This summer I switched my bike's wheels to cast aluminum wheels. I went from 19" steel rimmed, spoked, wheels on both front and back, to 19" up front and an 18" rear wheel. My bike handles 1000 times better (probably for more than one reason) than it handled with 19" wheels front and back.
This notion that the rim diameter is a critical component in handling seems like nonsense to me because I can still get the 18" tire's diameter to match up to the 19" tire's diameter, by just chosing a rear tire with a different aspect ratio... SO, my geometry would not change regardless of the rim size. The only thing that is changed is where the tire meets the rim... and that doesn't change any geometric proportions... so how does it cause weave??...
I understand steering rake angle and how the rake offset can effect steering. That seems logical, explainable, and based in physics and geometry but the whole notion that the size of the rim has some unexplainable effect on the bike's handling when it doesn't change the bike's alignment or geometry,.. I don't buy into without an explanation.
Hopefully someone will explain the principles of why they think I am wrong, rather than just say, "because it worked on my bike".
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But to answer the original poster's question, the narrower rim will work, but there will be more sidewall flex to the tire and a smaller contact area of the tire on the road than their would be with the manufacturer's recommended rim because the tire's profile shape will be compromised slightly by mounting it on the narrower rim... (The AM26's are a good choice. I run 100/90/19 up front and 110/90/18 in the rear. It was a huge improvement over the TT100's I've always used previously)
