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Geometry comparison: Cervelo P3 vs Felt DA 700
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OK, so I'm more or less past the "lusting after pictures" phase of shopping for a new tri bike, and into the data analysis phase of shopping. In comparing geometry specs of all the major bike mfgrs that appeal to me (Cervelo, Felt, QR, Softride, Litespeed, Guru, Aegis) two bikes seem to be the best fit for me- the Cervelo P3 or the Felt DA 700. I've compiled geometry specs in Excel for all these bikes, and I want to make sure I'm interpreting the numbers correctly and understand the effects of geometry variations. The numbers for these two bikes are:

Cervelo P3 Felt Da700
Seat tube angle 78 deg 76 deg
Top tube 560 mm 575 mm
Head tube length 130 mm 140 mm
BB drop 60 mm 70 mm
Head tube angle 72.5 deg 73 deg
Fork rake 43 mm 40 mm
Front-center 637 mm 633 mm
Rear-center 380 mm 395 mm
Wheelbase 1017 mm 1028 mm

The way I read these is: 1) both have essentially the same top tube length if the Felt is set up at 78 degrees, 2) both have head tubes low enough for me to get as low as I could possibly need, 3) the P3 has the aero advantage due to the shorter rear-center and rear wheel cutout, 4) the DA 700 has the handling advantage due to the lower BB drop, longer rear-center, and longer wheelbase. Am I interpreting these numbers correctly? Other thoughts here?

The one part that puzzles me is Felt's use of a 40mm rake fork with a 73 degree head tube angle. It seems to me that you could put a 43mm rake fork on the bike and get a longer front-center and longer wheelbase for better handling (like the Cervelo). Is this a tweak I should consider if I opt for this bike, or should I not be messing with the spec'ed fork?

A fair amount of my training and racing is in hilly terrain. Should I opt for better handling at the expense of optimal aerodynamics? Are the differences in geometry between the two bikes significant enough that I would even notice a difference in handling?

Thanks,
John


PS- sorry for the terrible layout of the numbers above. I tried to edit to make them more "table-like" but can't get it to look more legible. Hope it's understandable.
Last edited by: jkatsoudas: Jul 1, 03 22:39
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Re: Geometry comparison: Cervelo P3 vs Felt DA 700 [jkatsoudas] [ In reply to ]
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Sorry to bump this back to the top... I'd love some feedback to know if I'm on the right track in understanding these specs.
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Re: Geometry comparison: Cervelo P3 vs Felt DA 700 [jkatsoudas] [ In reply to ]
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These are both excellent bikes and the geometries are essentially identical from my point of view. They should both fit the same. I can't comment on the handling. I don't know whether those small differences would affect your handling much even if all other things were equal. In order to tell you would have to ride them. That may not be so easy since these are not exactly carried by every shop in town.

If I am thinking clearly, the longer rake of the P3 will compensate for the shallower head tube angle leaving you about the same trail in both cases. Be very careful about straying from the manufacturer specs on this parameter unless you know exactly what you are doing.

I don't think you will go wrong with either of them. I own one of the first P3s, and I love it.
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Re: Geometry comparison: Cervelo P3 vs Felt DA 700 [jkatsoudas] [ In reply to ]
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In Reply To:
3) the P3 has the aero advantage due to the shorter rear-center and rear wheel cutout, 4) the DA 700 has the handling advantage due to the lower BB drop, longer rear-center, and longer wheelbase


This logic escapes me a bit. Both the connection between chainstay length and aerodynamics as well as the connection between bb drop, rear-center, wheelbase and handling. There is of course a relationship between geometry and handling, but it's hard to reduce handling to better or worse. IT depends what type of handling you're aiming for, directness, stability, cornering, etc. Bottomline, ride them both and see if the handling appeals to you.


Gerard Vroomen
3T.bike
OPEN cycle
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Re: Geometry comparison: Cervelo P3 vs Felt DA 700 [gerard] [ In reply to ]
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Hi Gerard. Thanks for the feedback. My logic comes essentially from what I've read on this site. All I've learned about tri bikes, I've learned from Dan and this forum. My logic was based primarily on Dan's article titled "Bike Geometry" in the tech page. The section of the article titled "What dimensions affect handling" had the following passages:

"The chainstay length is integral to how the bike will handle, and so is the front/center. Generally, it's nice to have your chainstay as long as possible if you want the bike to track nicely through corners"

and..

"The bottom bracket drop also affects the bikes handling, in that the lower the drop the better the bike will handle in turns."

and...

"Why aren't tri bike front/centers longer? Why don't tri bike makers put shallower head tubes (and forks with correspondingly greater rakes) on their bikes? They probably should,..."

With regard to chainstay length and aerodynamics, what I was trying to say is that it seems like the Cervelo bikes use a shorter chainstay in order to get the rear wheel tucked in under the rider and get as much of it shielded by the seat tube as possible. The Felt bikes have no cutout, so the chainstay has to be longer in order for the wheel to fit.

The net of it is that both you and Art are essentially saying that the bikes are very similar, and that these small differences in geometry will not result in drastically different riding bikes. That's what I was trying to gauge. I don't know that a quick spin around the block on a test ride would expose the differences in handling, say, in high-speed descents (if I could even find an LBS that has both bikes in my size), so I'm trying to gleen as much insight as I can from specs (admittedly a dangerous endeavor). Thanks again.
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Re: Geometry comparison: Cervelo P3 vs Felt DA 700 [jkatsoudas] [ In reply to ]
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The trail is pretty close for both so the steering would likely not differ that much. If materials were identical a shallower head angle and more rake would be more comfortable than the same trail with a steeper head angle and less rake.

To me the BB drop is too small on both. It's not like anyone is pedaling through corners in a crit with these bikes. I would use 8.0 or even more BB drop. I have 8.0 on my custom road bike and it's sweeet on descents. The lower BB might decrease drag a bit too.

I don't know why front centers aren't longer either. Tri bikes all seem very poorly designed for proper weight distribution. I think because they take forward projecting aero bars as a given and design around that rather severe limitation.

Ideally I would use bars with the elbow pads a bit behind the fork steerer and shove the whole front end forward with a long top tube and front center and add a low bb. It might not look too cool with a Cadillac wheelbase, but at least it would handle less like a unicycle with a training wheel.
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