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Old 01-15-10, 07:42 AM   #1
guadzilla
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Planet X vs P2

Hi -

Anyone have any ideas on how the Planet X TT frame compares to the Cervelo P2 in terms of aerodynamics? Or any thoughts on whether to get the Planet X frame @ $600 or a clearance P2 @ $1300?

My budget can cover both - however, I dont really want to pay more just for the brand or if the differences are miniscule.

Would appreciate any feedback that will help me make a decision.

TIA,
V.
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Old 01-15-10, 07:59 AM   #2
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unless your a top caliber triathlete I doubt you will see a measurable difference between the 2 frames..... I am as much a cervelo pimp as anyone but id say get which one make you happy and go for it.... just my .02
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Old 01-15-10, 08:04 AM   #3
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If equipped the same, more than likely you will notice NO difference. As posted above.. If you have years of tri experience, you might recognize the slight differences but only if you had both of them to compare each other. All of these things can be corrected adjusting parts.

Good luck, post pictures.
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Old 01-15-10, 08:36 AM   #4
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Gotcha. I am nowhere close to being a pro-level endurance athlete - hell, my *goal* for this year is to do a sub-hour 40k. So Planet X it is.

I wont be getting it till Feb or build it up until Mar/April, but will post photos here when I do.

Appreciate the advice!

Cheers,
Vandit
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Old 01-15-10, 08:45 AM   #5
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good luck.... if anything invest the extra dough into wheels. you will notice the most difference there
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Old 01-15-10, 10:47 AM   #6
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Just to be a pain in your behind, I'm going to say this: the difference wouldn't be noticeable but it is (to me) significant. Unfortunately I've never seen data on the Planet X, though I have seen data on very similarly shaped bikes and I can tell you, those bike's test terribly for aerodynamics.

The Planet X has a 42mm wide headtube and it's downtube is 70mm deep x 38mm wide.
Similar to the Kuota Kalibur which has a 50mm headtube and a downtube of 72mmx38mm.
Also similar to the Orbea Ora(old Ordu) which has a 46mm wide headtube and a downtube of 75mmx40mm
One more is the Scott Plasma with a 50mm headtube and a downtube of 74mm x 45mm

For comparison the cervelo P2 has a 35mm wide headtube and a downtube of 80mm x 28mm

Here is a white paper from Trek which includes the Scott: http://www.slowtwitch.com/images/trekwhitepaper1.pdf
Also I've attached some data from Cervelo.

I know neither of those are exactly impartial, but the differences between a poorly designed bike and a well designed bike are not insignificant. I think you're looking at the difference between a 61 minute 40k and a 60 minute 40k when looking at the two bikes you asked about.

Inevitably someone who owns a bike with a 35mm wide downtube will get on this thread and say I'm an idiot and that a bike is a bike. However, I invite you to think of it this way, would you think carrying a 1cm wide and 60 cm long stick on your bike? Thats the difference in width between the Cervelo and Planet X on the downtube. I actually once went through calculating the difference on a purely CdA basis and the numbers add up to my estimate above.
Attached Images
File Type: jpg Cervelo brain bike data.jpg (39.1 KB, 16 views)
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Old 01-15-10, 09:41 PM   #7
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Wow Triguy, and I mean this seriously, I'm impressed. I thought I was a number cruncher. The next time I start posting aero questions I'll be waiting to hear your thoughts!

vkalia, please let us know what you do. I ride a P2 and love it. My wife rides a P2SL and is crazy about it too. I guess that makes me Cervelo biased. I do know they put the time into wind tunnel testing. That said, I saw the Planet X frames on sale and thought to myself, "one slick looking frame!" Don't know a thing about it's aero properties, but if you build one up please post for the rest of us to admire!
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Old 01-15-10, 10:13 PM   #8
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Triguy, thanks for that info... yes, that does make me my decision more complicated but it is good to know, nonetheless

However, going by what I'm reading on Slowtwitch, the Cervelo sizing may not be right for me.. I have long legs/short torso and am an ideal candidate for what they call "tall and narrow" frames. The P2 is a lot longer on the ETT, and so may not be the right geometry for me. The C'dale Slice seems to be a better fit, but personally, I'd prefer to just get a frame and build up from there.

Decisions, decisions...

One questions, however - the leading edge of the headtube may be less aero on the Planet X, but with a rider on the bike, wont the rider's thighs be pretty much behind this headtube? In such a case, would the headtube's contribution to the drag be as much in the rider+bike combo as it is on the bike-only setup? I dont know the answer to this - am merely asking.

V.
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Old 01-16-10, 04:33 AM   #9
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Triguy is correct in regards to the aero benefits of the P2 over the Planet X, but position is everything! As you say the P2 may not fit so I'd go with the frame that fits better...
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Old 01-16-10, 08:03 AM   #10
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To muddy the waters even more - I'm very much a long leg shorter torso rider - and a 56 P2C fits me very well. One thing I really liked about it was it had a long seat post, so I could get high and steep on it. It does all come down to fit. I would say that rules of thumb are good to narrow the field, but in the end fit is a very personal thing. Best practice is to try all of the frames you are considering and then go from there.
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Old 01-16-10, 10:12 AM   #11
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Plainsman - can you perhaps list your PBH/height, and also how much saddle-handlebar drop you run? And is your fit with the seatpost in the forward position (for the steep head angle)?

