Cannondale expand Hollowgram crank offerings
By Matt Pacocha in Deer Valley, Utah | Friday, June 22, 2012 11.38pm
Cannondale’s Hollowgram SI SL cranks were already among the lightest and stiffest on the market. Now the new, US-made Hollowgram SI SL2 model pushes the weight down to just 485g with rings, spindle and arms.
While the FEA analysis led Cannondale engineers to shave a claimed 10-15g from the clamshell style arms — which are then bonded together — while also making them stiffer, the real gains come from the unified chainring-and-spider system the company dubbed OPI (One Piece Integration).
“The engineers were looking at the crank arms and getting a gram here, or a couple of grams there, and a little bit of stiffness here and a little bit of stiffness there,” said Murray Washburn, Cannondale’s director of global product marketing. “And they said, ‘wait a minute, the whole spider-ring interface has so much material redundancy with all of the bolts and overlapping material. They found that to be the next place where they could really save weight and increase stiffness.”
Washburn said that the engineering team went through 17 different profiles in FEA modeling for the OPI spider before finally building samples. “Finally one of the engineers was looking at high-performance car wheels and looking at the multi spokes there were able to distribute the loads really evenly throughout the entire structure,” he said. “So we modeled up this 10-arm system and it tested out really well.”
Cannondale start with their patented method of 3D forging — which is also in use on many of their mountain bike components, including stems and Lefty suspension fork components — because, they say, it aligns the grains in the aluminum and makes for a more robust final structure.
The SI SL2 model is outfitted with the OPI chainring system, which comes in both standard and compact varieties
Washburn called the deflection on the one-piece forged then machined ring system, ‘non-existent.’ Cannondale have even used real estate on the back of the 10 arms that mate the two rings to machine to place additional shift ramps, which further aid in shifting. And because there are 10 arms on the OPI rings, he also said that loads are transferred more evenly than any other four- or five-arm crankset. As a result, Washburn said that the system shifts noticeably crisper than any other chainring system on the market, save for Shimano’s Dura-Ace. “Dura-Ace beats us by a thin margin there, but have a 100-plus gram savings over that crankset,” said Washburn.
The OPI rings will be available in standard (53/39) and compact (50/34) and in 10- and 11-speed configurations. Cannondale will use OPI on their top-tier road machines. The new one-piece ring set will also fit any generation Hollowgram crankset and cost around $150, which is reasonable when dealing in high-end replacement chainrings; i.e. less expensive than a single Dura-Ace outer ring.
The SI SL2 is still a CNC machined clamshell that’s bonded together; engineers were able to modify the machining to shave 15g or so and increase the stiffness slightly
Hollowgram SI: new 3D forged design
“At first glance it looks like a Hollowgram SI SL from last year,” said Washburn of the new crank. “But it’s actually a one-piece 3D forged hollow crank.”
By 3D forging the crank as opposed to CNC machining it, like the new SI SL2 and previous Hollowgram cranks, Cannondale have cut down on the time, and production complexity, it takes to make the crank, thus made it cheaper. “We end up with a crank that is as light as the original Hollowgram crank and even stiffer,” said Washburn. “This entry-level Hollowgram is the highest performing crank on the planet, other than the SI SL2.
“It’s the stiffest crank out there; it’s unbelievable,” he said. “We took out patents on this 3D forging technology years ago. And we’ve been progressively improving it to the point where we’re doing more complex shapes and more complicated designs. This is from the latest round of that.”
Washburn would not answer any further questions about how Cannondale actually forge the crank. “We really debated how much to disclose with this,” said Washburn. “We decided that we’re not going to disclose much because some of it is covered by our patent, and other bits not. So we want to leave it up to our competition to figure it out if they can.”
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Hollowgram SI looks the part, and Cannondale say it’s as light as the first CNC Hollow gram, not to mention considerably stiffer
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