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The 12-speed system, which consists of 12 cassette sprockets, has been applied to road bikes starting with mountain bikes, and has expanded to gravel, becoming the most common shifting system.
SHIMANO also launched a 12-speed cassette system for the GRX series, a gravel groupset, last September, opening the 12-speed era by having a 12-speed system for mountain and road as well as gravel.

Mechanical 12-speed shifting system, RX-820

It is true that the price appeal of 12-speed systems has recently decreased significantly as electronic systems have become mainstream. However, since it is not easy to create accurate shifting with a mechanical system within the tight gear ratio of 12 speeds, Shimano also released the Di2 electronic road drive system first.
However, Shimano, which has very precise technology in mechanical systems, applied the mechanical 12-speed system to the road groupset 105 and the gravel groupset GRX, showing both the advantages of 12-speed and its price appeal.

Recently, the difficulty in connecting cables for mechanical shifting has increased due to designs such as full internal cable systems and integrated cockpits, but mechanical systems that can be used freely without the burden of battery charging are still attractive.

Last September, Shimano launched a 12-speed mechanical gravel groupset GRX series.

There is little change in the design of the control lever compared to the 11-speed.

It’s connected by a cable, so you don’t have to worry about batteries like you do with Di2.

Various shifting options

The 12-speed GRX offers a variety of shifting options through chainring and cassette selection.

First, the chainring can be selected in 1st or 2nd gear. Gravel bikes often use a 1x drivetrain with a single chainring, but the gear ratio of a 2x drivetrain is more comfortable for riders who ride on both paved and unpaved roads.
The 1x chainring is available in 40T and 42T, and the 2x chainring is available in 48-31T options.

Available in 1x chainring (40 or 42T) or 2x chainring (48/31T) options.

The price of the 1x and 2x crankset is the same.
Consumer price: 331,000 won

2x system requires front derailleur.
Consumer price: 82,000 won

There are GS and SGS rear derailleurs depending on the cage length, and the prices are the same.
Consumer price: 170,000 won

The control lever can be purchased as a set that includes a brake caliper or as a standalone product.
2x lever + caliper set: KRW 536,000 (right), KRW 536,000 (left)
1x lever + caliper set: KRW 536,000 (right), KRW 504,000 (left)

In the case of the cassette, you can select a combination of 10-45T and 10-51T with a 1x drivetrain. For 10-45T, select a GS derailleur, and for 10-51T, select an SGS derailleur.
Cassettes available with 2x chainrings are 11-34T and 11-36T options.

With a 1x chainring combination, a maximum gear ratio of 42T (chainring) / 10T (cassette) = 4.2 is possible, and a gear ratio of 40T (chainring) / 51T (cassette) = 0.78 is possible.
2X chainrings are available up to 48T(chainring)/11T(cassette) = 4.36 gear ratio and 30T(chainring)/36T(cassette) = 0.86 gear ratio.

As a result, the 1x drivetrain has the advantage of simple operation and the low gear ratio of the 51T cassette, while the 2x gear ratio has a high gear ratio at the top, which is advantageous for high-speed driving and makes it easy to maintain cadence through tight shifting of 24 speeds.

The 1x chainring allows for simple operation and very low gear ratios when using a 51T cassette.

The 1x system simply applies a compatible mountain cassette to the Microspline Freebody.

2x system for high-speed driving with 48T chainring

For 2x systems that require a front derailleur, an HG Freebody compatible cassette for road use is applied.

Assembling Shimano GRX RX-820

The option chosen for this article is a combination of 1x chainring 40T and 10-45T cassette. I wanted to choose 2x, but the gravel bike I am currently using is a 1x only product, so my choices were limited.
Personally, I tend to drive on paved roads quite a bit, so the lowest gear of 40T (chainring)/45T (cassette) = 0.89 was sufficient. If you choose the 10-51T cassette, it is fine for mountain driving, but when driving on the road, the gear shifting range is too large, so it feels a bit burdensome.

