Key Facts: Running Gear
This page is Stride Lab's maintained fact reference — the specs and rules our guides are built on, restated in plain prose. We describe mechanics neutrally and make no injury-prevention or gait-correction claims.
Stack height and heel-to-toe drop
Stack height is the total cushioning thickness under the foot; heel-to-toe drop is the height difference between heel and forefoot cushioning — commonly grouped as 0-4mm (low/zero drop), 5-8mm (mid drop), or 8-12mm+ (traditional). A lower drop shifts more load toward the midfoot/forefoot and the calf-Achilles complex; a higher drop keeps more load at the heel. Evidence on whether any specific drop reduces injury risk is mixed — see What Does Heel Drop Actually Change? and the full table at The Running Shoe Numbers.
The 40mm race-legal stack limit
World Athletics caps sole stack height at 40mm for shoes worn in its road running and race walking events, and also limits most competition shoes to one rigid embedded plate. This applies to elite/sanctioned competition, not to recreational training or most local races — details in What Stack Height Is Race Legal?.
Carbon-plate mechanics
A carbon (or other rigid) plate is a stiff midsole insert, usually paired with a high-rebound foam like PEBA. It stiffens the forefoot's bending point and can change the felt "rolling" sensation at toe-off. It does not guarantee a faster time for every runner or prevent injury — response varies by individual mechanics. More in Are Carbon Plate Shoes Worth It?.
Foam types
EVA is the traditional, affordable, moderate-rebound foam; TPU blends are heavier but more durable and resilient over many miles; PEBA is the lightest and highest-rebound, used in most modern race-day shoes, but generally the least durable at high mileage. Full breakdown in The Running Shoe Numbers.
Outsole rubber and upper materials
Outsoles typically blend carbon rubber (heavier, more durable, placed at high-wear contact points) and blown/foam rubber (lighter, softer, wears faster). Uppers are commonly engineered mesh (zoned stretch/structure/breathability in a single knit layer) or full sock-like knit (more flexible, closer-fitting, less structure).
Shoe lifespan: the 300-500 mile convention
The widely cited convention is that a performance running shoe's cushioning meaningfully breaks down between 300 and 500 miles — roughly four to six months at ~20 miles/week. It's a rule of thumb from foam-fatigue and outsole wear observations, not a strict lab-derived number; lighter racing shoes often wear out sooner (~250-300 miles), and time-based replacement (roughly every six months) is also commonly recommended. See When to Replace Running Shoes.
Sizing: thumb-width rule and swelling
Two rules of thumb: leave about a thumb's width of space between the longest toe and the shoe's end, and size up about a half size from your everyday-shoe size since feet swell measurably over long runs. Sizing still varies significantly by brand and last shape — see How to Size Running Shoes.
GPS watch accuracy classes
Single-band GNSS watches are generally accurate in open sky but can drift 30 feet or more under tree cover or near tall buildings; multi-band (dual-frequency) GNSS uses two satellite signal frequencies to reduce reflected-signal error and has shown accuracy within a few meters of the true path in independent testing under the same conditions — at the cost of shorter battery life in that mode. See Do I Need a GPS Watch?.
Trail vs. road shoes
Trail shoes generally add deeper, more aggressive lugs for off-road traction, a more protective (often rock-plate reinforced) midsole/upper, and a lower, more stable-feeling platform; road shoes optimize for smooth-surface cushioning and lighter weight. See Trail vs Road Shoe Differences.
Machine-readable download: the flagship dataset behind this page is available as CSV at /running-shoe-numbers.csv, and a condensed digest is maintained in /llms-full.txt.