| Stem Fatigue Testing by Damon Rinard |
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Note: the actual testing of stems is over with, but please feel free to criticize or make suggestions about this page. Contact
The crew at Bill Holland Cycles performed some stem fatigue testing in 1995 or so. Bill Holland kindly gave permission for me to post the results here. On this page I'll try to describe the test protocol and other interesting bits about the testing.
I have included several charts on this page. There are charts ranking stems according to fatigue life, weight, stiffness, stiffness-to-weight ratio, and fatigue-life-to-weight ratio. This information was derived from the measurements used to accomplish the fatigue testing.
Setup
The fixture used was a rigid square steel structure with a fork steerer tube welded vertically into it. For testing, each stem was mounted in the fixture's steerer tube using its own expander bolt and wedge just as it would be installed in a real fork. All stems were mounted at the indicated maximum height line.
Static Loading
A technician bolted a long steel bar into the stem like a straight handlebar. Weights were added to one end of the bar until a torque load of 1651 in*lbf was on the stem. Downward deflection was measured parallel to the stem's quill at a point on the bar 5 inches from the centerline of the stem.
Fatigue loading
Loading during fatigue testing for all stems was +1651, -0 in.lb. at approximately 1 cycle per second, applied to just one side of the stem.
Feel free to contact me, for clarification on testing methods, etc., but please contact Holland Cycles directly to get a brochure or place an order:
And now, here's what you've been waiting for... the test results!
In the chart below,
STEM is the stem tested.
CYCLES is the number of load cycles to fatigue failure.
WEIGHT is the mass of the stem in grams.
DEFLECTION is how far, in inches, the bar moved with the 1651 in*lbf torque load applied.
ST/WT is the stiffness-to-weight ratio of each stem. It is 1000*(1/DEFLECTION)/WEIGHT, in 1000/(in*g).STEM CYCLES WEIGHT DEFLECTION ST/WT Holland, polished ti 2,323,090* 208 0.262 18.3 Holland, raw ti 1,090,440 208 0.280 17.2 3TTT Synthesis 610,500 269 0.310 12.0 Ritchey ForceLite 545,160 296 0.208 16.2 Cinelli Grammo ti 168,720 190 0.330 15.9 Litespeed ti 139,080 205 0.286 17.1 Profile TIG steel 91,200 219 0.312 14.6 *This stem did not fail. Machine was turned off after 2,323,090 cycles.Stem Fatigue: which stems last longer?
Stem Weight: which stems are lightest?
Stem Stiffness: which stems are the stiffest?
Stem Stiffness-to-weight Ratio: which stems are the stiffest for their weight?
Stem Fatigue Life-to-Weight Ratio: which stems live the longest for their weight?
A Cinelli XA was initially included in the test, but twice during fatigue testing the stem binder bolt broke. The stem itself didn't show any kind of failure, so after replacing the bolt the test continued to failure. Later the standard loading for fatigue testing was changed, so the data for this stem is not comparable to the others.
The 3TTT Synthesis failed during the night when the expander bolt's head broke off. However, the cone did not come loose and the test continued without the expander bolt until the deflection increased dramatically. We stopped the test and removed the stem, and only then discovered a crack growing from the corner of one of the slots in the quill hidden deep inside the steerer.
Most of the other failures were cracks in the quill tube, extension tube or the weld connecting these two tubes. Here's a sampling of the notes on failure modes:
Cracked in quill at bottom weld. Cracked in extension at quill. Welds polished around quill. Did not break. Cracked in quill, across weld. Cracked in quill, across weld. Quill cracked below bottom weld. Cracked along top of extension and on the compression side of quill weld. Cracked in quill, across weld. Cracked in extension at handlebar clamp. Across weld.Thanks to the crew at Bill Holland Cycles for permission to post this data.
Note from John Allen: certain stems are prone to early failure due to outright defective design or manufacture. See examples in a photo gallery and a Web page.
Copyright © 1995-2001
Last Updated: by Harriet Fell
