I think this calls for a quiz. What's wrong in these pictures?
That's right, this one was easy. No tension. This might actually call for a new qualification of minus tension. It's like a limp noodle! Not good. This is so beyond 1-2" of slack it is amazing that this bike was actually ridden in.
Next picture...How much "air" is ok? Well, you are not supposed to be able to lift the chain off the sprocket hardly at all, never mind off the sprocket beyond the tips off the teeth. Speaks for the chain and sprocket quality though, Drive Systems, which we put on some 10,000 miles earlier. A lesser quality sprocket would've sheared the teeth right off. Still, the chain could have easily lost contact completely and flown off to then lodge itself in the wheel. Instant crash would've ensued. Note to self: find out which company the guardian angels were hired from.
In this picture, two things are not like the others. If you look closely, two of the rollers that go around the pins are missing. Meaning that instead of minimal friction in a roller-on-tooth scenario there is maximum friction, pin-on-tooth, no rolling, just grinding. And look at the distance between the pins and the teeth! No wonder there is all that slack. This must've happened on the way to the shop, since chains don't last very long once they get to this stage.
Cheers! Three out of three bad scenarios, all in one chain. Cheers also to the guardian angels with a soft spot for the owner, who actually did diligently service his chain, even beyond serviceability, and luckily came to the shop in the nick of time.
My advice though: catch it a little earlier, since most bikes with chains like that come to the shop in a tow truck...
