Our performance goals for the towline included the following:
Minimize relaxed length. Towline should not drag on ground when unclipped.
Minimize weight.
Towline should extend to comfortable following distance with minimal force.
Towline should have good shock absorbing properties over
typical towing forces.
In the chart below, performance-related properties of WeGo Team Link Standard,
WeGo Team Link Race, and thin bungee are compared.
The properties
are discussed in detail below the chart.
WeGo
Team Link
Standard
WeGo
Team Link
Race
1/8 bungee
( 36" )
tied to 2 clips
Relaxed length
32
30
36
Bungee may
drag on ground
when unclipped.
Towline
weight
3.3 oz.
1.7 oz.
0.6 oz.
Force
required to extend line to comfortable following distance (60)
9 lb.
1.7 lb.
2.4 lb.
WeGo Team Link Race extends
more readily than bungee.
2 - 5 lb.
towing force (light to moderate towing on level
ground)
Length
37 - 54
64 - 77
52 - 81
Shock-absorbancy
(all values > .10 are equally good)
.12 -
.26
.12 -
.31
.06 -
.44
Bungee is stiff beyond
3.5 lb. force.
5 - 12 lb.
towing force (moderate to heavy towing on level, light
to moderate towing uphill)
Length
54 - 65
77 - 90
81 - 90
Shock-absorbancy
(all values >.05
are equally good)
.05 - .12
.05 - .12
.03 - .06
Bungee is stiff
during
moderate towing.
12 - 20 lb.
towing force (very heavy towing on level, moderate to
heavy towing uphill)
Length
65 - 84
90 - 99
90 - 94
Shock-absorbancy
(all values >.03 are equally good)
.05 -
.09
0 - .12
.02 -
.03
WeGo Team Link Race is shock-absorbing up to 15 lb.Bungee is very stiff throughout.
Summary
WeGo Standard serves well for moderate to heavy towing.
WeGo Race gives best all-around performance for towing at 15 lb. or less.
Bungee performs well for very light towing only.
Legend:
Good
Fair
Poor
Relaxed length
Ideally, when the follower unclips the towline and lets go, the
towline will not drag on the ground. Thus, the towline should be no
longer than the leader's inseam plus three inches.
Towline weight
Lighter weight is better, especially for
competitive athletes. We designed the WeGo Team Link towline
to be as lightweight as possible while exhibiting the other
important properties listed here, and while being durable enough
to withstand at least one season's heavy use.
Length during use
The ideal following distance for a person being towed
over trail or terrain is six to eight feet.
This allows the follower to see far enough in front of her/his
feet to anticipate obstacles.
Five feet is acceptable.
When towing over a smooth surface such as pavement,
it is only necessary for the follower to keep from stepping on the
leader's heels. In this situation, a following distance of about four
feet may be acceptable.
Shock-absorbancy
When we walk or run, our torsos do not move forward at a
perfectly constant speed. With each step, our torsos surge, then
slow. A static towline, such as a rope, transmits these micro
accelerations and decelerations, resulting in rapid (less than a second)
fluctuations in towing force. In short, a static towline is jerky.
Jerkiness is uncomfortable and results in fatigue as a person's
trunk muscles work to counteract these jolts.
Maximum efficiency and comfort are achieved when the
towing force is relatively constant, or changes gradually over the
course of many seconds or minutes.
Thus, it is important for a towline to absorb the micro
accelerations and decelerations.
Thin (approx. 1/8") bungee, a common towing solution in
team adventure sports, is shock absorbing at light towing
forces. However, at moderate and heavy towing forces,
it maxes out and approaches
the behavior of a static line. Even in situations
where towing is generally light,
moderate to heavy forces
come into play
at least momentarily when traversing rough terrain or going uphill.
Also, heavier towing is needed when a teammate "bonks"
(becomes extremely fatigued).
A towline is shock absorbing at a given towing
force when it extends easily at that force.
Thus, we measure shock-absorbancy as inches of stretch per
incremental pound of force.
We normalize this number by dividing by the towline's relaxed length.
Finally, at each force, we average shock-absorbancy across a four inch
window centered at the length of the towline when extended at that force.
The four inches corresponds approximately to double the amplitude
of the back-and-forth motion of a runner's torso with each step
(double because the towline connects two runners).
Desirable shock-absorbancy varies with towing force.
We find that, at light towing forces, a shock-absorbancy of at least
0.10 is desirable. At moderate towing forces, 0.05 is sufficient,
and at heavy towing forces, 0.03 is sufficient. More shock-absorbancy
beyond these values is not better.
