If the chain comes off while you're shifting gears on your bicycle, it might be due to insufficient derailleur adjustment.

When you intend to shift to an inner or outer gear, the chain can overshoot that gear and come off.

When this happens, you become hesitant to change gears.

Derailleurs can be adjusted for both position and stroke, so it's good to know how for a comfortable cycling experience.

Know the names, functions, and mechanisms of parts

Before making adjustments, it's good to know the basic names of the parts.

If you can handle everything 100% by yourself, it's not that crucial, but when talking with fellow cyclists, you'll often refer to parts by their names.

Just knowing the part names will help you follow the conversation, so it's important to know the terminology.

A "derailleur" refers to the entire mechanism that changes gears.

By switching the shift lever on the handlebar, a cable is pulled, causing the "front derailleur" (the part that touches the chain) to move left and right to change gears.

The range of motion of the front derailleur is called its "stroke."

Adjustment is typically done with two "adjustment screws," by tightening or loosening them.

By the way, the heads of these screws have a cross-shaped groove, so they are called "Phillips head screws" or "cross-head screws."

Also, while "screw" and "bolt" are similar terms, "screw" is a general term for anything with a threaded shaft, while "bolt" refers to something with a head and a cross-shaped or hexagonal recess.

However, generally, either "bolt" or "screw" will be understood.

How to adjust a front derailleur

Adjusting the front derailleur is something you can definitely do yourself, as long as you understand how the adjustment screws work.

All you need is a Phillips head screwdriver.

If the screws have a hexagonal recess (cap screws), you'll need an Allen key.

The two screws set the limit positions (stroke ends) for the LOW and HIGH sides, respectively.

First, switch the shift lever to the LOW side to change gears.

With the chain on the smallest gear (LOW), adjust the gap (clearance) between the inside of the front derailleur and the chain to about 0.5mm or 1mm.

At this time, the key is to ensure the chain does not touch the front derailleur when you spin it.

Adjustment is simply a matter of turning the screws.

When adjusting the derailleur, you'll need to rotate the wheel.

If you have a city bike with a kickstand, that's fine, but for a sport bike, you'll want to have a stand ready.

Searching for "maintenance stand" on Amazon or similar sites will turn up options for around 1500 yen.

They're not that expensive, so it's a good idea to own one, or you could borrow one from a friend to make your adjustments.

They can also be used for brake repairs and adjustments, so owning one won't be a hindrance.

Some are even foldable, so storage shouldn't be an issue.

For the HIGH side, you just reverse the inside and outside.

Shift the lever to change gears so that the chain moves to the largest gear.

With the chain on the largest gear, you just need to create a gap of about 0.5mm to 1mm between the front derailleur and the chain.

Don't forget to ensure the chain and front derailleur do not touch.

If the chain still comes off after adjustment

In most cases, adjusting the front derailleur will largely eliminate chain derailment.

However, there are times when adjustment alone isn't enough.

In such cases, the mounting position of the front derailleur itself might be incorrect.

Re-adjusting its position and angle can sometimes solve the problem.

Also, a surprisingly overlooked factor is the deterioration of the chain itself.

The chain might be twisted, damaged, or have reduced flexibility.

If it still doesn't fix the problem

If it makes noise, moving it repeatedly and trying to guess the cause is one of the pleasures of maintenance.

It's not fun when you don't understand, but the joy of predicting the cause, tinkering with it, and fixing it is incomparable.

If you can't figure it out on your own, you could ask fellow cyclists, or consult a bike shop for expert advice.

That feeling of joy and satisfaction when you truly make the bicycle your own through maintenance is one of its great aspects.

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