I have a Boardman Cyclocross, with Ritchey Disc OCR rims. Theres a sticker on the rims that reads ETRTO 622-18. I've currently got 700x32 Continental CityRide tyres on it, but I'd like to fit some thinner road tyres on it. However, despite searching on the net, the ETRTO stuff just has me massively confused. There also seem to be disagreement with different sites about what will fit on what. Does the 18 in the ETRTO number mean the thinner width I can go for is 18" or is this a faux pas and is my actual minimum wide some way higher? Hoping someone can assist!