blows the wheels out from under the vehicle, which automatically leans it into the wind, helping to reduce wander. The rider’s head is near the center of movement so the sensation of wander is less. And even if you go down (unlikely a high side), you fall a short distance and slide on the shell. By the way, foamshells don’t slide very far, unlike slippery composite shells.

Maybe as I get more miles (only 1200 so far, mostly on the bare trike), I will become more enamored with it. After riding the trike for a few weeks, I do notice that on a bike there is definitely energy being consumed to maintain balance. Now I understand why guys like Dave Balfour like trikes for 24-hour events.

I do love watching those front wheels turning, all from my human power. They are close and seeing the sun reflecting off the spokes, it’s mesmerizing. Can’t see the front wheel on a bike.

People in town are seeing this vehicle and saying, “I could ride that,” which is true. Very few can climb in a streamliner and ride off - way too much to deal with. And now with gas prices finally climbing to where they should be, my HPVs are all of a sudden becoming interesting to them.

Comments welcome!

John Tetz
Succasunna, NJ
September 2005

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