Wondering whether I can get a little free speed by replacing some original parts, est’d 7-10K miles.
chain, cassette, rings I clean and replace myself regularly. But cranks, BB, wheel hub stuff I haven’t ever messed with.
for a better roll, or even safety, when is a good time to replace (or disassemble & clean?)
I disassemble and clean all the serviceable bearings (typically hub, bb, headset) on my bike(s) about once a year. So every few thousand miles, probably. That might be a hair overkill, but it keeps me familiar with how things are wearing, etc. Things get replaced when they look worn.
Probably not the most scientific method, but it seems to be working. If you’ve owned your bike for 10k miles and have never touched any of this stuff, it’s high time you did. Things should spin freely with a hint of fluid resistance from the grease. There shouldn’t be any bumpiness, dryness, grittiness, etc - or any extra play.
Keep in mind that many of these parts are fitted with cartridge bearings these days, which means you just throw them out when they get bad.
Make sure you get the right tools before you begin, as each of the different parts will probably require specific tools - for hubs you need to know what size the cones are to get the right cone wrenches; each style of BB requires unique removal tool(s), etc. The headset will probably have the least-specialized tool requirement, since you just need to take your top cap and stem off, which should just require allen wrenches (unless you are old skool and using a threaded headset).