Suppose your bike experiences one flat tire, which you fix.

Now suppose a couple weeks later it experiences a second flat tire, which you fix.

Further suppose that you begin to wonder about the structural integrity of your bike tires; they’ve now gone flat twice in a short span of time, and at a closer glance the casing in the tires is starting to show through the rubber. It’s conceivable they need to be replaced, as you’ve put at least a few thousand miles on them and have used them since 2003.

In hypothetical response to this you ask someone knowledgeable how long bike tires last and how one would recognize when they need replacement. In response you are told that bike tires are suspect after five years (due to breakdown of the rubber) and should be replaced when the underlayer shows through.

You now have two entirely hypothetical options. First, you can replace the tires now. Second, you can continue using the ones you have until you can get to a cycling store “eventually” to buy new ones, but as it turns out you won’t make it to the store before your tire fails you a third time and you have to fix yet another flat (and actually a fourth as well, when you find your rear tire flat when you try to get to REI the next morning to buy a new pair of tires).

Now for the helpful cycling tip: replace old tires promptly and don’t wait for third flats.