Spoke Hole Ultimate Strength Test

Why Test Spoke Hole Strength?

Spoke holes, or nipples holes, are where a spoke is threaded into a nipple and fixed at the rim side. We call the area where the nipple pulls against the rim the “key area, or nipple bed” which needs additional reinforcement. Poorly manufactured rims are likely to crack at this high stress area due to the significant amount of tension in the spokes.

Testing Goal

Ensure that the key area around the holes has been precisely reinforced in the layup process so that there is no pull through.

Testing Standard

300kgf without hole cracks or spoke pull-through. Comparatively speaking, most wheels hold a final spoke tension of ~120kg/f.

Sample Profile

Model Size Width Depth Measured Weight Test Condition
AM728 650B 28/34mm 28mm 409g Divided into 3 rim blocks

Test Facility

The spoke hole tensile strength is tested on the Universal Testing Machine (UTM). The machine has a rigid base with a clamping device to hold the rim firmly. Above of which is a steel clamp that pulls the spoke upward, gradually increasing in force until the spoke breaks or it pulls through the rim. Pulling force, rim deformation, and the breaking point data are recorded.

Test Conditions

Testing Speed 5mm/min
Spoke Sapim Race (2.0/1.8/2.0)
Test Positions 3:00, 6:00, 9:00
Test Method Destructive
Nipples External Nipples
Hole Angle +/-6°

*Samples taken from 3, 6, and 9:00 positions to ensure the accurate average spoke hole strength of a specific rim is recorded.

Methodology

  • Step 1:Divide the rim into three samples.
  • Step 2:Install a spoke and fully thread on the nipple.
  • Step 3:Clamp #1 sample firmly on the rig.
  • Step 4:Pull the spoke into the jaws and tighten down.
  • Step 5:Use the testing machine to pull the spoke away from the rim and gradually increase the force until a destructive event occurs.
  • Step 6:Reset the test, and repeat the process with new components for the other samples.
test-machine-clamping-base-2.jpeg

Specifications

The two criteria hereunder must be fulfilled during our spoke hole strength test.

1. There should be no noticeable deformation around the hole which undermines the wheel functionality at/under 300kgf.

2. After the test, the sample must remain completely intact and without any hairline cracks.

Test Results

#1 Sample

No. Deformation (mm) Max Force (kgf) Force At Breaking/Cracking (kgf)
1 8.90 395.8 366.8

#2 Sample

No. Deformation (mm) Max Force (kgf) Force At Breaking/Cracking (kgf)
2 5.26 395.1 384.6

#3 Sample

No. Deformation (mm) Max Force (kgf) Force At Breaking/Cracking (kgf)
3 10.21 423.9 397.7

Conclusion

In #1 rim block, the spoke pops out at a force of 366.8kgf; in #2 block, the spoke breaks at 384.6kgf; and in #3 block, the spoke pops out at 397.7kgf. All exceed 300kgf. Test passed.

Testing with the conditions defined above will ensure our rims can withstand spoke pull forces beyond what you would encounter during hard riding.

© All photos and test data by Light Bicycle

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