Originally Posted by masiman
Both arguments are valid on the 27" vs 700c. You may or may not need to get new calipers as your existing ones may be able to reach. The ISO sizes for these rims are 630mm and 622mm, respectively. That is about 1/3 of an inch difference with the 700c being smaller.
27" tires are harder to find. You don't have to worry about tubes as they are pretty much interchangeable.
I have never ridden with mixed rim sizes so I don't know if you would notice it but I would think not unless you are an extremely serious cyclist.
That is awesome your kids are wrenching, hawki and dave.
It does appear the calipers can be adjusted down far enough. I'll have him try one of our other bike's wheels first to check that before buying. Will we need to stick with a 5 cog cassette???