First Ride: 2015 Norco Aurum Carbon

Keen-eyed observers may have spotted prototype versions of the 2015 Norco Aurum at various downhill races last year, but up until this point Norco had remained quiet about the bike's specifics. That veil of secrecy has finally been lifted, and to find out more about the bike we headed to Idyllwild, California, a small town located in the San Jacinto mountains. While it may not have the beaches and bikinis southern California is famous for, it is surrounded by plenty of steep, loose, and rocky trails, which made it a fitting location to get a feel for the new rig. The Aurum Carbon retains many of the characteristics that made the previous version so popular, including the 200mm of rear travel, but has received updated geometry, 27.5” wheels, and a carbon fiber front triangle.


Updating the Aurum

When Owen Pemberton, Norco's senior design engineer, began working on the new rig he sought to create a bike that was lighter, faster, and more efficient than its predecessor, yet retained a similar suspension feel. At the time, 27.5” wheels were gaining traction (no pun intended), so the decision was made to base the bike around that wheel size, and in order to achieve the desired weight savings, carbon fiber was the material of choice for the front triangle.

The resulting frame ended up weighing 3300 grams, a pound lighter than the alloy version, and Norco's testing results showed that it was the strongest frame they'd ever built. Once the prototypes were ready, Norco set their team members loose on the race course to put a season's worth of abuse on the bike before releasing it for the public, the same process they used with the original aluminum version of the Aurum.


The curvy profile of the front triangle is for more than show – it's a design intended to avoid any sharp angles at high stress junctions in order to maintain the strength of the carbon fiber. Norco has included downtube and chainstay protection, along with a unique integrated bump stop that also provides protection for the underside of the downtube during shuttling. A pressfit BB107 (the DH equivalent of a BB92) was chosen due to the larger and stiffer bottom bracket junction that it allows for, which creates more space for the main pivot and the lower shock mount. Rather than going with the 150mm rear end spacing that often accompanies a BB107 or 83mm bottom bracket shell, Norco chose to go with a 12x142 rear end, citing the improved heel clearance, and the fact that the bike was designed to be run with a 7 speed drivetrain. Even the base model version, the Aurum C7.3, comes with an SLX cassette that's been reduced to 7 speeds.

Downhill and bike park riding can take a toll on even the most meticulously maintained bikes, which is why Norco used only two bearing sizes throughout the entire frame. There are releases for each bearing, notches in the frame that allows for access to the outer bearing race to make removal even easier. The derailleur hanger has also been improved, and is now located inboard of the frame rather than being mounted to the underside of the dropout, making it less prone to snagging and getting broken or bent by hungry rocks or roots. In addition, cartridge bearings are now used at the upper shock mount instead of bushings, a change that's claimed to help increase the shock's small bump sensitivity.


Geometry and Suspension Design

The 2015 Aurum has a 63° head angle, a -12mm bottom bracket drop (which places it 5mm lower than than before), and between a 425 – 445 rear center measurement. According to Norco, the reason for having the rear center measurement grow as the frame sizes get larger is to help maintain the same rider weight distribution throughout the line. It's not the actual chain stay that's lengthening – it's the bottom bracket position that changes, moving slightly forward with each frame size. For 2015, the rear center measurements have been increased slightly, and each frame now has a different head tube length. That change that came about as a result of analyzing how riders were setting up their bikes in the real world.

According to Owen Pemberton, "We polled a cross section of current Aurum riders to get their view on the fit of the bike... What we found was that all riders were running some headset or stem spacers (or a combination of both) to get to their desired bar height. Because the old Aurum employed a single head tube length of 110mm we found that larger riders were needing to run a minimum of 35-40mm of spacers to get to their comfortable bar height (some riders a lot more). It is more efficient to put this height into the frame rather than spacers as it puts less stress on the headset bearings and the fork steerer/stanchions. We found that the combination of a bigger wheel, longer fork and a 120mm head tube length would put the reach/stack point right in the same zone as the minimum people were running on the old bike."

The Aurum still uses Norco's Advanced Ride Technology (A.R.T.), their take on a Horst Link suspension design, and the axle path remains unchanged from the 26” version, but the shock position has been altered in order to make it slightly less progressive than before, in order to allow riders to make the most of the bike's 200mm of travel.







Riding Impressions

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