difference in rear hub widths? I've recently upgraded my road wheel set on my cross bike to a set of hope hoops which came with hope mono rs hubs. At first they required me to adjust the rear dérailleur so that the shifting was working properly after a few weeks I finally put my cross wheel set in realising that the rear dérailleur required adjustment again. Is this because the hubs are different sizes or my poor mechanical work. The rear hub on my cross wheel set is a tiagra 4600: http://www.wiggle.co.uk/shimano-tiagra-4600-rear-hub/?lang=en&amp;curr=GBP&amp;dest=1&amp;utm_source=pla&amp;utm_medium=base&amp;utm_campaign=uk&amp;kpid=5360448791

road wheel set: http://www.hopetech.com/product/mono-rs-rear-hub/
A list of hub spacings is here. Obviously, you need to have a wheel which fits into the frame and matches the hub spacing (in some cases, you can squeeze a slightly bigger or smaller hub into a frame, such as for 27" -> 700c conversions, but this is peripheral).

Normally, when you swap a rear wheel to a different one, you will need to make slight RD adjustments - there are variations to where the derailleur sees the cassette.