Running Shoe Design

A couple of ill-educated thoughts on shoe design....

Padding and comfort in the upper.
Comfort is largely a function of how well loads are uniformly distributed across the foot.  If a load is concentrated in one area then the shoe will cause discomfort at that point.  A certain amount of padding is necessary in order to achieve this, but the amount will vary depending on the compliance in the upper.  Often the critical area is the heel... a stiff heel counter requires more padding to accommodate any difference between the shape of the heel counter and the shape of the foot, but if lots of padding is being used to mask a fundamentally poor fit then, over time, this will often compress making it hard to get a tight and comfortable fit.  The best shoes that for heel fit that I have owned are the Inov-8 Trailtalon 250 and Nike Terra Kiger 3.  Both have fairly minimal padding and a flexible heel counter that conforms to the shape of your foot.  By contrast, my Altra Superior V2.5s suffered with very poor heel hold once all the padding had compressed down.  The irony is that once any padding compresses, you lose the ability to get a good fit and those, once pillowy looking heels, start to cause slippage and blisters.

2) Stability, drop and heel shape. 
I often see comments about wider heels suggesting that they are more stable.  While in certain circumstances this can be true, I think that this opinion is derived from running on flat surfaces and perhaps with a heel strike.  By contrast, on the trails a wider heel is simply more likely to catch something and cant to the side, risking a rolled ankle.  The higher the stack height, the wider a heel needs to be to avoid an unstable feeling on flat ground, but in my experience as a mid to forefoot striker running on trails it is generally detrimental to have a heel much wider than the foot itself, which is probably a function of having something close to your natural perception of where your body is.    Interestingly I think that people often attribute instability to stack height or drop when, somewhat paradoxically, it is due to the width of the heel that is at fault.  An example of this is that the New Balance Vazee Summit 2 has a stack height of 10mm and many reviews suggest that it feels lower and more stable than that.  I believe that this is because it's narrow / precise heel profile tends not to catch on uneven ground and cant over, so people find it feels stable which they associate with a lower drop. In contrast, the Salomon S-Lab Sense Ultra (8mm drop) has a wide heel which, on uneven ground, cants the shoe to the side making it feel less stable.