In more detail.
Of course it is within the rules for you to do this. You might be thinking about saving time in transition or about not spending money on new kit. Fair enough. Or maybe a more sophisticated thinker would be considering the time and energy savings of clips against the time wasted in transition for a SHORT SPRINT event. In that short sprint event the transition time saving or loss will be the same as a longer distance event BUT it will be more significant because the event is shorter/quicker.
However you have to wonder why EVERYONE else will be wearing clips. I mean everyone else. It makes sense to wear clips to commute you know…
Let’s start by assuming that you will be at LEAST wearing straps over your running shoes. Why? Well, simplistically so you can pull up AND push down whilst pedaling. A more even pedal stroke is more efficient and more powerful, especially when practiced.
Without forgetting that after the bike dismount you may have to run quite some distance in your bike shoes or bare feet if you are good then, even if you do the calculation of how much slower straps are vs clips and then compare it to the time taken to save changing shoes you may still forget one more subtle thing. The clips make your RUNNING EASIER. Simply because you will save energy on the bike and spread the effort over more muscle groups by using clips. Therefore your legs won’t be quite so exhausted on the last run.
If you are a good runner dabbling in triathlons / duathlons for the first time (without proper brick preparation) then you will be amazed that as soon as you start running your legs will not work as normal. If you’ve been trying hard in a sprint duathlon/triathlon then that last 5k will feel like the last 5k of a half marathon to you. Clips help them feel as normal as possible (which is still awful!!) – let’s say like how they would feel at the end of a 10 mile race.
With Duathlon it is slightly trickier a calculation as there is the potential to use the same pair of shoes for the entire race and avoid TWO changes. I did some calcs and still came down on the side of clips even for a SPRINT Duathlon.
Having said all of this. I did the GRIM off-road (5:20:5) Duathlon a couple of years back and you don’t get much change out of 2 hours because of the tricky nature of the terrain. I’m doing it again this year and will be reverting to clips as I think it will be considerably faster – despite the short-lived joy I had at powering past people in transition (they all, and more besides, caught me).
Another issue you will find with wide-soled training shoes is that they catch on your bike straps. Not ideal. It even wore out my straps when I tried it…not ideal mid-race.
So the only time I would try this would be on your first triathlon/duathlon.
You can get clips and shoes for under £/$100. The stiffer the sole the better and make sure the cleat is in the right place.