Cervelo P2 SL - Time Trial/Triathlon Bike- 2007

The P2 SL comes from a long line of high-performance time trial/triathlon bikes that starts all the way back in 1996 with Cervelo's first production model, the P2. With features such as the (for the time revolutionary) aerodynamic shapes, internal cable routing, horizontal dropouts and extended seat mast, the P2 was a no-holds-barred speed machine. It was also impractical and expensive.

For the 2000 model year, we wanted to make the benefits of the P2 available to a broader range of customers, but we were adamant that performance could not suffer as a result. At the top of the list of featured that were impractical was the seatmast. The seatmast made it impossible for a medium or large P2 bike to fit in a standard (or even a custom) bike bag, which is really a big drawback considering how often people travel with these types of bikes. We eventually had a company make a custom bag for us that fit the P2, but airlines and UPS would constantly create trouble because it was oversized.

So the challenge was to remove the seatmast, boost or at least match the overall aerodynamics (though maybe through improvement in one spot to offset losses elsewhere on the frame) and find ways to make the frame less expensive to purchase for our customers. To replace the seatmast, we designed an aero seattube/seatpost combination that had several benefits.

Firstly, it ensured the same seamless aerodynamic shape from bb to saddle that the seatmast did. Secondly, by significantly narrowing down the width of the seattube and seatpost we were able to reduce the frontal area of the frame, an important factor in aerodynamics. Almost coincidentally, these changes also reduced weight of the frame, yet another benefit. Lastly, thanks to some clever engineering the changes also lowered our manufacturing costs. At the same time, our very strong growth had given us much more clout with suppliers, giving us a further opportunity to make the new P2 more affordable.

When the new P2, dubbed the P2K, was introduced just before the 2000 season it created immediate excitement. Remember, this was the year where many manufacturers gave up on TT/tri bikes or significantly worsened their performance because of the new, limiting UCI rules. Yet the new Cervélo P2K offered our renowned P2 performance without the impracticalities from before and at roughly half the price. No wonder that year after year it picked up top honors in the roadbikereview.com customer awards, as well as Best in Class distinctions from the major triathlon magazines. It was even used by professional cyclists and picked up a World Time Trial Championship title along the way (by far the least expensive frame to have such honors).

The next step in the evolution is the P2 SL. The tubing has been refined with the Smartwall 2 set, further reducing the weight while increasing the stiffness. The finish is upgraded to an anodization to offer the best possible scratch-resistance. The parts kit is stepped up another notch to DuraAce, offering pro performance at a very affordable price. The result is that the P2 SL is still ahead of its time today while it continues to build on ten years of family history carrying people to their personal TT/Tri victories.

The aerodynamic downtube of the P2K is differentially butted, which means that the wall thicknesses around the perimeter are not constant. The reason we vary these wall thicknesses is that the material isn’t as useful at each spot. Both tubes are especially needed to provide lateral (sideway) stiffness. It also provides in-plane (vertical) stiffness, but that is not a critical factor, as the frame structure by itself already provides ample in-plane stiffness. It is actually a good idea to try to reduce the in-plane stiffness (and thus increase comfort), which can also be accomplished with the differential butting.

The variable wall thickness we use means that we have more material on the sides (the high-stress points in the lateral load case), and less on the top and bottom of the tube (the high-stress points in the in-plane load case). The result is a frame with increased lateral stiffness, reduced in-plane stiffness (more comfort) and the highest possible stiffness-to-weight ratio.

77-78 degree seattube angles have become more and more common for time trial and triathlon bikes in the past few years. Whereas in the past time trialers often rode at more shallow angles in the 74-75 degree range, the situation is no longer as lopsided. Riders like Zabriskie, Voigt, Julich and many of their Team CSC colleagues now ride at 77-78 degrees, and if it weren’t for the restrictive UCI rules on saddle position, some might even ride steeper. Other teams are starting to catch on to this trend as well, and no wonder if you look at the results Team CSC garners in time trials.

But even if you aren’t a professional cyclist, there are compelling reasons to ride steep on a time trial bike:

With lower back flexibility often a limiting factor, a steep seattube angle allows you to attain a flatter back without having to change your body’s “internal” angles (hip angle, knee angle, etc). Basically, a steeper seattube angle rotates the rider forward around the bottom bracket, thereby leaving the internal angles intact while positioning the back more horizontal. A steeper seattube angle can allow you to even open up your hip angle, thereby reducing the strain on your lower back as well as making the pedal motion less restrictive. For triathletes, several studies have shown that running times after riding a bike decrease if the bike was ridden with a steep seattube angle. That said, a steep seattube angle is not for everybody and it remains a personal preference, so we offer our TT/tri bikes with adjustable geometry, allowing for an effective seattube angle anywhere in the 74-79 degree range.

As you move through the range of effective seattube angles, the effective toptube length also changes.

Note that we say effective seattube angle, as the standard seattube angle is really a very inadequate dimension. It does not describe very well the position of the point that actually matters for fitting, the saddle. A 75 degree seattube angle with a large setback seatpost and the saddle pushed backwards is a lot less steep than the same seattube angle with a zero-offset post and the saddle forward. The variation between these two situations can be as much as 3 degrees, yet both are called 75 degree seattube angles. So to really be able to intelligently compare positions, it is better to use effective seattube angles, which is normalized for a standard seatpost setback and a saddle position in the middle of the range. In the example above, we would call the first situation an effective seattube angle of 74 degrees, and the second situation an effective seattube angle of 77 degrees. In other words, you can achieve the same position for the saddle (and therefore the rider) with different seattube angles, as long as the seatpost and saddle position are adjusted to create the same effective seattube angle.

In the geometry tables below we list the dimensions for 75 and 78 degree effective seattube angles, roughly corresponding to the two positions of the adjustable seatposts if the saddle is clamped in the center of the rails.