I'll highlight specific parts, explaining which ones are better for DIY and which ones should be entrusted to professionals, along with the reasons why.

■Parts You Should Replace Yourself

Parts you should replace yourself are those that can be checked regularly and replaced easily.

Regular checks are essential, and diligent maintenance keeps your bike in good condition.

• Air Valve

If your tire is losing air quickly, check the air valve before suspecting a puncture.

Examine the tire's air valve itself, and if it's a Schrader valve, check the valve core.

Surprisingly, this can often be the problem causing air to leak easily.

In this case, you can easily fix it with a valve core bought at a 100-yen store.

• Lights

Lights depend on the type you're using, but nowadays, dynamo (generator) lights are rare. Rechargeable or dry-cell battery lights are probably the mainstream.

While repairing a broken one isn't a bad idea, you're often advised to buy a new one.

That's because they aren't that expensive.

Surprisingly, not many places repair them either.

It's usually better to replace them with new ones, as they'll be cleaner and last longer.

For lights, LEDs are often used, but they gradually dim over time.

Ultimately, replacing them is cheaper and results in a better condition.

• Saddle

You usually only need to replace a saddle when it's torn or otherwise damaged.

Repairing it would involve reupholstering, which would make the labor cost high and expensive.

It's recommended to replace it with a new one, which is cheaper and fresh.

Be careful when your bike falls, as the side of the saddle can hit the ground and tear. If you're careful about this, you might not even need to replace the saddle, so keep that in mind.

• Kickstand

Kickstands have moving parts, and if a spring breaks or rusts, you should maintain it yourself.

If you buy rust remover, its price will be comparable to that of a new kickstand (of course, if you choose an expensive kickstand, there's no end to it...).

As a practical matter, it's difficult to order parts for a broken spring, but replacing the entire kickstand is relatively easy.

It can be attached with just a few bolts, so no special skills, tools, or experience are needed.

You just need to attach the new part in the same way the old one was attached.

• Tires (and Tubes)

You might want to replace tires and tubes yourself.

You can ask a bike shop to do it, but it can be surprisingly expensive.

In addition to the cost of the tire and tube parts themselves, there are labor costs.

Labor costs alone seem to be around 1200 yen for the front wheel and 1800 yen for the rear wheel (it varies by shop).

Since the parts cost is separate, you can expect to pay anywhere from 5,000 to 10,000 yen for one wheel, even at the lower end.

If you buy tires and tubes from a home center or online, both front and rear can be had for around 3,000 yen.

While it's good that you can choose whatever you like, there's a risk of not being able to install them if you get the size, width, or type wrong.

You'll know for yourself if you can replace them, so if you think you can, give it a try.

From the author's perspective, I think replacing them yourself fosters a greater attachment to your bike.

■Parts Best Left to a Bike Shop (Professionals)

Generally, parts that are best left to professionals are those where a mistake in maintenance or part replacement could lead to danger or damage the bike itself.

• Chain

When replacing a chain, a special tool is required for removal, and a special measuring device is needed to check if the chain length is appropriate or stretched.

Even if you buy these tools, storing them until the next chain replacement can be cumbersome, and it's questionable whether they can be kept in good condition until then.

It's better to leave chain replacement to a professional.

• Brakes (and surrounding parts)

When it comes to brakes and their surrounding parts, there are various components such as brake levers, brake cables, and brake pads.

However, if you're replacing something, it's likely to be the brake cables and pads.

Both are consumables, so they'll probably need replacement sooner than other parts.

While you might be able to replace them yourself, if they're not installed correctly, the brakes might not work, leading to danger in an emergency.

Unless you have a certain level of experience and confidence, leave it to a shop (professional).

• Derailleur

Replacing a derailleur or gears (sprockets) sometimes requires special tools.

Again, buying these specifically is expensive, and maintenance is difficult.

Furthermore, if not installed correctly, it can become dangerous in an emergency.

Similar to brakes, it's best to leave this to a shop (professional).

• Wheels

It is recommended to purchase complete wheels.

Assembly is very difficult and requires considerable skill.

In that regard, buying a complete product is foolproof.

Installation itself is not that difficult, so you should be fine doing it yourself.

• Frame

Replacing a frame is a big deal.

The process is essentially the same as building from scratch, so it's best to leave it to a professional.

If you have an environment where you can learn from a professional, gradually trying to do it yourself can be a good learning experience.

However, always have critical parts like the brakes and derailleur mentioned above checked by a professional.

By maintaining your bike yourself in this way, you'll check it more often and be able to ride safely and comfortably.

On the other hand, for your safety, be sure to leave tasks that require professional attention to the professionals.