^ To be fair, the P5-Three is only supposed to give up ~10g of drag to the P5-Six from the different fork+brake cover.
In short, the P5 was designed to increase drag on the frame, but decrease overall drag on bike+rider.
confirms that the quality of frames (from a performance perspective) is really quite high amongst most of the leaders, and not ton of speed is given up if you instead opt for the one you prefer, for handing, aesthetic, etc. reasons.
Tour Magazin have really improved their wind tunnel testing. Robert Kuehnen and I talked a bit at Eurobike and via email, and I'm glad to see they've adopted many of our suggestions. And - to their credit - they declined to allow us (or any bike company) attend their tunnel test.
However, when comparing data, please remember the P5 has a drag increase on the frame, which is there to reduce drag on the rider's back - and Tour magazine's set up has no back. We haven't tested legs-only, so sorry, I don't have an estimate as to the magnitude.
You can see the effect on the air flow (and drag reduction) starting on page 10 in the P5 white paper:
http://www.cervelo.com/media/docs/P5-Technical-White-Paper-cd55ee37-81a3-4d19-8b4f-39946cd71205-0.pdfQuote:
Seat tube aero zone
As part of our aero zone research, we’ve isolated areas where slightly unconventional airfoil shapes can work well, again taking into account the local airflow. Specifically, it’s rare that a truncated airfoil works well in typical flows, since the aft low pressure recirculation zone “sucks” on the back of the object, adding drag by “pulling” backward on the frame or component’s rear-facing surfaces.
Figure 13 Air flow characteristics over a semi-aerodynamic body. Stalled flow in aft wake indicates a low-pressure zone that adds drag by “sucking” on aft-facing surfaces. This drag can be reduced by completing the sharp trailing edge shape of the body, tapering the surfaces to follow the lines of the natural air flow.
However, in particular locations a well-designed truncated foil can help in both expected and in unexpected ways. For example, it generally works well to truncate an airfoil to allow the following components to draft. For example, Cervélo pioneered the seat tube cutout that allows the rear tire to draft in the truncated space behind the seat tube.
On the other hand, it’s counterintuitive that the P5’s truncated seat post and seat tube foils reduce drag, since truncated airfoils without a following body normally increase drag. In fact, the P5 uses the low pressure zone created by these truncated foils to redirect the air coming off the rider’s legs & back, delaying separation and reducing aerodynamic drag on the rider and bike system, despite slightly increasing drag on the bike itself.
Figure 14 CFD image showing air velocity contours. Low speed air behind the seat post and seat tube (blue) indicates a low pressure zone, which normally increases drag but in this case pulls the air down the rider’s back to delay separation (arrow), thus decreasing drag.
This is an unusual exception, and only proves the rule that it’s best to use truncation only where it makes sense. This breakthrough was possible because Cervélo has been testing and designing bikes with riders for many years now. One effect is that a P5 tested without a rider shows a slight increase in drag; the rider must be present to gain this aero benefit.
End quote.
Cheers,
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