hvvelo wrote:
Hi Eric -
Great thread and I really like this concept of pad x/y to understand the fitting - it has significantly de-mystified things for me! What I'm struggling with a bit more is trying to relate that to the rim brake models, esp. the 2014+ P3s.
Some background that may help understand where I'm at:
Height - 5'11.5", Inseam - 32"
Pax X = 419 to back of pad, 463 to center
Pad Y = 706
Pad Z - I'm not 100% sure how this is measured but my pads are 5" inside-edge to inside-edge, or 9.5" measuring between the points that they curve upwards. (and thus 7.25" between the centers of the flat parts)
I have been using a redshift seat/aerobar setup on a Trek H2 geometry 56 cm road bike for the past year after discovering "aero" - making periodic steps down in 5 mm increments, training about 50/50 in both TT and road positions. Combined with reducing stem from +13 to -6 deg and increasing my reach a bit with the stem change have all helped me improve speed a lot. Have been doing some 10 mile TTs each week and recently did my first 40k TT at just under 59 mins, flat 3-lap no wind course, at 248W - comfort felt great, esp. with the redshift seatpost - so I think I'm not in a terrible position, but I suspect I should work to get longer/lower when on aerobars. I just don't want to keep pushing my road bars lower to make it happen as I don't always ride with the aerobars. I've enjoyed it enough to want to get a TT bike to have more freedom in position. Goals are unlikely to go beyond 40k - not into triathlons - just cycling.
To keep my costs somewhat in control, I have been looking at 2014-2020 rim P3s. In addition to being well regarded as highly adjustable, I believe they should handle my existing rim brake 65 mm aero wheels that are max 28 mm width but taper down to ~26.7 mm max tire width when using GP5000TL 25s.
I feel like I have ample room to go lower, which is probably obvious in my pad x/y result coming off the road bike w/clip-ons. What I can't find is a X/Y parallelogram chart for the P3 - only the newer P3x. The P3x suggests to me I'd want a L/56 as I'm at the very upper left (which I'd expect given starting on a somewhat constrained road bike aerobar position) and I'd absolutely anticipate moving into that 56 sizing chart on a dedicated TT bike setup from day 1. But does this chart apply to the rim P3 as well?
I'm also not averse to a rim P5 if the right deal came along, but it seems like I'm dangerously far off the parallelograms for the P5. Still, the closest here also looks like 56 although it would take a big jump long/low just to get into that zone, and I like the idea of standard components on the P3 to have more flexibility to follow a fit roadmap being newer to this. And if I understand some discussion in this thread correctly, the P2/P3 platform may be able to expand these "parallelogram" zones more broadly with bigger range of stem sizes - in which case maybe I should stay away from P5 for now?
I also understand the P2 is identical frame, but I'd also be a bit more worried about front fork clearance with my wheels.
Given all of this, would greatly appreciate your input on whether 56 is indeed the right call across the Cervelo rim models - and please let me know if anything else would be helpful!
Thanks,
Colin
Well you can thank our forum moderator and fearless leader Dan Empfield, creator of the tri bike, the tri wetsuit, and the triathlon and now all bikes X/Y coordinate fit system for that. It's one of those discoveries that was impossible to make but completely obvious in hindsight, like it was a property of the universe just waiting to be discovered.
Another thing Dan articulates is how to build a mortal bike, and in his (and my) opinion, you start with the bars and work back. When he published his project, the bar du jour was the 3T Ventus, actually the only fast option at the time really, but now there are lots of good options like Vision and TriRig. Once you know what bar you want you work backwards to bike brand and bike size, etc.
I say that because while the Cervelo NP3 was and is a fast bike, the OEM bars that it came with weren't always the best in terms of what you'd get now with a P5d, P3x, or even P-Series.
At any rate... Pad Stack of 709mm and Pad Reach of 419mm. You are in the upper left quadrant my friend, ie. slack or upright. On a mortal bike that means unsightly spacers under the stem to get you where you need to be. I'm questioning this fit... on the P3x charts you are too high for a size L and too far to the left for a size XL... off the charts IOW.
You say you've been "adapting", working downward in 5mm increments. Have you tried going longer in a similar manner? This would bring you into the orthodox fit range and likely make you more comfortable. That said, whatever you're doing is working because 59:xx 40km TT on 248w AP is amazing.
How tall are you? I would ride a 58cm NP3 if it were me and I'm 6'2". Really I'd ride a 61cm but I'm vain. You might do well on a 58cm with a short stem, or on a 56cm with a longer stem and some spacers. Best to find a cockpit system that allows you to raise pads and extensions independently of the basebar. So yes, the general relative quadrants of the charts apply to the NP3 as well. A tri bike will automatically bring you forward and down some, and when it does you'll land in the 56cm frame size fit range.
Make sense?
Eric Reid
AeroFit |
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