02 Dec 2019

Just how good is Shimano's latest 12-speed drivetrain? To find out, we've put the Shimano SLX M7100 groupset up against SRAM GX Eagle to see which comes out on top

Wil reviews the new Shimano SLX M7100 groupset against SRAM GX Eagle

Earlier this year Shimano rolled out not one, but two brand new 12-speed groupsets – Deore XT M8100, and SLX M7100. This double-release was something of a surprise move from the Japanese brand, which has traditionally only released one new mountain bike groupset each year. Then again, it’s no secret that Shimano has been dragging its heels when it comes to dedicated 1x drivetrains. While SRAM can currently boast having no fewer than eight dedicated 1×12 groupsets (two of those being wireless electronic drivetrains), Shimano has just three. On top of that, Shimano suffered hefty delays in getting XTR M9100 to market last year, which gave up further ground to its US rival in the ongoing battle for drivetrain supremacy.

Of course the Japanese brand isn’t one to rush things. And as the world’s largest component manufacturer, and the owner of some of the world’s largest machines for producing those components, Shimano tends to take its time before hitting the ‘on’ button. Having finally given the green light to the new Deore XT M8100 and SLX M7100 groupsets back in June of this year though, Shimano is ready to return fire in a big way.

Shimano rolled out its first 12-speed groupset last year – XTR M9100. Supply and manufacturing issues hampered its introduction though.
shimano deore xt m8100 derailleur mech
For 2019, Shimano has two new 12-speed drivetrains, including the much-anticipated Deore XT M8100 groupset.
shimano slx m7100 1x12 drivetrain groupset disc brakes 4-piston
The SLX M7100 groupset wasn’t hyped up in the media as much, but we think it’s perhaps the most exciting groupset on the market right now.

Less Bling, Less Bucks

In the world of drivetrain hierarchy, Shimano XTR and SRAM XX1 are the self-proclaimed big dogs at the top of the ladder, with XT and X01 sitting one rung below. Occupying the third, and more sensibly-priced position is Shimano’s SLX M7100 groupset, and SRAM’s GX Eagle groupset.

Both SLX and GX Eagle are heavily modelled on their more expensive counterparts. A more utilitarian approach to materials however, sees both groupsets coming in at around 1/3rd of the price of XTR/XX1 while possessing much of the same functionality. For riders less concerned about grams and bling, SLX and GX Eagle allow you to put more of your dollars into your bike’s suspension, wheels and tyres, or perhaps just directly back into your wallet.

For the past couple of months, I’ve been testing a Shimano SLX M7100 groupset that’s comprised of a 1×12 drivetrain and 4-piston disc brakes. If you’d like to take a closer look at all the options, confirmed weights and Australian pricing, be sure to check out our the detailed first look story here.

In this review, I’ll be focussing on the SLX 1×12 drivetrain. More importantly though, we’re going to look at how it stacks up against its main rival; SRAM’s popular GX Eagle.

shimano slx m7100 1x12 drivetrain
I’ve been testing a 1×12 SLX M7100 drivetrain and the 4-piston Enduro brakes.
sram gx eagle 1x12 drivetrain
I’ve ridden a load of GX Eagle groupsets since its introduction back in 2017. It’s popular for a reason.

Cost

First thing’s first. Cash money. This one’s pretty easy to quantify, because Shimano SLX has SRAM GX Eagle beaten, hand’s down. While a GX Eagle 1×12 drivetrain costs $850, a Shimano SLX M7100 1×12 drivetrain is listed at $593. That’s about 30% cheaper.

…which is over double the price of a Shimano SLX M7100 cassette…

While all of the individual SLX components cost less than their GX Eagle counterparts, the biggest price difference can be found in the cassette. A SRAM XG-1275 cassette has a list price of $329, which is over double the price of a Shimano SLX M7100 cassette. The construction is quite different between the two, but regardless, that’s a hefty difference for a consumable item.

Bear in mind that these drivetrain prices don’t include the bottom bracket. Since there’s a kerbillion standards these days (SRAM makes over 20 different BBs for their DUB cranks!), you’ll have to buy one separately. That’ll set you back $49 for a Shimano PF92 BB, and $69 for SRAM’s DUB PF92 BB.

Winner: Shimano SLX M7100

shimano slx m7100 crankset 1x12
Shimano’s SLX groupset is priced incredibly well – the drivetrain is 30% cheaper than GX Eagle.
sram gx eagle crankset
Both GX Eagle and SLX come in at around 1/3rd of the cost of SRAM and Shimano’s flagship groupsets (that’s XX1 and XTR).

