About a year and a half ago Lennard Zinn wrote an article in Velo News regarding the importance of the use of torque wrenches. In the article he mentioned an informal study done on division I bikes found that most every bolt on the bike was over-tightened; sometimes by twice the manufacturers recommended torque. Furthermore, it was found that only a couple of team mechanics made used a torque wrench in their frequent bike checks. The over-tightening of the bolts was probably the result of the common tightness check, when the mechanic would gently snug the bolt just to make sure it was tight, over time these “snuggings” resulted in the over-tightening.
What I am getting at is that “snugging” is a relatively well-established technique and a very, very common behavior. Up until recent years very few failures could be directly attributed to it. That is not so much the case. In this day of 350g full carbon forks and sub 100g magnesium stems, the once effective and benign (albeit stupid) mechanical practice, now can cause immediate and severe damage. A recent and controversial post mentioned the failure of a carbon fork at the tour of Qatar. Since the fork was tested to withstand much greater stresses than the rigors of its use, the assembly of the stem and headset were questioned as the cause of the failure. This is a bike assembled by a professional mechanic, what can be expected by lesser qualified mechanics and non-mechanically inclined bike owners. How many owners of ultra-light stems put their bikes together in the hotel room after a flight using nothing but a fold out mini-tool?
Of course the use of a torque wrench will solve this problem. The fact of the matter is that most individuals, and many shops don’t use torque wrenches. A torque wrench is only good if there are torque specs to go along with it. While some products, Syntace areo bars for instance, print their torque specs on directly on the part, easy access to torque specs is not always the norm. This also assumes that torque specs are accurate. I have seen several instances where manufacturer recommended torque was not adequate to prevent the bolt from loosening, or the part from sliding.
Question 1
Is there a point where parts become so light that the margin for improper installation is to small for the part to be considered safe for the average rider? Have parts on the market now reached that point?
Question 2
For those involved in the manufacture and design of bikes, to what extent is reasonably improper installation taken into consideration in the design and testing of the product?
Question 3
How many of own/use torque wrenches out there? What are you observations on the adequacy and accuracy of torque ratings?
Thanks for entertaining such a long post
What I am getting at is that “snugging” is a relatively well-established technique and a very, very common behavior. Up until recent years very few failures could be directly attributed to it. That is not so much the case. In this day of 350g full carbon forks and sub 100g magnesium stems, the once effective and benign (albeit stupid) mechanical practice, now can cause immediate and severe damage. A recent and controversial post mentioned the failure of a carbon fork at the tour of Qatar. Since the fork was tested to withstand much greater stresses than the rigors of its use, the assembly of the stem and headset were questioned as the cause of the failure. This is a bike assembled by a professional mechanic, what can be expected by lesser qualified mechanics and non-mechanically inclined bike owners. How many owners of ultra-light stems put their bikes together in the hotel room after a flight using nothing but a fold out mini-tool?
Of course the use of a torque wrench will solve this problem. The fact of the matter is that most individuals, and many shops don’t use torque wrenches. A torque wrench is only good if there are torque specs to go along with it. While some products, Syntace areo bars for instance, print their torque specs on directly on the part, easy access to torque specs is not always the norm. This also assumes that torque specs are accurate. I have seen several instances where manufacturer recommended torque was not adequate to prevent the bolt from loosening, or the part from sliding.
Question 1
Is there a point where parts become so light that the margin for improper installation is to small for the part to be considered safe for the average rider? Have parts on the market now reached that point?
Question 2
For those involved in the manufacture and design of bikes, to what extent is reasonably improper installation taken into consideration in the design and testing of the product?
Question 3
How many of own/use torque wrenches out there? What are you observations on the adequacy and accuracy of torque ratings?
Thanks for entertaining such a long post