In the pursuit of the lightest possible gear, there always comes to a point of diminishing returns. Exotic, lightweight materials can quickly become cost-prohibitive, but RockShox has been able to deliver the lightest 100mm fork on the market while still achieving a reasonable, $799 price point.

2021 RockShox SID SL Ultimate Features:

  • Brand new 32mm lightweight XC chassis
  • Charger Race Day Damper is ultralight
  • Adjustable rebound on lower left leg
  • Lockout function with blowoff (worked with Trek’s lockout system)
  • Revised DebonAir air spring maintains higher ride height and is tuned for XC
  • Ultra-low friction SKF wiper seals
  • Maxima Plush damping fluid to reduce friction and silence damper noise
  • Machined/anodized crown
  • Signature SID Blue (tested) and Ultimate High Gloss Black colors
  • Remote options include TwistLoc remote
  • Suspension sag markings on left stanchion for easy setup
  • Weight: 1330 grams / 2.93 lbs (actual, uncut)
  • MSRP: $799-$869
2021 RockShox SID SL Ultimate Review

The perfect match for the Trek Supercaliber.

The SID SL Ultimate is your secret weapon

With the Trek Supercaliber 9.8 test bike, I learned a thing or two about secret XC weapons. That bike’s secret weapon is the lockout system which allows you to eke out just a little more speed during standing efforts. Those in my generation will recall playing Spy Hunter, with its secret weapons that allowed you to smoke the enemy. After installing the RockShox SID SL Ultimate, I felt like Spy Hunter with one more weapon — confidence and comfort on the roughest terrain.

As the world’s lightest production XC suspension fork, the new SID SL Ultimate drops a half-pound from the stock Fox 32 SC fork on that bike. And, while the Fox SC is a great fork, the added 1 cm crown width aboard the SID SL Ultimate provides a significant mental boost because it just looks wider. That extra width does provide a stout foundation and the SID doesn’t mess around in that regard. I’ve got zero quibbles about either fore/aft or lateral flex on the SID. Noodly cross-country forks of yesteryear are thankfully long gone and the SID ranks among the best forks I’ve ridden in this class.

RockShox SID SL Ultimate and Trek Supercaliber 9.8 Review

The RockShox SID SL Ultimate on the Trek Supercaliber 9.8.

With the SID SL, you can either choose to integrate the lockout with your existing system or use the TwistLoc remote. I’m pretty particular about my grips (Ergon GA3 or GE1), so the TwistLoc just isn’t my cup of tea. To set it up with the existing lockout, all it took was threading the cable in and locking it in place — it worked like charm. I’ll add that the lockout feature is great for road approaches or standing sprints. Outside of that, I kept things wide open, and with good reason (this thing is smooth).

Part of the beauty of the new DebonAir air spring is how well it sits at the top of the travel. If you’ve ever ridden the Specialized BRAIN shock, it feels a lot like that. The fork basically sits at full extension with just a slight platform to it. Once you hit a bump, it engages in milliseconds. You’d think it might feel harsh, but it doesn’t at all. That initial blowoff is really subtle and allows the SID SL to sit taller and maintain the proper geometry for aggressive cross-country riding. Bumps of all sizes are swallowed up in a jiffy.

RockShox SID SL Ultimate Review

Plowing through whatever gets in the way.

It’s pretty incredible because the fork doesn’t feel harsh on even the smallest bumps and also feels progressive and smooth on rough terrain. It’s somewhat mind-boggling to have such versatile travel in a lightweight fork. RockShox engineers have done well with this one and it sits at the top of the World Cup XC podium a lot.

And, should you forget to unlock the fork, it blows past the lockout to save your butt from disaster. But, under normal lockout conditions (standing sprints or climbs), the lockout is always maintained.

RockShox SID SL Ultimate Review

The SID SL is so responsive and fast — the perfect XC race fork.

As far as the setup, I weigh 170 lbs. and settled in at 105 psi with the rebound right in the middle. At that pressure, I did max out the travel on a few rides over rough terrain, but I never felt it bottom out. I only knew I bottomed it out because of the rubber ring. It ramps up nicely, but confidently lets you use the full travel.

The ride character of the SID SL Ultimate really allowed me to ratchet up the intensity on descents. With it, I had more confidence, more comfort and the added confidence of a wider platform. I felt like I could descend faster and fresher than the stock fork. Dropping weight and adding confidence was a win-win for me.

The Good

  • The lightest production XC fork available
  • Smooth, progressive travel (you can comfortably use all 100mm)
  • Sits high in the travel and engages in a millisecond
  • Wide chassis adds to confidence
  • Lockout works great and blows off if you forget
  • Rides quietly as you blow through the travel
  • Sag gradients and travel markings on the stanchion are awesome
  • That simple brake line grabber is way better than zip ties

The Bad

  • Using TwistLoc would require using special grips (or, you could just go with the fork lockout version for $799)

The Bottom Line: 2021 RockShox SID SL Ultimate

If cross-country is your game, the 2021 RockShox SID SL Ultimate should be your weapon of choice. Suiting up with the SID is like giving your bike super powers. It sits high for accurate, responsive handling, but smoothly and predictably compresses through the full 100 mm when needed. I have loved the added confidence and control that the SID has provided — it’s light, reliable and fun to ride at red line speed.

Buy Now: Available from JensonUSA

About Author

A native of the Pacific Northwest, Jason quickly developed a love for the outdoors and a thing for mountains. That infatuation continues as he founded this site in 1999 -- sharing his love of road biking, mountain biking, trail running and skiing. That passion is channeled into every article or gear review he writes. Utah's Wasatch Mountains are his playground.


    • Yes, some RockShox forks are opposite of Fox. This particular Fox shock and the SID SL are the same (push to lock). It worked out great, but I can’t say that it will work that way for all RS/Fox combinations.

      Trek does sell the SID SL on their top Supercaliber builds if you check out their site. What bike are you looking to install it on?

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