Bike Towing System 2

From 4LPH41337.com

Building Another Bike Towing System For Adventure Racing

Medical Tubing Tow System

Well, I am back at it again. Upon discovering Flex PVC at the local Home Depot, my mind instantly latched onto the word flex and the gears started spinning. If you read the first article on building a dog leash-based towing system, the one problem with that design was that the PVC would break under abuse (so yeah, both times were my fault, but still), leaving me having to carry around a broken towing system for the remainder of the race. Flex PVC to the rescue!

Stretching Medical Tubing

This time, I wanted to try a new towing system design--the medical tubing method. At the USARA National Championships last year, I saw a plethora of these types of designs for towing systems. In general, they weigh less than the dog leash towing systems, but the down side is that the medical tubing puts a constant pull on the towee. This means less efficiency than the dog leash design (where the pull on the towee by the dog leash is actually quite small), as the towee frequently has to tap their breaks to maintain safe distance from the tower--regardless of towee pedal speed or ease of travel.

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Parts and Tools

So let's get to it. Here's what you need (all of which you can get from Home Depot):

1/2" x 5/8" Flex PVC
3/8" Latex (a.k.a. Medical) Tubing
2 Hose Clamps
2 Non-Load Bearing Caribiners (1 preferably very small)
String of some sort
PVC Cutting Tool

Note: Ignore the 3/8" x 1/2" Flex PVC in the photo--I tried out the smaller version of the Flex PVC as well to see if I could make it lighter but the tighter piping made the medical tubing retraction...shall we say...dangerous to the tower's back side. The photos reflect the 3/8" x 1/2" Flex PVC, the primary differences in assembly being that once I switched to the 1/2" x 5/8" Flex PVC, I cut it shorter and the medical tubing retracts fully to the end of the PVC rather than hanging down.

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Assembly

First thing you need to do is cut the Flex PVC to length. This will be different based on wheel size and frame design, but I cut mine in such a way that the end of the PVC extends slightly beyond the back end of the back tire. This is to prevent retracting medical tubing from getting stuck in your rear wheel. With the dog leash design, we could rotate it to the side for unhooking. This is not the case with the medical tubing design, so care must be taken.

Threading the Medical Tubing

After the Flex PVC is cut, it is time to thread the medical tubing through it. The medical tubing is latex and sticks a bit to the inside of the Flex PVC, so I found the best method was to first run some string through the Flex PVC, then tie it to the medical tubing. Once tied on, it is easy to pull the tubing through. Tie one end of the medical tubing around the smaller of the two caribiners.

Clamping To Bike Seat

Affix the end of the Flex PVC closest to the caribiner to the framing of your bike seat using the small hose clamps. Make sure that the exposed end of the metal is pointing away from where your leg will be while riding. Some mountain bike seats may not have framing that jives with this medical tubing design, in which case it might be possible to attach the towing system to the horizontal bar of the frame (provided the Flex PVC piece is cut longer). Otherwise, you are out of luck, and I recommend taking a look at the dog leash design.

Stretching Medical Tubing

Once it is attached, you will need to gauge how long you want it to be. This should be based on both yours and any potential towees' riding comfort levels. At first I was worried that the medical tubing might break if stretched too far. However, latex has proved quite suitable for stretching. While the medical tubing is stretched, tie off the larger caribiner at the point at which your towees will be comfortable while riding. Let the tubing retract to see how it does and where it sits. For reference, mine has roughly a half inch of slack between it and the end of the Flex PVC when fully retracted.

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Summary

Tangle-Free Storage

It is certainly an inexpensive system to make, requiring a mere $10 for the materials used in the system and another $20 for the PVC cutting tool, which has other applications. As mentioned, there are trade-offs between the medical tubing design and the dog leash design, but I have a suspicion that replacing the rigid PVC sections on the dog leash design with Flex PVC would take stress off of the break point in the event of it getting kicked or stepped on (as was the case in previous breakages). Nevertheless, the medical tubing design is lighter, inexpensive, and less involved to make. Both are good for getting the job done. But after four races of using the medical tubing design, it has not broken once.