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Oct 2019
9:22am, 18 Oct 2019
5,574 posts
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jda
I don't know for sure about plate vs foam. Plate will intrinsically be very efficient but that only matters if it bends enough to store a significant amount of energy. It has been reported that the foam is very efficient (returns a high proportion of energy) and it certainly compresses a fair bit.
I'd have thought that the toeing off force is sufficient to cause quite a bend in the plate, but no numerical estimates for now...
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Oct 2019
9:33am, 18 Oct 2019
9,142 posts
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larkim
I'm no engineer (!) but if I simplified it to the foam being the big energy return mechanism, but needing stiffness because otherwise the foam is too sloppy so the CF plates required, that feels like common sense.
The air pockets are odd additions - maybe an air pocket is even better than Pebax in terms of return / weight, more likely it has some different properties (e.g. speed of return of energy?) that make it the right device at that point.
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Oct 2019
9:52am, 18 Oct 2019
5,576 posts
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jda
Yes, I would think it is more efficient in principle but needs structural support which takes away from that.
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Oct 2019
12:21pm, 18 Oct 2019
15,426 posts
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Bazoaxe
can the shoe lengthening the leg be right as a benefit. My Asics Gel Cumulus have just as big a heel and I probably have at least as long legs when wearing them ?
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Oct 2019
12:44pm, 18 Oct 2019
9,148 posts
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larkim
I guess you'd need to read the referenced paper "Pontzer, H. (2007). Effective limb length and the scaling of locomotor cost in terrestrial animals. Journal of Experimental Biology, 210(10), 1752–1761." to convince yourself of that. It seems to make sense to me that if you have a longer limb / lever that weighs the same the stride length will be longer but you'll be able to maintain the same cadence. So that would be faster. (There woulf actually be a real energy cost to travelling the limb further each stride, but it might not outweigh the better stride x cadence speed equation)
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Oct 2019
12:52pm, 18 Oct 2019
15,428 posts
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Bazoaxe
My point is that my legs are longer with ASICS on so why are the vaporflys better
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Oct 2019
12:54pm, 18 Oct 2019
5,583 posts
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jda
Lighter, that’s all. The calcs depend on the point of comparison and that article was presumably comparing to more conventional thinner shoes. But the benefit of adding height will depend on the added weight.
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Oct 2019
12:55pm, 18 Oct 2019
9,149 posts
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larkim
You'd lose the 1% advantage then Baz. They compared the Nike Streak (23mm heel height) to the VF (31mm heel height) and said that the 8mm increase could account for up to 25% of the VF advantage. If you had the same heel height in both, you're only wearing VF3%s 
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Oct 2019
12:56pm, 18 Oct 2019
9,150 posts
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larkim
And yes, as jda says - the mass of the shoe will make a difference in energy cost.
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Oct 2019
1:12pm, 18 Oct 2019
15,429 posts
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Bazoaxe
ah right, that makes sense. The VF is defo lighter than the Asics.
here is a different question. Ive worn orthotics for years. I am not sure if I need them or not, but they helped solve an injury issue and so Ive stuck with them. I use them in ll shoes. They will add to the weight of the VF, should I consider ditching them ?
Only issue is that I know if I don't wear then now I get foot arch issues
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