I am commuting 7 miles a day (round trip) in all weather in New England (temperate, moderately wet climate, cold winters). Overall I am putting about 1000 miles per year on my commuter bike, a 2009 Giant Transend DX with lower-end Shimano components (Alivio and whatnot).
I lube my chain and check brakes and tire pressure weekly, but how often do I need to get the hubs and bottom-bracket taken apart and lubed?
Looking at the spec of your bike it says the BB is a cartridge unit. This probably isn't serviceable -- it's designed to be replaced when worn out, so just keep riding it until it grinds or gets excessively sloppy.
The hubs might be serviceable. If you ride a lot in nasty conditions, or you're aggressive with the degreaser you might want to service them. However, if they're well-sealed (like most modern hubs and in particular Shimano hubs) then they almost never need servicing. If you're worried, learn how to service them yourself and see what they look like. If they're still packed with grease and nice and clean inside they don't need servicing. Servicing them isn't hard but it's a bit fiddly -- you'll lose a bearing under the fridge, then you won't be able to remember if there should be 9 or 10 balls, and whether they're 3/32" or 1/8" or 5/32", and so on. Don't do it for fun.
I ride a lot. My Campagnolo Neutrons have probably seen 10,000+ km. In that time I've had a look at the bearings once or twice. Still greasy, still smooth. The rims will wear out before the hub bearings do.
This is a very subjective opinion. A standard like "change your oil every 3000 miles" doesn't exist as far as I know, although here is a suggested one.
I ride about 3,000-4,000 miles a year and my rule of thumb is to do the hubs every 300 - 500 miles or so, and the bottom bracket twice a year. Works out to a hub overhaul about every other month. Both of these are more frequent than the suggested schedule.
That said, there have been a couple of times I have ridden in an area and ended up with the bottom bracket or hubs completely submerged. When that happens I like to overhaul them at my earliest convenience; preferably within a day or two.
Another point here is - I do the maintenance myself. Hubs are easy and you should be able to learn to do them yourself from a book and with a $10-15 investment in tools - bottom brackets are a little harder and you will probably just want to include that as part of a "shop service" unless you want to learn and invest a little more in doing your own maintenance.
At 7 miles a day on road riding, assuming you have well sealed hubs and bottom brackets I would expect you to be able to go well over a year before having to grease and repack.
A lot depends on the space you have and if you are happy to do the work your self – if you have a warm dry workshop then you may decide that doing maintenance more often is a good trade of to make your components last longer. However if doing the maintenance is a pain to you, or you are having to pay a bike shop with all the inconvenience of taking the bike to the stop in your car, you may decide that you would rather just replace the bike/components after a few years.
Greasing and packing your hubs every time to put on a new tire on is a good option, as it is easy to remember to do it.
I would personally with your type of riding, only consider getting the bottom bracket done when the bike has to go into the shop for something else or after a few years if you have not had to visit the bikes shop in the mean time.
A friend of mine goes to the trouble of installing a grease nipple in the shell of each hub. Then, instead of having to take the hub apart, all you need to do is pump more grease in every so often and wipe the excess that comes out around the axle away. This has the advantage of pushing any dirt and gunk out of the bearings when you add more grease.
As far as I know, most modern hubs and bottom brackets are designed not to need service. Bottom brackets in particular are often constructed in a way that they cannot be disassembled.
My experience:
My bike (good quality, but not top-of-the-line) is about 7 years old, and I ride around 2,000 km per year. I have never serviced the hubs or bottom bracket, so far without any problems. I don't do extreme off-road riding, but I do cycle in winter and in the rain, plus the bike is sometimes parked in the rain.
So if you are not using your bike under extreme conditions, you may not need to worry about maintaining the bearings at all.
Water (and its cousin mud) more than anything affect grease bearings. The more rain, and or mud that you ride in the more often you will need to repack your grease bearings. When they are freshly packed pay attention to how easily the wheels spin when you hold them off the road or the bike is upside down. Then do this every so often and if they seem to be getting even the least bit slower then it is time to pack. You will get a feel for their condition over time. I do mine every 1000 to 2000 miles and I ride mine through everything.
