3T designs for the real world, and for the gravel roads in that world, people want to use 700x35-40c tires. It’s useless to put a narrow aero rim behind such a tire. You’d be adding the weight without the aero benefit of such a wheel as the airflow never really “sees” the rim.

After testing two dozen prototype wheels in the tunnel, the Discus 45 | 40 LTD was born. 45mm deep for good aerodynamics without excessive cross wind vulnerability. 40mm wide to match up those 35-40mm tires. The result is speed never seen before on gravel roads. And while the shape is optimized for the 3T Exploro, the Discus 45 | 40 LTD makes any gravel bike faster.