I just adapted our triple crankset to a quad with a 24-tooth smallest chainring. I put a 12-26 cassette on the back (10-speed), and on our first ride we had to drop down to the lowest gear combination (24/26, 700c wheels) a couple of times when the road went above 10% gradient. That gear worked well for us then, so we're going to stick with the 26 as the largest cog. We might add a smaller cog, an 11 in place of the 16 tooth, at a later date, though, because the biggest chainring is only 53 teeth. Alternatively, I'll buy a 56 tooth for the front.