RockShox SID 29 World Cup XX fork

New superlight 29er option lives up to SID pedigree

BikeRadar score3.5/5

It's hard not to love a fork that can shave close to 1/3lb from a cross-country race bike, even when upgrading to a 15mm through-axle, and the superlight SID 29 World Cup XX will certainly be highly coveted by racers. But concessions have been made to hit that benchmark weight; most notably, a little stiffness has been lost due to the carbon crown.

Ride & handling

This baby is smooth, damn smooth. With the Dual Air spring tuned properly the new SID absolutely rips downhill, even set with just 80mm of travel. The carbon fibre crown on the World Cup model offers a certain smooth-feeling Je ne sais quoi to the feel of the fork, likely due to the material's high-frequency damping effect.

SID 29's BlackBox carbon crown borrows from both SID 26 and Revelation carbon CSU (crown, steerer, upper assembly) designs

The air spring has a higher volume than previous models, and thus offers a slightly less progressive ramp-up. But getting full travel definitely depends on where you’re setting your sag. With 20 percent, we found ourselves on the lower end of RockShox’s recommended pressures, even with the spring’s added volume. For this reason, we'd recommend using the negative air chamber and/or damper to adjust the feel of the fork, not the positive chamber.

The XX damper with its X-Loc remote is pretty much the same as last year’s, save for the new DNA spring tube. RockShox say this offers better consistency and damping performance. We found performance to be almost identical; it’s a simple damper that offers good control that’s adequate for the travel category.

On the rebound side, the damper is upgraded to RockShox’s Dual Flow design and this clearly benefits the fork. On fast downhills the SID seems to react more quickly and ride slightly higher in its travel. We generally ride on the mid-to-light side of damping setup recommendations; the Dual Flow design will provide even greater benefit to those who like a heavier setting, as it allows that heavier initial feel with the ability to more quickly recover from deep-stroke hits.

The Dual Flow rebound is the most noticeable damper performance upgrade to the fork

Given that our test sample was equipped with a 15mm axle, we were expecting the new fork to be stiffer. Fore-aft rigidity seemed fine, as well as stiffness in the sheer plane side to side. However, under hard cornering we could feel twist in the legs (transverse plane), accompanied by the sound of rotor rub, on a perfectly adjusted brake.

We put this to RockShox's Jeremiah Boobar, who verified that the carbon World Cup crown/steerer/upper (CSU) assembly isn't quite as stiff as the alloy version. According to the company's figures, bending stiffness is eight percent lower and torsional stiffness 15 percent lower (with a 15mm Maxle Lite axle), although a testing tolerance of 10 percent needs to be taken into account.

This means larger or more aggressive riders may be better off opting for the alloy CSU SID XX instead, or looking to the new, trail worthy SID 120 or the stouter Revelation 29, which can be chopped down to just 120mm of travel. The new SID isn't the stiffest 29in cross-country fork out there, but this wasn't RockShox's intention; rather that intention was to build a fork for 29in wheels that lives up to the Superlight Integrated Design (SID) tag, which this fork seems to admirably. 

Chassis improvements

RockShox have shaved a truck load of weight from the chassis with the redesign of the SID and Reba. Our sample weighs 1,600g, but that's with a full-length 265mm steerer tube, 15mm axle, X-Loc remote lockout and RockShox’s 39g expanding headset preload plug. Pull out the axle, expander and cut the tube and you’re right at RockShox’s original sub-1,500g target weight.

A meticulous gram saving exercise has resulted in drilled bushings, a butted aluminum air spring shaft, new air caps, scalloped Power Bulges, DNA damper tube, and the ultimate option — a carbon CSU. Tapered steerer models have a shorter-than-usual taper (85mm rather than RockShox's standard 108mm) so they can fit in short 29er head tubes, especially those found on smaller size bikes.

The DNA damper differs by way of a lighter 'helix' shaped spring tube; we couldn't tell a discernable difference in damping

Damper options

We had zero issues with the XX DNA damper, which is the best performing remote lockout in the business, especially if you’re using other SRAM components, because it mates so well with their shifters and brake levers (by way of MatchMaker X). However, we didn't notice any difference between the latest version and that on a two-year-old RockShox Reba we were comparing it against. We're also keen to try the new, more advanced RCT3 damper that RockShox unveiled with the fork.

Handlebar lockouts are really only good for those traditional straight up, straight down cross-country courses where you’re pushing the button twice a lap. Anywhere else – particularly short-track events, where we found we were locking and unlocking the SID an estimated 36 times in the course of a 30-minute race – fiddling with the lockout is a distraction from the more important business of pedaling and steering. On top of this, you’re forced to compromise the damper’s downhill abilities, as it’s absent of a high-speed circuit.

We see the new RCT3 damper as potentially a much better option for the average rider, as it offers three settings — open, platform and lockout — and the ability to tune low-speed compression. If the damper works well, we can imagine running the platform setting for a whole race, which would mean we wouldn’t touch the damper once. It comes down to individual preference, but it's good to see RockShox offering riders the choice.

We wished for the RCT3 damper on the STXC course

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