Changed mine at around 25K miles. Still well within spec, (despite using the forbidden carb cleaner, brake cleaner & WD 40 for periodic cleanings*) but figured while changing tires, might as well throw a chain and sprockets on too.
*Disclaimer - said forbidden solvents purged off of chain with compressed air prior to fresh lube. Lube = aerosol white grease, $3 a can. Goes on as a liquid, sets up as a grease. Excess comes off with an old rag. Cleaning interval: 2 to 9 weeks after I figure, "Geez, that chain is looking kinda dirty." To each their own.
