Sunday, April 27, 2014

Constrained maximization of shoe life and finances given different shoe costs

Running shoes aren't cheap, so I'm always thinking about ways of cutting costs, given that I go through about three or more pairs a year. Aside from the usual ideas of stocking up when the shoe models I like are discounted to make room for the next year's model, I've recently come up with a new plan that takes into account the different prices of shoes that I use.

First of all, the shoes. Currently, I rotate a pair of Brooks Glycerin 11s (second from the right in the picture) with a pair of Saucony Kinvara 2s (fourth from the right). Glycerin 11s list for $150, and that's more or less the price you pay for them (less any storewide discounts, like Road Runner Sports' VIP membership). Kinvara 2s have been out of production; the current model is the Kinvara 4, which lists for $100 but are at a 25% discount on the Saucony site, and possibly cheaper elsewhere. Both models are set to be replaced soon by the next edition. As you can see, there's a big price difference between the two brands; even if we don't take into account the fact that Brooks seems to exert more control over how retailers discount its shoes, the per mile cost of using the Glycerins is going to be ~50% higher than that of the Kinvaras.

Second, my actual shoe usage. I use the Glycerins for easy runs, and the Kinvaras for shorter, faster runs, including speed work on the track. Until recently, when I altered my running schedule, I'd estimate that about 60-70% of my weekly mileage was in the Glycerins. Now, however, I've been trying out a routine of Monday long run, Tuesday speed work, Wednesday cross-training (with maybe a short easy run), Thursday medium distance easy run, Friday speed work, and Sunday easy run. Instead of switching shoes every day, and thus having the Thursday run in Glycerins, it occurred to me that I can rotate one pair of Glycerins with two pairs of Kinvaras.

This is possible because I've been finding the Kinvara 4s at pretty good prices (it was the Amazon Gold Box Deal of the Day a couple of weeks ago), and I broke out the first pair I bought to make sure I liked it, as sometimes shoe models change significantly -- i.e., the Nike Air Pegasus 28 to 29 transition. So, right now, I can rotate the Glycerin 11s with Kinvara 2s and Kinvara 4s (white/yellow). When I retire the Kinvara 2s (in an estimated 200 more miles), I can swap in a new pair of Kinvara 4s (blue/gray). Meanwhile, the Glycerin 11s still have an estimated 400 miles left on them. If I use them only for the weekly long slow easy run, which tends to be 10-12 miles for me, it should be something like 40 weeks before I have to replace them.

What this schedule would manage for me is to tilt the distribution of the roughly 3+ pairs of shoes a year from ~1.7 to 1 Glycerins a year, and of course increasing the number of Kinvaras.

Third, the non-financial standpoint. This is the one aspect I'm not sure about, but my tentative thinking is that this should be fine. The Kinvara 2/4 is a lighter (7.7 oz) shoe with minimal heel to toe drop (4 mm), but it's definitely not a minimalist shoe. I don't think I'd run a half marathon in a pair (although there are people who run marathons in them!). I have raced several 10Ks in Kinvaras with no ill effects, so I'm pretty confident that I can go 7-8 miles in them, which is about as long as my non-long runs go.

The bottom line: I got fitted for shoes at Road Runner Sports a little over two years ago, and since then, I've gone through two pairs of Nike Air Pegasus 28s, one pair of Brooks Glycerin 11s, one pair of Saucony Kinvara 2s, and am about 3/4 of the way through another pair of Kinvara 2s and 1/5 of the way through another pair of Glycerin 11s. (It'd be even more shoes but I've been going over 600 miles, well over in some instances, on most of them.) Usage has thus been tilted approximately 2/3 toward the more expensive trainers, but I can flip it the other way with this new shoe rotation.

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