Weight

As with price, grams are just as easy to quantify, and here SRAM wins one back on Shimano. Confirmed weight on our Scales Of Doom for a GX Eagle 1×12 drivetrain is 1766g, while SLX M7100 comes in at 1882g. Again, this weight is without the bottom bracket.

There isn’t a big weight difference in any single component. However, the SRAM XG-1275 ‘Full Pin’ cassette does come in 79g lighter than the SLX M7100 cassette (448g vs 527g). You can see where the extra grams come from in the SLX cassette, which simply has more meat to it.

For the weight weenies out there, it’s also worth pointing out that both the cassette and crankset are your best point of call for weight-saving upgrades.

Is the weight difference a big deal? You’d have to be a pretty sensitive rider to notice that 79g, but it’s still worth noting that more weight at the rear wheel can affect performance on a full suspension bike. In theory, a lighter cassette will help improve suspension reactivity by reducing unsprung mass.

For the weight weenies out there, it’s also worth pointing out that both the cassette and crankset are your best point of call for weight-saving upgrades. Going to an XX1 crankset (420g) and cassette (357g) would drop 300g over the GX equivalents, and a Shimano XTR crankset (548g) and cassette (369g) would lob off 244g off the SLX equivalents.

Winner: SRAM GX Eagle

sram gx eagle cassette 1x12
SRAM uses a ‘Full Pin’ construction for the GX Eagle cassette. It doesn’t shift as crisply as an X01 or XX1 cassette, but it is a helluva lot cheaper.
shimano slx m7100 cassette 10-51t 12-speed
The SLX cassette is nearly 200g heavier than an XTR cassette.

Installation

I found setting up the Shimano SLX M7100 1×12 drivetrain to be a relatively straightforward affair. Fitting the Hollowtech II cranks is exactly the same as previous generation XT and SLX cranks, with a near-foolproof bearing preload system. Tighten the main plastic crank bolt until the wee safety pin drops down into its guide hole in the axle, then torque the two bolts to lock down the non-drive crank arm down.

One detail I absolutely love is the guideline that Shimano has etched into the back of the jockey wheel cage, which is there to help you align the mech with the 51T sprocket to set the B-tension.

It’s a slightly more convoluted process for getting the right chain length. This is the PDF manual you’ll want on hand to help with setting up a Shimano 1×12 drivetrain, which includes how to determine the correct chain length and adjust the rear mech. Cable tension and limit screws are tuned as normal, though it’s worth flicking the Shadow Plus friction clutch off while you’re adjusting gears in the workstand. One detail I absolutely love is the guideline that Shimano has etched into the back of the jockey wheel cage, which is there to help you align the mech with the 51T sprocket to set the B-tension.

shimano slx m7100 crankset
Shimano’s Hollowtech II system is still the benchmark for ease of installation and removal.
shimano slx m7100 derailleur
There’s a faint etched line on the top of the jockey wheel cage, which is there to help you align it to the 51T sprocket. Love that feature!

I witnessed exploding Eagle mechs on two separate bike launches last year

Tolerances required for modern 12-speed components are tight, so clean cables and a straight mech hanger are a must whether you’re running SRAM or Shimano. That said, I have found SRAM Eagle derailleurs to be particularly sensitive to improper chain length and B-tension setup. I witnessed exploding Eagle mechs on two separate bike launches last year – the first one was due to a too-long chain, and the second was from incorrect B-tension setup. In both cases, the chain lodged itself between the lower jockey wheel and the cage, before it ripped open the whole cage.

A few months later in the latter part of 2018, SRAM quietly introduced a new lower jockey wheel design, which has a wider shelf to prevent the chain from bouncing off and getting jammed in the first place, even if things haven’t been setup properly. I’ve not witnessed any issues since.

sram gx eagle derailleur
SRAM changed the design of the lower jockey wheel last year, and it now features a wider ‘shelf’ to prevent the chain from jamming between the cage and the pulley.

For anyone out there who’s experiencing shifting issues with an Eagle drivetrain though, I’d highly recommend checking out SRAM’s instructional video, even if you bought a complete bike with the drivetrain already fitted. Utilising the red plastic B-tension tool is absolutely critical to position the upper jockey wheel the correct distance from the 50T cassette sprocket. And if you have a full suspension bike, make sure you check this measurement while sitting on the bike to sag the suspension.

