I'm trying to wade through old threads to find my answer, but I'm struggling. So I'm creating a new thread.
I don't race triathlons, but I race time trials. For what it matters, I have Renn disc rear and a Flo 60 (old style) front wheel.
What are the best race tires?
Clinchers or tubs?
With the older wheels I'd really worry more about the tire width for the aero on the front wheel for sure over pure CRR tests. If you toss an amazing new age 23 or 25mm tire up front on an old 21mm width it's going to be about as aero as a box truck.
Out back, if your bike has a decent fairing leading to the rear disc it won't matter as much and can run a 22 or 23 or so.
Tubs, if only ever gluing up for a competition then I'd do a 19mm Podium TT up front for sure.
To learn to ride my disc/trispoke setup with tubulars without breaking the bank I bought a Conti competition tub. I'll buy and glue up a Podium TT if the time arrives to really lay it on the line.
I bought a cheapo Giro for a spare tire.