Bike Towing System

From 4LPH41337.com

Building A Bike Towing System For Adventure Racing

Note: Doesn't hold up in sub-freezing temperatures, when the PVC appears to not handle the stress of flexing well.

Tow System

Experienced adventure racing teams know that for the team to travel more quickly, methods need to be employed to reduce inequity in the abilities of the members. Towing is a commonly used tactic used to help the team move together at a pace that is quicker than the individual members can handle on their own.

Dog Leash

In researching how to build my own, I realized that there are a few types of tow systems designs developed for adventure racing. Most of the designs either employed rubber/medical tubing or a retractable dog leash as the tow rope. I chose to use the dog leash, and bought the smallest retractable cord leash I could find, which turns out to be the most expensive piece of the two system, pricing in at somewhere between $20 and $30. Make sure to not get the retractable ribbon leashes, as they easily get jammed while retracting.

Tow Rope

PVC was often used to extend the tow rope beyond the tower's tire so as to not get entangled in the tower's tire. PVC pipe parts became the primary material used for the tow system's frame. It took a few parts to get it right, but the final system has proved effective. Since dog leashes generally extend far further than is desirable for towing, the tow rope was cut to length before the bungee cord was tied onto the end. I cut the tow rope to 9'3", which seemed to allow for the dog leash to retract it even at speed and also not rack the towee's nerves at speed.

The towee attaches to the tow rope by hooking the carabiner from the tow rope to an open hook attached to the steering stem of his or her mountain bike. I say open hook because a closed hook the desire is to have the riders detach if either of the two riders crashed at speed.

Side View

For the dog leash tow system, the hand hold on the leash needs to have enough space for the mountain bike seat post to go through it. There also needs to be enough free space on the seat post vertically to support the dog leash, the tow frame, and anything else one might have mounted on it during and adventure race, such a bike repair pack or rear bike light.

Top View

The dog leash is threaded through the PVC piping, again to give it clearance from the tower's rear tire. Both the leash and the PVC frame are mounted by taking the mountain bike's seat post out and then putting the post through the dog leash and frame. This design enables both the leash and the frame to rotate around the seat post. This is important when the towee is unhooking from the tow, as testing has shown that during retraction the carabiner on the tow rope swings in an upward-facing concave curve, which sometimes results in it getting caught in the rear wheel's spokes on the tower's mountain bike. This would be a very bad thing at speed. Thus, when unhooking, the process is:

Towee indicates that he or she is unhooking.
Tower acknowledges, and swings the towing system frame to his or her right or left, so that it is clear of the rear wheel during retraction.
Towee unhooks and the tow line retracts.
Tower swings the towing system frame back to being over the rear tire again.

One thing that was noticed early on, is that the PVC frame's rotation was very liberal. I created some friction by sticking some insulating foam on the inside of the of the frame mount (where the seat post goes).

Detachable Tow

After adding foam in the frame mount to prevent rogue rotation of the towing system frame, the frame became very difficult to mount, as there was little space to insert the seat post into the frame mount. This created the need for a semi-permanent mount, so I wouldn't have to constantly put on and remove the towing system frame throughout the year. Both the ability to unscrew the rest of the towing frame from the frame mount and the ability of the dog leash to slide down past the bike mount enabled this. So, the frame mount stays on during training, and before a race, the dog leash is slid above the frame mount, then the tow system frame screwed on to the frame mount.

As to the parts, I tried to keep the plumbing parts to 1/2" parts, but unfortunately had to mix in a bunch of 3/4" parts (more weight) due to availability at my local Home Depot. So here is the part list for the towing system:

Tow System Labelled

Reducing Tee - 2 1/2", 1/2", 2 1/2"
Reducing Coupler - 3/4" F to 1/2" M
45 Degree Elbow - 3/4" I actually used a 3/4" bend for this, sawing the PVC in half to create the 45 Degree Elbow
Flexi Classic Long Retractable Cord Leash - 26ft Medium The leash cord was cut to 9'3".
Reducing Tee - 3/4", 3/4", 1/2" I sawed off the top 3/4" part, effectively making this a reducing coupler 3/4" F to 1/2" M with a hole in the top to allow for the threading of the tow rope.
Pipe - 1/2" 21 1/2" visible length. You may want to make a little longer or shorter to comfort.
Bungee with Integrated Carabiner.

Lastly, I added an ounce or two by slathering on some black paint--without which it would not be 1337.