What the kit is worth
Shoes, spikes, rackets, strings, suits and balls, brand by brand, measured by the papers and modelled by the physics, then turned into the only number that matters: how much more often you win.
Effect, then speed, then a chance of winning
Every comparison runs the same three steps, and every step is printed with its source.
A number with a grade
A shoe's running economy from a treadmill study; a racket's restitution from its swingweight; a suit's drag from a towing tank; a ball's drag crisis from a wind tunnel. Literature, physics, or a maker's claim, and it says which.
Economy is not speed
Running costs more per metre the faster you go, so a 4% metabolic saving buys 3.4% at 3 m/s and under 3% at record pace (Kipp, Kram & Hoogkamer 2019). Drag scales with speed cubed, so a 4% drag cut is a 1.3% time cut. A heavier racket swings slower but hits harder, and the two nearly cancel.
Against an equal rival
Athletes vary race to race by a known amount: about 1% on the track, 1.8% over a marathon, 0.8% in the pool. The gap the gear opens, divided by that noise, is the probability of finishing ahead. Small gaps in low-noise sports are worth the most.