Epic REACT Mods and Carbon Fiber experiments

What type of carbon fiber inserts would you prefer?

  • I feel the need for speed... I'm only gonna use them for races, so who cares if they hurt a little

  • I'm all for compromise - give me as much additional speed as you can with all day wearability

  • Give me Cloud 9 - I want the float on clouds feeling all the time, who cares about my time

  • Size 9

  • Size 9.5

  • Size 10

  • Size 10.5

  • Size 11


Results are only viewable after voting.
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Joined Feb 28, 2018
There is another factor in shoe performance that I feel the Epic React nails and many other "running shoes" do not. It is important for the shoe to flex sufficiently in mid/outsole and upper that you can do a full heel lift in them without binding.

The lower leg and foot forms a lever system that stores and releases much more energy than the latest energy return shoes (50% versus 4%, respectively!). A shoe should not interfere with that mechanism.



During the beginning and ending of the running stride, at both forefoot landing and toe-off, the foot and calf are in a heel up position. Here are two screen grabs from Jamie's review of ER2.





Note the foot, calf, leg position. Also note the ER does not interfere with this natural motion. If I look at the slowmo video of shoes Kofuzi has reviewed, most of them prevent this natural motion. You might not feel it during the run, but it is costing you efficiency and may eventually lead to injury.

Fortunately, there is a very easy way to test for this. Just put the shoes on in a store and do a standing heel lift. Did you feel any binding? Did the instep flex enough? I strongly believe the complex weave structure of the flyknit upper in the ER and Phantom is unmatched in instep flexibility.

The built-in toe rocker in the new IR tries to force this heel up motion, much like the stiff ZoomFly, which Nike says the toe rocker was copied from. Both are bad ideas. Worse yet are the new "high performance" running shoes with a rigid curved rocker plate. Fortunately, the Vaporfly has plenty of flex in both mid/outsole and upper and allows a great natural leg motion, which is why it is also a great running shoe.
 
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If you notice, Nike put the seam between the REACT and rubber outsole right at the metatarso-phalangeal joint, point C in the diagram above. Yet another reason I like the ER outsole, and prefer the Epics over the Odyssey or Legend variants with more outsole rubber. Point C is the most important point on the foot for running performance. It is the axle in the wheelbarrow analogy in the post above. Would you weld the axle in position on a wheelbarrow? Of course not, then why do shoe companies make this section rigid on running shoes?

 
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I realize this is a Nike forum, but sometimes the best way to understand how Nike gets it right is to see how competitors get it wrong. I've said before other shoe companies may have added a carbon fiber plate to their shoes, but they don't seem to yet understand what it does and why it helps.

The latest example is the Saucony Endorphin Pro. They have the right foam, Pebax. They have a carbon fiber plate. They have a lightweight mesh upper. But they fail to understand what the plate does and/or how it works in conjunction with the foam.

The shoe is not even out yet, but listen to the following two marketing pitches at a shoe show:

In the first, their shoe guru says they made the carbon fiber plate stiff and curved in the forefoot to add efficiency:


In the second, another shoe guy says they made the toe box rigid to add the additional lever arm length to the shoe so the glutes could more engage.


I'm not even sure where to start... Yes, having a rigid curve in the forefoot does feel more efficient and smooth, but you are limiting the natural energy return your muscles system has. So, test runners might say it feels great, but you are not more energy efficient, nor are you faster. I made rigid CF curved plates for my shoes, and yes they feel amazing, but they were not more efficient. And yes, making a shoe longer in order to make your lever arm of foot longer does fling you forward more and will feel faster, but if you take real world data, you will find it does not make you faster nor does it increase energy efficiency.

The best way to understand this is to stare at my wheelbarrow analogy pic, copied again here:



You want to maximize shoe energy return without affecting the 50% energy return of the leg structure. Lever B is the lever arm. Making the shoe longer by making it more rigid only lengthens the portion to the left of point C, which does not give you real leverage. Point C is the axle in wheelbarrow and the point of rotation. Putting a rigid brace across point C to prevent C from rotating is defeating the whole point of the foot/leg design.

So why is this not a problem with Nike and their Vaporfly? Look at the pic of their plate, from their website, and you see they always stop the plate at point C, the metatarso-phalangeal joint. Remember everyone talking about the "fall off a cliff" feeling they give? This cliff is at point C, so that the foot can still properly rotate around point C.

 
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With the disclaimer that I am no shoe or foot expert, I have to disagree with Ted from Saucony when he says, "“And one of the key elements is it is very stiff, so reducing the amount of flexibility in the forefoot creates more efficiency, your muscles have to work a little bit less, become more efficient”.

Yes, a stiff plate will work your foot muscles less, because it is preventing them from working the way they are supposed to while running. Thus the runner becomes less efficient, not more. If their runners set new PRs, then it is because of the bouncy Pebax foam and lightweight of the shoe.

Look at this screen grab from Kipchoge's recent 2 hour marathon run. Note the forefoot flex at the metatarso-phalangeal joint, point C. The most important feature a shoe can have is forefoot flex at point C. And Saucony intentionally got rid of it. The majority of Nike running shoes have it.

 
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From the RoadTrailRun youtube review of the Infinity Run.



After just a few runs, look at the creasing in the midsole where point C would be. You can tell the foot wants to bend there, and the shoe is fighting it. Yes the built in rocker will help this transition, but no forefoot curve can ever be as fast as the shoe simply bending like rotation around an axle. The Epic React and Vaporfly bend here. The IR fights bending here and the midsole just creases. Over time and a couple hundred miles, I would expect the foam midsole to develop its own crease/seam/"axle" here.

