The later models came with 17" rims. You can get a new 18" rim and lace it to your hub, or you can get a stock 18" wheel from an earlier model. Just be sure to use your sprocket carrier and spacers since the later model sprocket carrier is different than the earlier ones. Everything else (including brakes) is the same. I swap back and forth between 17" and 18" rear wheels on my K8. There seems to be a wider selection of 18" tires.
