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Interbike Tech: Kona Finds the Magic Link

  • By Matt Pacocha
  • Published Sep. 24, 2009
  • Updated Oct. 12, 2012 at 12:50 PM EDT

Magic Link suspension designer, Brian Berthold, used to engineer Formula 1 cars. Photo by Matt Pacocha

Kona introduced the Magic Link on its Coilair model three years ago as a chassis for trail riders who want a bike to pedal up hill as well as it goes down and vice-versa.

The system is comprised of a dual-shock linkage, where the secondary shock flips the linkage between a climbing mode and descending mode depending on the forces acting on the bike, either pedaling or braking and bump input. What Kona wanted is what all full-suspension bike manufacturers want in a trailbike, a platform that does everything well. .Kona’s solution is far from simple; rather it can be considered “Magic.”

The man responsible for Kona’s Magic Link suspension design is Brian Berthold, a former Indy Car and Formula 1 suspension engineer. Berthod is also the designer of the Brake Therapy floating disc brake mount and Kona’s DOPE (drop out performance enhancement) floating brake system.

Berthold’s inspiration for the Magic Link came from the active suspension systems found in F1 competition. These systems allowed for the suspension to adapt to the conditions they encountered. Use of these systems were qualified as drivers’ aids by FIA, the sport’s governing body. All drivers’ aids, including active suspension, traction control and other computer-controlled systems were banned in 1993.

The Magic Link is controlled by a secondary shock that switches the design between the climbing and descending modes. Photo by Matt Pacocha

“I don’t like messing with my suspension to just climb or descend,” said Berthold. “I wanted to make a bike that pedaled better without making the suspension ineffective, so I started by just making a list of what I wanted.”

Berthold’s list included steeper angles, firmer spring rate, a cockpit and seat angle that puts your weight more forward, shorter chainstays and a slightly higher bottom bracket for climbing. On the flip side, he wanted the opposite of all of these attributes, plus he wanted to transition between the two sets of performance attributes without conscious inputs from the rider.

“So in my mind, I try and figure out how I can arrange some linkage to make this happen,” he said. “In Formula 1 we once had active suspension [controlled by computer]. I liken this to mechanically active.”

In Berthold’s mechanically active system, the wheel is the sensor, the chainstay is transmitting the information and the Magic Link is the computer that’s telling the suspension what to do. In use, inputting pedaling force causes the Magic link to push forward and achieve all of Berthold’s ideal features for climbing. Letting off pedaling force, for even a second, puts the system into a neutral mode where there is an instant reduction in spring force at the moment of impact, based on the laws of springs in series.

“It’s all force balance,” Berthold said.

The initial movement the Magic Link also provides a slight rearward path reducing hang ups on climbs.

“The thing about bike suspension is that all designers have their priorities,” said Berthold, adding that some would want rearward path while some would want a certain progression. “Put us all in a large room and we’ll argue about which one is the most important. Everybody picks their priority. They’re not wrong; they’re just better for one or another.”

Berthold said the nobody will argue the fundamentals of frame geometry, which is that steeper angles are better for climbing and that slacker is better for descending.

“Not one of those engineers arguing about suspension design will argue with what this bike does,” he said. “Nobody is going to say, ‘Why do you want the bike to get slacker on the downhills or steeper on the climbs?’ and that’s a cool thing.”

The Magic Link has been around for three years and it’s just now coming into form. For 2010 Kona adds a new two-model platform with 6.3 inches of total travel to the existing Coilair 7-inch models.

The two new bikes – Abra Cadabra and Cadabra – feature lighter more trail oriented component kits and lighter frames. Through the use of hydro-formed tubing and intricately forged parts, Berthold said the two Magic Link bikes best fit his original concept, it’s just taken three years to get here. The Cadabra costs $2,800 with a mix of Shimano SLX and XT components, while the Abra Cadabra leads the line at $3,700 with a full Shimano XT group and top of the line Fox suspension components.

FILED UNDER: Bikes and Tech / MTB TAGS: / /

Matt Pacocha

Matt Pacocha

Pacocha, the VeloNews test editor, started in the industry sweeping shop floors at 13. Since then he’s wrenched, raced mountain bikes on the national circuit for four years, worked at IMBA (International Mountain Bike Association) for two years, raced on the road in Belgium for six months, and served four years as the tech editor for VeloNews. And, of course, Pacocha is the staff's resident cyclocross fanatic.

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