I have come to a cross road in looking at buying my new tri bike. I like both the P3 in 55 and the KM40 in 52, they both seem to fit well, and I like both of them. I am about 5 9 and 170 pounds with a 32 inseam,and cant make up my mind on these two great bikes. The KM40 has 650 wheels and the P3 has 700’s which does not make much of a difference to me. If some others on this forum had the same choice between these two bikes, and the fit was good on both of them, which way would you go?
Thanks-
Let me understand the question correctly. You rode a P3 in a 55cm and a KM40 in a 52cm and you are wondering which one to buy. You rode new technology, the most sought after P3 and an older albeit good technology KM40. The only question would be are you looking for superstiff and fast (P3) or not so stiff and moderately fast (KM40)? They are both good bikes.
Is there any real evidence that the P3 is faster than the KM40?
Not that I can afford either right now, but they are both sexy bikes.
Just a word of caution - At 5’9" with a 32" inseam you shouldn’t be on a 55 Cervelo, you should be on a 52, possibly a 51.
You’re asking this here, you secretly want to buy the P3, don’t you? 
It sounds like you are a bigger fan of the P3, yes I rode both bikes and liked them both very much. I will use it for Ironman and 1/2 Ironman distance. I think either way I go will be good, I am just having a hard time making up my mind. The P3 as you said felt stiffer, but they both felt fast… I know in the long run I am the one that has to make a decision, I was just wondering what some of the hard core triathlete’s on this forum thought.
Thanks-
I have never ridden a P3…passed a bunch of them on my KM40 though…(I write this as the Cervelo ad hovers above me so no doubt my PC will crash soon) The Kestrel is an awesome bike and is comfortable and fast (provided you train hard). The P3 gets a lot of good press so if it fits it is probably not a bad way to go either. If I was going aluminum, I would also check out Elite.
Check out Elite with its round tubes?? I guess wanting a bike to be aerodynamic is too much to ask for. You could have at least said QR Caliente ;-). I am not trying to bag on you, Elite seems to make some good bikes. I am just saying that there is a reason for the popularity of a P3. Oh, as a disclaimer, I do own one. What am I thinking, duh, I WANT you to get the KM40 or the Elite or any other bike except the P3, Trek TT, Lotus, or the Cheetah. Or better yet, get the most aerodynamic bike according to Triathlete magazine, the Giant, lol. I like having top level AG bike splits =). You know the saying anyway, it is all about the engine. So do not worry about the bike so much, just eat more donuts to add some sugar and hyperactivity to the engine and your bike split will be just fine.
I own a P3 and like it very much, although I was thinking about buying a KM40 also. I like the one piece Km40 not the multi piece Airfoil Pro. I have heard the KM40 to be much more comfortable for long races. I am about 5 10 and ride the 55 P3, it does not feel to big for me? I have a chance to get a good deal on a 52 KM40, I just dont know if it is worth trading in the Cervelo, I am sort of in the same bind. The Km40 appears plenty fasted as long as the rider is good, I think Chad Hawker averaged a 25 mph bike split at the Kona 1/2 last year on one…
It sounds like you are a bigger fan of the P3
Actually, in terms of pure looks I think the KM40 takes the cake (I know Tibbs will violently disagree
.
I can’t for certain, but I do recall that the P3 is the fastest double diamond bike. But the KM40 isn’t a double diamond now is it. I remember reading somewhere that the KM40 is faster than a P3. But its all academic, pick the bike you like better. I ride a softride, comfortable and aero. Too bad my engine needs some work. Those 2 bikes are on my short list for when I get my next bike, in about 5 years or so.
I almost bought a Kestrel, but then I rode the Cervelo P2K. Not even a close choice. I’d trade up for the new P3 if I had the cash.
clm
Thanks for the input, I think I am going to go with the P3… And I am 5 10 not 5 9 and the 55 seems to fit nicely…
I like my P3 very much, I was just thinking the ride of carbon might be better for longer races… Cathy you rode the KM40 and the P2k, is the KM40 really that forgiving being carbon? Why did you not like it that much?
Yeah. I’ve read from folks that think I should be on a smaller sized P3, but I think I fit pretty well on mine?
I’m a hair under 5’9" with a 30" inseam and have a size 54" P3. Maybe I’ll take some position pictures and post them on there for folks to review (if that hasn’t already been done to death yet).
5’10" 54 P3 and it fits great!
Cathy you rode the KM40 and the P2k, is the KM40 really that forgiving being carbon? Why did you not like it that much?<<
Not really sure if I can say why. The feel of the P2K was just better for me.
clm
**rundown **
Nooooooo. Get the KM-40 if your doing Ironmans. Much more comfortable for the long stuff. If you have your heart set on the P3 though, you should also check out the Aegis T2. It is a very simular in design to the P3 but it is made out of Carbon and IMO will be way more comfortable than the P3 over the Ironman and 1/2 Ironman distances. Another bonus with Aegis is their warranty.
“We build bikes for life: the finest commitment in the industry. Our unique hand-crafted process enables us to back every frame and fork we build with both a lifetime warranty and a lifetime crash replacement program. When you think about how hard you ride, you’ll realize just how much faith we have in our bicycles.”
My take:
The p3 is nice (in the larger sizes) and it sure is aero and it is supposedly moderatly comfy (though I’ve never ridden it.)
The KM40 is a classic (a Chevy z28 if you will) and it is designed for comfort, decently aero.
If this is a dedicated tri-bike and you only intend to race on it, by all means pick up the P3, but if you intened to do all of your iron training on it also, I think you’ll enjoy the soggy benefits of well enginered carbon. (And the extra miles you end up putting on it will help you in the long run.)
My best advice though would be, buy both of them, put a couple hundred miles on each, decide which you like better, and mail the other one to TSR.
The next greatest signature…when I feel like it…
I test rode both, and went with the KM40 because it felt more comfortable to me and seemed to absorb potholes and vibration better, although the Cervelo was much better than my old steel. I was comparing 650, so if you compare 650 vs 700 you will definitely see more difference in comfort there than in the bike frames. As far as aerodynamics, don’t worry about it…by the time you put a water bottle on the frame there is no difference, if there was any to begin with. Some other items to consider of a more practical nature…do you want 2 water bottles on the frame?..no-can-do with a KM40. Does the Cervelo seatpost present any issues? (behind the seat water bottle carrier, seat pack, etc). When you ride a Kestral people point and gawk and hot women want to be your friend…when you ride a Cervelo, well, most people assume you are some sort of aerodynamics engineer and hence a dork. Sort of like a Porsche Carerra vs Mosler Consulier 
Dan (a computer hardware engineer = definitive dork)