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We recently got a new mountain bike for my son via craigslist, it is a couple year old Transition Bottle Rocket and came with a E-Thirteen SS+ chain guide/tensioner.

He would like a lower gear for when we go up the hill to get to the good downhill trails.

Can we add a front derailleur and shifter to allow two front chain rings allowing a lower gearing for going up and one for when he goes down the trail.

He has a nice large 32 tooth on the rear cassette but still would like something a bit easier to spin up the hill

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2 Answers

up vote 7 down vote accepted

This is a common setup for many freeride bikes, as it allows uphill peddling and a bash guard. However only certain models of chain guide support this, and the one your son has doesn't officially (though it wouldn't hurt to try if you have crankset to test, might affect derailleur...). The DRS is eThirteen's 'official' dually chain guide.

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+1. Dual chainring chainguides exist, but yours isn't one of them. –  joelmdev Dec 5 '11 at 15:40
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I thought the question was, will a single-speed chain tensioner (the kind that allows you to get chain tension right on a single-speed bike with vertical dropouts) provide enough variability in chain length that I can shift a front derailleur. The answer is probably not. The chain will either be too loose in the lower gear or too tight in the higher gear. All you need to do is use a cheap rear derailleur as a chain tensioner. No shifter or cassette. This will provide enough slack to shift to the high gear, and take up that slack again when you shift to the low gear.

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The bicycle has a rear dearaileur and 9 speed cassette with vertical dropouts. The chain guide/tensioner is attached to the bottom bracket. The bike has a single chainring and my son would like a double chainring setup so he can get an easier gear for climbing. I did not know about the DRS from eThirteen allowing for a double chainring and still providing chain retention. –  Glenn Gervais Dec 8 '11 at 18:21
    
There are two main types of chain guide: the ones you describe pretty much only appear on single speed bikes (fixies, trials, dirt jump, etc). The type the OP is talking about are for bikes that need gears, so the devices wraps around the front ring (usually only one of) and squeezes the chain as it joins and leaves the teeth. They usually incorporate a bash plate to protect the ring as well, they are used on DH, freeride, enduro, etc. bikes. –  cmannett85 Dec 8 '11 at 21:26
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