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Cervelo claims to find the great compromise in the new Rca

  • By Caley Fretz
  • Published Mar. 14, 2013
The all-new Cervélo Rca is the latest from the brand's high-end development center in California. It weighs about 670 grams in a size 54, and drops into the 500s in small sizes. Most impressively, though, is Cervélo's claim that the new frame is 7.4 watts quicker against the wind than the R5ca. Photo: Caley Fretz | VeloNews.com

SANTA MONICA, California (VN) — Cervélo’s Skunkworks-esque California division, the small lab in Garden Grove, California, that trickles out some of the lightest, stiffest, and most expensive frames on earth, has developed a new toy. It’s called the Rca, and with it, Cervélo aims to hit an elusive sweet spot between weight, stiffness, and aerodynamics. The objective, to quote project director David Killing, is to “improve on aerodynamics [of the R5ca] without compromising other parameters.”

That’s a lofty goal. Of course, there are compromises in every frame. The persistent difficulty is in determining which features should be held in the highest esteem, or which factors are the most valuable. The answers to these questions determine the compromises engineers will need to make as they develop any new product. In the case of the Rca, aerodynamics was the third priority, behind weight and stiffness. The frame had to hit the R5ca’s figures in the latter two first; then the team could look at shedding drag. It was from this set of engineering objectives that development began.

See our detailed gallery of the new Cervélo Rca >>

The final product looks to have checked all three boxes, at least according to Cervélo itself. The Rca weighs about 670 grams for a 54cm frame — about 30 grams lighter than an R5ca. It bests the R5’s stiffness figures, too, increasing torsional stiffness and bottom bracket deflection by three percent each, according to Cervélo’s own lab testing. It achieves both while also lopping off a claimed 7.4 watts at 30 miles per hour. It’s no S5 in the tunnel, but Cervélo claims it is significantly quicker than other superlight frames, without compromising the weight that put it in that category in the first place.

It’s also going to cost you $10,000 for the frame and fork, and Cervélo is only making 325 of them. Such is the price of exclusivity, we suppose.

Tweaking shapes with drag in mind
The California series frames have always been about low weight and high stiffness, and the Rca is no different. But to add in aerodynamics, changes had to be made to tube shapes; changes that would normally have a negative effect on those two performance columns upon which the California frames have made their name — counting grams, and resisting input forces.

Narrow is aero, but it’s also heavy. Narrow tubes need thicker walls, and more material to maintain stiffness. That’s why the Rca, like the Trek Madone and Scott Foil before it, does not use traditional aero shapes.

The silhouette of much of the frame closely matches that of the R5 and its Squoval tubes. But a few select areas, those that were deemed less important to maintaining stiffness, were tweaked to reduce drag.

Cervélo went through 93 different digital frame designs, running finite element (FE) and computational fluid dynamics (CFD) analysis to pinpoint how each iteration was stressed and how it would fair against the wind. The goal was to better understand how each parameter — from a slight tweak to the down tube shape to the way the seatstays attach to the seat tube — affects frame performance. Engineers identified areas that were less sensitive to shaping, meaning that weight and/or stiffness would be less likely to lose ground due to a chance in tube shape.

Four areas became the focus: the head tube, down tube, seat tube, and seatstays. The head tube is narrower, bowing in like an hourglass between the upper and lower bearings. The shape is similar to that of the new Giant Propel, although slightly less exaggerated.

The seatstays are slimmed down slightly compared to the R5, and are also twisted 90 degrees from their R5 alignment. They are now tall and narrow rather than short and wide.

The Squoval tubes of the R5 already feature sides that bow outwards, like a piece of hardcase luggage that’s been packed too full. The shape was more aerodynamic than a regular square tube, Cervélo says, and can be easily turned into a good Kamm-tail simply by adding a small nose to the leading edge. Such a nose was applied to the length of the seat tube, and the lower half of the down tube. The new shape, with its aerodynamic nose, has been dubbed Squoval 3. The upper half of the downtube was left in its regular Squoval form, as it’s a vital area for maintaining torsional stiffness.

The new frame, then, looks quite a bit like the R5. Put simply, it doesn’t appear to be all that aero, much like both the Madone and Foil. But when it comes to wind, looks can be deceiving.

According to Cervélo, the Rca losses 74 grams of drag relative to the R5ca, which they claim was already faster than bikes like the Specialized Tarmac SL4 (102 grams of drag slower) and Cannondale SuperSix EVO. All testing was performed at about 30 miles per hour and 74 grams of drag is about 7.4 watts.

Again, according to Cervélo’s wind tunnel figures, the Rca sits close to the other Kamm-tail aero frames currently available, most notably the Foil and the new Madone.

Keeping to tradition with the Cervélo Rca

Without improvements in carbon and construction technology, there would have no no way to keep the Rca’s weight and stiffness in line with the R5ca, given the adjustments in tube shape. With the outside shapes determined, engineers had to look inside the frame for additional gains.

The use of what Cervélo calls Bulkheads — carbon braces inside the tube walls near the BB and head tube areas — adds only 2.2 grams but six percent more stiffness in both areas. A system called “Comfortply” was utilized to determine the location of various fiber types, optimizing the use of stiff versus strong fibers in an effort to remove unneeded fibers all together. The result, Cervélo says, is a reduction in weight and an increase in vibration damping.

Resin was looked at, too, and Cervélo settled on a 3M product called Powerlux, becoming the first to use it in the cycling industry. It improves interlaminar shear and compression strength of the carbon fiber it surrounds through nano technology, allowing Cervélo to reduce frame weight while maintaining strength. It’s also seven times more expensive than regular resin, so is only used in key areas — behind the head tube, near the bottom bracket, and other spots where we see high compressive loads.

No tiny stone was left unturned. Hollow carbon fiber dropouts save further weight, and Cervélo reversed the usual bonding direction at the dropouts, bonding the stays into the dropouts instead of the reverse. The change saves five grams, as the stay no longer needs to be overbuilt and then machined.

A few other smart features point to Cervélo’s usual attention to detail. A magnet is embedded into the carbon fiber near the bottom bracket for use of crank-based power meters, and the cable stops are completely future proof. The plug-and-play system is compatible with mechanical, electronic, and even hydraulic systems.

The Rca is part engineering exercise, part legitimate product. So exorbitant were the research and development and production costs that despite the outrageous price, Cervélo CEO Phil White says that the company still loses money on each frame. But if the trickle-down effect works here, the tech found in the California models may slowly make its way down to the rest of the line. If this is the case, the Rca is a welcome addition. Perhaps we’ll see a semi-aero, all-around frame for the masses from Cervélo sometime soon.

FILED UNDER: Bikes and Tech / Quick Look TAGS:

Caley Fretz

Caley Fretz

Tech Editor Caley Fretz can usually be found chasing races along the backroads of Europe or testing bikes and gear in the mountains outside Boulder, Colorado. If you can't find him there, check the coffee shop across from VN World Headquarters.

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