February 6, 2013

How do you know when a shoe is 'dead'?

If I got €1 for every time I get asked this I wouldn't need to sell shoes, but if I didn't sell running shoes in +Amphibian King Galway I wouldn't be asked.

Its a perpetual question in a never ending cycle.

With a penchant for logical thinking and understanding of the built environment and how engineering ties all things together I like things that have a definitive answer. You know, black or white, grey is boring kind of thing.

Unfortunately the answer to "How do you know a shoe is dead?" is the proverbial long string. The short (cop out) answer is the rhetorical "it depends on the individual". Ball firmly back in your court.

I like to understand the answers that I give to people. So here goes my take on it....

Running shoes are made up of many different parts, these parts vary in their function and as part of the nature of material they have a finite lifespan. It is this lifespan which defines when a shoe is 'dead'. Manufacturers test their materials and in a manner no different than the claims of car manufacturers saying "x km per litre" (or MPG if you're old school) they have an idea of when a shoe can be expected to be past it 'best before date'.

I'll often hear or read of someone who manages to get 1000 miles from their running shoes and that the 500mile thing is just a marketing gimmick to get people to buy shoes. 

No, its not. 

If you think about it you realise its common sense to build a big safety factor into the claims. Could you imagine the backlash if shoe manufacturers claimed 1000miles life in the shoes? 

"Here, I only got 600 miles outta my shoes, look at them!"

Shoe companies could use more durable materials, but then the shoes will feel wrong. They won't provide as much cushioning, or else more cushioning will be needed (more = more weight too) and they would probably be more expensive and so on.

Where am I going with this? There's a massive caveat with running shoe life claims.

This is the thing, there is a constant, which is important for the way I'm thinking. The durability of the shoe materials under normal conditions is tested to approximate 500 miles of good quality response and cushioning. After this period the durability is deteriorating and materials science would have you understand the deterioration will be at an accelerated rate rather than at a constant. (more deterioration = less ability for materials to recover = more deterioration etc. in a circular fashion). 

Also note it's not a time based breakdown, its simply as a response to the compression and recovery of the materials in the midsole. Over a finite amount of compressions the ability to recover, ready for the next compression is what has deteriorated.

I like to think of it in terms of the way Ikea showcased their product testing.

So with the constant discussed, we know to expect 'around' 500miles, we now need to consider the variables.

This is down to the individual doing the running and where the piece of string comes into it.

Assuming you have been correctly fitted in +Amphibian King for your shoes in the first place the main factors affecting how long your shoes will last you are (in no order of importance):
  • weight
  • footstrike
  • suitability of the shoe for the surface
  • duration of runs
  • frequency of runs
  • maintenance & aftercare
If you are a 120kg person running 20km x4 times per week in ACME Running Shoe Brand Z you are obviously not going to get the same lifespan (in the same shoe) as a 70kg person running 10km x8 times per week.

You will be putting a higher impact load into the material and shortening the recovery time of the shoes through the higher frequency of loading. If you add in running in wet conditions with shoes that never fully dry, you are further accelerating the degradation process.

This is why most seasoned runners will rotate several pairs of shoes through a season. You will always have a fresh pair, dry and ready to go out the door.

But, how do you know when it's dead?

I don't know, you need to tell me. 

The best way to find out is to record your mileage in the shoes. Check your diary from time to time and when / if you feel the response is gone, its time to change your shoes when they are in or around the 500 miles. 

If you get 1000 miles from your shoes before they fall apart, change them at 900.

If like me, you run in your shoes and wear them to work, the rules are different.


jedistev said...

good article! some people said know when the leg/knee or feet start pain on old shoes as you know it time to start replace new shoes

Unknown said...

Hi jedistev,
Return of aches and pains can be an indicator of shoes gone past their best. I would think you have let yourself go too far when that has happened.

The body is incredibly adaptive and will adjust with the shoe, to a point, that point being the limit of your tolerance which is where the aches kick in. You then have to readjust back to the structure of the new shoe = 'breaking a shoe in'.

I'd suggest bringing in the new shoes just before this starts to happen, rotate them with the old shoes and you will stretch the overall combined life of both pairs.

Thanks for taking the time to read! Happy running.