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Stack and Drop

Foot Health Running Terms Stack and Drop

The running world is littered with important words and phrases: fartlek, VO2 max, intervals, proprioception, splits, the list goes on and there is a plethora of information out there on those words if you so desire. We won't confound you with all the information and definitions of those other running words – today – but we do want you to know about two of the most important running related words when it comes time to pick out a new pair of kicks: stack and drop.

Any shoe company that actually has an idea about running will be able to provide you with these numbers (if they don't, they're probalby not really running footwear), the question is "what do these numbers mean, and how does that effect my selection?"

Caliper measuring the stack height on a pair of World Beaters with veggie tanned leather.Stack refers to the thickness of a sole, from the bottom of the outsole (the rubber that kisses the ground) to the top of the footbed (the part that kisses your soles). Drop refers to the difference in stack height between the toe and the heel of the shoe. Generally speaking, any shoe on the market has some sort of heel-toe drop. Some drops may be a visible heel as on a work boot or a woman's high heel shoes; still others will just be a heel that is thicker than the toe as on a traditional running shoe.


Let's consider stack first; stack and cushion aren't interchangeable terms, but we can usually assume that a shoe with a bigger stack provides more cushion. When minimalist running first took hold in present day running culture, cushion was out, and low stack was in. Less stack typically means that you will feel the ground more precisely which will aid in proprioception in turn helping you become a better, more injury free runner. A lower stack also means that you'll feel more inconsistencies in your stride – something we don't always want to take care of. Presently, maximalist shoes seem to be fairly popular. Where a low stack minimalist shoe can range in the 3-11mm range, the stack of a maximalist shoe can get upwards of 30+mm – that's over an inch of material between your foot and the ground. While a low stack increases proprioception and ground feel, a larger stack can make up for weaker feet muscles that aren't ready for what you're putting them through. Some people prefer a maximal stack for long runs or at the end of a long race. For others, a tall stack alleviates discomfort from Morton's Neuroma. At Simply Shod, we prefer a shorter stack and have resourced a number of different materials that vary in height to help you gradually lower your stack. However, we're well aware that a low stack just doesn't work for everyone. While we won't build up to 31mm, we have built huaraches  upwards of 21mm, pretty high for a huarache if you ask us.

The original prototype: sandals with a very rudimentary heel lift creating a 6mm drop.Now that stack is covered, let's look at drop. This is probably the more important term to know when it comes to preventing injuries. A typical running shoe has a heel-toe drop of 10+mm – that's almost half an inch difference between the stack of the heel and the stack of the toe. To get an idea of how big this is, take your shoes off, lift your heel off the ground, and slide a stack of six quarters underneath your heel; that's about they typical offset of a traditional running shoe. Now jump to a minimal shoe with zero heel-toe drop. It may not seem like much, but that 10+mm is a huge difference to your Achilles. If you go from a 10+mm drop to a 0mm drop, your Achilles will now have to stretch an extra half inch every step. Consider that most elite runners are at about 180 steps per minute (recreational runners are usually a bit lower). In a half hour run, that's over 5,000 steps. You wouldn't go into the gym add weight to your bars and try to do more reps, so don't do it with your Achilles. It's important to lower drop slowly, over many miles. There are a number of reasons shoes have a drop, but when it comes to running a large heel-toe drop may allow a runner to overstride and land with a heavy heel strike.

Tready Sole+6: a 6mm drop with a custom 21mm stack in the heel.
The Tready Sole+6: 6mm drop with a customized 21mm stack in the heel.
So where do we go from here? Figure out the stack and drop of your current shoes; you probably don't have a caliper that can measure them, so find the information online. Running Warehouse is an excellent resource when trying to determine the specs of a particular running shoe. Now armed with your current shoe intel, assess your running.
  1. Where will I be running? What kind of terrain? Think about the differences between concrete sidewalk, grass covered trails, and rocky mountain tops. 
  2. What kind of distances will I be running? As we mentioned earlier, some people like a taller stack for longer runs and the same can be said of a larger drop.
  3. Do I have any issues with my feet that may be alleviated with a thicker stack? A thinner stack? We all know running is an expeirment of n=1, but some people swear that a tall stack alleviates their Morton's Neuroma, still others will tell you that a low stack cured their plantar faciitis. 
  4. Do I have any injuries that may be alleviated with a higher drop? A small stack may help alleviate a tired or injured Achilles tendon.
Whatever you decide, it's best to change slowly and work shoes into your rotation gradually. If you still can't decide and want some advice or still have questions, you can always email us and we'll do our best to get you answers.

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