Is anyone familiar with the sizing of both the 310 and 315? I have tuned in a good fit with size 11.5 in the 310 and wonder if I need to change sizes to move on to the 315.

I'll likely continue to use the 310 for trail running, but I need just a wee bit more cushioning for long days when backpacking. My understanding is that the 315 should help out a bit with this.

like all roclite they tend to be a bit more narrow in the toe box. I think the flyroc (along with the 295) runs pretty much true to size. I think the 315 runs 1/2 a size small. Folks from zombierunners could tell you more clearly the differences.

--Mark

I started off in 315s and switched to 310s for backpacking. The wider toebox makes long days on the trail more comfortable as your foots swells. I still use the 315s for trail running where it's snugger fit is fine for shorter durations.

If you are transitioning to 315s from 310s for thye extra cushion then I would probably go up half a size, a point that was made by the running shop staff where I purchased my shoes.

My favorite pair are the 310's for all the reasons provided and I also have a pair of 315s for the extra cushion. I have average width feet and wear 11.5 in both sizes. I did not feel a need to go larger or smaller based on the difference in width. I live near Zombierunner so it's easy to just go in and try them on... The 315's are a bit more narrow, but I manage the fit with the socks as long as length is good.