At how many miles on a motorcycle do you generally need to start replacing worn out parts?
Depending on how hard you are on the bike. You can go through a rear tire a year, brakes front tire every other year. I've gotten 25k miles out of a well maintained chain sprocket.
Motorcycles are not like cars in that the same make/model/year of a car starts wearing out at the same time for most of the owners. Motorcycles are much more influenced by the storage (outside/inside), amount of use (daily/weekly/monthly), weather conditions, braking (city/rural), and how the rider used the clutch. Some people wear out certain parts (such as brakes) every year and others go for a decade with just oil changes on the same make/model/year.
Really depends on the bike, engine format and size can affect tyres, chain and sprocket wear. Many of the other consumables will be part of your service schedule.
