First Look: Cannondale 2015 F-Si 29 Carbon and Black Inc XTR Di2 version

29er Cross Country
Full Technology and Product Descriptions

Information below is provided by Cannondale.

Asymmetric Integration

The heart of the F-Si’s System Integration is the all-new, Ai, asymmetrically offset rear triangle and drivetrain. the offset shifts the rear hub and drivetrain 6mm to the right, delivering super short chainstays without any of the usual compromises, and a rear wheel that is dramatically stiffer and stronger because the spoke tension and angles are equal on both sides.

We then integrate this with our new Ai HollowGram spider, which moves the chainrings an equal 6mm to the right, balancing the system and maintaining perfect chain-line, shifting performance and Q-factor.

Cannondale Ai technology

This elegantly simple approach – Ai – enables us to have our cake and eat it too. The extra space created by shifting the drivetrain outboard enables us to have:

  • The shortest chainstays on the market, for incredible traction, stiffness and agility.
  • Up to 60% increase in rear wheel stiffness.
  • Dual chainring compatibility with super short stays.
  • Tons of mud clearance.
  • Ample tire clearance with the chain and front derailleur.
System 29 Geometry

When it comes to the way a bike handles, geometry is everything. The difference of just a few millimeters here or a half a degree there can significantly impact handling. We developed a winning 29er geometry for the F29 but World Cup competition is changing. With courses becoming ever more technical, steep and brutal, we knew we needed to rethink XC geometry completely. The result is F-Si – a bike that defines new-school XC handling and speed.

Cannondale - F-Si 29 Carbon Geometry Chart

How Cannondale did it:

Super Short Chainstays

  • Shortest 29’er stays on the market (429mm).
  • Extremely agile in tight and technical terrain, especially when navigating switchbacks.
  • Puts more of the rider weight over the rear wheel, dramatically increasing rear wheel traction on steep climbs.

Slack Head Angle with 55mm Offset Lefty

  • Progressively slack 69.5° head angle mated to the Lefty’s proprietary 55mm fork offset, complements the nimble rear end with equally agile and capable steering.
  • At high speeds, the added stability of the slack head angle enables the rider to attack rough terrain with confidence.
  • In slower, tight, technical sections, the extra fork offset and resulting lack of “trail” keep the steering quick and nimble.
New Lefty 2.0

A bike as radically new and boundary-pushing as the F-S i demands an equally radical fork to complement its freakish handling and stiffness. That’s the New Lefty. For the uninitiated, Lefty has always been the lightest, stiffest, smoothest, and most durable front suspension on the start line, and for 2015, the F-Si features the all-new Lefty 2.0.


  1. New 29″ Specific Offset
    To complement the F-Si’s ninja-like rear end handling, the new Lefty uses a 55mm offset, which is longer than the competition. When combined with slack head angles, this creates the perfect balance of high speed stability and low speed agility.
  2. New XC Damper
    Who says an XC rocket can’t borrow technology from the enduro world? The new Lefty gets the same new smooth and supple damper technology found in our new SuperMax forks, but tuned for XC. Available with either PBR (pushbutton) or XLR (handlebar remote) lockout options.
  3. New Oversized Clamp Area
    The new Lefty gets an updated structure which grows to 44mm in diameter at the clamp areas. This keeps the fork svelte, but adds even more stiffness and strength.
  4. Inverted Design
    The inverted design is not just stiffer and stronger, it’s also better lubricated. Gravity holds lube against the seals and bearings for longer life and smoother action.
  5. Hybrid Needle Bearing System
    For maximum control, SuperMax’s proprietary needle bearing assembly keeps the suspension smooth, no matter how hard you brake, corner, or land.
  6. Dual Integrated Crowns
    Stiffer and stronger than single crown setups. For 2015, the new Lefty has multiple clamp widths, lowering the front end heights of our small, medium and large sizes.
Race-Friendly Features

The F-Si was designed for the uncompromising XC racer and the proof is in the details.

  1. External Cable Routing
    Because it’s first and foremost for XC racing, the F-Si features full external cable routing. It’s lighter than internal routing and it makes service and cable changes a breeze.
  2. Quick Release
    A racer needs to be able to make quick wheel changes and thus far, nothing can can compare to a quick release in terms of speed. Using a standard QR enables us to make alighter frame and spec a lighter rear hub. With the F-Si we have created a frame and rear wheel that is not only lighter and simpler than the competitors’ 142x12mm through-axle systems, but is also stiffer!
  3. Di2 Compatible
    Shimano recently debuted the new XTR Di2 components and the F-Si is fully compatible with cable routing ports and battery placement within the frame or seatpost.
Speed Save

Micro-Suspension Technology

Speed Save technology reduces fatigue and improves control and handling by reducing the amount of shock and vibration a frame transmits through to the rider. By pairing precise tube shapes with sophisticated carbon lay up, we are able to create areas on the rear chainstays and seat stays and seatpost that can deflect to absorb shock, while staying completely rigid laterally and torsionally. The enhanced vertical compliance provided by these combined features greatly improves rider comfort and rear wheel traction, so that you can ride faster, longer.


