... and you're attributing all of that to the lack of clearance for bigger tyres?
FWIW, as a pipe-smoking cardigan-wearer who has never raced but who has done a bit of CFD in his time... anybody who takes that report seriously is truly clueless.
I'm most impressed by their models showing uniform laminar inflow to the parts of the bike they're interested in. That's funny enough in the first picture, at the head tube, where they have uniform laminar flow coming out of the back of the brake caliper (to demonstrate the amazing benefits of their faired head tube - down tube junction). But it's really really funny in the second picture showing uniform laminar flow hitting the seat tube / chain stay region, as if there's nothing upstream to disturb the flow. ORLY?
The standard joke in the CFD scene is that it's really an acronym for "Colour for directors". You can use CFD models - however flawed the model - to make pretty colourful pictures that will impress senior management who have no idea about fluid dynamics. Cervelo show us that you can also use pretty CFD pictures to impress bike geeks who want to be impressed.
For all numerical models, the junk-in-junk-out rule applies. That's especially true with CFD, where the detail of your incoming flow is absolutely critical to the results your model will give. If you're really careful with CFD, you can get numerical results that show some correlation with experimental results... but it's not always easy to do. And ignoring upstream obstructions is a really good way to ensure it won't happen.
No I'm not attributing it all to a lack of clearance for tyres. However I would expect that is part of the overall package.
I do a bit of also ran racing and really enjoy tt as my favourite cycling event.
I have a tt bike an aero road bike and a round tubed more traditional road bike.
I first got into tts on the round tubed road bike and ran that std, then with aerobars then deep section tubular wheels and finally as the bug bit a tt bike with disc rear.
I ran the roadie with clip ons in much the same position as the tt bike.
The tt bike was 30 secs per 8 km lap faster than the roadie. I would attribute a fair bit of that to the aerodynamics of the bike, along with rigidity and for me, longer cranks on the tt.
I still have the original bike and now the S5. I race handicap and scratch races with the same guys. I am significantly more comfortable on the S5 during a race than the older bike. I attribute that to the small savings in watts as helping to recover a fair bit when on your limit.