Richard - keep in mind that tire design plays a huge role in the leverage effect that causes tubeless tires to burp under load. Sidewall height varies from tire to tire, as does true casing width. I would argue that the careful choice of tire plays as big (or bigger) role than rim width does. A tire with a comparatively low sidewall height, narrow casing, firm casing and firmer compound will maintain its shape and break traction before burping the sidewall. Taller sidewalls, thinner/wider casings and sticky compounds are more prone to pulling off a narrower rim. The taller the casing, the longer the lever. All that being said, I run a 28mm I9 EN wheelset and ride it hard, no problems. The weight savings of a 24mm rim are not worth the potential hassle of losing air even once IMO.