After mountain biking in muddy conditions I clean my mountain bike with a high pressure water blaster. I'm assuming that after this I should re-lube my chain?
I've heard you should keep high pressure water away from your bike, because it can easily work it's way into the bearings, even sealed ones, especially around the bottom bracket and wheels. Pressurized water will push the oil out of the spaces between the chain links, and it's probably not a good idea to use pressurized water at all. You should be able to sufficiently clean the dirt off your bike with some light water, or, if you want to really thorough, use a chain cleaner. And you should always relube after cleaning regardless of which cleaning method you use.
1You are correct on the reason why you should not use high pressure to clean off a bike. The only reason you ever see Pro Mechanics doing it is because they have 9 or more bikes to clean every night and spend the time to check everything over after cleaning. Always use a sponge or a hose with cascading water to clean a bike. May 16, 2013 at 13:21
2Yeah, if you're a pro mechanic working on pro bikes, and your components are provided as part of you sponsorship deal and replaced frequently, go nuts, it's the fastest way to clean a bike. But definitely not recommended if you want to improve the longevity of your parts.– KibbeeMay 16, 2013 at 13:42
+1, Always re-lube. It helps if you can remove the water in the chain first. I wipe my chain down and then blow the water off the chain (being careful to avoid spraying hubs and bottom brackets) as much as possible with my air compressor before re-lubing.– BenzoMay 16, 2013 at 14:02