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PostPosted: Sun Mar 17, 2013 7:51 am 
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I like the weight and appearance but if I were in that income bracket, it wouldn't even get a look in.

Rolo or something custom for me thanks.


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Posted: Sun Mar 17, 2013 7:51 am 


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PostPosted: Sun Mar 17, 2013 12:36 pm 
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F45 wrote:
Strange that they list the aerodynamics of the Madone 7.9 but do not include it on the weight chart.


Very strange.

The Madone aerodynamics come out looking pretty good (very close to the RCA everywhere except at zero yaw). Someone weighted the 50 cm Madone frame at 752g. That probably means it's as light as a standard R5 (certainly lighter than the R3), but with better aero.

I noticed that they put the Foil (and the Venge) in the weight chart, but not in the aero chart.


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PostPosted: Thu Mar 21, 2013 1:49 am 
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Image

Again this...if you have a frame with a completely round tube, and if the tube is lets say at 40° (downtube), then the shape/profile is elliptic. I know that aerodynamic isn't simple, but I would rather avoid to compare it like this, even if you consider that all other profiles are at 40°...because from this chart you can conclude that any bike with a round downtube is more aero than the "aero frame" (with the "Squoval 3" profile)..

nickl wrote:
I noticed that they put the Foil (and the Venge) in the weight chart, but not in the aero chart.

Very strange.. :mrgreen:

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PostPosted: Thu Mar 21, 2013 5:37 am 
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I did an aerodynamic study on just this. The fact is, the thickness percentage of the elliptic profile of a round tubed bike is still enormous compared to what they are showing in the chart. That has a HUGE effect on how much drag an elliptic profile has due to the increased size of the wake and separation due to the adverse pressure gradient. The headtube and seattube are not at as much of an angle as the downtube, either, so they will have even more drag.

The chart that Cervelo is showing is a pretty typical drag chart for various shapes. I have textbooks that also show drag of the square/circle/triangle. I am pretty sure they know how much drag the elliptic profile of a round tubed bike generates. The specific truncation of these kamm tails is not as good as the pure airfoil, but it does simulate a higher chord length airfoil to some extent. This will be far better than the high thickness ellipses that you are thinking of (but not as good as a thinner ellipse).


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PostPosted: Thu Mar 21, 2013 11:23 am 
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May I ask you if you have any other similar charts? Just interested, I study quite a lot aerodynamic in the past few months, and would really appreciate to hear more from someone who has more experiences.

Otherwise here just one more photo where they (I think that it's from Scott) compared it with round tube, well it isn't really a completely round tube (it's wider):
Image
What I want to say, those testings/charts are always a bit "adapted" to show even bigger differences, at least from what I can found.

Otherwise I don't doubt that they (Cervelo, Scott, Trek,..) know what they're doing, but would really like to see more details . It would be interesting to see all the profiles of a frame with completely round tubing and an aero frame like this (in different sections), just to compare it based on those charts that are shown.

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PostPosted: Thu Mar 21, 2013 9:37 pm 
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Very true Berk. The lack of some weight and aero data and that type of charts reduce the credibility of the white paper.

I haven't seen any plot that shows the relation between aspect ratio and Cd for an elliptical shape neglecting Re effects but I suppose that the gains due to the relative angle between wind speed and tube axis are bigger for round tubes than for airfoil tubes. The real aspect ratio of a round DT is about 1.5:1

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PostPosted: Fri Mar 22, 2013 4:22 am 
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It's still a very very thick ellipse. You cannot ignore Reynold's number, because at such low Re, it's far easier to have early separation. As wind tunnel testing has shown (and correspending CFD that for the most part correlates with the data from the tunnel), this elliptical profile cannot come close to true aero profiles or even truncated kamm airfoils. It all has to do with the radius curve of the spline (especially towards the back to encourage flow to become slightly turbulent but stay attached longer) and the thickness of the tube.


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PostPosted: Fri Mar 22, 2013 1:48 pm 
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justkeepedaling wrote:
It's still a very very thick ellipse. You cannot ignore Reynold's number, because at such low Re, it's far easier to have early separation. As wind tunnel testing has shown (and correspending CFD that for the most part correlates with the data from the tunnel), this elliptical profile cannot come close to true aero profiles or even truncated kamm airfoils. It all has to do with the radius curve of the spline (especially towards the back to encourage flow to become slightly turbulent but stay attached longer) and the thickness of the tube.


When I say ingnoring Re effects I was referring to the effect of increasing chord length change while keeping tube width constant. At Re=40k-50k, a 50% longer profile should give the same results wheter we adjust Re or not

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PostPosted: Mon Mar 25, 2013 3:35 am 
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Does anyone know the ETA for small(ish) size (48 or 51) if ordered through a local LBS? Any additional feedback on this frame?


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PostPosted: Tue Mar 26, 2013 1:31 pm 
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Epic-o wrote:
Very true Berk. The lack of some weight and aero data and that type of charts reduce the credibility of the white paper.


I wouldn't say "credibility", but rather "neutrality". Credibility implies something they say is false. In that regard, it appears to be amazingly credible. They're just leaving out things they don't want to say. You need to read a bit between the lines.

Can you get a more aero frame? Yes, but it will be much heavier. Can you get a frame as light? No, but if you take the one which is close, it will be less aero.

I think Foil and Trek come the closest in terms of making the tradeoff the best.

