The short answer is Yes. In general it’s a good idea to race in a relatively new, but broken in, pair of shoes. The reason for this is that you want the shoe to have as much spring and cushioning left in it as possible to propel you forward. The caveat is that you don’t want the shoe to be right out of the box, because then it may be stiff and cause injuries or blistering. So when is the right time to switch?
If you plan on wearing the same exact make and model shoe for the race, then you can get away with two weeks of break in, or approximately 20-50 miles. Presumably you legs and feet are already used to the shoe, so this number of miles should be able to get rid of the stiffness in the material and wear down the hard edges of the rubber sole. I’ve gotten away with a 1 week break in period before, but I’d recommend sticking to 2 weeks. The week before a race your mileage is going to be tapering off pretty quickly, so two weeks gives you the chance to get in a couple of longer and harder runs.
If you plan on wearing a completely new shoe, or even a new model of shoe, then I recommend wearing them for a full month. You should still be in full training mode at that time so it gives you a chance to slowly get used to the shoe. It also gives you a bail out plan in case you find that you can’t tolerate the shoe. For instance, if during the first two weeks the shoes becomes very uncomfortable, simply switch back to the same make and model that you were training in before and consider buying a duplicate pair to break in for the race. If the shoe is drastically different than the one that you train in, make sure you start with short distances at first and build over two weeks to a longer or harder run. Overall, 4 weeks should give you the chance to do a longer run in the new shoes and put at least 50 miles on them.
Finally, for people who want to use a racing flat or similar, the key is to get in at least two harder runs with the shoes before the race. These types of shoes are fairly flexible and require less breaking in, but you still need to make sure your feet tolerate them. Try to do one hard workout in them at race pace, and at least one other workout at close to race pace for half of the race distance to be sure that you can handle running in that type of shoe.
Don’t start thinking about this at the last minute! I’ve been there before and trust me it’s not worth getting blisters and losing toenails over. Plan ahead during your training and you’ll thank yourself later. Let me know what you think, and if you have any personal advice please comment below.