older model running shoes

I think it'd probably be pretty safe to buy the previous year's model - say, they just came out with the "12" model of your shoe - getting the "11" on sale is probably fine. I guess it comes down to who you think is trying to make more money - the running store trying to push the new model, or the running stores who show up at race expos with truckloads of out-of-date shoe models selling them for 40% off. I doubt either is really concerned about whether the shoes are "bad" or not.

I've heard similar comments as well.  I believe one of the things I was told is that as the shoes sit on the shelf the internal cushioning materials can become "brittle".  Not in the sense that it falls apart, rather it loses it's "peak" ability to absorb the pounding....

I however tend to think it's as much a ploy to keep selling the new shoes at $120 rather than the closeouts at $85....

Yup.

From here

I cannot find this "written communication" from Dr. Wilder, so don't flame me for quality or lack of research backing up this statement.  I bring it to you for discussion.

That being said, I don't buy the older model shoes.  I'm "older", run a lot, and have been injured in the past.  Being injured sucks.  Not running is like ripping out a valuable piece of my life. 

Yea, often some coin can be saved on closeouts, but running is important to me so I spend the extra.  Placebo, peace of mind, or backed by science, I really don't care.

I used to work as a plastic materials chemist and still work in the plastics industry.  Plastics and elastomers of the types used to manufacture shoes do have a limited shelf life.  The variables on how long they last are storage temperature/humidity/UV history to name a few.  In an ideal world stored at room temperature in a vacuum they would last forever.  Plastics will absorb water into their structure especially cross linked elastomers and they breath with humidy and temperature.  Really how long your training shoes last depends on storage more than anything else.  Cool dry conditions will make them last longer.

God I sound boring!

I found an email address for Dr. Wilder (see my post above).  I emailed him the question regarding running shoes and shelf life.  His response is below...

Dan: In response to the question regarding stale shoes:  This is a question that is frequently asked, but unfortunately we don't have any data correlating the use of old shoes to specific running injuries.  Although it is reported that the polymers in running shoes will demonstrate degradation over time, what percentage of degradation then becomes significant clinically has not been established.  Based on recommendations from shoe engineers we have collaborated with in our SPEED Clinic Lab, who have reported that degredation seems to increase after about 2 years, I have recommended that folks use shoes before they turn 2 years old.  So, buying a couple pairs or even three pairs as a model is getting ready to expire is probably reasonable, but more MIGHT pose an issue.  Again, this is a recommendation and should not be considered a hard and fast rule.  Hope this helps.