BallisTec Carbon

High-Strength, High-Stiffness Carbon Construction

BallisTec is Cannondale’s high-strength, high-stiffness carbon construction. It starts with a base structure composed of ultra-strong fibers originally created by the military for ballistic armoring, and high-strength, high-impact resins similar to what is used in the construction of carbon baseball bats. Ride-feel tuning and stiffness comes from precision addition of high and ultra-high modulus fibers and the result is some of lightest, stiffest and toughest frames out there.

SAVE 2 Seat Post

save2-seatpostThe SAVE 2 seatpost found on the F-Si is the evolution of our standard-setting SAVE post. With SAVE 2, we shaved off 47 grams while also increasing deflection by 20 percent. On the new post, we were able to manipulate the “natural” leaf spring curve of the post to our advantage. The new, linear deflection curve of the SAVE 2 post offers more deflection at lower loads, but also more support at higher loads – which means better comfort, especially for lighter riders, and a more controlled, linear feel while maintaining full strength and support at maximum loads.


SiSL2 and Si Cranksets

Simply the lightest, stiffest, bad-ass-est cranks ever to be bolted onto a mountain bike, the HollowGram SiSL2 represents the latest evolution of the crank that started the BB30 revolution. These hollow cranks are created by bonding together two machined, heat-treated clamshell halves with a super-strong anaerobic bonding agent. The result is a crank light and stiff enough for our top road race machines but tough enough for a lifetime on the trails, as the full-throttle performance of our CFR and Sho-Air Cannondale Pro XC teams shows. Since the spider is interchangeable, HollowGram cranks are compatible with all major double and single chainring options, including Ai and XX1.

Cannondale F-Si 29 Carbon Team

We will be spending some time in the next two days riding this brand new World Cup race machine in Albstadt, Germany during the World Cup XC race. We will report back on our first ride impressions soon. Stay tuned.

Cannondale - F-Si 29 Carbon in Garda, Italy

Be sure to click through the gallery below for more great photos.

About the author: Gregg Kato

Gregg Kato studied journalism and broadcasting in college while working many different jobs including deejaying, driving a forklift and building web sites (not all at the same time). Kato enjoys riding local Santa Cruz trails. Besides being an avid mountain biker, he is also a motorcycle fanatic. Two wheels, one Passion.

Related Articles

NOTE: There are two ways to comment on our articles: Facebook or Wordpress. Facebook uses your real name and can be posted on your wall while Wordpress uses our login system. Feel free to use either one.

Facebook Comments:

Wordpress Comments:

  • The Pittsburgh Left says:

    Interesting bike. Am I right in thinking this requires a special wheel? The asymetrical rear would make a better wheel, but it would need to be built up special for this bike since the center plane of the bike does not intersect the center of the hub, it would instead intersect the center of the flanges (same length spokes can be used). Single speed hubs don’t have the different length spoke problem, but would if built for this bike. a SS hub would have longer spokes on the drive side if built for this bike. I guess it’s not an issue since a standard hub can be used for SS and this bike allows equal spoke lengths on a standard hub. Can this bike even convert to SS?

  • Jeff Sayegh says:

    Can’t wait for the 27.5 version

  • Larry says:

    It will not require a special wheel or hub.. Its the way the frame is designed… Its offset..

    CANNOT WAIT TO GET ONE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  • J-Flo says:

    Nice to see new efforts at innovation on the hardtail front. But I am not sure the world needed yet another rear wheel standard. The specs aren’t clear; apparently the rear axle is a 142mm with QR? As stiff as a 142x12mm? Riiight. They say the QR also allows a lighter rear hub, but they spec a DT350 on the rear of the top end Black Inc. model. That’ a good hub, but not light and I am afraid this part of the story does not add up.

    Even if the hub is a standard 142mm hub it will need custom end caps and the spoke lacing will be custom for this frame; so the rear wheel will not be interchangeable with other 142mm frames. Maybe that doesn’t matter because the front wheel is not standard anyhow.

Leave a Reply

Your email address will not be published. Required fields are marked *





© Copyright 2019 VerticalScope Inc. All rights reserved.