Cervelo Dual vs. P2k?

Triathlon Forum
1

I just read the updated review for the Cervelo Dual on Tom’s Bikesportmichigan.com site (excellent site btw, makes me want to drive there from Dallas to get fitted). My questions is: Is the P2k with the additional $$$? I can see that the upgrades from the dual could not be reproduced for the price difference. I really just want the seat tube cutout added to the dual for maybe $100 without the other $500 in upgrades.

-kb

2

For bang for the buck it’s probably very hard to beat the Dual.

The P2K is spec’d better but having Ultegra over 105/Tiagra won’t make you any faster. The rear wheel cut out is supposedly an aero advantage but now John Cobb is telling us the rear wheel cut out is of relatively minor importance compared to aero seat stays, which neither of these bikes have. If both these frames were aero tested I’d be surprised if there is that much difference between them.

The 650 wheel size is more available with the P2K but that may/may not be important to you.

The only thing that I’d question is the fork on the Dual. Don’t have specs for it but it just doesn’t look as aero as that on the P2K.

It’s really up to your budget as to whether or not the P2K is worth the extra $$ over the Dual.

3

The P2K is spec’d better but having Ultegra over 105/Tiagra won’t make you any faster. The rear wheel cut out is supposedly an aero advantage but now John Cobb is telling us the rear wheel cut out is of relatively minor importance compared to aero seat stays

  1. The Dual comes with Ultegra, not 105/Tiagra
  2. I doubt that John says that, it seems entirely inconsistent with years and years of windtunnel data gathered by many, many people. Of course he is the most consistently misquoted person on this forum (if he says something sometimes doesn’t work under certain condition he is quoted as saying it never works just because people like absolutes).
4

Thanks.

-kb

5

“1) The Dual comes with Ultegra, not 105/Tiagra
2) I doubt that John says that”

  1. My mistake. I haven’t looked at the 04’s but was almost sure that the 03’s had 105 derailleurs with a tiagra cassette. The first Dual I saw was at the Toronto Bike Show almost a year ago but haven’t paid much attention since.

  2. Thought that I saw something in reference to the Javelin Arcole on John’s old forum (now down so I can’t look it up) in which he either said or was quoted as saying that he felt aero chain/seat stays offered more aero advantage than does a wheel cut out. Not that the cut out offers no advantage, but less than the aero seat/chain stays.

So what is your feeling as to how much advantage the P2K frame has over the Dual because of the cut out. I know you have your theoretical formulas for the earlier One/P2K/P3 on the website based on Jim Martin’s work but have you guys actually wind tunnel tested these frames? I remember last year there was some talk about you and Phil doing some wind tunnel testing but don’t recall hearing anything more about it.

6

I would just add in here, the ST forum mantra “Buy the bike that fits” Repeat 5 times,

Seriously, its important in this case since the Dual and P2K have substantially different geometries.

7

“Dual and P2K have substantially different geometries.”

Actually they’re reasonably similiar. Are you sure you didn’t mean the Soloist?

8

No, I meant the Dual. While the P2K and Dual share a seat angle, that’s about it. The Dual is shorter than the P2K for any given frame size (or taller for any given reach, depending on how you look at it), especially at the smaller end of the size run. Granted, in the 58 and 61 cm sizes, they are quite similar. Also, the Dual and P2K don’t follow the same sizing runs, so there may be a Dual that fits better than any P2k can, or vice versa.

Also factor in the chainstay length and front centre dimensions, which will affect the balance of the bike in the various seat positions. Of course I’m assumng that the geometry charts are correct.

Cheers

J.

9

I know you have your theoretical formulas for the earlier One/P2K/P3 on the website based on Jim Martin’s work but have you guys actually wind tunnel tested these frames?

The input for the formulas IS windtunnel data. People often misunderstand Jim Martin’s article, they are not theoretical aerodynamic advantage, the only theoretical part is the conversion from drag data to time savings (and the theory used for that is based on standard physics formulas). So the drag data comes straight from the tunnel (the lb. of drag you see in the tables), the time savings stem from Jim Martin’s formulas. Also note that these time savings are not just theoretical either, since there is SRM validation performed afterwards to double-check the theoretical time savings.

To answer your other questions, yes all the frames have been in the tunnel either in prototype version or finished product, usually both. But the best data for us comes from prototypes where we can add and delete features such as a cutout, so we measure the exact effect without any noise.

The cutout - if done properly - provided the best drag reduction we could find. For the seatstays, the key seemed to be to keep them as small as possible, due to the turbulence created by the feet of the rider. That’s why on the P3, although they are aero shaped, they are still very small both in frontal area and in chord.