I ran a series of four 5K races to compare two Nike shoes:
- ZoomX Streakfly
- ZoomX Vaporfly Next% 2 (two races)
The races were on the same course, one week apart. The weather was good all four races.
The Lunaracer is an “old school” racing flat with minimal cushioning.
The Streakfly uses the same foam as the Vaporfly but lacks the carbon plate. Instead it has a half-length plastic plate. Nike markets the Streakfly for 5K and 10K races. The Vaporfly is intended for marathons.
The Vaporfly is Nike’s racing shoe with the carbon fiber plate. It’s about an ounce heavier than the other shoes.
I ran seven seconds faster with the Streakfly and 39 seconds faster with the Vaporfly.
My stride length increased and my cadence slowed with the faster shoes. The Streakfly increased my stride length 2cm and the Vaporfly increased my stride length 4cm. My cadence slowed from 187 steps per minutes to 186 and then 184 in the third race.
In the fourth race I focused on increasing cadence and ran 187 spm without changing my stride length. This got my best time of the series. The Vaporfly shoes increased my stride length 4cm without slowing my cadence. Doing the math, 4 cm per stride is 7.46 meters ahead every minute, or about 145 meters ahead by the end of the race. (The lower average heartrate included the first half mile, when my heart rate monitor kept slipping and then fell off. It wasn’t measuring my heart rate accurately.)
Ground contact time was also shortest in the final race.
The result was the Streakfly was about 0.5% faster and the Vaporfly was about 3.25% faster.
Nike claims that the Vaporfly is 4% faster. This likely would have been true for a marathon. I’ve heard that with the Vaporfly your legs don’t get as tired during the marathon; this doesn’t matter in the 5K.
Vertical movement increased from 7.1cm with the racing flats to 7.6cm with the Streakfly and the Vaporfly. Vertical ratio also increased. Vertical movement normally isn’t good but with these shoes seems to be a positive.
The Streakfly doesn’t seem to have any advantages. It’s only marginally better than an old, many miles pair of racing flats. It’s more cushioned than the racing flats, which might reduce injuries, but I expect that the foam will quickly lose its cushioning.
The Vaporfly is clearly the fastest of these three shoes. I was concerned about stability as my left knee felt wobbly on a warmup run, which another runner confirmed visually, but I had no problems in the race or afterwards.
I made these measurements with my Garmin Forerunner 245 and “Pro” heart rate monitor.