Shimano GRX Di2: The 12th sprocket is here - the gravel drivetrain put to the test
The new GRX Di2 model from Shimano does many things right, both technically and functionally. However, it does not bring any new innovations for the gravel bike that could be expected from a high-end product. The limited range of gear ratios is aimed at the mass market and therefore does not fit in with the growing diversity of the gravel bike world. In particular, the fact that there is no option for just one chainring could put off potential buyers.
Background information on the Shimano GRX Di2
In 2019, Shimano was an instant success with the 11-speed GRX groupset. The first groupset made specifically for gravel bikes was a safe choice for anyone looking to equip a new off-road bike. Customers and manufacturers trusted that the company, with its many years of expertise in mountain bike and road bike shifting, would combine the best of both areas and deliver the usual Shimano quality. As a result, the groupset was found in various quality levels on production bikes. Whether as an entry-level version with only ten mechanically operated gears or with top-class flair as a 2x11 electric drivetrain: the right Shimano components for the gravel bike were particularly in demand.
Although most buyers were satisfied, Shimano mainly focussed its range on affordable and mid-price categories. More demanding gravel riders looking for something special may have been disappointed. Sram used 12 instead of 11 sprockets for its AXS, which was presented at almost the same time, leaving Shimano behind right from the start. The "XPLR" models of the road bike groupsets offer interesting options with a single chainring and cassettes that have sprocket sizes similar to mountain bikes.
The competition: Sram and Campagnolo
Sram became particularly popular with drivetrains without derailleurs and achieved a considerable market presence with high-priced bicycles. Campagnolo presented the Ekar drivetrain in 2020, which with 13 sprockets offers the most comprehensive single-speed drivetrain currently available for off-road riding. In terms of the 1x11 groupset, the GRX from Shimano was a rather poor compromise; and the inexpensive 1x10 drivetrain is almost unusable off-road, as the gear range was too narrow. With Campagnolo and Sram, significantly lighter (albeit more expensive) bikes can be built. The Japanese have so far lacked a competitive high-end product for high-quality gravel bikes in their portfolio.
And now: Shimano GRX Di2 - high expectations
Nobody would have expected that a new edition of the Shimano GRX drivetrain would completely overturn the existing order, as the Japanese usually pursue rather conservative strategies. Nevertheless, the expectations for an update of the GRX Di2 were quite high - not least because the update of the mechanical GRX last summer was rather restrained and not particularly breathtaking. Parallel to the mechanical 105 road groupset, it received an additional twelfth sprocket, a new rear derailleur and slightly modified shifters, but overall it remained largely unchanged. It can theoretically be configured as a 1x12 drivetrain with components from the mountain bike sector, but there are only two sprocket options in the corresponding XT groupset (10 -45 and 10 -51), which require a Microspline freehub due to the smaller initial sprocket. However, this is only available for a few road and gravel bike wheels, which makes the configuration rather complex.
The Shimano GRX Di2 gravel drivetrain put to the test
Even a first glance at the new top gravel model from the industry leader reveals that the update to the GRX Di2 electronic groupset is merely a gentle facelift from Shimano. It adopts the braking and drivetrain systems from the mechanical version, with only the shift brake levers, front derailleur and rear derailleur being truly new. However, the changes to these elements are rather minor, but more on that later.
In practice, the functionality of the groupset leaves little room for criticism. As with the newer road bike groupsets, the grips are now wirelessly connected to the shifting components, with Shimano promising a battery life of up to four years. The shape and mounting have been slightly adapted to better fit the typical flared handlebar ends of gravel bikes. This ensures a more ergonomic transition to the handlebars and allows the brake levers to protrude less to the side. Otherwise, the contact points have remained largely unchanged.
Haptics at the contact points
The appealing design of the shifters is still unrivalled, especially when your hands are resting on the grips. The hand rest is large and non-slip; the small, steeply raised grip at the front end provides a good hold. The grips are also very slim so that even smaller hands can grip them well, especially on rough rides. The fingers also have a wide contact surface on the brake levers. Thanks to the high starting point of the brake lever and the "Servo Wave" braking force support, there is no need to switch to the lower link, even on steep descents, as sufficient braking force is available. A freely configurable additional button, which was previously hidden under the grip rubber, has now been placed close to the thumb on the inside of the lever. However, this is somewhat stiff for a gearshift function, for example.
The shifting behaviour
As expected, the shifting behaviour of the new Shimano GRX Di2 is excellent both front and rear, but the front derailleur is quite loud. The howling motor noise is reminiscent of the early Di2 generations, while the current road bike front derailleurs are significantly quieter and visually less conspicuous. The new rear derailleur works quickly and precisely. The tried-and-tested damper reliably prevents the chain from rattling in the event of vibrations. The gear ratio with two chainrings at the front and an 11-36 cassette - technically on a par with 105 - should be a good fit for most applications. There are gear reduction options for uphill riding as well as fast gears, and the twelve-speed gear layout is pleasantly finely graduated. However, if you want to go bikepacking with luggage in alpine terrain, you will quickly miss the very light gears on the GRX Di2.
Only made for 2x cranks
In contrast to the mechanical version, the rear derailleur is not designed to handle sprockets with more than 36 teeth. An alternative to the double crankset with 48/31 teeth is also not available. Therefore, operation with a single crankset without a front derailleur is simply not possible with the new GRX Di2. Although there is the option of using the slightly sportier 11-34 version from the road bike groupsets, Shimano does not offer any other alternatives.
Conclusion on the new Shimano GRX Di2 gravel bike drivetrain
The lack of a drivetrain option with a chainring could cost Shimano customers, as the ease of use of these drivetrains is now an important purchase criterion for many riders. This also limits the options for wider tyres: although the maximum 47 millimetres should be sufficient for most gravel riders, those who prefer heavier terrain and wider tyres may be forced to switch to the competition. Nevertheless, it is clear that the Shimano GRX Di2 will once again find many buyers. In particular, attractive complete bike offers, which depending on the brand are around 5000 euros and therefore comparable to bikes with Sram Force, will contribute to the spread of the GRX gravel drivetrain. Those who don't want a front derailleur will simply go to Sram.
On top: wheels and pedals
To complete the GRX groupset, Shimano is adding the corresponding wheels and SPD pedals to its range. The RX880 wheelset is supplied with 32 millimetre deep carbon rims with an internal width of 25 millimetres. Tyres from 32 to 50 millimetres wide are recommended by Shimano. The manufacturer gives the weight as just under 1400 grams. A special feature is the quickly interchangeable freehub body; there is both the classic HG standard and a Microspline freehub, which enables XT mountain bike cassettes to be fitted. The retail price is 1649 euros. The matching GRX-SPD pedal is not an innovation, but the mountain bike pedal from Shimano's XT groupset in a matching design. The pedals weigh 342 grams and cost 135 euros.
Jens Klötzer
Editor
