Adizero Prime X 2 vs Mach X 2

With 50mm under the heel, the Adizero Prime X 2 sits a full 10mm over the World Athletics limit for road racing, so no record or championship result run in it will stand. adidas built it that way on purpose, as a carbon-plated experiment in how far stack can go, and most reviewers ended up treating it as a very expensive super trainer rather than a racer. The softness won nearly all of them over. The weight was a different story: it put on a lot over the first Prime X, and several testers struggled to hold faster paces in it. Lab testing and two of the reviews rate it well for long runs and marathon-pace sessions, while one US panel called it a step backwards and preferred version 1. Coach's UK review lands in the middle, calling it great fun but priced above legal racers that do the job better. If you want an adidas marathon shoe for race day, the Adios Pro 5 is lighter, cheaper and legal. We'd buy the Prime X 2 for how it feels on long miles, and only once the price has dropped.

Heel rub is the first thing to know about the Mach X 2. Nearly every review mentions it: the heel collar is thin and unpadded, several testers got blisters in the first few runs, and another found it dug into the Achilles. Get past that and the ride is why people put up with it. It's a rockered, snappy super trainer that reviewers took from easy runs to track reps, and Believe in the Run graded its performance an A.

Doctors of Running were less convinced, finding it heavy for fast running and unstable for one of their testers. Hoka has since released the Mach X 3, which reviewers rate more highly, so the 2 makes most sense as a discounted buy. At £180 RRP it's hard to choose over its successor, but check the price table, because an older super trainer at a good discount is a different proposition.