A New High Performance Control Cable System:
Design, Test and Evaluation
by Kenneth W. Moll, Senior Technical Staff, W.L. Gore & Associates
HISTORY OF BICYCLE CONTROLS
The Macmillan Ordinary bicycle evolved by 1895 into the pneumatic tired safety bicycle.
In the last 100 years such innovations as the freewheel, rod operated brakes, cable operated gears and brakes, two and three-speed hub transmissions, multiple speed derailleur transmissions, and the development of strong lightweight composite and alloy frames and components have improved rider comfort and safety. More recent innovations in transmissions have included such systems as the Shimano Hyperglide© system and chainring ramps improving positive shifting performance.
In the past decade or two, significant innovations have been made in controls made necessary by the improvements in actuators. Recent examples are the top mount or thumb shifter, the Shimano Rapid-Fire© system, and most recently the twist-grip index shifter controls pioneered by the SRAM Corporation’s Grip Shift© system.
Another recent attempt at reducing the ergonomic impact of using the thumbs and fingers extensively is typified by the weak spring derailleur system. These systems, while clearly reducing the force required by a rider’s thumb or finger, are handicapped by the weaker return spring not as easily overcoming the effects of increased friction in cable systems due to contamination, freezing, etc.
SHIFTING, BREAKING AND THE TRANSFER OF FORCES
Brakes and gear shifters are usually activated by cable systems patterned after the invention of Frank Bowden, founder of the Raleigh Bicycle Company. Conventional Bowden type cables consist of a flexible inner wire, usually of a steel alloy, encased in an ideally incompressible outer housing.
When a housed wire is placed in tension for the purpose of transmitting force from a control to an actuator such as a derailleur or brake caliper, there is an equal and opposite reaction force transmitted by the housing from the actuator mount to the control mount.
For precision positioning, this reaction force must be transmitted with as little
displacement as possible. Any compression in the housing or excessive clearance between the inner wire and the housing liner will result in hysteresis. This will be perceived by the rider as missed shifts, or "soft" and "sloppy" brake performance. This phenomenon is one reason the modern interrupted housing systems, including a new type of housing, were developed, reducing the impact of housing compression. Another benefit is reduction in both friction and weight resulting from reduced housing lengths.
THE EFFECTS OF CABLE ROUTING
When a cable within its housing is routed around a bend, depending on the internal clearance and bend radius, there is a corresponding increase in drag. The tighter the bend, or the more bends there are, the higher the drag. Modern fully suspended mountain bikes have exacerbated this problem by requiring tighter bends, routing through internal tubing, or rerouting to accommodate rear suspensions. To insure a minimum of bend induced drag, cable system designers have attempted to maximize the clearance between the inner wire and the housing liner. There is a significant penalty to be paid with larger clearances because the pathways are much larger for contamination to enter and cause problems, and the potential for increased hysteresis.
CONTAMINATION AND MAINTENANCE CONCERNS
With the introduction of the interrupted housing systems required for index shifters, the potential for contamination entering between cable and housing and causing difficult, is dramatically increased. In addition to the primary point of contamination entry at the end
of the housing nearest the derailleur, there are now two or more additional points of contamination entry. These occur where the cable housing is fitted into the braze-ons. A dirty cable can result in difficult to impossible shifting, and cause premature wear on actuators and controls. This requires frequent cleaning, adjustment, and premature cable replacement to maintain functionality.
IMPROVEMENT NEEDED
With this background, we can define an "ideal" control cable system. The features of such a system would include friction free operation, elimination of wear and wear induced changes in performance, elimination of periodic maintenance and adjustment, a high tolerance for dirt, mud, road salt and other contaminants, and long life.
Since a leading cause of rider frustration is poorly performing shifting systems, the benefits to the rider will be reduced hand effort and fatigue and accurate repeatable shifting regardless of riding conditions.
Benefits to bicycle designers and manufacturers will be the ability to explore new design options that demand tortuous or lengthy cable routing. There can be reduced warranty
costs, and a new level of customer satisfaction with "user-friendly" control systems.
A UNIQUE SOLUTION
RIDE-ON©
HYPERFORMANCE™ BICYCLE CABLES
THE DESIGN
In early 1991, engineers and technologists from W.L. Gore’s Medical Products Division facility in Flagstaff, Arizona discovered that a Gore-Tex© expanded PTFE coated high-strength wire would provide an exceptionally low friction, long life shift control cable system. During 18 months of product development, there were material and process
optimizations, and extensive reliability and life testing including field testing. Only then did the Ride-On-Hyperformance™ Cable System meet the quality and performance standards required to support a one-year product warranty. The product evolution progressed from a coated wire to a coated wire plus a continuous liner to a coated
wire plus a continuous liner plus a sliding umbrella seal.
