Hi kmill23,
The R-series uses a special lower headset bearing.
A significant increase in fork stiffness and strength, and a matching decrease in weight, are the reasons we invented the 1 3/8" lower steerer. Bigger ( like one point five inches) can be too stiff, and adds weight to the fork and frame. As we’ve engineered better and better forks over the years, the right sized steerer in the right application is the result. We call this Evolved Steerer Design. More info can be found here: http://www.cervelo.com/…-steerer-design.html
As far as I know, no other bike companies have adopted this fork diameter yet (though they could), so I believe this lower bearing is currently a Cervelo-only item.
Edited to add: Good news: A little Googling suggests that Specialized has a similar size bearing. Wheels Manufacturing offers a replacement: http://wheelsmfg.com/...balls-and-races.html
Edited again to answer your question about specs:
49mm OD x 37mm ID x 6.5mm36 x 45 degrees
Cheers,
Thanks for all this info…now that I am sorted away, and since I have curious engineering background (albeit electrical/RF/Comms), I assume the reason you can use symmetrical 1 1/8th on the P3 vs the R series is because we won’t be riding our P3’s on Paris Roubaix and other assorted GC dream destroying cobbles in France and the Ardennes 