American Custom Bicycles in Steel, Titanium and Ti/carbon mix

Weight Savings - XX Bike Frames

Seven Evergreen XX

Custom decaling and build kit on this bike are for display only. They are not included.

XX Chainstays XX Seat Post Clamp XX Brake Mount

What is XX?

Simply put, our XX bikes represent a complete rethinking of every part of the frame. We started from a cost-no-object perspective, and only when we’d understood what was possible did we make the final decisions with a cost-benefit analysis.

Although, the industry has used lightness as a primary selling feature for several decades, what we see is that every year frames get heavier. “Advances” in component technology too often weigh more than their predecessors: Disc brakes, thru-axles, tapered steerer forks, PressFit bottom brackets, wider tires, etc. They all add significant weight to a bike.

For the XX bikes, we’ve done a clean sweep of every aspect of the frame to remove any hidden grams from the past decade’s list of industry “improvements.” We are fortunate to have data from thousands of Seven bikes in the real world, so we are able to extrapolate which new features can be integrated without a single failure. On top of that, we’ve done extensive fatigue testing of new build techniques and applied all of that to the XX bikes.

The XX build process removes from four to eleven ounces from a typical Seven SL or SLX build without sacrificing ride characteristics or service life. From our perspective, this is the holy grail of cycling weight reduction. How are we able to remove 10-20% of the weight from a frame without negatively affecting performance? To begin with, we thought about every single gram, not ounces, grams. Single grams add up quickly. This is what XX delivers.

Here are nine design features that save weight but have no negative impact on performance – no loss in frame stiffness or durability:

  1. Asymmetric dropouts. By pairing our standard non-drive, flatmount dropout with a non-matching, road thru-axle dropout, we save about 60 grams and increase drivetrain stiffness. The non-drive dropout has to have a span of nearly 4” from axle-center to rotor-edge. It’s an extremely long dropout that is a lot heavier than a piece of tubing. The drive side dropout, on the other hand, only needs to be about 1.5” from axle to tube-end. The new asymmetric design is lighter, but it’s also stiffer (and Seven’s dropouts are already the stiffest in the industry).
  2. Asymmetric chainstays save about 6 grams and increase drivetrain stiffness. Not only do the dropouts require non-mirrored chainstays, we’ve pushed this to its limit by altering the chainring, tire, and crank clearances specific to the drive and non-drive side of the frame. The chainrings on the drive side require more clearance than the non-drive side, which has no rings. These asymmetric stays save a few more grams but, more importantly, they increase drivetrain stiffness. Lighter and stiffer; we’ll take any improvement that combines both.
  3. Maybe it’s counter-intuitive, but we save more weight by using a titanium oversized 30.9 mm seat post. Depending on the length of the seat post we save a few grams in the post itself but mating that to a 30.9 seat post sleeve provides valuable weight savings while not sacrificing any ride quality or performance. The XV upgrade omits this feature.
  4. More aggressive bottom bracket machining saves 14 grams and has no impact on frame stiffness. We have always machined our raw bottom bracket shells down after welding to reduce weight, but now we’ve pushed our CNC program to shave every gram from the inside of the bottom bracket shell without reducing service life.
  5. We save about 12 more grams by enlarging the frame’s breather holes, the holes that allow gas to pass between the various tubes during welding, based on rider size, intended use and component choices. We optimize the breather holes for each frame depending on tube diameter and wall. This is taking the promise of rider-specific tubing beneath the surface, to places the rider him or herself will never see.
  6. Tube butting saves about 30-45 grams. We’ve introduced a new butting process that enables us to tune the butting to remove an addition 1.5 ounces, on average, from our already sophisticated proprietary process. We optimize the butting based on all the rider input, type of frame, intended usage, and rider attributes.
  7. Modified tube profile selection saves between 30 and 60 grams. For the X-Series, we’ve pushed Seven’s proprietary approach to tube profile selection farther, combining tube diameters and wall thicknesses in new ways to take full advantage of our US-milled titanium’s core strengths.
  8. We modified our flat mount brake adapter to save 13 grams, without altering braking response.
  9. A slightly more compact frame design saves about 18 grams while increasing frame stiffness. By increasing the top tube slope by just 2 degrees beyond Seven’s typical design standards, we save weight and improve performance.

Make your XX bike even lighter with an optional internal seat post binder saves about 33 to 45 grams. There are three aspects of this feature that reduce weight. First, the internal binder is about 15 grams lighter than a standard seat post binder. Second, the seat tube extension can be 2-3.5 cm shorter and therefore saves another 18-30 grams. Third, we use a 30.9 mm seat post sleeve. The thinner sleeve we use with the larger diameter post saves 30 grams over a standard 27.2 mm seat post sleeve.

XX bikes are not meant to have racks mounted on them, nor are they recommended for designs that call for super-stiff drivetrains (i.e. 9 or 10 on our stiffness rating scale).

XX specifics for disc brake frames:

  • About 11 ounces of weight savings
  • XX tube butting
  • Compact frame design
  • Asymmetric dropouts and chainstays
  • Modified bottom bracket. English (or T47 upgrade*).
  • Modified breather holes.
  • XX flat mount brake adapter

XX specifics for rim brake frames:

  • About 6-8 ounces of weight savings
  • XX tube butting
  • Compact frame design
  • Modified bottom bracket. English (or T47 upgrade*).
  • Modified breather holes.

* T47 upgrade incurs additional cost and additional weight.

Thinking More Deeply About Weight

There are three impacts that weight reduction in a frame (or component) can have on a bike:

  1. Sometimes reducing weight can mean improved performance. We climb faster on lighter bikes, and lighter bikes are easier to handle. They make steering with the body, instead of just the hands, more effective. Think “body English.”
  2. Lighter can also mean more flexible. Flexibility can be good, but often it’s bad. The first Ti bike frames, for example, were thought to be too flexy, too “noodly.” Experienced bike builders understand how to make flex work for the bike, rather than against it. For example, lateral flex is often seen as a negative, while vertical flex is generally beneficial. That vertical flex improves traction and tracking. Riders at every performance level appreciate the comfort of a bike that absorbs shock vertically.
  3. Lighter generally also means shorter service life. When pursued as an end in itself, weight reduction increases the incidence of warranty issues. Every Seven frame carries a lifetime warranty, so we avoid any weight saving feature that limits service life. Historically, that’s why our frames are not the lightest on the market. We have no interest in pushing the limits of durability or safety.

Generally, when chasing weight goals, the resulting frames exhibit all three of the impacts above, and we’ve all seen that as the industry has chased lower and lower frame weights in carbon road bikes.

The majority of Seven’s titanium SLX models took advantage of points one and two, while carefully avoiding service life challenges. Our SLX frames were a lot lighter than our SLs, and they offered a softer ride, too. This is a positive trait or a negative, depending on your size and how you ride, and we often steer larger and more performance oriented riders away from SLX frames. Every frame we build remains rider-specific, optimized for the person who is going to ride it.

The base design goal with the XX bikes was to eliminate weight without sacrificing frame stiffness or performance, to use our years of experience building double and ultra-butted frames to push the level of refinement we can offer our riders.