Jonny all I know is that I have a mtb with 29 inch wheels parked in my garage. I also have a set of FIR Net 97 wheels sitting right next to it. They fit on the bike and when I feel like riding my mtb on the road I put them on. They ride like a charm. Now if they would fit with rim brakes I do not know. With discs they are great. On the mtb wheels I am using standard Shimano XT disc hubs. On the cyclocross wheels I am using DT Swiss Onyx disc hubs. As a matter of fact the tubes I use on the mtb wheels are 700Cx45 while the cyclocross tires get 700Cx25. I can assure you that these are not 27 inch wheels.