I've highlighted the creasing in this pic:

 
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So what can happen when a running shoe is not flexible enough at point C, by either having a plate there like the Endorphin or too thick a midsole like the Infinity Run and many other shoes? Well, here's a video clip from Road Runner Sports 50 mile review of the new Saucony Triumph 17:


I don't want anyone to think I'm picking on Saucony, as I'm not. I love the Freedom 2 and can't wait for the Freedom 3. I just found this clip and thought it gave a great explanation on how the feel differs with a stiff forefoot.
 
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As Nike approaches the launch of the Infinity Run model, more info is trickling out. The Epic React series had a "seamless" flyknit upper. It was one large piece of fabric knit on a massive loom with reinforcements added where needed with heat activated glue. The Infinity Run upper has a "3 layer engineered mesh" with a whopping 6 seams, as highlighted in pic below. Now, that is not necessarily a bad thing, as perhaps it lets them redirect forces in directions desired. But I've kinda gotten used to seamless uppers, especially when wearing thin running socks or going sockless. For me this is another reason why the ER is superior to the IR.

 
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Let's talk about "relief cuts" again. As you know, I cored holes in the forefoot of my Epic React forefoot foam, to allow it room to move under compression. As foam is made thicker it will also resist bending more as it will bunch up on the inside of the bend and reach the limits of its stretch on the outside of the bend. Usually midsole foam is thin enough that this is not a problem. However, recently shoe companies have been making the foam thicker and thicker (higher and higher stack heights). As the midsole foams have gotten lighter through gas injection processes, shoe companies are making stack heights even higher.

OK, shoe companies, if you are reading this ( and I know you are), you need to start molding or cutting relief cuts in the midsole foam. Salomon calls this "decoupling", which is a great term for it, as relief cuts not only allow bending but also decouple the motion of one part of the foot from another. The midsole foam can be tuned by these cuts.

If you look at the Salomon Predict, it has relief cuts on both the outside and inside of the midsole foam. Here is great pic of the relief cuts on the inside from a RoadTrailRun:



So what happens when the midsole foam gets too thick and there are not relief cuts? Here is a pic from Jami's review of the Saucony Triumph 17:



If you watch the video in slow motion, you will see the shoe only contacts the ground in the forefoot. The heel never even touches the ground. And it is not because the runner is a "forefoot" striker. It is because as mentioned in Road Runner Sports review, the thick midsole is resisting bending at the important point C.

So let's look at the Infinity Run midsole. The inside is smooth with no relief cuts, and the outside only has features to hold the rubber outsole. The forefoot is smooth. There does appear to be a decoupling line added to help forefoot transition, highlighted in this pic from the video on NDC:



I've been impressed with Salomon most recent designs. Their latest running shoe is available in three versions with the "decoupling line" placed in three different locations depending upon the application. The slowest shoe has it rearward, and the fastest shoe has it forward (at point C). The "balance" shoe has it halfway between the two. Here is a pic from RoadTrailRun I annotated:

 
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Their latest running shoe is available in three versions with the "decoupling line" placed in three different locations depending upon the application. The slowest shoe has it rearward, and the fastest shoe has it forward (at point C). The "balance" shoe has it halfway between the two.
I should clarify that the decoupling line Salomon is referring to is the gap down the middle of the out/midsole from front to back of shoe. They not only moved the forefoot flex point, but also this line from center to edge with each model. So the flex characteristics vary drastically from the slowest to fastest models.

Here is a pic from RoadTrailRun's video of Salomon sales pitch in Austin:



It is similar to the Nike Volmero 14, where there is a full length gap from front to back of the shoe with a pronounce hole in the heel. Except in the Salomon shoe, the gap also extends through the midsole. I think there should also have been some lateral relief cuts around point C.
 
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Since it is the start of a new year, I thought I would give a status update on my first laceless Epic React prototypes. These were my first pair, and I have kept them in my rotation as a longevity test. I've honestly lost track of how many miles are on them. NRC app shows over 350 miles, but I didn't start using the app until 6 months after I made these shoes. Long story short, they are holding up great. Other than insole compression, there is little to no wear and tear, and no difference in running feel.



The two locations of a little bit of exposed midsole wear after 100 miles have not gotten any worse. It seems the REACT wears to a point and then simply stops wearing down, though that might be my imagination. Here is the heel point of wear:



Many wear testers have posted about the heel pull tab breaking after a while, and mine finally gave out on the right shoe when I pulled it on too fast while standing:



I still have my first pair of carbon fiber inserts I ever made (that came out usable) in these shoes, and they show no loss of spring, no cracking, no changes. They still work great, though I have greatly improved my design since these were made:



My daughter has a pair of Rise that have developed a hole where the big toenail hits the flyknit. Again, many online posters have had the same problem with flyknit shoes. I accidentally bought these a half size too small, and she has long toenails, so this is understandable. None of the phantoms I bought her a half size up show any wear in the flyknit yet.



Unfortunately, Nike has moved away from true flyknit uppers in favor of engineered meshes. The IR upper is called "lofted flyknit" but they then admit it is a three layer engineered mesh. Nike has also discontinued the Epic, Rise, and Phantoms, so once my supply of shoes is gone I'll have to move on to other shoes and brands.
 
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