FIRST LOOK: Shimano GRX 2x12 long term build

At the start of September Shimano released three new GRX group sets, all based around an updated design for a 12-speed cassette. There's a 1×12 option using a 10-45t 12-speed cassette and short cage derailleur, plus another that uses a 10-51t cassette and a longer cage derailleur. You can read our first ride impressions of the GRX 1×12 group set after the launch.

There is also a 2×12 model to suit those who prefer two chain rings and a closer range cassette. These groups use a 31/48t chain ring combination, with an 11-34 cassette and a 12-speed chain. The chain and cassette are HyperGlide+, meaning the shift ramps speed up the shifting for both up and down shifts, creating faster and more secure shifts. This is the same system as on Shimano Deore, SLX, XT and XTR 12-speed group sets.

A closer look at Shimano GRX 2×12

After riding the 1×12 models at launch, we have been sent a 2×12 group set for long-term review. This has the 105 spec 11-36t cassette for a wider range, although that misses the HyperGlide+ shift speed and precision.

The group set has been built onto a Factor LS gravel bike. I previously had this frame set built with 2×11 GRX, and have ridden it since June, including at the Australian Gravel Championships in Derby, Tasmania. 

The Shimano GRX 2×12 group set is mechanical only (for now) so this was a straight swap from the 2×11 group. Some parts remain the same, like the crank arms. But the shifters have a new shape and new hoods for better grip and comfort. They are also designed to suit flared bars to have less pressure on the heel of your palm.

The brake calipers are new, allowing 10% more pad clearance. This is also a new rotor design, which you will also see on rotors larger than 160mm for mountain bike group sets. The updated design completely removes any heat warping from the rotor for drag free running even on long descents where brakes are being worked hard.

This is just one rear derailleur model for Shimano's GRX 12-speed line up. However to change from 2×12 to 1×12 would involve a new derailleur, cassette, freehub body, a new chain ring and likely a longer chain as well.

Having ridden the 1×12 GRX I loved the shifting and range, and the new hood shape for ergonomics. The 2×12 option should provide a great range and the versatility for a gravel bike or all-road bike. I do question why Shimano don't have the 11-36 cassette with the HyperGlide+ shift ramps, as this may seem like a subtle difference but it was a huge benefit when Shimano introduced it with their 12-speed mountain bike group sets.

New Shimano wheels 

Released in conjunction with the 12 speed GRX group sets are fresh carbon hoops from Shimano. They're a full carbon clincher rim with tape for tubeless and valves fitted, they roll on cup and cone bearings but they can swap freehubs. Given the 2×12 cassette uses a Shimano HG spline and the 1×12 uses MicroSpline, Shimano engineers got to work to deliver the freehub interchangeably we have all wanted for years.

The rims have a 25mm internal width and 30mm depth, and clocked in at 776g for the rear and 658g for the front, with tape and valves. That's 1424g for the wheels which is quite respectable for a gravel wheel set.

I've used this opportunity to also test out the Pirelli Cinturato RC 40mm gravel tyre from FE Sports, and the gravel Tubolight EVO rim inserts. I have been using the Tubolight SL for over 12 months in my XC bike, and this is a slimmed down version that weighs about 35g per wheel. I've found inserts for a gravel bike are a must have, as it lets me ride the bike like I want to with pressures for the narrower tyres to be useful.

The Pirelli XC RC mountain bike tyres are the leading XC tyre in my mind, and this tread pattern has a similar look, so I have high expectations for these tyres in terms of rolling speed, grip and casing quality.

I'll be getting some time on the dirt on this new build, so keep an eye out for a coming issue for a full review of Shimano's 2×12 GRX group set, new wheels, and the Pirelli tyres and Tubolight gravel inserts.