BENCH TESTS
The need for quantitative data to compare with industry standards led to the use of a standard laboratory test which measures cable system efficiency under simulated loading and use. The test setup is illustrated in Figure 1. The test weight of approximately 14 Kg. results in a cable tension in the range of 32 pounds force. These values were found by tensiometer tests to be in the normal range of a variety of bicycle cable routings and shift system designs.
The length of stroke was established to simulate a rear derailleur being shifted from lowest to highest gear and was set at 35 mm. The test radius is set by routing through a standard bottom bracket guide, and is 19 mm. The cycle rate is 2000 strokes per hour, which was
found to be slow enough to eliminate the potentially confounding effects of local heating on the outcome, yet rapid enough to allow efficient data gathering. The test is run for 10,000 cycles with measurements made initially and at each 2,000 cycles thereafter.
The efficiency is calculated as follows:
Efficiency = w/fn x 100 (%)
where
w = the test weight
fn = the measured force at n test cycles
Baseline data were gathered on the most commonly used premium quality cable systems. All data were analyzed using commercial statistical software.
THE RESULTS
The most obvious result is that the Ride-On© cable system efficiency after 10,000
test cycles was approximately 4% lower than new conventional cables tested under identical conditions. At the beginning of the test, at 0 cycles, the Ride-On© cable system’s 15% advantage widened to 29 % after 10,000 cycles. The reduced deterioration with use
means that shift system performance is much more constant and accurate over a longer period of time.
Another measure was derived from the data to indicate the actual effort required by a rider to move the derailleur from gear to gear. This characteristic is labeled "effort" and is the
numerical difference between the force measurement and the test weight moved by that force. The effort required to move the test weight is a truer measure of the "loss" in the system, and is the most perceptible measure to a rider. When averaged over the entire populations tested, and over the entire range of the test (0 to 10,000 cycles), the conventional cable’s average effort is 25.6 pounds force while the Ride-On© cable system effort averaged only 7.8 pounds force. This 70 percent reduction in shift lever effort translates to an immediate perceptible performance improvement to the rider.
| Test Cycles |
Ride-On Efficiency (%) |
# Systems Tested |
Conventional Efficiency (%) |
# Systems Tested |
| 0 |
87.9 |
156 |
72.5 |
13 |
| 2000 |
85.2 |
150 |
61.4 |
10 |
| 4000 |
81.9 |
146 |
58.1 |
10 |
| 6000 |
79.7 |
148 |
54.7 |
13 |
| 8000 |
78.2 |
139 |
51.7 |
13 |
| 10000 |
76.5 |
139 |
49.7 |
13 |
ROAD AND TRAIL TESTS
While bench testing provides comparative data, it cannot include the deleterious effects of contamination from dirt, water, sand, spilled energy drink, road salt, sweat, and ice buildup that can occur during actual riding. To evaluate any adverse effects that may occur due to these factors, an extensive field test program was planned and conducted using both road and mountain bikes in a wide variety of climates and seasons. Test riders were requested to complete a riding diary as well as evaluate the cables under test. There were 110 riders in the test program, including professional, team, and OEM factory test riders. The field test results validated the laboratory results with a high degree of correlation. The test rider reports were essential and helped to determine commercial viability.
COMMERCIAL RESULT
The Ride-On© derailleur cable system has been available commercially since the summer of 1993. Brake control systems were introduced in the Spring of 1994. There are currently hundreds of thousands of satisfied riders throughout the world using this innovative cable
system. The novelty, non-obviousness, and commercial value of the Ride-On© cable system design were validated by the issuance of United States Patents.
RIDER BENEFITS
The increased system efficiency and sealed design provide a number of features with their attendant rider benefits.
"The continuous flexible tubular polymeric liner allows for much less contamination of the entire cable system, which will dramatically offer the following advantages over other cable systems that are currently on the market:
Less friction
Less wear
Less frequent replacement
Less maintenance/ adjustment
Longer life
Reduced compression of housing(s)
Greater gear-shifting accuracy
Greater range of design options
Less expensive than upgrading to more
expensive derailleurs and shift levers
Reduced effort/ stress/fatigue /overuse
injury."(1)
These features and benefits make riding more enjoyable, improve competitive performance, and enhance the overall riding experience.
CONCLUSION
The Ride-Ons cable system is the first significant advance in bicycle control cable in the last twenty years. Every other component of a bicycle has been improved dramatically. Components are lighter, stronger and more durable.
The Ride-On system allows the rider to take full advantage of the improvements in control components like never before.
Hyperglide and Rapid Fire are trademarks of the Shimano Co.; Grip Shift is a trademark of SRAM Corporation; Gore-Tex, Ride-On, and Hyperformance are trademarks of W.L. Gore and Associates, Inc.
REFERENCES
l.)Edmund R. Burke, Ph.D., unpublished personal communication, 1993.
Kenneth W Moll, B.Sc. in Physics/Applied Mathematics Senior Member of the American Society for Quality Control; Certified Quality Engineer. A senior member of the technical staff at W.L. Gore and Associates Medical Products Division, Flagstaff Arizona since 1974.