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I don't own a bicycle. Whenever I go cycling, I would need to rent one. The first thing that I always check is to see if the brakes are working properly.

Sometimes, I have no idea that the gear is faulty until I encounter a steep slope where I need to paddle hard. This may cause the gear to jump or slip if it is faulty. Other times, when I change the gear, the paddling suddenly becomes inefficient, with constant grinding noises from the gear.

In the end, I try not to change the gears at all to avoid the above problems. I would like to know if there is a way to visually inspect the gear and tell the shop assistant that, "Hey, the gear is faulty!", instead of coming back halfway to do the exchange.

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Its going to be difficult to inspect things like gears visually, but there's nothing to stop you spending the first five minutes of your rental just riding around the block to make sure everything checks out. – PeteH May 26 '13 at 7:36
@PeteH, the problem is the terrain is usually quite flat around the bike rental area to be able to test the gears properly. – Question Overflow May 27 '13 at 3:02
you should be able to click through lowest to highest without much of a whimper, I'm not sure you can do much more of a test than that – PeteH May 27 '13 at 8:33

If you're talking about a derailleur-style bike, a quick check is to suspend the rear wheel somehow (sometimes you can hang the nose of the seat on something, eg, or see if the rental place doesn't have a work stand) and crank the pedals with your hand while you shift through the gears. On a bike with indexed shifters the transitions should be smooth and you should hear no more than very slight "chatter" from the chain once the transition is complete.

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Also, avoid running the smallest chainring with the smallest cog/largest chainring with largest cog...this is called cross chaining and will often result in a lovely grinding sound as the chain drags along the front derailleur cage. – WTHarper May 26 '13 at 13:49
Is it possible to tell based on the amount of slack on the chain when switched to the lowest gear? I am more concern on the gear slipping when climbing up a steep slope. – Question Overflow May 27 '13 at 3:33
@QuestionOverflow - Place the chain on the smallest front sprocket and middle rear sprocket. Look at the derailer and chain. The derailer should not be curled up all the way (though close) and the chain should not be slack. – Daniel R Hicks May 27 '13 at 12:29
@QuestionOverflow - But slippage is often due to a worn chain/sprocket. Place the chain on the large front sprocket and pull out on a link near the front side. The chain should not pull away more than about 2/3rds of the height of a sprocket tooth. – Daniel R Hicks May 27 '13 at 12:32

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