Stem Fatigue Test
by Damon Rinard

Note: the actual testing of stems is over with, but please feel free to criticize or make suggestions about this page. Contact Damon Rinard: drinard@yahoo.com

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.

Test Protocol

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, Damon Rinard, at drinard@yahoo.com for clarification on testing methods, etc., but please contact Holland Cycles directly to get a brochure or place an order:

Bill Holland Cycles Inc.,
3735 Kenora Dr., Suite B
Spring Valley, California 91977
USA
voice: 619-469-1772
fax: 619-469-1795

And now, here's what you've been waiting for... the test results!

Raw Data

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?

chart: stem fatigue results

 

Stem Weight: which stems are lightest?

chart: stem weights

 

Stem Stiffness: which stems are the stiffest?

chart: stem stiffness

 

Stem Stiffness-to-weight Ratio: which stems are the stiffest for their weight?

chart: stem stiffness

 

Stem Fatigue Life-to-Weight Ratio: which stems live the longest for their weight?

chart: stem fatigue life to weight ratios

 

Notes

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.

Home back to Damon Rinard's Bicycle Tech Page

Copyright 1997 Damon Rinard drinard@yahoo.com

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