I'm a big fan of doing faster workouts in racing flats—lightweight, low-profile running shoes designed for road races. The light weight allows you to go run faster, and the lower heel-to-toe differential gets your ankles, calves, and Achilles tendon used to working through a broader range of motion. This can help prevent lower leg injuries and calf soreness that can crop up when you do a longer race in spikes.
|You can see creases from the crumpling|
Partially thanks to the now-fading minimalist movement, racing flats have gotten a lot lighter and lower to the ground over the past several years. While this is great from a performance perspective, the drive for ultra-light shoes sometimes causes design flaws to be overlooked, and this can ruin an otherwise-great shoe.
I've been wearing New Balance's RC5000 flat in track workouts and road races for about nine months now, and overall, it's been great. But recently I've had problems with the shoe's insole crumpling up under my toes. Usually, if a racing flat has an unusually-thin insole, as the RC5000 does, it is glued down so this does not happen. This is the case with virtually all insoles in spikes as well—having a flap of foam or fabric peel up under your forefoot during a race or workout is extremely irritating. But New Balance either chose not to glue it down, or used an inferior glue that can't withstand the stresses of fast running.
In any case, I decided to glue the insole back into the shoe so I could keep using these flats. I contacted New Balance to see if they had any advice on what adhesive to use, but their response, quoted below, wasn't particularly helpful:
We don't recommend gluing your insoles in your shoes. We make our shoes with removable inserts to allow you to further customize your shoe fit through the use of our upgraded insoles or your own orthotic. You can try another type of insole, such as Dr. Scholl's. Another idea is trying a different lacing method to keep your insoles from moving
So instead, I did some research. Surprisingly, there is not much on the internet about how to fix a running shoe insole that's peeling or crumpling up under your foot. I've used Super Glue (cyanoacrylate) to fix a peeling insole before, but that was on a pair of Nike spikes with a flat, smooth surface immediately underneath the insole. The bottom of the New Balance flat has a mesh overlay, visible above, and I suspected that Super Glue would not adhere very well to it and could potentially leave hard lumps under my feet. So that wouldn't do. I considered a number of other adhesives, like contact cement, epoxy, and barge glue, but they didn't seem like good candidates: they either dried into a hard, brittle substance, cured nearly instantly, or wouldn't work well on foam EVA and fabric. I settled on using Shoe Goo, a polymer adhesive that hardens into a strong but flexible rubbery substance after curing for several hours.