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P2K Sizing
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Need help with P2K sizing. From my measurements and fittings on other bikes it looks like I need to choose a P2K based upon what seat angle I most likely plan to ride, size 55 for 75 degrees and 58 for 78 degrees. To me it looks like you choose the frame size (by top tube length) based upon the angle you will most likely ride, if you then switch the seat post the other position becomes somewhat of a compromise. One being a bit too long or too short. I would think switching the seat post around would also call for a stem change. Am I understanding this correctly? I am not sure of the exact angle I plan to ride, so any thoughts what is the best way to go, frame based upon 75 as ideal or 78?
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Re: P2K Sizing [sbinzer] [ In reply to ]
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Read this and all the other tri bike articles in Slowtwitch http://www.slowtwitch.com/...chctr/headtubes.html

You can't compare a road bike with a tri bike. The geometry is so different that the rules for one don't apply to the other. Your tri bike will have a steeper seat angle and a shorter head tube. This is putting you in a more forward position and actually shortens your top tube if you measure it compared to your road bike. However, with the shorter head tube you are lowering your handle bars. This is the same effect as lengthening the top tube from a biomechanical riding position. So although the tube is physically shorter, the reach is still the same. Read Dan's articles if you don't get this.

I think you might want to email Gerard at Cervelo on this, but IMO you certainly don't want a tri bike a bigger size than your road bike. Of course realize that different manufacturers can also measure theior bikes differently. Most people buy a tri bike the same size or one size smaller than their road bike .
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Re: P2K Sizing [sbinzer] [ In reply to ]
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Do it right. Contact cervelo via e-mail or a phone call and get their opinion. I wrote to them for sizing my P3 and ended up with a smaller frame than I would have put myself on. They will ask for some standard measurements (inseam, crotch to sternum notch, overall height) and apply these to frame size. Figuring out seat angle is a bit trickier. I haven't finished building my P3, but I told them I was planning on riding the steeper configuration.

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