Is that a version 40 or a version 41?

Why do running shoes have version numbers?

Running shoe brands update their main models on a regular schedule. The name stays, because runners search for it and buy it again, and the number goes up by one. Nike's Pegasus, Brooks' Ghost and the ASICS Gel-Kayano all work this way.

Each version is a separate product with its own product code and its own colourways. When a new version comes out, shops keep selling the old one until it runs out. So for a while, the same shop can list two versions of the same shoe next to each other, at two prices.

Fashion trainers such as the Dunk or the Samba keep their design from one release to the next, with small changes in the details, as the chapter on retros shows. Each new running shoe version is sold as an improvement on the last, so the changes are the point.

What changes from one version to the next?

The biggest changes are usually inside the midsole, the foam layer that does the cushioning. Two recent examples:

• Nike Pegasus 40 to Pegasus 41. Nike moved the midsole from React foam to ReactX foam, and added Air Zoom units under both the forefoot and the heel.
• Brooks Ghost 15 to Ghost 16. Brooks moved the midsole from DNA Loft v2 to DNA Loft v3, a foam made with nitrogen. Running Shoes Guru measured the toe box at 4.5 inches wide on the 16, against 4.25 on the 15.

The upper changes too. The mesh gets a new pattern, the padding around the heel is thicker or thinner, the tongue is reshaped. And each version launches with its own colourways, which is the most useful change of all for identifying one from a photo.

Which of those changes can a photo show?

Some of them, and rarely the ones that matter most for running. A new foam is inside the shoe. You will not see ReactX in a photo, and you will not see a difference in weight.

What a photo can show is the outside of the midsole and the upper. Look at these, and compare them with product photos of each version:

1. The side wall of the midsole. Its height, its shape, and any lines, grooves or cut-outs moulded into it.
2. The mesh pattern. The size and shape of the holes in the upper, and where the pattern changes from open to closed.
3. The heel. The shape of the heel counter, the padding around the ankle, and any pull tab.
4. The printing. Where the model name sits, and whether the version number is printed with it.

Where brands print the version number varies. It can be on the tongue, the heel, the side of the midsole or only on the insole and the box, and a brand can move it from one version to the next. Treat any visible number as a strong clue, and do not assume a missing number means an older version.

For comparison photos, use review sites that test each version. RunRepeat, for example, photographs every version it reviews and cuts one shoe in half, so you can put the Pegasus 40 and 41 side by side at the same angle and see the midsole shape change.

How do the colours tell you the version?

This is the most reliable method from a photo. A colourway is released on one version of a shoe. When the next version launches, it comes in a new set of colours. So the colours in your photo usually point to one version.

Search the model name without a number, plus the colours: Brooks Ghost grey and orange, for example. Look at which version numbers appear in the titles of the matching results. If every listing with those exact colours says Ghost 15, Ghost 15 is the version to search for.

Plain colours are the exception. All black and all white are sold on many versions of the same shoe, so they tell you little about the version. For a plain pair, you are back to the midsole and the mesh.

Which variant of that version is it?

One version number can cover several shoes. The main running models are sold in variants that share the name and the number, and in a photo they can be hard to tell apart.

• Waterproof. Brooks sells a Ghost 16 GTX and Nike sells a Pegasus 41 GORE-TEX. GTX and GORE-TEX mean the upper has a waterproof layer. Look for an upper with a smoother surface and fewer open holes than the standard version, and check the listing title for GTX or GORE-TEX.
• Wide fit. The Ghost 16 is sold in a standard width and in wider fits, with letters such as 2E on the label and in the listing. A wide pair looks the same in a photo. Only the label or the listing tells you.
• Trail. Some road models also have a trail version, with a deeper tread on the sole and a tougher upper. The sole is the quickest way to spot one.

Search the standard version first. If the results do not match the upper or the sole in your photo, add GTX, GORE-TEX or trail to the search and compare again.

Does the version matter to you?

It depends on why you want the shoe.

If you want the look, the version may not matter, and the older version is often cheaper. Running shoe reviewers at Tom's Guide and Solereview both advise checking the previous version once a new one is out, because shops put it on sale to clear it.

If you want to run in it, the version matters more than it looks. The feel of the foam, the width of the toe box and sometimes the fit all change. The Ghost 16's wider toe box is an example: a runner with narrow feet who liked the Ghost 15 might find the 16 looser. If you already run in one version, try the new one on before you buy it online.

If you are buying second-hand, check the version in the listing and in the photos. A seller may list a pair only by its name, and the price of an older version should be lower.

What if the pair is several versions old?

Videos stay online for years. A shoe you saw today may be three or four versions behind the one in shops now. Once a version sells out, you can only find it new in clearance sales, and after that only second-hand.

If the colours tell you the pair is an old version, decide again what you want. For the look, search the current version in the closest colours. The name and the general shape will match, and the details will be newer. For the exact pair, search the old version number on second-hand sites, and read the condition notes carefully. Foam in a running shoe wears out with use, so a worn pair of an old version will not feel the way it did when new.

What about sizing between versions?

A new version can fit differently, even in the same printed size. A reshaped toe box, a new upper or a thicker tongue changes how the shoe feels in length and width. Reviews of a new version usually say whether it fits the same as the last one. Read two or three before you order your usual size. The guide to converting sizes covers the size scales themselves.

How does this affect a Snagfit search?

Snagfit describes the shoe it sees and searches current listings. For a running shoe, the results can include the current version and the previous one, because they look alike. Read the version number in each listing's title. If you want the pair from the video, use the colours to decide which version it is, and pick the listing with that number. If you only want the look, the older version in the results may be the better buy.