When assembling a bicycle these days, the first thing to do is to connect the cables with the handlebars pre-assembled on the frame. Because it is a mechanical system, the brake hose and shifting cable must first be inserted into the internal cable route, then cut to an appropriate length and the handlebar and lever must be assembled first.

There is nothing special about the work after that, but the 10-45T cassette requires the use of a GS derailleur to ensure shifting. When I installed the SGS derailleur as a test, the low and high gear shifts were not adjusted at the same time.

Internal cable work is easy when the BB is completely separated.

Connect the brake first.

The length of the hose is generous, so cutting is necessary at an appropriate length.

Hose requires specialized tools because its cross section must be cut cleanly.
Mechanical Support: BMC Seoul Store

Insert the insert into the end of the cable.

The new control lever has an olive inserted inside to close the hose. It can be easily assembled by inserting the hose all the way and fixing it.

The shifting cable must be inserted from the outside of the lever to the inside.

The cable comes out from the inside of the lever through a part covered by a transparent cover.

Once the internal cable work is completed, insert the BB.

Before inserting the crank, raise the safety pin that prevents the crank arm from falling out even if the bolt is loosened.
The safety pin can be easily raised by completely loosening the outer bolt.

After inserting the crank arm, lower the safety pin again and lightly tighten the bolt.
Using the crank insertion tool, insert the crank arm until there is no play.
Afterwards, lock the fixing bolt to complete the crank arm assembly.

Disc rotor assembly

Cassette assembly. Make sure that the last small sprocket is correctly inserted and then secure it.

The derailleur has GS (left) and SGS options.
The 10-45T cassette must use a GS derailleur, and the 10-51T must use an SGS derailleur.

When the chain is hung on the largest sprocket and chainring, cut the chain to about 2 lengths remaining.

It is convenient to connect using quick link.

Install the chain so that the letters face outward, and install the quick link with the arrow pointing in the direction of rotation.

Set the shift using the fine adjustment screw and knob.

The 1x did not have a front derailleur, so it was easy to assemble.

There is a lever in the center that controls the movement tension of the derailleur.

When you push down, the pivot moves smoothly, making it easier to remove the wheel, and shifting is a little smoother.

When the lever is raised, the chain does not bounce easily even on rough gravel, making it quiet and reducing the risk of the chain falling off.

Precise mechanical shifting quality

As someone who has mostly used electronic shifting systems recently, it has been a long time since I assembled and tested a mechanical transmission. And, as expected, Shimano’s mechanical shifting showed satisfactory quality.

It feels different from the fast and accurate shifting of Di2 electronic shifting, but the mechanical shifting, which changes depending on the speed of the lever you press, is good because it retains the feeling of analog. In particular, the movement of the derailleur, which is felt depending on the amount of pressure on the lever, is attractive because it allows you to finely adjust the sense of control.
Moreover, mechanical shifting eliminates the burden of battery charging and reduces the burden on price.

Mechanical shifting system with the advantage of analog emotion and control sense

As expected from Shimano, I was able to feel the accuracy and quality of the 12-speed mechanical shifting.

The advantage of a mechanical system that allows driving at any time without the burden of battery charging

In addition to shifting, I liked the GRX lever because it was easy to place my finger on the brake lever even when holding the hood or holding the drop. In the case of gravel, there are many times when riding with your hands constantly moving between the hood and drops. The Shimano GRX lever was very satisfactory in this regard.

It is important for riders who go on gravel, especially long-distance adventures, to reduce the weight of their luggage. In the case of electronic shifting, it is often necessary to bring a charger and auxiliary battery to prepare for unexpected discharge. In this regard, a mechanical system could be a good choice to relieve some of the worry and weight. In particular, if the shifting reliability is as high as the Shimano GRX RX-820 series, it would be an even better choice.

The mechanical hood is slightly larger than the Di2 electronic.

The grip on the hood is satisfactory. Personally, I prefer the GRX Di2 hood design.

Operating the brake lever while holding the hood

The design makes it easy to operate the brake lever even when holding the drop, increasing riding satisfaction.

GRX RX-820 groupset reduces price burden and maintains performance

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