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PostPosted: Tue Mar 26, 2013 5:41 pm 
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djconnel wrote:
Epic-o wrote:
Very true Berk. The lack of some weight and aero data and that type of charts reduce the credibility of the white paper.


I wouldn't say "credibility", but rather "neutrality". Credibility implies something they say is false. In that regard, it appears to be amazingly credible. They're just leaving out things they don't want to say. You need to read a bit between the lines.


When they say that is the best combination of aero and weight and don't show certain data of frames that could have similar performance in that scale you have doubts about their claims. That's credibility

I don't want to be too critical. Both Cervélo and Trek white papers are the benchmark of the industry and many companies should copy them but there are still some aspects to be improved

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PostPosted: Tue Mar 26, 2013 6:22 pm 
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djconnel wrote:
Can you get a more aero frame? Yes, but it will be much heavier. Can you get a frame as light? No, but if you take the one which is close, it will be less aero.

I think Foil and Trek come the closest in terms of making the tradeoff the best.


I may have to disagree with you. Jooo alluded to this earlier: Rolo.

Can you get a frame as light? Yes, it can be done. Especially for that price. At the price Cervelo is asking, a person can get a custom Rolo or Crumpton's lightest, or even a Spin. Heck, at that price Nordischer-Rahmenbau could make you the lightest and most rare. Plus you won't have to be held to the BBRight blackmail.

Can you get a more aero frame at that weight? Yes: the Rolo may be more aero and just as light.

But, then again, Cervelo nor other companies are willing to put actual competitors such as Rolo into their whitepapers. Actual competitors are those in the same price bracket or level of production. If the California is precision-hand-laid carbon layup by experts, then it falls in line with the custom-frame market. Not even the top-of-the-line Foil claims to have that service in production.

An A2J Rolo is 640g as a production frame in 56. Cervelo is claiming 667g for 54.
Crumpton built out a CUSTOM geometry frame to 666g (680g with hanger) - viewtopic.php?f=10&t=98607&start=105#p842573
A Spin is 643g.

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PostPosted: Tue Mar 26, 2013 8:23 pm 
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mythical wrote:

One caveat about the RCA: it's BBright. It seems we can't have it all after all. Any weight savings made with the frame is paid back in crankset weight due to the limited selection of compatible cranks, although the THM Clavicula is available with BBright solution, but it won't be the lightest. For a truly light build, I would've liked to have seen it BB30 with a Hollowgram SiSL2 SpiderRing option. Maybe a THM M3 with custom spider-less integrated chainring combo instead? If you go with a frame this light, you might as well go with the lightest components, especially since it isn't about the money anymore.


Would you trade flexy frame to get light cranks?

THM Clavicula's are quite nice. If I remeber mine where 340g/175mm/130mm BCD. AX's are too flexy, and I don't know similar weight but same stiffness cranks. I have those in my R5Ca. I ordered BBright versions from THM, but as bearing seem to sit over CF, not alloy, in their solution, least my ones, I made new bb housing and bondet that to frame. It was like +9g but as bearing is now 9mm more wide, stiffness should be better. Since THM's are not real Bbright cranks, why not...

I leaving this week for 2 weeks to Spain, and hoping to enjoy R5Ca there. Not the latest version, first one. (it's 5,7kg with Powermeter and training wheels/saddlle for riding 2000km/2 weeks, 4,7kg with ww-parts,Speedplay pedals/1x cage, used then as sunny ride/recovery bike, 56cm size) It's different, even other Cervelo's are nice, this beast is different. More response, better power transver etc. I know, hard to understand, but belive me, forget price, and pleace, go for test ride....and critice after that IF still you feel so. It's just fantastic frame.

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PostPosted: Wed Mar 27, 2013 2:57 am 
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The R5ca used BBright Directfit. This placed the drive side bearing about 11mm from the edge of a 86mm spindle. This prevented you from using the Ax Lightness or Clavicula cranks without some special care. Both of these cranks are the world record holders for light cranks and they weigh 330-340 grams depending on length ect… The Ax Lightness only being available in compact 110mm.

So the R5ca forced most people to use a heavier crank, my favorite is the THM M3 crank and it weighs 375 grams if I remember correctly. At this weight or a little heavier you start to find other choices.

The Rca requires BB cups to hold the bearings just like other Cervelo frames. These will add approximately 30-40 grams, but now you can use the Ax Lightness or Clavicula saving you 40 grams or so.

I think a lighter solution would have been a BB where the bearings press directly into the frame and have the bearings 86mm apart. That would have resulted in the best of everything. Overall I think BBright is a good solution, just not the absolute lightest possible.

As far as crank stiffness I have bikes with THM M3, Clavicula, and Ax Lightness. The tests will show differences in stiffness but I have not been able to tell the difference myself when riding.


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Posted: Wed Mar 27, 2013 2:57 am 


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PostPosted: Wed Mar 27, 2013 3:23 am 
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prendrefeu wrote:
Can you get a frame as light? Yes, it can be done. Especially for that price. At the price Cervelo is asking, a person can get a custom Rolo or Crumpton's lightest, or even a Spin.


This is a good point. They are restricting the analysis to "stock" frames, clearly. Spin isn't available in the US. But Ruegamer was that light back in, err, 2009? But if I worked for Cervelo, I wouldn't be chasing down custom frames for the white paper.

I think we agree the white paper shows it's an exceptionally well-engineered frame, even if the white paper is biased in its presentation.

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