AJA 26: Sunglasses, Nitrogen, Tire Temperature, and Cyclocross

My question is on the topic of gravel tires, wheels, and aero:
For context, I like to run wide, slick, fast rolling gravel tires on both road and gravel, which in my opinion is the perfect choice for road surfaces in eastern Canada, which tend to be a mixture of smooth and poor pavement, and smooth gravel. Average speeds between 30-35kph.

After listening to a previous episode on CdA, my understanding is a slick 38mm tire set up on a rim like the discus 4540 (40mm external width, 45mm deep) would actually have a better Cd term than a 28mm tire set up on a rim like the Zipp303 with a 27mm external width, as the former set up respects the rule of 105. The A term in CdA would be worse for wide tire as it has a 10mm x 28” greater frontal area than the 28mm tire.
My questions:
(1) Is my understanding correct that the wide tire would have a better Cd, but worse A?
(2) Given the better Cd and worse A, which set up is more aero overall?
(3) How close are the 2 set ups in terms of aero? Is there an order of magnitude watt difference between the 2 set ups?
(4) What is the cost in watts of running a tire/rim combo that does not respect the rule of 105, and are running something like a 0.8 (eg. 32mm tire on a 27mm wide rim) which is common in many gravel and road set ups, at speeds of 30-40kph?
(5) When I watch a race like Roubaix, I’m find it hard to believe no one runs a truly wide tire, say a 38mm ultra fast rolling slick tire (like a reneherse Barlow) set up on a 105 respecting rim (like the 4540 rim), at the appropriate pressure. Will we ever see this?

-Thanks!

A couple of questions for Josh,

Is the Cannondale Lefty Ocho fork “accidently aero”?
I was looking at my Cannondale Scalpel front on, and couldn’t help thinking that the A in the CDA is significantly lower than a standard MTB fork.
Do you know if any testing has been done on this? As an XC race bike, it may reach the speeds whereby it does have a benefit and I would be keen if anyone knows what speed that would be.

Quick release locking lever position, one for the old school aficionado’s.
Again, considering CDA, I am careful as to where I place my quick release lever when I lock my rim brake wheels on to my road bikes.
Obviously, any position other than horizontal increases CDA.
My question is should the lever face forward to pierce the air, or rearward, trailing behind? Has any work been done on this?
Love the podcast, my body thanks you for the tyre pressure advice.

I’m surprised you did not see the reason for high pressure non-supple tires in bmx racing, (if that is where the question was aimed).

Bmx courses are as close to velodrome surface perfection as possible. The goal for racers is to make all the transfers from launch to landing as smooth as possible, to reduce affects on momentum.

I have no bmx experience, but just watching it’s easy to understand the surfaces and tires are closely related due to near perfection.

I have a aero question for Josh about a cycling adjacent sport. Eliud Kipchoge recently broke his own marathon world record while wearing a relatively loose top that visibly flapped in the breeze. I understand that the power to overcome drag changes dramatically with speed but even at the 13mph average speed he maintained for just over 2 hours (2:01:09) it would seem to me that minimizing drag would be worth something. Did Kipchoge leave time on the table or have I just been listening to too many podcasts about long socks and special textured base layers? Thanks!