Sigma: Installation and F.A.Q.

 Jun 26, 2013 article & images by Nick Salazar

Sigma is here! Get yours in the TriRig Store!
Sigma: perhaps the first aero stem designed specifically for triathletes.

When we announced the Sigma Stem back in September, it was greeted with a good deal of excitement. As with our other products, we tried to find a unique solution to certain aerodynamic and fit problems that can't be found anywhere else in the market. The goal with Sigma was to create a stem that combined superlative aerodynamic design with mechanical simplicity.

The basic mechanics of the Sigma are identical to that of a standard stem. But of course, there's a little more to the Sigma than you get with a standard stem, so we've created step-by-step installation instructions.

Sigma Installation
  1. Trim your fork's steerer tube so that the top of the steerer tube rests approximately 3mm below the Sigma's headset cap. Note: The Sigma is designed to be used without any spacers above the stem. However, if you are still refining your stem position, it can be temporarily used with spacers above the stem, but only with the cable cover removed.
  2. With the cable cover removed, install the Sigma onto your fork as you would any other stem. Follow the torque specification of your headset for the headset bolt. Use 5-6 Nm of torque on the two M5 socket screws that tighten the Sigma to your steerer tube.
  3. Install your handlebars in the usual manner. Use 5-6 Nm of torque on the four M5 socket screws that tighten the handlebar clamp. As with any stem, you do not want to immediately torque any bolt to its maximum torque spec while other bolts are significantly looser. Instead, tighten each bolt just a little bit at a time, taking several passes to arrive at the final torque specification. Also, check the torque spec of the stem periodically to ensure that the bolts do not become looser over time.
  4. The Sigma has an integrated cable stop for use with centerpull brakes like the TriRig Omega. If you wish to use this routing option, run your front brake cable housing directly into the cable stop. The optimal housing length will depend on your particular equipment, but for aerodynamic purposes, it's best to attempt to route the cable such that it hides behind the frontal profile of your handlebars. That is, attempt to route the front brake cable housing so that it is not visible when viewed from the front of your bicycle.
  5. Once the stem and handlebars are in place, use the cable cover to collect all the cables and hide them within the body of the Sigma. Use 3-4 Nm of torque on the countersunk screw to attach the cable cover. to the stem. Depending on your particular setup, it may be advantageous to collect only some of the cables beneath the stem cover, leaving others outside. Because the cable cover is not a structural element of the Sigma, it can be removed or re-installed at any time for travel or adjustment purposes.
  6. The Sigma includes in integrated BTA mount for easily attaching a bottle cage directly to the stem. This optional mount attaches directly to the front of the stem via the included M4 hex screw with 2-3 Nm of torque. Once the mount is in place, remove the stem cover bolt and install the bottle cage using standard M5 bottle cage bolts (not included), using 2-3 Nm of torque. The rearward bottle cage bolt will pass through the stem cover and into the stem.

Please click through to the next page for a list of frequently-asked questions about the Sigma.

Tags » sigma,  sigmainstall,  stems,  tririg
  • Here's a handy geometry chart for the Sigma Flat. The nominally 90mm stem adds 81mm of reach and 22mm of stack, measured from the top/center of your headset.
  • Here's the identical chart for the Sigma 35. As you can see, the reach is identical, and stack increases by exactly 35mm.
  • The TriRig Sigma is perhaps the first aftermarket stem made specifically for triathletes.
  • The Sigma's Cable Cover lets you collect and route your cables internally, yet doesn't require recabling if you want to move something around. This is because the Cable Cover is not a structural element of the stem, and can be removed at any time.
  • The Sigma has an absolutely TINY frontal profile. This helps reduce drag and makes your front end a lot cleaner.
  • Here's the Sigma +35 sitting on my Specialized Shiv.
  • Your bike's steerer tube should be cut such that the top of the steerer tube sits 2-4mm below the Sigma's headset cap mounting surface.
  • Once trimmed, the Sigma's headset cap allows you to preload the headset and install the stem. The Cable Cover is put on last, after the stem is fully installed. This makes it really easy to do your initial cable routing, but in most cases also lets you avoid recabling if you want to make changes down the road.
  • The Sigma's recessed bolts sit below your bars, rather than in front. This allows the bolts to be accessed for adjustment even if your aerobars are filled with BTA equipment, computer mounts, etc.
  • Here's an example of how the Sigma's cable path might work. In some cases, you may not want to route every available cable through the Sigma. The beauty of the system is that you can change it up at any time. If you suddenly find your cables have to take too sharp a bend while routing through the Sigma, you can easily change that without needing to recable the bike.
  • If you are still dialing in your steerer tube length, you can run the Sigma without its Cable Cover. When you have the stem height dialed, then you can trim the steerer tube and replace the Cable Cover.
  • Every Sigma comes with a BTA mount. This small piece bolts on to the front of the stem as shown here. That leaves two bolt holes spaced exactly like a water bottle cage. This makes it a snap to set up a BTA bottle on your Sigma.
  • A closeup of the BTA mount installed on the Sigma.
  • This shot gives you an idea of what the stem looks like all cabled up, and with the BTA mount installed.
  • Weight of the complete Sigma Flat.
  • Weight of the complete Sigma +35.
  • A few more glamor shots of the Sigma.
  • Sigma flat from underneath.
  • The Sigma +35 is a nice way to add 35mm of stack height without resorting to stem spacers.
  • The Sigma +35.
  • Here's a breakdown of the parts that come with each Sigma sold. Starting from the top, going clockwise: Stem body and faceplate; Cable Cover (and M5 countersunk bolt), 1-inch steerer shim, Headset Cap (and M6 countersunk bolt), BTA mount (and M4 cap screw).
  • The Sigma's inner cavity also has a cable stop for use with centerpull brakes like the TriRig Omega.
  • Here's how the Sigma's centerpull cable routing works with the TriRig Omega. Clean as a whistle.
  • Now THAT'S what I call a clean front end. Yeah, we've published this photo before, but it's a great way to illustrate how the TriRig Alpha, Sigma, and Omega come together into a harmonious whole.

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