There are a few areas of bike design that have all sorts of theoretical disadvantages-until you look at the other options. Front forks are perhaps the most obvious, putting your main braking force on the end of a pair of long springs while making it all part of the steering, too. On paper it's a mess, but in practice, there's little to touch it for effective front suspension.
A chain final drive is, when you think about it, a pretty poor setup, too. What other high-precision operating system on your bike is stuck out in the breeze, with nothing more than an occasional squirt of sticky oil to protect it from dust, water, grit, spiny anteaters and whatever else the road tosses at it? Imagine your valve gear was similarly designed (as it was on the very earliest bikes)-you'd be changing cams and rockers every few hundred miles.
Yet your chain survives thousands and thousands of miles, despite getting every last pound of thrust your bike's engine produces pinged through it. Wheelies, hard starts, savage gear-changes-these all put massive strains on what is, essentially, a bunch of tiny steel plates, pins and rollers all pressed together.
An old, worn-out chain saps...
An old, worn-out chain saps power and destroys sprockets. Check your chain often: Keep it lubed and properly adjusted and it'll last. For the style conscious, you can even color coordinate your links.
So why chains? They're actually incredibly efficient at transmitting power. That's why they're used on racing bicycles: nothing else can make the most of a rider's leg power with minimal loss. Indeed, if a chain is enclosed, lubricated and tensioned properly, it's a superb power transmitter. Cam chains and primary drive chains will last almost the full life of an engine these days.
Chains are light, especially in comparison to options such as shaft or gear drive, and they allow the simple changes of final drive gearing that are essential for racers. They're extremely tough and resist snapping, which belt drive systems can't manage, and they're much narrower than either shaft, gear or belt final drives.
Futuristic options to replace chains include hydraulic drive systems, and if electric bikes ever become a realistic option, they may use direct-drive motors mounted inside the wheel hub. But we're betting that the humble chain and sprocket, like the front fork, will be with us for a while yet.
What's In A Chain?
A roller drive chain is made up of inner and outer plates, joined together by riveted pins. The pins also hold rollers and bushes between the plates, which engage in the teeth of the drive sprockets. An O-ring chain has small rubber seals (in the shape of an "O") between the bushes, rollers and side plates, which hold a special grease inside the bushes to cool and lubricate them. X- and W-shaped rings have also been used. These have an "X" or "W" shape in profile, which gives extra sealing lips on the side plate to hold more lubricant in place.
Cleaning
Your chain gathers old lube, grit and dirt, so it's worth giving it a regular, good clean. Again, there are loads of powerful spray-can products, which generally do a good (though pricey) job.
A cheaper option is to use kerosene or diesel fuel. Whatever you use, work it into the chain with a stiff paintbrush-with the bike on a stand-while turning the back wheel. Wipe off any excess after cleaning and allow the chain to dry. Then lube the chain as normal.
Lubes
There are literally dozens of spray-on chain lubes available, and it's hard to be definitive on what's best. The most important thing is to use it, and use it properly. Little and often is the key to good chain lubing, and proper application reduces fling off and waste.
Apply lube when you get home from a run because the chain will be warmer, which helps the lube penetrate and quickly evaporates the solvent used in the lube. Leaving the lube on overnight or longer also helps it stick properly to the chain.
Put the bike on a stand and turn the wheel by hand while spraying the lube into the bottom chain run where it feeds onto the rear sprocket. Let it dry for a bit, then wipe off any excess with a cloth.