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. Using racing flats for your road and track workouts can help prevent lower leg injuries and calf soreness that can crop up when you do a longer race in spikes.
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.
The repair process: gluing down the loose insole
The actual repair process was pretty simple. After making sure the shoe and the insole were clean and dry, I applied a thin layer of Shoe Goo to the outer edge of the insole’s forefoot (highlighted in the photo below), flattening out the glue bead with the shaft of a Q-tip—I didn’t want to use any adhesive under the weight-bearing area of the insole in case the glue left any lumps or hard spots. That wouldn’t feel too great on the sole of your foot during a race!
After waiting for three minutes for the glue to firm up a bit, I put the insole back into the shoe, making sure not to get any Shoe Goo on the upper and being careful to get the insole alignment right.
I had removed the laces entirely so I had an easier time getting the insole inserted into the forefoot of the shoe. Using my fingertips, I pushed down hard on the edges of the insole to squeeze the adhesive into the mesh, and to smooth out any creases or bumps. If the glue holds, there’s no do-over with this! Fortunately, Shoe Goo doesn’t fully cure for several hours, so you can fix any mistakes if you’re quick about it.
To make sure the insole did not peel up, I re-laced the shoe and stuffed it tightly with newspapers from forefoot to heel. I let it sit this way for two days.
Today I took the repaired flats for a spin at my high school’s 2-mile cross country alumni race on wet grass with some tight turns. So far, so good: even though the shoe got quite wet and I ran pretty hard in it, the insole feels secure in the shoe, and I had no issues with peeling or crumpling during the race! I also didn’t feel any lumps or hard spots where I put the glue after it cured. I’ll update this page if I have any problems in the future.
Update: These shoes held up great for the rest of the fall, winter, and spring seasons, and I ended up setting lifetime PRs in the 3k and 5k after doing all my workouts in this pair of flats!