In the previous article, we outlined some basic pointers on trail running shoes, mainly from the perspective of beginners. By 'beginner', we mean any runner who is either starting to get serious about trail running or is someone who is making a transition from roads to the trails. In other words, anyone who is just starting to cover 15-20% of their weekly mileage on any non-road, non-pavement, non-track surface is a beginner trail runner. We've also taken the liberty to classify all runners as beginners who don't really care about the technical details of trail running shoes.
This article, on the other hand, goes a slight bit deeper and tries to answer the same question from a technical or specifications standpoint and highlights the key factors to consider - this is not a deconstruction of the shoe. The question?
What trail running shoes should I buy?
If you're looking for a straight-to-the-point answer, here's where you should be looking - or, on the other hand, if you want an even deeper dive, the advanced section is the one for you.
Drop
In shoe terms, drop is the height difference between where your heel sits and where your toe falls when you're wearing a shoe. Typically, the heel is a bit raised with respect to the toe, which means that most shoes have a heel-to-toe drop. This could be as low as 2-4mm ('low drop'), 4-8mm ('regular drop') or 8mm+ ('high drop'). Then there are the coveted 'zero drop' shoes which have the heel and toe touchpoints on the insole at the exact same height, resulting in a difference of 0mm from heel to tow. The logic behind designing this drop stems from the idea that having a drop gives you a 'forward' dynamic and, therefore, helps achieve higher speeds with better efficiency.
The flip side, however, is that this logic is mainly applicable to running on smoother surfaces, i.e., roads, pavements and tracks. On trails, drops don't really bring any significant advantages if the terrain fluctuates over varied surfaces.
But this does not mean that drops are bad. It's advisable to go for trail running shoes that don't deviate significantly in drop from your regular road shoes. The reasons for this are simple - a) while trail running shoes come in zero drop, minimalist etc. flavours, road shoes are mostly available with regular or high drop, which means that, b) the drop, however small, results in micro-adjustments to the running form, which essentially means that a greater deviation between drops on your road running and trail running shoes will end up demanding more form changes from you frequently, resulting in increased injury tendencies.
A rule of thumb here is that if you're using a high drop road shoe, then don't go below a 6mm drop on your trail running shoes. If you're using a regular drop on your road shoes, you can try a low drop on your trail running shoes.
On the other hand, if you're a pure 100% trail runner (or a hiker looking for a lightweight pair of shoes), it can be argued that a drop doesn't matter at all - you can go as high or as low as you feel comfortable with.
Stack
The stack (or stack height) is the combined thickness of the outsole and insole of any shoe. In other words, it's the minimum height from the ground at which your foot rests inside the shoe. Trail running shoes, because of deep lugs, rock/thorn protection, and choice of durable materials, typically have a higher stack. This is not to say that trail running shoes have a higher stack compared to road shoes (cushioning adds to the stack there), but a stack height of 20mm+ is commonplace when it comes to trail running shoes.
Generally speaking, a lower stack height is associated with better control and stability. This is mainly to do with the fact that a lower stack gives a better 'ground feel' as compared to a higher stack. This, however, has a disadvantage of lower protection against blunt objects like stones, pebbles or sharp objects like thorns and cut rocks.
Arch
Pronation and arch support is a big factor in choosing the right road shoes. For trail running shoes, however, a neutral arch is best suited. This is because surface and terrain irregularities will make your feet twist and turn naturally, and any form of artificial 'support' will only act as a hindrance to the natural torsion of the ankles and feet.
However, this is not to say that you should only look for trail running shoes with an unsupported arch. If you are a heavy overpronator and use pronation support arches on your road shoes, it is important that you carry that dynamic forward on your trail running shoes as well. Same goes for underpronation.
The wise way to think about this is, "how can I ease into trail running and not make drastic changes".
Material
The choice of material determines the durability, flexibility and portability of trail running shoes. While the ideal world is full of super lightweight shoes that can protect you against a nuclear attack while being rollable into a teeny tiny ball for transportation, the real world is very much a trade-off.
When it comes to material, the number one (and arguably the only) consideration is this - how safe do your trail running shoes make you feel?
The outsole is usually made of rubber on trail running shoes. This gives a natural protection against small stones, pebbles and even thorns to a large extent. The outsole, however, can make the shoe 'stiff' if it's a thick outsole with deep lugs. A stiff shoe, as a result, does not mould with the natural shape of the feet. This means that if your primary or target running surface is rocks and boulders (think mountain trails), you might want to go for a lighter or more flexible material for the outsole, but at the cost of ruggedness and protection.
The midsole is typically made of foam, which adds cushioning to your feet. Additionally, shoes also have a lightweight insole for added cushioning. These are removable in most trail running shoes, so you can just use your shoes without them if you don't want that extra bit of padding, or if you're struggling to find those half sizes.
The upper is usually meshed synthetic fabric, marketed by different brands under different names, that essentially provides for ventilation and comfort. However, to make the shoe structurally strong, the outer is not entirely meshed and there are foam reinforcements at the toe collar and at the heel counter.
The bottom line here is that the terrain where you'll be (or you want to be) spending most time will determine how you want the material of your trail running shoes to aid with your running goals. Before buying any trail running shoes, it's best to simply check the specifications for the materials used.
Shape
As one of the underrated and often overlooked aspects of trail running shoes, the shape of the shoe is, in fact, one of the biggest determinants of comfort in trail running. You read it right - it's not cushioning, it's not the material, it's not the arch - it's simply the top-down shape of the shoe.
Mobility goes from the hips to the toes and all the way back and forth. The freer or more comfortable your toes are, the better you'll be able to move. Additionally, the toe splay also determines the stability of foot landing.
A wider toe box, which is nothing but the front half of your shoe, is generally accepted as being better in this regard than its narrower counterparts. However, as with every other factor, this is also not universal. Toe box width needs to be in relation to the shape of your feet, as going for trail running shoes with an extra-wide toe box will only result in feet sliding sideways on each footstrike.
The heel counter is another important element of the shoe shape as it needs to perform the critical function of keeping your foot held in place. However, the design of heel counters is fairly standard and all trail running shoes give a good hold on the heel.
Sizing
Finally, the size of the shoe. There's not much difference in how one should look at sizing of trail running shoes compared to road shoes. The only rule of thumb to follow is that trails are more prone to harsher and more diverse weather and climates - which means trail running shoes may be subject to more heat, water, probably thicker socks for the cold, and so on. Further, trail outings are often longer in duration and feet need the ability to expand in the heat.
So following the same guidelines as road shoes, but with a degree of non-negotiability, a half or full size larger, depending on what other layers you'll be wearing on your feet, is the suggested decision.
So, What Trail Running Shoes Should I Buy?
Here we go again! If there was a list of recommended shoes that would universally address all the above factors, we would have listed that out. But in that case, you would have already known of it. The answer is the dreaded 'it depends' - and it really depends!
If it's cold and wet or hot and humid, you need breathable shoes. If it's jungle or broken gravel surfaces, you need better thorn and rock protection. If you want better grip and ground feel, you need a lower stack. If you are going to spend long periods of time on trails, you need better comfort and a wider toe box. If it's technical terrain, you need unsupported arches. The permutations and combinations are infinite.
While with beginners, it's a simple choice of going with whatever is available at the time and price of your convenience - but for more curious or knowledgeable runners, it essentially comes down to where you'll be spending most of your trail running time and what you really need out of your trail running shoes.
Curious to know what the advanced edition looks like? Or would you rather simplify the decision?