Yeti's dramatic new Seven up close

What no chainstay?

With a whopping seven inches of travel, Yeti's new Seven mountain bike sounds like a downhill sled - but it isn't. Instead, this is a bike that Yeti intends to be ridden up the mountain as well as down it. To achieve that Yeti has made a significant design move and shed the right hand chainstay.

The designer responsible for the Seven is Yeti vice president Steve Hoogendoorn, and he took BikeRadar through the major points of the Seven.

Hoogendoorn says he is slightly mystified by the reaction to the new machine which has been turning heads for the last two days at the off-road demo day at the Interbike show. But, he laughed, "I've been looking at it on my computer screen for the last two years!"

What he's been looking at is a bike with no right hand chainstay, a design decision taken because of the way it dramatically simplifies building a long-travel frame. "As you go longer, you run into issues, " says Hoogendoorn. "The tyre hits the seat tube and it's hard to keep the chainstay clear of the front derailleur. On our 575, at the end of the travel, the chainstay is just a millimeter from the front derailleur if you are in the small ring." Solution: Ditch the drive-side chainstay. Problem: keeping what's left stiff enough. Solution: a whacking great carbon left-hand chainstay and bearings big enough to rotate a swing bridge.

In a nutshell, the Seven is a "long-travel enduro platform, that's super-light and efficient," Hoogendoorn says. Of course "super-light" in seven-inch bikes means a different thing than in hardtails, but the Seven's claimed weight of 7.25lb with a Fox DHX Air shock is impressive for the class, and Hoogendoorn says it builds up into a bike around 30lb.

That weight has been achieved by extensive use of carbon fiber. The huge left hand chainstay is one big, beefy lump of carbon. It has to be, in order to provide the strength and stiffness necessary, says Hoogendoorn, but there's another advantage. "It's hard to figure out all the forces on so carbon gives us the flexibility to change lay-up to deal with the loads."

The dog-bone is also carbon - "much stiffer than we could achieve with aluminium," says Hoogendoorn - and despite being aluminium the seat stays are not exactly wimpy.

The whole shebang is held together with bearings - rather than bushings - that contain an extra ball per cartridge, which helps improve durability in the small-arc application of a suspension pivot. The main pivot contains two, one-inch diameter pre-loaded angular contact bearings, and at the rear a special pivoted connector joins the left hand seat and chainstays. The rear wheel uses a 12mm axle which is removed with a 5mm Allen key.

For numbers fans, the Seven has a 67.5 degree head tube and 13 3/4in bottom bracket height with 17in chainstays. The intended fork is a 160mm travel Fox 36 and production frames with have 1.5in headsets rather than the 1 1/8 shown here.

The Seven will be available in March or April of 2008, in sizes S, M and L, and will retail for US$1,899 with a Fox DHX Air rear shock. Color choices include turquoise, White, Ano Bronze and Ano Black. Complete bike pricing isn't yet determined.

Visit Yeti Cycles [http://www.yeticycles.com]

© BikeRadar 2007

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