My frame is WD Cycle Elite and it has 65mm clearance for a tire. (As far as I can tell putting a ruler against the frame and using my eyeball instead of micrometer.) The Schwalbe web site says the Crazy Bob tire width is 61mm.
https://www.schwalbetires.com/tech_info/tire_dimensions That would mean I have 2mm each side. Is it worth the risk?