"Tightening screws" is an essential task in bicycle assembly.
There are many types, ranging from hex bolts to Phillips and flat-head screws.
I'm sure everyone has touched them at least once, right?
Since screws are just tightened or loosened, they are relatively easy parts to handle.
However, it’s a different story if someone asks, "How much force did you use to tighten them?"
In order to properly manage this tightening force with numbers, there is a technical term called "tightening torque."
When I first started out as a mechanic, I wasn't taught numbers, but rather vague expressions like "tighten it like it's your parent's killer" or "tighten it until it won't turn anymore, then give it a little more." I remember thinking, "But both my parents are still alive!" (laughs).
Anyway, setting that story aside.
These days, the world is flooded with lightweight aluminum and carbon parts.
If you tighten these parts with all your might, they will break in an instant.
In other words, tightening screws with full force is a big no-no.
Here is an example of what happens when you overtighten.
This is a Thomson X2 stem cap.
It’s beautifully cracked.
This is a perfect example of overtightening.
In this condition, the handlebar isn't properly secured, which can lead to a serious accident if the bars twist while you're riding.
Please be careful.
Now, hearing this might make you even more unsure about how hard to tighten things, but depending on the part, the value is actually written right on it.
For example, it looks like this.
This indicates that you should tighten the stem cap to 5.1 N/m.
To measure this, since it's impossible to do by feel, you use a "torque wrench."
It’s a tool like this.
By setting the gauge to this, you can tighten it exactly to 5.1 N/m.
With this, both your parts and your tightening force are taken care of.
Screws are the parts of a bicycle you are most likely to handle, but every screw has a proper tightening torque. I hope you manage them properly and enjoy a safe and comfortable ride.