Unequal aero rim depth on tri bike

I asked some friends what they used for the Ironman 70.3 Hawaii. The bike course is the north half of the World Championship course and famous for intense crosswinds. The race director does not allow disc wheels. The popular setup was a moderately deep front and twice that in back. I am looking at HED Jet RC which does not quite double. Choices are 46mm, 60mm, and 90mm. Weight difference is small, only a few ounces. I have been using the Mavic Cosmic wheels that came stock on my Cervelo P3 when I bought it in 2015. Pro cyclists always use same depth front and back. Is there a reason? Is it a UCI thing? What are some reasons not to go with 46/90?

Welcome to the forum @garydunn808! It has been a while since I’ve been involved in triathlon, so take this with a grain of salt, but I recently went to a 38/50 on my carbon road wheels. 38 up front and 50 in the rear to go for that middle ground between what weight and aerodynamics. Riding around Boulder, we have some pretty serious crosswinds in the springtime, so the hope was to reduce the sail effect on the front wheel for safety while keeping some aero benefits. One reason to not go with 46/90 could be comfort level if you’re in heavy winds, along with your weight. The bigger the profile of the rim the more area the crosswinds have to push against. If you’re a light rider, that can be problematic. 60mm would seem like a reasonable place to generate aero benefits while striking a balance between aero benefits and usability in a variety of conditions.

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How have you found that combination of 38/50 as I’m going to treat myself to a fancy set of wheels for my 65th birthday early next year and was thinking about getting different depth wheels? BTW I don’t compete except against my friends.

@carytb, I really like them. I really only purchased those wheels as a treat for myself too. Really not doing any road racing with them, so it was a complete fun purchase. Since getting on them, I really dig them. I haven’t ridden equal depth carbon wheels (aside from my MTB) so can’t really speak to the big differences vs. equal depth wheels, but in terms of not feeling the front wheel get tossed around in some of the Boulder crosswinds, that has been the biggest benefit for me - keeping the aero boost without getting pushed around in the wind. And have noticed some nice PR’s along the way too. I hope that helps!

I think the think to think about is what is the rear wheel doing. My understanding is that it is hardly providing any aerodynamic benefit since it has little frontal area. Thus, a 46mm or 90mm rim on the rear is not much different. UCI pros also typically ride in a peloton so carrying around a heavier 90mm rear wheel doesn’t make much sense for them.

Since the high yaw angle wind at Kona yields the most benefit with aero wheels, you really want to go as deep as you are comfortable with. Are those winds gusty or constant? Googling pics of Kona triathlon, 60/90mm looks very common.