Ok. Should I get the 52 or the 55cm? (I want 700c wheels). I’m 6’0" with long arms and legs and a slightly shorter waist than normal. (inseam from crotch to floor is 34.75"). I normally ride a 57 or 58 road bike, though I have my 56cm Santa Cruz Roadster set up as a TT bike and it has a 56cm top tube. I would normally select the 52, BUT I ride in a slam position. I’m much more comfortable reaching because I’m missing half of my T-12 vertabrae thanks to a drugged up truck driver.
Anyone have a memorable sizing experience similar to mine?
Your dimensions are nearly identical to mine. I’m 6’0" with a 34.4" inseam. I’m riding a 55 cm P3, but I’m riding it with the seatpost flipped forward and the saddle all the way forward on the rails- an effective 81* seat angle, and I still need a 9 cm stem to get the correct reach. If you want to ride slack in the slam position you’ll definitely need a 52 cm P3 IMHO.
“If you want to ride slack in the slam position you’ll definitely need a 52 cm P3 IMHO.”
J: Wouldn’t the opposite be true? In other words, with the 55 I’d be able to reach and still be about 78 degrees, whereas with the 52, I’d be riding at about 75-76 at the same reach, no?
Re: "Wouldn’t the opposite be true? In other words, with the 55 I’d be able to reach and still be about 78 degrees, whereas with the 52, I’d be riding at about 75-76 at the same reach, no? "
Isn’t that what the “slam” is? (75-76 deg seat angle, or even slacker). My point was that if you want to ride in the 74-76 degree range, the 55 cm P3 is going to be too long in the top tube for you. Here are the measurements from Cervelo’s website:
So my point is that if you’re like me, then you would need a top tube of about 54-55 cm. You can get this by riding a 55 cm frame steep, or by riding a 52 cm frame slack.
The P3 is a bit more aero than my Roadster, the head tube is shorter than my Roadster (so I can get lower), plus I love the design of the P3. I’ve also been experimenting with shorter distances at 78 degrees using a Profile Fast Forward seat post and can do it for about 10 miles without cramping up my back. I might decide to do my sprint races at 78 and my longer races more slack.
And, now that I don’t have to buy that ugly gray color, I’m thinking of plunging. I just don’t want to regret my sizing.
When your body is as beat up as mine, you have to make a lot of accommodations.
J: My fear with the 52 is that I’ll be at 71-72 degrees when I’m in the slam position. (I should probably add that my slam is a modified slam. Probably about 3-4 cm back.) My fear with the 55 is that I’ll be reaching too far, even with, say a 90mm stem.
I don’t think you’re inseam length matters as much as your upper torso & arm length due in relation to top tube length. I’m 5’8" but have a long torso & arms and ride a 52c w/ 700c and I had to actually put on a longer stem in order to get a proper fit. So you have to look at all your body dimensions not just height & inseam.
I guess I don’t understand why you would want the P3 if you are going to ride at a shallow seat angle. This is not a 72 degree kind of bike.
Art Franke
Hmmmm, Tell that to the CSC team, or any of the other pros riding this frame.
The pros are like cats. They can curl up in any position and be perfectly comfortable. Old farts like Robet and I don’t have that luxury.
Robert seems to be trying to make this bike work over a large range of seat angles. I love my P3, but when I want to ride with a slack seat angle, I go for the road bike. The P3 won’t do this for me, even if it does for Tyler.
Re: “My fear with the 52 is that I’ll be at 71-72 degrees when I’m in the slam position. (I should probably add that my slam is a modified slam. Probably about 3-4 cm back.) My fear with the 55 is that I’ll be reaching too far, even with, say a 90mm stem.”
I don’t quite follow the first part. Your seat angle isn’t dictated by frame size. By virtue of the reversible seatpost, the Cervelo’s have probably the widest range of seat angles in the industry. If you want 74 degrees (or 72, or 76, or 80) you can have it. The real concern is that you can get the reach you need with a stem in the 90mm - 140mm range. As you noted, a 55 cm frame set up in a slam position will have too long a reach for you unless you used something like a 70mm stem or a Look Ergostem. The 52 cm, on the other hand, would work in the slam with an acceptable stem (on the shorter range of acceptable), or in a steeper setup with a stem on the longer range of acceptable.
As an aside, I’m curious as to why the slam position is more comfortable for your back? One of the benefits of a steeper position is that you can get low and still maintain a 90 degree hip angle. If you want to ride slack and low (which you indicate you do if you’re concerned about head tube height) you’d end up with a pretty acute hip angle. I can’t imagine that this would be very comfortable for someone with back pain. Might I humbly suggest that a properly fitted steep setup would be both faster and more comfortable for you over all distances.
Make sure you go through a full fitting process before buying a P3— I’d guess that you’d have a ton of headset spacers if you rode a bike that small in a slam position— Maybe even enough to make the bike unsafe. Other bikes with taller headtubes might be better for you.
3cm behind the BB is not slack or the slam position. If you set your P3 up in this way your will have a comfortable forward position with an open torso, thigh angle.
The worse thing you can do for your “bad back” is try and ride slammed on a bike that is too small for you. You want the 55 because of it’s low front end. You will compress your torso, thigh angle and put huge strain on your back.
It also sounds like you struggle to stay down in the areo position for any length of time. I would go and see a pro bike fitter who can watch you on an stationary trainer. With your back problems you may have all sorts of alignment issue that a pro will pick up.
You can ride slack on a P3/P2K/Dual. This would be a 74 degree position with the seat post mechanism turned back. I know lots of people who ride Cervelos at this angle and it works great for them. But these are not the bikes to ride in Cobb’s “big slam” position because it’s essentially a modified road bike position. It’s described here.
BTW, to answer the original post, I’d guess the 55 cm frame is likely the way to go. The 52 cm 700 bike shares dimensions closer to the 54 cm 650 frame. Either the 52/54 seem to suit me at 5’9.5". A six foot guy would likely be on the 55 I would estimate.
In other words, with the 55 I’d be able to reach and still be about 78 degrees, whereas with the 52, I’d be riding at about 75-76 at the same reach, no?