Can I run a dual crankset with a chain guide tensioner?

Question

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

Answer 1

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.

Answer 2

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.