Hey @johnnyfitz if you are going to wear them with a specific boot 90% of the time I’d buy whatever size the guide tells you. I bought mine for my LL Bean winter boots and they seem to do fine on everything from trail running shoes to ski boots. On my running shoes sometimes they slip down a little, but they are completely usable. Mine are old and the rubber connecting the chain has broken in two spots, but I repaired them with zip ties and they function just fine. Did they break because I stretched them over ski boots? I doubt that is the case because I continue to use them on those boots and I haven’t had any more connections fail. The main drawback to buying a smaller size and stretching to a larger boot is that they won’t wrap around the top of the boot as much and they may pop off. Hope this helps.