Wrenching Your Own Bike: Torque

Here's a great primer from Jay Seiter of Pedro's on why setting certain fasteners to the proper torque specs, especially on a carbon bike, is critically important:

As a human powered vehicle, the weight of a bicycle is a major contributor to performance. This requires engineers to push the limits of each material and design they choose. The engineer must factor in material properties, part shape, riding conditions, product life, and more. [...] While carbon fiber allows for more optimal design and provides a far higher strength to weight ratio compared to steel and aluminum, it is also more susceptible to crushing and cracking when improperly set up. Simply put, the margin for error is much smaller. For this reason, using a torque wrench has become essential.

Read the whole interview at Pink Bike.

I keep 3 different torque wrenches on hand: the first is a 30+ year old S-K beam type wrench that is dedicated to torquing down my bottom bracket and my cassette. I bought it way back when I had a motorcycle. It's long beam allowed me to ease up to the required torque nicely. Being a 1/2" drive wrench, my Pedro's External BB socket and the 1" socket for my Park Cassette Lockring Tool go right on.

The big advantage of a beam type torque wrench is that they are very stable. If you are a little rough with it and bend the needle away from zero, you can simply bend it back - it's the main beam of the tool that is the part that is calibrated. Now, that's not saying I think it would still be accurate if you drove over it with your car, but it does not require the care of a click wrench.

The two other wrenches are click types, both of them 3/8" Craftsman wrenches, one with a lower range (25-250 in-lbs or 2.98-28.2 N-m) that handles low torque duties such as the pinch bolts on my non-drive side crank and handlebar stem bolts. The other one (10-75 ft-lbs or 13.5-101.6 N-m) handles torquing that is too much for the small one to handle and offers precision the beam wrench cannot provide - this one is almost exclusively used on my car.

One big advantage of the click type torque wrenches over the bar type is that when you have to achieve a high torque, sometimes you have to position your body to pull on the wrench in such a way that you can't see the needle and the gauge. This is especially true when you are working on your car and you are under there with your hands and the wrench deep in the workings of your car. You just feel the click through your hand when the set torque is reached.. However, more care is required in their use and storage as the Jay said in his interview with Pink Bike.