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  • Shimano GRX RD-RX812 Rear Derailleur
  • OptionsShimano -
ShimanoGRX RD-RX812 Rear Derailleur
$113.99

Item # SHIU19E

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  • Black, Rear ($113.99)
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Item # SHIU19E
Description

GRX RD-RX812 Rear Derailleur

If you've dabbled in gravel racing and riding, chances are you already know how important a large gear range and tidy setup is, and if you have yet to experience it first hand, we can assure you, that we covet simple drivetrains with few opportunities for failure, and as many gears as possible to get us up poorly-graded hills that make up the Crusher and Kanza. With that said, it took quite some time for component manufacturers to jump on the gravel bandwagon, but with the Kanza's starting line amplifying from sub-50 cyclists to over 3,000 in just twelve years, its a welcome sight to see Shimano launch its GRX gravel-specific groupset that finds the perfect balance between MTB and Road, with a sleek and streamlined drop-bar setup, and improved modulation and bump compliance to handle off-road conditions. Shimano's GRX RD-RX812 follows in the footsteps of Ultegra RX which was launched last year, which took queues from the Shadow mountain bike derailleur, adding in a clutch mechanism to reduce chain slap and dropped chains for a quieter and more secure ride both on and off-road. When in the on position, the clutch increases the spring force to provide crisp shifting and zero chain slap and is easily flipped off for wheel changes. What we find to be big news is that Shimano crafts the GRX RD-RX810 for both 1x and 2x setups, stepping outside of the 2x only comfort zone that the brand had held to, with this short-cage model being optimized for an 11 - 34t cassette.

Following in the footsteps of the revamped Dura-Ace and Ultegra groups, this GRX derailleur gets its Shadow cage treatment placing it closer to the frame and under the cassette keeping it out of harm's way and less likely to take the brunt of a driveside crash. This also allows the derailleur to move in a much more linear path allowing for shorter throws with less effort. The RX812 model comes in one cage length, long, which accommodates an 11-42t cassette allowing for a wide range gear ratio when paired with a double without the usual huge jumps between the cogs like on a 1x setup, ranging up to an 11-42t cassette.

Sticking to what the brand's customers know well, Shimano continues to use the Dura-Ace, Ultegra, and Tiagra designation with the GRX line, with this particular model falling under the Ultegra umbrella, which means it gets the usual materials and finishes that we expect from a groupset that's just one step from the top. Its weight, smoothness, and durability make it more than capable of racing against the competition on course, or the sun to your campsite for the night on a bikepacking trip.

  • Shimano's off-road ready derailleur for charging down rough gravel roads
  • Shadow clutch mechanism increases spring tension to eliminate chain slap
  • Clutch is easily flipped to make wheel changes and flat fixes a breeze
  • Derailleur cage tucks closer to frame to avoid hits and bumps
  • Compatibility for both 1x and 2x drivetrains
  • Durable alloy construction handles mud and off-road adventures
  • Works with current Shimano 11-speed road shifter/brake levers
  • Low-profile Shadow design helps avoid damage from impacts
  • Long cage allows you to run lofty 11 - 42t cassettes
Tech SpecsWeight
Tech Specs
Material
alloy
Cage Length
long
Capacity
31t
Cassette Range
[maximum] 11 - 42t, [minimum] 11 - 40t
Gearing
1x11, 2x11
Compatibility
current road dual control lever, GRX levers
Recommended Use
road
Manufacturer Warranty
2 years
Weight

Actual Weight

Actual weights are measured in-house by the Competitive Cyclist team.

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Grams

Oz

Black, Rear
265g
9.35oz

Claimed Weight

Claimed weights are provided by the vendor.

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264g

Reviews & Community

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A Big Step in the RIght Direction

  • Familiarity: I've used it several times

Gravel has been the fastest growing segment for the past few years and Shimano has finally done something about it. GRX is a much needed drivetrain but doesn't quite go far enough with gearing for us casual riders in the mountains.



To start with, performance and looks are on par with Shimano's road groups, so really good. It's a very clean looking groupset. So if you've liked your Ultegra drivetrain but want easier gearing, going to GRX makes good sense. There's some compatibility between the two groups too which is nice.



This rear derailleur interestingly enough has only a 5mm shorter cage than an SLX which fits a 46t cog so despite Shimano's stated max cassette size as 42t I plan to try it with an 11-46t eventually just to see what happens.



I've had a 105 shifter paired with an SLX rear derailleur and 11-42t rear cassette (using Wolf Tooth's excellent Tanpan adapter) on the bike until now so I already knew what to expect for gearing but GRX really does shift crisper without that adapter and this group feels lighter weight.



So with no substantial complaints on the quality of this group my big gripe is the gearing options. Shimano has provided good options for a lot of riders on flatter terrain and for gravel racers but us bikepackers and for those big days in the mountains we need better options. Sram's AXS drivetrain mullet builds are popular for that giant 10-50t range, Shimano should have used their Micro Spline freehub to allow for a 10t cog and made the derailleur for 46t cassettes, then with more chainring options they'd have a perfect, more versatile group.

A Big Step in the RIght Direction

Is grx compatible with ultegra shifters?

Looking forward to hear how it works with the 46t. I'm running an xt/tanpan with eyes on going to the grx rd but dont want to limit myself to a 42.

Looking forward to hear how it works with the 46t. I'm running an xt/tanpan with eyes on going to the grx rd but dont want to limit myself to a 42

Looking forward to hear how it works with the 46t. I'm running an xt/tanpan with eyes on going to the grx rd but dont want to limit myself to a 42