Bicycle gear system?..?

How often does it break?..do you have to ever replace the chain or cassette?or is it an easy fix,what part get damaged after a great deal of shifting?is it a cord or something thats easy to fix or something that costs alot please answer?..

Shifting systems, like any other mechanical system, takes maintenance. Generally it has to do with proper lubrication and the occasional replacement of worn parts which will eventually include every component in the system.

If the system is in good working order then it is rare that anything gets damaged- rather it becomes worn. The most expensive single part that would eventually require replacement is the crank (if the chainrings can't be replaced) or rear derailleur... but these items will handle thousands of miles of usage.

The items likely to need the most frequent service will be the chain and shift cable. If the chain is used too long then other components will be affected which include the cassette and chainrings.

Bicycle shifting systems are pretty durable.

Shifter cables wear out the most. For the best performance, it is recommended you can replace cable housing when you replace cables. (I don't think many people do this, though.)

Shifters can break, but are pretty durable. Wrecks are especially tough with brake/shifters. Keeping the cables and derailleurs clean and shifting smoothly significantly reduces the force required to shift and prolongs shifter life.

Derailleurs are exceedingly durable. The biggest thing that will wear out a derailleur is a constant chain rub. They need to be kept in proper adjustment. Even kept in a state of benign neglect, derailleurs are usually good for thousands of miles. Keep them clean, lubed and adjusted and you should get tens of thousands of miles.

Bicycle drive trains, the chain, cassette and chain rings, are the most likely part of a bike to require replacement. When the chain no longer meshes well with the cogs, and the bike begins to ghost shift, it is time to replace the drive train. Note: indexing of the derailluer needs to checked prior to replacing the drive train. A road bike, is usually good for many, many thousands of miles. A mountain bike, used in all type of weather, may need a new drive train every few hundred miles.

There are a couple schools of thought regarding replacement of bicycle chains. One school says to replace chains regularly. The concept it to replace the chain before it stretches and wears the chain rings and cogs of the cassette. The other school says the entire drive train wears together so you need to replace all components simultaneously. Otherwise, the more worn pieces will cause new pieces to wear down quickly. I tend to be in the "replace it all" school of thought.

Hope this helps.

Too add, it also depends how much you ride. I ride between 5,000-7,000 miles a season, so I replace almost the whole drivetrain each season. There are some parts you can go cheaper. Some.....stay with your gruppo. For example, I go through front derailleurs like crazy. I was spending $60-$70 on the mid to high end Campy. But now I just buy Veloce fronts. Just $40. For the rear one, I stick with the higher end because it doesn't wear as fast.....I think. Hehe!