S and S Machine
Bicycle Torque Couplings (BTCs)
Your Travel Bike........Your Only Bike!

Bicycle Torque Coupling Deflection Test

These tests demonstrate that in torsion, tension and bending, a tube that has an S and S Bicycle Torque Coupling installed will be stiffer than a plain section of Reynolds 531 bicycle tube. The details of how the fixtures work are included. For a quick review of the results, see the photos with the purple dots. The dots show how much flexing takes place. In each test there is more flex in the plain tube than in the tube section with the coupling. The results and conclusions for each demonstration are also included.

The combination test fixture

• This fixture is actually three independent test fixtures mounted on one base for compactness. We originally made it as three fixtures but later combined them as our booth space at bikes shows became limited.
• Only one test is performed at a time.

Standard test criteria

• Each test compares a 4 inch section of Reynolds 531 tube to a 4 inch section of Reynolds 531 with an S and S Bicycle Torque Coupling installed.
• In each fixture a single load is applied to both test sections simultaneously so that the force is equal in both samples being compared.
• In each test the coupling was tightened with our standard 6" spanner wrench.
• Flex is measured with dial indicators. The purple dots represent the amount of indicator movement in thousandths of an inch.

Torsion test fixture

     Tube only           Tube with coupling

Torsion test

• Fixture layout: The fixture has a tube that is bolted in solid on the left end and is free to rotate in a bearing on the right. A lever is attached to the end of the tube beyond the bearing.
• Application of load: When the lever is pushed down it twists the tube.
• Measurement method: A collar with an arm is attached to the tube and a dial indicator is attached to the arm. A second collar with an arm is attached 4 inches away. The indicator plunger from the first arm rests against the second arm. Two indicator assemblies are attached to the tube. One is placed in the plain section of tube and the other is placed in the coupled section of tube with a collar on each side of the coupling. When the lever is pushed down the arms on the collars move closer together. The indicator shows the amount of twist between the arms. A stiffer section will allow less twist.
• Results: There was.020" twist in the tube section without the coupling. There was .009" twist in the section with the coupling.
• Conclusion: This test demonstrates that in torsion the tube section with the coupling is stiffer than the plain tube.

Tension test fixture

         Tube only            Tube with coupling 

Tension test

• Fixture layout: The tension test fixture has a tube that is bolted in solid on the right and it goes through a hub on the left that can slide but not rotate. A threaded collar with a lever is screwed onto the hub until it bottoms out against the end of the fixture. (See the threaded collar and lever in the first photo)
• Application of load: When the lever is pushed down it moves the hub to the left which pulls on the tube.
• Measurement method: Two collars are clamped to the tube 4 inches apart. A dial indicator is mounted to one collar and the plunger rests against the other. Two indicator assemblies are attached to the tube. One is placed in the plain section of tube and the other is placed in the coupled section of tube with a collar on each side of the coupling. The dial indicators show the amount of stretch between the collars. A stiffer section of tube will allow less stretch.
• Results: The collars in the plain tube stretched .005". There was .001" stretch in the tube section with a coupling.
• Conclusion: This test demonstrates that in tension the tube section with the coupling is stiffer than the plain tube.

Tube only                 Tube with coupling

Bend test

• Fixture layout: The bend test fixture has two tubes mounted vertically. One tube has a coupling installed and the other does not. A linkage connects the tubes at the top. A lever controlled eccentric mechanism is located in the center of the linkage.
• Application of load: When the lever is moved the eccentric mechanism shortens the linkage which pulls the tubes together causing them to bend. The mechanism holds the tubes together once the lever has been flipped for a more accurate reading.
• Measurement method: A collar with a 4 inch vertical arm is attached to the tube. A dial indicator is mounted on top of the arm. The plunger of the indicator rests against the tube. An identical assembly is installed on each tube and they are positioned on the tube the same distance from the fixture base. The indicators show how much bending takes place in the 4" section of each tube. A stiffer section of tube will allow less bending.
• Results: The indicator in the plain section of tube bent .010". There was .006" bend in the coupled tube.
• Conclusion: This test demonstrates that in bending the tube section with the coupling is stiffer than the plain tube.