My problem is that for the next 4 months or so, I am in a pretty remote location in Asia, and so unable to get a proper fit done. I'm trying to narrow things down as much as possible beforehand and get a frame that is more or less right - I can always tweak the fit later.

V.

PS: Thanks to everyone so far for their very helpful posts - compared to the controlled anarchy of the Road Biking forum, y'all are almost as mellow as mountain bikers
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Old 01-16-10, 10:43 AM   #12
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hey vkalia, good question on the headtube. From what I can tell, the headtube matters because the wind hits it first before hitting your legs. This is why Specialized, Giant, Felt and Look all find ways to make their headtubes deeper. Just like the front wheel mattering more for aerodynamics than the rear wheel, the headtube in the bike matters.

You know, I think it's a shame that Cannondale doesn't offer their non- Hi Mod frame separately, I think it could be very competitively priced. However, a good high narrow bike that I think comes in a frameset is the Specialized Transition.

Fit issues are tough to address. All bikes have built in lee way, seatposts move and stems come in different lengths. However, on the ends of the spectrum, some bikes just don't fit some riders. For instance, I fit well on a bike with a 40mm reach and 50mm stack. This puts me on a 52cm Felt. However, I think a Cervelo woud also work in 51cm, Jamis, Cannondale in a 54 may work too. However, Blue definately would not work, Specialized transition would most likely not work either, I'd need a super long stem.
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Old 01-16-10, 11:04 AM   #13
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(edit: Triguy beat me too it on the Cannondale. He's right too, some just won't fit. I tried and tried to make a Trek work, but when I got one with a short enough top tube, the seat post came all the way out of the tube before I could get it high enough!)

vkalia,

I would be glad to. Let me pull some numbers together. I'll snap a pic of my setup too - just promise to ignore the messy surroundings! Just curious, where in Asia are you? We have some friends stationed over there.

One frame I would have tried if there was ready access then (and the prices were what they are now) is one of the Cannondale Hi-Mod models, simply due to their stack and reach numbers. The Kuota numbers looked pretty good too, and I road one, but giving the relatively similar price points between the K-Factor SL and the P2C I went with what I considered to be the frame with the most data to back up its claims (and I liked the color scheme, that's legit, right?)
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Old 01-16-10, 11:35 AM   #14
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This was my IM setup. I ride with a pretty flat back. You can see that my stem is now set somewhere around the middle of my spacer stack. My fitter tells me I should be able to go lower with no issues (and I trust my fitter) so I may drop it a bit for early season sprints. Measured from the top of saddle (minus a hair since you don't really sit on the high point of an Adamo) to the center of the base bar, I come up with about 7 inches, or 17.78cm. The distance from the center of BB to top of saddle is right around 82-82.5cm. My cycling inseam (in stocking feet) is somewhere between 35.5 and 35.75 inches (90.17-90.8cm). I am 6'-1" if that helps. There might have been a better fit for me out there somewhere, but I'm blissfully unaware as I can ride this setup very comfortably for hours.

(edit: Yes all, my chain is on the next to biggest cog. You should see my driveway though - we call it the Col du Driveway)

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Old 01-17-10, 10:16 AM   #15
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Triguy - thanks for that explanation. Yeah, it does make sense that the wind-cutting surface should be as small as possible.

Plainsman - thanks for that photos. That's one damn sweet-looking setup. You and I are very similar in build - I am a hair over 6'0" with a 35.4" PBH and longish arms to boot. I have a 5" drop on my road bike, and on aerobars, 6-7" should be manageable quite easily as I often feel that I can go even lower while in the drops.

I am going to try out that Adamus saddle, btw. It looks a lot more taint-friendly than pretty much any other saddle I have seen!

V.

PS: I am in the Andaman Islands, off the coast of Thailand. during diving season...
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Old 01-17-10, 12:58 PM   #16
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My pleasure, and you're welcome. The longish arms help - and the longer in the leg/arm and shorter in the torso build is not as uncommon as some might think. By the Competitive Cyclist fit calculator method my forearm is 15.5 in and my arm length is 29.5 in. I was professionally fit on this bike by Jim Cunningham of Jim Cunningham Coaching, and he had helped me check out other frames as well. BTW, this is a 56cm.

I really had no saddle issues with the stock Cervelo (Trilon) saddle on rides up to 60miles. It was beyond that where the problems kicked in. The Adamo Road was what I used for IM distance, and it was fine. My wife rides the Adamo Typhoon and thinks it's the best thing since sliced bread. I found it a little too soft. If I had the funds, I would like to have gone with the new John Cobb saddle, but at $80 or so, the Adamo was tough to beat. I kinda like the funky look it has too. Be forewarned though, my back side did not get used to until I had logged around 200 miles. It has more to do with time than distance.
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Old 01-17-10, 03:28 PM   #17
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Another vote for the Cervelo

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