Shoe Hacks: Nike Vaporfly Minus 4 and ASICS HypoSpeed 6...

New 25Apr2021: NEXT% Hack Video

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But were they any faster than the standard ones? Sadly not! See experiment video:

Click here to open video at

Raw data for that experiment on Strava and Garmin Connect, analysis spreadsheet here: hyperspeed_vs_vaporfly.xlsx.

Vaporfly 4%

Vaporfly showing removed bits

Good grief, has he really been chopping lumps off those exquisitely-designed and eye-wateringly expensive Nike Vaporfly 4% shoes? Oh yes. Read on.

Introduction and ASICS Hypospeed 6

I have a problem with road-racing shoes in running. I mean here's a random picture of some track spikes, built for speed -- they're all about the forefoot, with a mere vestige of heel:

example spikes

Here for contrast is an ASICS Hyperspeed-6 road racing shoe. Also built for speed. But suddenly there's a big goofy heel, thicker than the forefoot -- why so different from the spikes above?

normal hyperspeeds

But you're going to say I cheated there, those were track spikes, and surely I'd be glad of that heel cushioning at the end of a marathon? Well here I am near the end of the 2018 London Marathon. I'm just about to touch the ground -- with the edge of my forefoot:

marathon forefoot landing

You only have to look at the damage to my shoes (and my feet) to know all the action is on my forefoot. I just don't need those built-up heels, which add useless weight -- and mass on your feet has to be lifted, accelerated, and braked repeatedly, so it counts extra. I sometimes get 1000 miles out of a pair of trainers, which requires a repair or two with Shoe Goo to rebuild the forefoot, but end up with basically unworn heels which have been unnecessarily carried for all those miles. My heels do touch the ground in mid-stance at marathon pace, but there's simply no impact or shear to require any padding. Here's me in the same marathon, with my heel touching the ground:

marathon heel touching mid-stance

Nobody (except perhaps Altra) make road shoes without built-up heels. And even the Altra Escalante Racers are a bit heavier than I'd like. So I took to modifying my own shoes, firstly to save weight, and also to perhaps gain some additional achilles stretch/rebound, to improve efficiency. Here's the shoe I was landing on in that marathon on the scales after I cut about 12mm of the heel away -- note it is about 30g lighter than the standard version (was 184g, now 153g):

modified hyperspeeds

The original had a heel drop of 6mm, so now it is about -6mm -- i.e. forefoot padding is thicker than the heel padding. Not even Altra make negative drop shoes. They feel pretty strange when walking, but as soon as you're running -- as a forefoot striker -- they feel great. Here they are together for comparison:

hyperspeed comparison

Nike Vaporfly 4% becomes Vaporfly -4 mm

Everyone is really excited about the Vaporfly 4% (and now NEXT%) shoes. They are super-expensive but claimed to improve running efficiency by 4% (hence the name), which is massive. They have a carbon fibre plate which was rumoured to act as a spring -- which seems like cheating -- but analysis determined it was mainly the extra-thick bouncy foam which was doing it. I held off buying them for ages, because I didn't want to be the only one who'd just bought performance with my credit card. Then in London 2019 I turned up at the championship start and it felt like I was the only one not in these shoes -- I was literally left behind, and just felt stupid.

But the Vaporfly shoes have a bigger heel drop of 10mm, which given the padding overall is a massive thickness. Quite a few people have complained that the "high heels" feel unstable in corners. And the total shoe weight of about 220g was much higher than I'd got used to with the Hypospeeds shown above. At the same time, I didn't want to miss the chance to get the rumoured performance gains, so it was time to try the same trick. Time to get the scalpel out... I bought a second hand pair on eBay (in case I trashed them), and got to work.

So first I had to decide how much to take off. I started by marking out a 10mm reduction, but there was so much thickness left, and I've been happy with those negative drop shoes above, so I risked going deeper and marked out again at 14mm in mid-heel, tapering to zero in the middle of the foot, for a -4mm heel drop:

Vaporfly marked at 10mm and 14mm

Off it came, cutting from both sides with the scalpel, and then working down into the 'canyon' until I got mid-way, trying to keep it reasonably parallel to the original sole:

Vaporfly 14mm removal

For good measure I decided to chop off the peculiar heel points, which are probably just there to look cool (to be fair the additional mass is negligible -- it's the dense sole that adds weight, not the spongy foam):

Vaporfly heel point removed

From bitter past experience I've found exposed shoe foam is slippery on wet descents, and skiddy surfaces like the Cutty Sark paving in London. So I add back some dobs of Shoe Goo, which work well to restore grip:

Shoe Goo dobs added

Overall I saved about 20g on each side, to leave a just sub-200g shoe -- still heavier than I'm used to, but if the magic bouncy foam works well enough, it's worth carrying around. To be honest I probably could have started my cuts nearer the toe, especially on the inner edge, to lose a bit more weight. Maybe later. Here's the before and after, and the bits I chopped off:

Unmodified shoe 219g

Modified shoe 197g

Underside view

38g of waste cut from the pair

Out of interest, after I'd run a few training miles in them, the bright white areas show where they're not really touching the ground significantly:

38g of waste cut from the pair

Feel and Performance

The Vaporflys, like the Hyperspeeds before them, feel pretty strange when walking. When I stay overnight for races I usually wear my race shoes to avoid carrying another pair, and the Hyperspeeds could actually be uncomfortable on the heels when trudging round a city. But once I'm running -- they feel great. Before this surgery, I was aware of the Vaporfly shoes pressing on the underneath of my heels. Afterwards, that was gone.

A training test run before and after modifying the Vaporflys didn't show any great performance increase, but did hint at a slight improvement. My first race (see race log) was the Hatfield Broad Oak 10K on 27May2019. Did a miracle occur? No. My fitness (as demonstrated in London that year) was not great, and I was quite heavy by my own scrawny standards. But given my recent form, I was actually reasonably quick. Not conclusive, but encouraging. Watch this space for future trials. Maybe alternate training laps with different shoes would be the experiment to do...

NEW 03Aug2019: I have now done the experiment. See here.


You are quite likely to cut yourself doing this, in my experience. I wear gloves and safety specs (in case the blade snaps). You may also wreck some perfectly good shoes, or suffer some horrible running injury from using altered shoes. You may also gouge chunks out of your dining-room table or contract a horrible disease from leaving mud on your kitchen scales... If you do any of this, then the risk is entirely yours!

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