Thursday, 27 October 2016

Tech Talk: Specialized Stumpjumper FSR 650B

Spez Stumpjumper FSR 650B

When it comes to heritage, prestige and experience, the Specialized Stumpjumper FSR rules supreme. From the very beginning it defined every generation of innovation, changing from hardtail to full suspension, and stood as the yardstick by which all were measured. 

The Stumpjumper has always been Specialized’s do-it-all trail bike. As such, they haven’t gotten too carried away adding heaps of travel and making it overly long or slack. A 67-degree head tube angle makes for a surefooted descender, and the 74-degree seat tube angle creates a comfortable pedaling position. The Stumpjumper now offer significantly shorter chainstays thanks to the Taco Blade front derailleur mount first introduced on the Enduro 29. The chainstays are about as short as you can get for a full suspension bike at 420mm (16.5″).

Short Chainstay

The front triangle is carbon fiber paired with aluminum seat and chainstays. Like Specialized’s other carbon mountain bikes, the Stumpjumper features a SWAT (Storage, Water, Air, Tools) door behind the water bottle cage. If you’re unfamiliar with the SWAT concept, it’s a removable trap door located underneath the water bottle cage that allows you to put a tube, tools and anything else into your downtube.

SWAT door open

The water bottle cage screws into a flat and wide plastic door on a hinge, and the door clips positively into place with no hint of a rattle when riding. Inside the frame the carbon is immaculately smooth, the internal cables are housed inside moulded piping, and a little plastic net clips into place at the bottom to stop anything from dropping down too far towards the bottom bracket. Specialized includes a tube inside a protective wrap and a small tool roll, sans tools.It’s a handy way to always have your bike ready to rip without needing to cram tools in your jersey pockets or carry a pack.

This shock features "autosag" from Spez

The Rockshox Monarch RT shock gets a bespoke "Rc Trail Tune" and "Autosag" side valve for easy setup of the 150mm travel. Jan Talavasek created Autosag so that it is super easy to set up your sag. The idea is that it's quick, correct and repeatable. Specialized tuned Autosag with Rock Shox and Fox, depending on was making the shock at the time, so that the shock settled into its travel where we though you would want the experience on each bike to be. 

Most shocks have a port that balances the positive and negative air chambers inside the shock. The Autosag system works on that balance. You over-inflate the positive air chamber so the bike is totally extended, the riders sits on the bike in their riding gear with the shock fully open, the press the Autosag button and it bleeds out the excess air. It automatically balances the positive and negative chambers to whatever sag-level Specialized set. The rear shock uses a custom cradle to connect to the shock driver yoke, which in turn connects to the u-shaped linkage of specialized FSR kinematic (The arrangement of pivots and linkages in a suspension system and how they interact)


Head Angle: Angle of headtube in bicycle frame

Seattube angle: Angle of seattube in bicycle frame

Chainstay: The tube connect BB house with rear drop out

Sag: The amount of suspension travel used up when the bike settles with a rider on board.


Ride On!

No comments: