
Full Review
Shimano GRX Di2 12-Speed
This isn’t the Shimano review everyone has been waiting for. And while I wanted to wait to complete the review on Shimano’s gravel-focused GRX 12 speed Di2 until new XTR sees the light of day, I think I’ve been hearing rumors it’s just around the corner for at least 18 months, and like my four year old I’m tired of waiting. So don’t expect any answers around whether XTR is fully wireless this go around, or if there's cross compatibility with Shimano’s other Di2 models, but we can dive into the riding experience of Di2 GRX and how it’s held up since the First Look last year anyway. This is also not the just-launched and much-expected drop bar, LinkGlide-equipped Cues. That’s a whole separate arrangement of parts, replete with a myriad of cost competitive options geared around drivetrain simplicity and longevity that'll undoubtedly be popular with a wide swath of users.

It's been six years since the mechanical XTR M9100 launch, and a whopping ELEVEN years since XTR Di2 launched. Will we finally see a new electronic mountain gruppo from Big Blue this year?
So with what we don’t have out of the way, what do we have? This is RX825 GRX - Shimano's XT-ish level gravel groupset, in battery-driven Di2 form. There are a lot of technical details to cover off on 12 speed GRX - the First Look from back in October would be a good place to start if you’re not a Shimano nerd with an iron trap for a memory. There are a total of four gruppos, covering 1x, 2x, mechanical, electronic and four cassette options that aren’t all cross compatible, so do your research. Currently, if you want to shift your 12 speed GRX with electrons, the only option to choose is between a 11-34 or 11-36 cassette. It’s worth noting that there’s very likely more cross compatibility than Shimano recommends - there’s a whole aftermarket of bits and bobs here - but for this review I’ve kept it to “things on the chart”, which means a 2x with 48/31 rings, the wider range 11-36 cassette, and you’ll need to be mindful of pull ratios (if mechanical), clearances, etc. Currently, if you want to shift your 12 speed GRX with electrons, the only option to choose is between an 11-34 or 11-36 cassette.

12 (relatively) tightly spaced gears, shifted in what Shimano calls "semi-wireless" fashion, the derailleurs are wired to a central battery, and the brifters are wireless. Photo: Deniz Merdano
GRX Carbon Gravel Wheels
I’ve hooked you in with a drivetrain review, but before we dive into the nitty-gritty there, we need to talk about hoops. I’d argue a good set of lightweight wheels with good compliance and vibration characteristics is one of the highest value upgrades you can make to most mid to low end gravel bikes. Hopefully they’re also doing circles around a good hub. Putting the 24-spoke GRX Carbon Gravel Wheels (WH-RX870-TL) on Kona’s Ouroboros was an immediate, enormous positive change and I’m a fan of these wheels.
They’re pleasantly light, not harsh, and Shimano hubs are known for longevity. I’ve given them plenty of good rock-smacks, and the 25mm internal width strikes a nice balance, allowing you can run tires all the way from relatively narrow to pretty big (30mm-50mm by Shimano’s estimation). They’ve been easy to set up tubeless, and while not the most compliant, lightest, or anything -est, that’s ok; Shimano has found a nice balance of all the inherent engineering and manufacturing compromises that a wheelset for off-road drop-bar bikes demand. While they’re certainly not cheap, ringing in at $1,400 US, they’re likely a very noticeable upgrade that’ll last for a long time (as long as you keep the cup-and-cone bearings serviced), if you’re trying to stave off some new-bike-itis.

While the wheels are very non-flashy, they're a worthy upgrade if your gravel bike rolls on a drivetrain with an HG or Microspline cassette. Photo: Cooper Quinn

The 25mm inner and 30mm outer width works very well with a +/- 40c tire - a great do-it-all size. Photo: Cooper Quinn

Shimano has a storied history of hubs - they might not be a high-bling option, but they're proven to be fast-rolling and durable (well, as long as we're not talking about Sylence...) so long as you don't mind dusting off your cone wrenches. Photo: Cooper Quinn

You can swap between HG and Microspline freehubs - there's no XD or XDR option. Freehub engagement feels solid, albeit not the fastest engagement if that's a concern for you.
Range and Resolution
Back to drivetrains… and there’s no avoiding a discussion on gear range and resolution as part of this review; for many drop bar folks the tradeoffs between range, resolution, and number of derailleurs are hotly debated and while there’s no universal answer, finding the right solution for each rider demands compromises to find your optimal setup. This is generally simpler in the mountain bike realm, because we can (within reason) lower our gear resolution demands. Mountain biking is dynamic; the ups, overs, arounds, and undulations mean you’re constantly changing speed and output, and cadence is always fluctuating.

Seen here, SRAM's T-type is currently the widest-range 1x system on the market. When mountain biking, most riders are willing to forgo some gear resolution for range. Photo: Cooper Quinn
This is in contrast with road and gravel, where grade is frequently more consistent over long distances, and settling into the right combination of power and cadence matters. You’ll discover that finding the goldilocks gear is more relevant. This is even more true if you’re riding in groups or pacelines where your speed is dictated by others as much as yourself - being able to match speed with your preferred cadence requires tight gear resolution. For this reason, road bikes have long defaulted to corncob-esque cassettes; gravel (and CX) evolved from this lineage and 2x GRX is on this end of the spectrum, where range is achieved with a front derailleur rather than an enormous cassette. While brands keep adding to the rear gear tally (we're up to 13 now in road/gravel land), range and resolution are inherently at odds with one another.

Shimano's CS-7800 road cassette had an 11-21t spread; as I was a nerd, I ran a corncob like this on my downhill bike because I didn't need gear range. As they say, it was the style at the time, but modern DH 7 speed clusters achieve the same goals.

Shimano offers a variety of range vs resolution options to cover different use cases, however none of the wide range 1x options are available electronically. Presumably, this will become available with the eventual launch of XTR.
But now we have to look at a few charts. Because while the three images above from Shimano help tell the story of how different drivetrains are designed for different riders, let's get into a bit of a detailed look at what this means, practically speaking.

Shimano GRX 11-36t cassette and 41/38 front rings (top) vs SRAM 10-52t on a 42t ring. Range is very similar, however the larger jumps are clearly visible. Please disregard my penchant for 1,000 tabs.

The widest range GRX 1x setup will net you less range than 2x, and less than SRAM's electronic offerings.

SRAM's new(ish) 13 speed Red XPLR gruppo adds a gear and reduces range to gain resolution. It's also very expensive (as is DuraAce), and while it shifts significantly faster than mountain T-type, it retains most of the shift quality.
The biggest takeaway for me from the above charts is that the overall gear range available with the combination of cassette and chainrings I have for review is wider than comparable 1x setups, but only marginally. Depending on your choice of front ring, you're losing a bit on one end or the other, but in practice what I've found is that I'm always slightly disappointed in the lowest gear on this drivetrain.
Some things to keep in mind there - I'm regularly riding stupid mountain bike grades, and often hauling a trailer but I'm also reasonably strong (I know my significant other would struggle on this drivetrain since the low gear on her gravel bike is currently 38-50). For casual riders who aren't in a hurry, there are very limited drawbacks to going with a smaller front 1x chainring to get the lowest gear they'll need. Riders out for a cruise, or newer riders, will also likely not see the benefits in a 2x systems, and enjoy 1x. That's not news, but I find it worthwhile to state here as I've come across a common perception that 2x will be automatically better for folks who are casual and wanting a lower gear, and/or that the additional range will be beneficial.
Shimano doesn't think so, nicknaming the 2x system as "undroppable", and in practice this is what the 2x system is aimed at: folks who want to go fast. Realistically, the Ouroboros was probably a mismatch for this drivetrain; a bike built to blend the pointy end of gravel with a bit of mountain bike; definitely not an Unbound race bike.

I built my custom titanium Landyachtz around UDH, in order to run SRAM's wide-range T-type mountain drivetrain. It's currently running a narrower range 13 speed SRAM XPLR setup, with significant resolution gains and a bit of range loss. Photo: Cooper Quinn

I reviewed Garbaruk's 1x11 50t setup, and the lack of resolution with that much range over 11 speeds was not ideal for me, but otherwise it performed well. Photo: Cooper Quinn
Conclusions
I can't pick the best solution for you - but practically speaking one of the reasons I was very keen to test this new Di2 version of GRX was because it has a front derailleur. I haven't enjoyed one in a couple of decades, and I was keen to test the accompanying gear resolution. My hope was the electronics would make the system function similarly to 1x; remove the need to think, bang gears up and down. Done. It's not that I can't shift a front derailleur. I've done the dance, but I'm just not the type of person deriving deep satisfaction from lifting off the power for that fraction of a second and executing the perfect, seamless simul-shift from both brifters. I just want to pedal.
And while that experience is the reality of GRX in full Synchronized mode, it doesn't tell the full story. It's still a big jump when the front derailleur decides to shift. As much as I tried, I never quite knew when that shift was coming, and there was always a question of "is this the one?" in the back of my mind. Fortunately, Shimano gives you plenty of buttons, and I found a happier place in Semi-Synchronized, where a tap of one button yields an app-determined amount of rear shifting to accompany the front shift. I could decide when to do it, but didn't have to think about it beyond that.

I was hopeful adding a computer to the front derailleur experience would make the experience more seamless, but ultimately it didn't quite pan out. Photo: Deniz Merdano
We're currently spoiled for choices when it comes to drivetrains, and realistically they're all going to function at a level that was unthinkable not that many years ago. When was the last time you went on a ride with a major mechanical? For me, as much as I wanted to love the additional resolution, I don't ride gravel in a way that demands it, or is worth the the tradeoffs in overall weight and complexity. I'll be keeping a close eye out to see how any future XTR derailleur and cassette might figure into this picture, as a widerange, 10-51 12-speed option would go toe-to-toe with a SRAM 'mullet' gravel drivetrain. This will be a very interesting comparison.
If you're a reformed roadie, racer, someone who spends a lot of time riding in groups, or live somewhere with less obnoxiously steep terrain, GRX is a high-performing groupset with a few app quirks (check the First Look) that might feel right at home for you.

If you're the kind of rider who's consistently half-wheeling your friends, finding yourself in a paceline, or you're fussy about cadence, talk to your doctor. 12-speed GRX Di2 might be for you. Photo: Deniz Merdano

Comments
Couch_Surfer
2 weeks, 2 days ago
GRX rocks. Di2 rocks. Shimano is excellent and has the additional benefit of not being an American product.
Fuck SRAM and every American shitbag stocking them.
If it’s not CDN made, buy anything but American.
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Caspar Beronius Christensen
2 weeks, 1 day ago
Non US citizen here as well .. but really not that many Sram products - if any at all - made in USA.. : https://www.sram.com/en/company/about/locations cheers
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Offrhodes42
2 weeks, 1 day ago
Please do not group all of us Americans together with the evil-orange-man and his sidekick Musk. Also, please let me into Canada for the MSA World Cup.
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4Runner1
2 weeks, 1 day ago
We have no choice. US has turned its back on Canada.
Also, Canada is not for sale.
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Sven
2 weeks, 1 day ago
You can ungroup yourselves by all voting accordingly.
Forever neighbours.
Never neighbors.
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Andy Eunson
2 weeks, 1 day ago
Acknowledged. But not all Germans voted for Hitler either. Trump’s no Hitler, yet. But he shows hints of that.
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Bikeryder85
2 weeks, 1 day ago
I don't mean to be the dissenter here, but the "everyone I dislike is Hitler" card is getting old. (Not trying to pick on you Andy, I mean it as a general state of mind and am including all negative political comments on both sides)
I'm not thrilled with Trump either....but neither party put forth a good candidate and Kamala was laughably bad.
The tariffs suck, I agree...but I'm not over here blasting Trudeau on every bike site because I disagree with his policies.
Can we please not let these comments be like PB?
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loren
2 weeks, 1 day ago
Kamala Harris was- and is- an INFINITELY better human being, executive, presidential candidate, and lawmaker than Donald Trump. Case closed.
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alhoff
2 weeks ago
You closed the case?
Shmarv
1 week, 1 day ago
@Bikeryder85: There are more than enough examples from Trump's first administration, his recent actions, and his new BFF's formal affiliations with the neo-nazi AfD to make the connection. Hopefully our southern neighbours figure it out in 3.75 years (if not sooner) that something "different" doesn't make it better.
But I do agree -- this site is for bikes, not politics.
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araz
2 weeks, 1 day ago
I don't get the downvotes for Offrhodes' comment. By all means if you feel like you can't support US companies right now then don't -- there are plenty that I'm not going to be giving my money to. But also understand that there are a lot of us down here that tried our best to keep this administration from coming to power, are deeply upset by what's happening here, and are struggling to figure out what we can do about it.
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Offrhodes42
2 weeks ago
Thank you. The entire Northeast was blue for Kamala. I am in New Hampshire. I do not support the current administrations agenda at all.
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Kenneth Perras
2 weeks, 1 day ago
I agree that we need to make an impact with our dollars to some degree, but it would be unfair to paint all of America with the same brush. Many US companies such as Sram are caught in the crossfire involuntarily. Zooming in a bit, Illinois, Sram's head office state, has consistently been Democratic in political history.
On topic, I just built an 11spd GRX gravel bike for my partner, using new GRX components paired with 10 year old, used XTR Di2 junction boxes, wires and battery, and it fired up like new. Quality stuff.
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Pete Roggeman
2 weeks, 1 day ago
Good perspe.ctive, Ken. Also, cool anecdote about the XTR/GRX frankenbike. Photos and details would be cool to see.
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loren
2 weeks, 1 day ago
Back off there, bro: you're paintin' with a very broad, sadly reductive brush with that comment. I live in California, I loathe Donald Trump and his absolutely idiotic "policies", I own a bike store, and I stock SRAM products.
For you to lazily conflate being an American with being in league with Trump is almost as bad as the terrible positions of Trump himself.
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Pete Roggeman
2 weeks ago
The vast majority of us understand that. We're not going to let this get out of hand so, broad brush to all - if comments sections get too political or too abrasive, we'll start closing in a bit.
To our US friends that aren't happy with the current administration - we hear you and we appreciate your support as well as the fact that you're also feeling lots of things right now. Just understand that this recent threat is a heavy one to us and left us feeling very vulnerable. 'America's hat' jokes are one thing when they're delivered with a wry smile. '51st state' comments repeated more than once start to get a little ridiculous when paired with threat of a tariff war.
You likely can't empathize with what it feels like to have our purported closest ally and trading partner to the South threaten us the way we just were. Everybody is feeling very tender above the 49th right now and a 30-day stay on these tariffs isn't exactly reassuring. We basically just got told that over a century of cooperation is worth nothing. That fucking stings. BUT that ain't the fault of any of you. And we have a lot of friends who work at SRAM - in North Vancouver and elsewhere - as well as lots of other great US-based brands - and we know this isn't their kind of game, either.
Let's all please treat each other within this community respectfully. We can argue about politics elsewhere. Here, we're all riders.
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araz
2 weeks ago
Thanks Pete. Well said. I really don't want this forum to devolve into a political shit show -- I come here to try to escape all that!
I will note, however, that a lot of us south of the border can very much empathize with your feelings of anger and vulnerability. The fear of having traditions, institutions and rights built over the course of decades being thrown in the trash for no good reason is ever present down here now.
That said, I will try to keep my engagement here focused on the good stuff of bikes and trails!
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luckylegs
2 weeks ago
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luckylegs
2 weeks ago
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Blofeld
2 weeks, 1 day ago
When you say we “can swap between HG and Microspline freehubs”, do you mean by purchasing a rear wheel with a different part number? I reviewed the tech doc when you posted the first look article, thinking this rear hub looks exactly the same internally as the Micro Spline SLX-XT-XTR products. I realize your intro couched knowledge of compatibility issues, but I’d like to know what you know!
I sometimes feel like the only person left on the planet still running Shimano MS hubs. Occasionally, usually while picking dozens of spacer pieces out of my freehub splines, I wonder if the design will ever be improved upon. This GRX line gives me hope that at least small parts will be available for a few more seasons.
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Cooper Quinn
2 weeks, 1 day ago
Ah, hm, interesting. I hadn't been deep enough down the rabbit hole here. And, this is probably (definitely) important. If I'm interpreting some buried Shimano spec sheets correctly, it looks like the RX870 wheelset I have isn't Microspline compatible. I'd assumed it was, given the hub image in the piece above was provided by Shimano in the media kit.
Looking at the RX880 wheelset, which is slightly different using different hubs with j-ben spokes, and the spec sheet doesn't actually show any freehub compatibility, but is listed in multiple online sources as having freehubs that are swappable between HG and Microspline.
This is obviously an important point, I've reached out to my contact at Shimano for clarity and will report back when they respond.
Direct links
RX870 specs: https://productinfo.shimano.com/en/product/WH-RX870-TL-R12-700C
RX880 specs: https://productinfo.shimano.com/en/product/WH-RX880-TL-F12-700C
Road/Gravel compatiblity chart: https://productinfo.shimano.com/en/compatibility/C-454
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Blofeld
2 weeks, 1 day ago
I appreciate the follow-up. The links to the RX880 wheelset from the compatibility chart show HG spline L2 and micro spline options. As you mention, the RX870 wheelset appears to be HG only, and looks like the freehub is removed with a 16mm hex wrench, just like the mountain hubs of old. Digging further, the freehub part numbers on the RX880 are distinct from the mountain hub part numbers, but look virtually identical.
The unfortunate part is that the few websites I’m seeing stocking the RX880 freehubs have the MSRP at £129, which is close to used DT 350 territory.
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ReformedRoadie
2 weeks, 1 day ago
You rang?
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Cooper Quinn
2 weeks, 1 day ago
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ultimatist
2 weeks ago
Good stuff, Cooper. I'm riding similarly stupid grades in the SF Bay Area (25%+, scalable only when tacky, etc) on my Diverge, and I love my 2x 11sp GRX. I ride many of my gravel routes from home, with road miles where it wouldn't be fun to deal with high speeds or fast groups on a 1x. There's also the drivetrain efficiency and wear considerations of a 10 speed cog and a bad chainline.
Shimano may be slow and methodical, but they know what they're doing re: efficiency and durability.
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Cooper Quinn
2 weeks ago
I really enjoyed my time down there last year - if you missed it I spend 6 days circumnavigating the whole SF bay. And yeah... you've got some steep hills.
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ultimatist
2 weeks ago
I read and enjoyed your trip report. Even flagged a few Marin trails to visit when I get a chance. LMK if you come back, I can show you some amazing legal and bootleg east bay gravel.
If you're tracking developments on the pointy end of gravel racing, will be interesting to see if running 2x can be made compatible with demand for XC size tires.
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Cooper Quinn
1 week, 6 days ago
No kidding. The combination of larger tires plus short chainstays plus front derailleurs is... a challenging one for engineers. Although, we are seeing gravel chainstays get longer, and increased q-factors.
I'd love to get back down there - I've got a place to stay in Berkeley basically anytime, so it might happen.
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bingobus
1 week, 1 day ago
I'm currently riding an 11-42 with 2xGRX set up, it may be able to take an 11-46 but I haven't tried. You just need to put an XT cage on your rear der. https://www.youtube.com/watch?v=ynpFsE8snww
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Crabbypants
1 week, 6 days ago
Oh geez, I saw this article and thought to myself “awesome, something to distract me from the dumpster fire going on around us”. Then I read the comments ☹️.
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Cooper Quinn
1 week, 6 days ago
Here, have a puppy.
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Crabbypants
1 week, 5 days ago
Oooh a puppy!
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James Heath
1 week, 3 days ago
Not to be That Guy, but... if you're thinking about boycotting SRAM and want a good 1x 13speed alternative... Campagnolo Ekar still exists and its discounted quite heavily in a lot of places at the moment. Everyone seems to forget about it, particularly on the more MTB-focused sites who haven't thought about Campagnolo since Euclid. 3 different interchangeable cassette options (9-36, 9-42 and 10-44, with 10-48 on the new GT group). Mechanical shifting, and *mostly* made in Europe. Worth a think
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Cooper Quinn
1 week, 3 days ago
I'm certainly aware Ekar exists, but I've never actually seen it in person (on a bike, in a shop... nowhere).
You kinda lose me when you need to peen chainpins, but I'd absolutely give it a shot.
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jhtopilko
2 weeks, 1 day ago
Many people in Canada have bought American for years and will continue to. I have GRX 2x11 and agree this a good change but not necessary to me.
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Dave Tolnai
2 weeks, 1 day ago
Danielle Smith's alt account?
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JohnC
2 weeks, 1 day ago
Nice review again. I am a fan of 2X on my gravel for all the reasons you noted; it becomes even more desirable when bikepacking as having closer ratios allows me to find the comfort spot if it is windy or rolling terrain. I just wish someone would design a more functional dropper lever when using a left shifter. I don't have di2 but run GRX 800 series 2X and it is absolutely bullet proof and high functioning; have a ton of km's on it and almost no service needed. I tend to be in the big ring most of the time on smoother gravel such as the Fisherman's / Spur road loop but when doing more technical stuff or steep climbs I stay in the small ring. I don't find the need to dance between the small and big rings that often so having the closer ratio at the back just increases comfort and ability to maintain a consistent pace.
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Caspar Beronius Christensen
2 weeks, 1 day ago
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Sethimus
2 weeks, 1 day ago
uhm can i have the parts numbers for these 10-34/36 cassettes from shimano? pretty sure they are only making road cassettes for hg freedrives, therefore only 11-34/36 available. is it too much to ask for a reviewer to get this right!?
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Cooper Quinn
2 weeks, 1 day ago
If you check the first look, I have a full chart of all the options. And yes, you're correct they're 11-34 and 11-36.
I hope someday you're able to recover from the deep injustice this minor typo has inflicted upon you. My sincerest apologies.
EDIT: It's also correct in the gear range charts here.
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