After tight comes loose: This flippant mechanic's saying about the abrupt end of a screw's life applies more than ever in the modern bicycle world. The hunt for the last gram does not stop at screws. Where steel bolts with a solid eight millimetre diameter used to hold the fort, several five millimetre titanium screws now often have to hold their heads up. There is not much room for manoeuvre between reliable "tight" and dangerous "loose". Manufacturers should therefore pay more attention to screw connections. For example, a designer's rule of thumb is often neglected, which states that with hard aluminium materials, the screw-in depth of a screw must be at least 1.4 times its diameter.
Even if you know the required torque: With a rusty bolt, it takes some force just to move the bolt, whereas a new bolt lubricated with high-quality assembly grease hardly rubs at all. With a few exceptions, all bolts on the bike should be greased - unless the manufacturer expressly forbids it. Also bear in mind that components settle: If components are screwed together, the parts adapt during operation, the joints become smaller and the clamping force of the screw decreases. It is therefore important to check the tight fit of the parts shortly after assembly.
Conversion factors from older torque specifications to internationally valid SI units:
1 kgcm = 0.0981 Nm
1ft.lb = 1.3558 Nm
1 in.lb = 0.113 Nm
1 Nm = 8.8508 in.lb
1mkg = 9.8067 Nm
Please also read our Market overview of torque spanners in the category Test & Technology: Accessories
