This same question regularly comes up over on the V-Twin Forum. (My other ride is a Dyna Wide Glide). One issue that concerns bikers more than four-wheelers is that regular burns hotter than premium. In other words, my DWG on regular will shed more heat against my legs. I suspect that heat is also one reason why an engine designed for premium will not last as long on regular. However... the consensus among bikers is that you can safety run regular in the cold months and use the premium only when it's warm out with no impact on performance.

I realize that this does not consider the more-knowledgeable-than-I xF folks who have chipped in regarding the engine design and computer issues associated with burning regular. I just thought I'd bring this up for those who do want to consider regular. Me, I usually burn premium but occasionally I might pump regular or mid. Like Harleys, the xF is, I believe, designed for 91 octane and since all premium around here is 93, you can blend some lower octane in and still have fuel that meets the design specs.

Guy