If the Shoe Fits

by Super Dave, Industry Expert

The most common complaint from runners is: "Why did they discontinue my favorite shoe?" The explanation for this is part marketing, part innovation and part staying ahead of the other shoe manufacturers.

The second most common complaint and a harder one to answer is: "Why can't they get the fit right? A size 10 isn't a size 10 anymore!"

As little as six years ago, it was common for shoes made in the USA to fit true to size, and shoes made overseas, in places like China, to fit at least a half-size small. Today, even that standard isn't true. Shoes from both the Orient and the U.S. run anywhere from true to size to as much as one-and-a-half sizes small. Almost every shoe company has run into this inconsistent fit problem.

Parts is Parts
The basic components used to create the structure of any running shoe are the midsole/outersole, the upper, and the shoe last. The midsole/outersole is the part of the shoe that protects you from the rigors of running. Midsoles are usually made of EVA that is compressed or injected into a mold that matches the curvature and shape of the shoe last. The outersole is glued to that formed midsole with a strong adhesive. The shoe last is a very dense, foot-shaped form that creates the shape and fit of the shoe.

Every shoe company has at least two different lasts. One last has a straighter shape and is used to make motion control shoes. The other is more curved and is used for stability and cushion shoes. Some companies also have lasts specifically for racing shoes and for women. Each last has a size that matches the size of the midsole mold. In other words, a size 10 last is used on a size 10 mold. At this point, a size 10 is a true size 10.

The final part of the shoe puzzle is the upper. There are a number of different ways uppers are constructed but, for the most part, they are either combination or slip construction.

With combination construction, a fiberboard that starts at your heel and goes to just under your arch is glued to the bottom of the upper, acting as base of support. With slip construction, the upper has an extra flap of material hanging from each of the sidewalls. The two flaps are sewn together and, when you pull out the insole of your shoe, you see the stitch line of the slip running down the middle of the shoe.

Once the midsole/outersole and upper are constructed, the shoes are put together. The upper is stretched over the last to create the shape. If the shoe is a combination construction, the fiberboard is then glued onto the bottom of the upper. From this point, the construction of both slip and combination is the same. The upper with the last inside shaping it is glued to the already molded midsole. From there, the shoes go through a cooker that hardens the glue, and then they are cooled. The last is pulled from the shoe, laces are threaded, paper is stuffed to maintain the form and the shoes are boxed.

Slip vs. Combination
In general, a slip-constructed shoe will fit at least a half-size smaller than a combination constructed shoe. After watching the whole process and actually making a couple of my own shoes, I think I can explain this phenomenon. When I said the upper is stretched over the last, I was not kidding. The forearms of the men and women that make shoes are very strong from pulling or stretching the uppers over the last.

When that last is pulled out of the shoe, the upper has a natural tendency to shrink to its more natural form. The combination-constructed shoes shrink less because the board is glued to the upper after the upper has been stretched over the last. The board is not stretched over anything and therefore retains its shape better. Today, as much as 80% of all running shoes have a slip contruction.

Another thing that affects the size of your shoe is the material used in the upper. The more layers of nylon, synthetic leathers, and heat molding, especially in the forefoot, the smaller and narrower a shoe will fit. The trade-off when the shoemakers use less layering is a flimsy, less durable upper.

One solution to this fit problem is to ask each manufacturer to check the sizing when the shoes come off the assembly line. If the shoes are fitting abnormally small, change the size tag during production. In other words, now a 9.5 is really a 9, and so on down the line. Aside from the cost of doing this, however, there is a logistical problem to this solution. In many of the factories overseas, one assembly line may make one brand of shoes in the morning and another brand in the afternoon. With the number of running shoes sold today, imagine if they changed the tags of the wrong shoe!

The Bottom Line
The bottom line is that we as runners must make sure we get the right shoe and the right fit, regardless of the number on the size tag. The most important thing you can do is to pay very close attention to the fit of a shoe instead of the size marked on the shoe. I, for example, am on the small side of a size 9, but most of my shoes are a 9.5, and some are even a size 10. It took me over a year to convince my wife that her size 7 foot belongs in a size 8 shoe. I finally convinced her by bringing home the 8, tearing off the tags, and having her run in them. After about a week, I broke down and told her they were 8's. Since then, she has never run in any size smaller than an 8.