I wrote earlier about two recent incidents of Thomson Elite seatposts breaking during use, without any prior warning to the users (see here and here). I persisted in trying to extract as much information from Thomson about these happenings. Two phonecalls and an email to them never went through due to some obvious hindrances but just earlier this week, I was able to converse with David Parett, a manager and PR specialist at L.H Thomson Inc. Although they are a relatively small company, they seem to take pride in the fact that apart from the cycling side of the business, they're also a contract manufacturer designing and making parts for clients such as Boeing, Trane, Ford, Coors, Reliance Electric and so on. One can imagine that to gain the trust and business of such big name companies, you'd find it absolutely necessary to have sound manufacturing and quality control down on the floor.
One of the owners of the posts (with the broken head) sent it in to Thomson for analysis. When I talked to the user, he made the comment that he was 100% certain he used a torque wrench to tighten the bolts before use (documented here by 'Apacherider'. He reported he used a Park Tool torque wrench that only goes to 60 in-lbs which is the max torque recommended by Thomson for the bolts). However, the following is what Dave had to tell me from first impressions. Read it, and leave a comment if you would like to roundtable a discussion.
DIVOTS IN THE SEATPOST CRADLE
Dave : "There is no question that this failure was related to torque. This was easy to see as when I got the broken post, two divots caused by the bottom clamp had formed in the cradle of the post. We know how much torque that takes, and it is a big number. The user may feel they torqued it properly but there is ample evidence that is not true. I think most parts will fail if abused in such a manner. Imagine overtorqued handlebars, stripped pedal cleat bolts, etc. Or think of a car. If you torqued a sparkplug to 3 times the suggested value,what do you think would happen? We know from testing here at Thomson that there is no other way one could create those divots unless you overtightened the clamping bolts."
DISTORTED BOLT HEADS
Dave : "I also observed that the bolt heads are distorted. The bolts are grade 12.8. We know how much torque it requires to distort the bolt heads, and it is in excess of 125 inch pounds. Further, the metal shows no signs of material contamination, and the post is within spec as far as dimensions go. We have a lab here and we have examined the post. Moral of the story is, 2.5 to 3 times the recommended torque will break things."
ANODIZATION AND FATIGUE LIFE OF 7075-T6 AL
Dave : "I verified our anodic coating thickness. It is about .001" thick. Yes, anodizing cuts fatigue life, almost to 50% the original. But we engineer around that. Our post is heavier than it would otherwise have to be to deal with that. If you thinned it out, it would be susceptible to being crushed by clamping. Paint or powder coat cannot provide this kind of corrosion protection.The ridges may help with slipping, help keeps the finish from scratching and is also cosmetically appealing to some people. The finish changes near the radius at the seatpost head to help prevent stress riders."
ABOUT THE BROKEN BOLTING EAR AND THE BENDING FUSE
Dave : "The other post has not come back here as far as I know, but all our testing indicates it takes in excess of 600 pounds of force to cause an ear to fail and it would not fail in the manner it did. A brittle failure like that is again related to torque. Testing here shows that the original design idea is still valid. A riding event or accident results in a bend. All components of the top of the post, bolts, clamps, barrel nuts, ears are stronger in relation to the tube. If there is a big hit, the post will bend and the clamping mechanism will not fail. You can negate this by putting the ears under severe tension with torque."
SOURCING, STANDARDS AND QUALITY CONTROL
Dave : "The anodizing is done in Reading, PA, The Al ore is from Quebec, CA and the extrusion is done in Minnesota. All the fasteners are from Chicago and Cleveland. All of them are certified and rechecked by us. There are barrel nuts and bolts in receiving inspection right now, placed under a heavy load. If we observe any failures in the entire shipment, it will be tested and possibly rejected. I don't think anyone does that but us.
From filming riding, we have a series of in-house tests that were used in design and are still used on every lot of material. Bolts, washers and everything are checked for ultimate strength, fatigue life and corrosion resistance using a 500 hour salt spray test. We also had a German lab check our posts to the CEN standard. We think the CEN is a poorly designed test, but we passed it as well. The 500 hour salt spray test is run on samples from each anodize lot to verify quality. Further, we have a fatigue tester. We can put a post in it, set the bolts at the level the customer had them and create that failure. There just is no question of what happened after that.
We expect our products to last for 10 years in the field under normal conditions. If a customer experiences an issue, we replace the part for goodwill. My frustration with all this is there is not a single company out there that does 10% of what we do to check incoming material quality, 100% checks at each machining operation, and certification and testing of all components. Our bike parts are built to the same standards, in some cases higher, than the airplane parts we make."
ADDITIONAL RESOURCES :
Seatpost Clamp Mechanics
Torque & Tightening Components : Perspectives from Easton R&D (pdf)
Thomson Elite Setback Seatpost Failure
Thomson Elite Bolting Ear Failure
Torque Wrenches, Their Types and History by Charlie Zarek
Torque Wrenches - How Good Are They?