Do Shoes Have a Useable Lifespan?

I just got, and set up a pair of Lake winter cycling shoes. Today I went out for a short shakedown cruise, mainly to check to see if my cleats were positioned properly. While I don't really know about additional warmth, as today's temps were in the 60s, I immediately noticed the improved power transfer as compared to my 5+ year old Mavics. The Mavics have well over 20,000 miles on them. In my hands the sole flexes quite a lot, especially compared to the new Lakes.

So, do we think that the Mavic shoes have worn and broken down and have otherwise lost stiffness, or are the Lakes just that much stiffer to begin with? All internets opinionz welcome..

I have a pair of Avia shoes that I purchase about 25 years ago. I still use them. The soles don't flex at all.

Dan

Don't know about your shoes. My old pair of Sidi Dominators went ~50,000 miles before I lost them, with no apparent change in sole stiffness. My new Sidi's feel the same as the old.

I have a pair of Lakes from about 2008 seem stiff as new.

Which Mavic shoes do you have? I have a pair of Mavic Ksyrium Pros, and they aren't nearly as stiff as my PI Pro Leader shoes.

Difference is in the shoe specification, not the relative age of the two pairs.

+1. Modern shoes with synthetic soles don't soften up with age. Old leather soles definitely softened with age.

I had wood soled shoes back in the day. They stayed nice & stiff.

Yeah, Mavics have not been the stiffest, traditionally.

That said, shoes can get clapped out for other reasons than sole stiffness degradation, so Yes, they do have a usable lifespan typically.

Nylon and other synthetic outsoles definitely fatigue and demonstrate degraded stiffness.

Fatigue endurance | AMILAN® | TORAY PLASTICS | TORAY

https://www8.basf.us//PLASTICSWEB/dis...01a5e180004880

So that's between 6 and 7 million fatigue cycles in my estimation. Definitely enough to compromise some sole materials.

Now that is interesting!
Hell, there are still snow skis made with wood cores, so why not?

I only perused the articles quickly, but I believe you misconstrued them. The first one did relate to fatigue with use, but did not specify what fatigue means. I assume breakage. And there is no description of the mechanical properties right up to the catastrophic failure. The test was how many cycles could the test specimen withstand at each amount of bending force per unit area (stress) before "failing". Now OP is not asking about catastrophic failure, but rather about stiffness after many stress cycles but prior to breakage. The article does not address that question. It isn't mentioned at all.

In fact it would not be surprising if the shoe sole actually became stiffer as it approached the fatigue limit as the bending is really a form of "cold working" of the material. It is not altogether outlandish to think that the nylon crystallinity would be increasing over time as the material is bent back and forth.

Actually then, the answer to OP's question may be, "Yes, cycling shoes have a useful lifetime," if you define lifetime as the interval up to catastrophic breakage of the sole due to fatigue. I have never heard of that happening, however. So the point is moot.

The second article isn't about repetitious flexing at all, but rather about the effects of heat and moisture on the mechanical properties of glass-reinforced nylon. That does include flexural stiffness, but has nothing to do with changes in properties with use. The effects of temperature and humidity on nylon are instantaneous. They have nothing to do with age. And in the conclusions the authors make clear that the effects are reversible with changes in environmental conditions which occur all the time. So this article is also irrelevant to the OP's question. But it is interesting that on a hot, 99% humidity day any nylon-soled cycling shoe could feel noticeable less stiff than on a dry, cold day.

Now leather-soled cycling shoes did become more flexible with wear as you would expect. They were common up through the 80s. Hence the use of wood in some shoes for more permanent stiffness.

Yes, you are right about the articles, and my point in linking them was merely to support my assertion that synthetic materials fatigue in various ways and do not have an indefinite service life.

Fair enough.

It looks like you posted that irrelevant information in an attempt to refute my statement that synthetic soles don't soften with age.

I may be overstating the obvious, but I was only talking about loss of rigidity, and mainly in regards to the sole of the shoe. I was not talking about breakage. Breakage, of course, is visible and obvious. Gradual reduction in above mentioned rigidity, if that's truly what takes place, would happen in such minute increments that the rider would never be able to notice or gauge the changes.

Also, any suggestion of "cold working", or work hardening, of material can not apply categorically. Any type of hard plastic, nylon, carbon fiber, etc., used for rigid shoe soles, is not malleable at ambient temperatures in the way steel or other non-brittle metals can be.

Isn't that how fatigue happens? Even to plastic? Just like steel, nylon is semi-crystalline. The crystals provide strength and stiffness. The amorphous regions provide ductility. Flexing the material (working it) causes crystallization at the flex point which results in brittleness due to the loss of amorphous material. Hence fatigue failure.

By my (possibly erroneous) calculations, a cadence of 80 would require 208.3 hours of riding for a million cycles. At 15 mph, that would be 3,124 miles, so 6 million cycles would be less than 20K miles. I don't think my shoes have softened to the extent that I can notice, and certainly have not failed, in a bit more miles than that. (I have Sidi Zeta shoes from 2006, which have some sort of synthetic but not carbon soles, try to keep a cadence between 80 and 90, and don't average 15 mph for all my riding).

Ignored My Shimano Spud sandals , re discovered them , they had rotted away , sole and nylon stiffener, and straps was all that was Left.

Sneakers wear out quickly as the rubber soles flex, compress and wear out with daily use. The more use they receive, the more quickly they wear. I walk an hour a day usually and can't go more than 3 months or so without replacing sneakers.

Bicycle shoes don't flex and are now usually made of synth. materials and can last for decades.

I've never had an issue with the soles. However, I destroy the tops every couple years and need to replace

Uhh... no. Work hardening is a specific treatment to malleable metals, and is used to increase strength and rigidity, not to induce fatigue or cause failure. Apples and oranges, my friend.