It isn’t impossible, but it certainly requires a whole lot more muscle than Shimano’s Hollowtech II system.

Abide by those rules, and GX Eagle is also pretty easy to setup. The new DUB bottom bracket system may have annoyed standards-phobes when it debuted last year, but I’ve been thoroughly impressed with the fit and finish of the new bearing and seal system. The preload collar makes it easy to remove axial play, and so far, long term durability has been positive.

My only complaint is that the main crank bolt requires an enormous amount of force (54 whole Newton meters!) to tighten it down. To remove the cranks, I use a heat gun, a very long torque wrench, and a friend to stand on the opposite pedal. It isn’t impossible, but it certainly requires a whole lot more muscle than Shimano’s Hollowtech II system.

sram gx eagle derailleur b-tension tool setup
Setting B-tension on an Eagle mech is absolutely crucial to proper shift performance. Make sure you use this red tool to do it properly.
sram gx eagle crankset dub bottom bracket t47 threaded bsa
The DUB bottom brackets have performed well. But installing and removing the crank requires more brute force compared to a Shimano crank.

In regards to installation and setup, there are a couple more details to note.

Firstly, Shimano does offer greater gearing flexibility, with SLX being available with both 10-51T and 10-45T cassette options. I’ve been testing the bigger option, but the smaller spread will appeal to racer types who prefer a tighter gear range. And even if it is a shrinking market, SLX is also available in a 2×12 setup for those who want maximum range, and own a bike that will fit a front mech. That said, SRAM does have more crank and BB solutions, including fatbike specific options.

There’s still a long list of brands who aren’t signed up yet though, and that does put up a barrier for some riders who are looking to change over to a Shimano 12-speed groupset.

Secondly, Micro Spline. Yes, in order to fit one of Shimano’s new 12-speed cassettes, one must have a specific Micro Spline freehub. I actually quite like the design’s chunky splines, which allows a lighter alloy freehub body to be used, with less chance of the gouging that Shimano’s HG freehub body design was prone to.

dt swiss micro spline freehub body
Annoying license restrictions with the Micro Spline freehub design have no doubt slowed uptake of Shimano’s 1×12 drivetrains.
shimano slx m7100 12-speed 1x cassette 10-51t
The Micro Spline design is necessary in order to accommodate the 10T cog that Shimano is using on its 12-speed cassettes.

However, the Japanese brand has been very tight with licensing its special freehub body design, and at the time of writing, there’s still only a handful of names outside of Shimano who have hubs available with a Micro Spline fitting. These include DT Swiss, Mavic, Industry Nine, Newmen, Fulcrum, Giant, Syncros, Roval and Bontrager. Thankfully, this will be changing for 2020. Shimano announced recently that it would be relaxing the licensing process, and we understand that both Hope Technology and Hunt Bike Wheels will be offering up Micro Spline freehub bodies from January 1st onwards.

There’s still a long list of brands who aren’t signed up yet though, and that does put up a barrier for some riders who are looking to change over to a Shimano 12-speed groupset. SRAM’s competing XD freehub design is much more prevalent, making it an easier option from a compatibility perspective. For this reason, it’s a tie when it comes to installing these two drivetrains.

Winner: Tie

shimano slx m7100 10-51t cassette 12-speed
I’ve been testing the 10-51T cassette, though you can also get a 10-45T option too.

Ergonomics

While both SLX and GX Eagle do in fact, shift gears, they are less feature-rich compared to their higher-end offspring.

For example, the SLX shifter skips the rubber pads on the levers that you’ll find on XT and XTR. They still get the nice traction grooves though, which improves tactility and grip, with or without gloves. The physical action of the paddles is lighter too, most notably in the up-shift lever. I actually prefer this light action compared to the punchier feel from the XT and XTR shift levers, which do provide a very positive and audible ‘click’, but require more thumb force to engage.

shimano slx m7100 shifter
The traction grooves on the SLX shifter paddles give it great tactility.

One key omission from the SLX shifter is the lack of a double up-shift, something that I’m very fond of on Shimano’s XT and XTR shifters. It’s not a big deal, but I do miss not being able to quickly up-shift two gears in one throw. I plan to upgrade to an XT I-SPEC EV shifter soon, which will also lose one more clamp from the cockpit. The new I-SPEC EV system works really well, allowing for 14mm of lateral and 20° of rotational adjustment for the shifter body while mounted to a Shimano brake lever. This provides greater adjustment than SRAM’s longstanding MatchMaker system, and that gives you more flexibility for getting the levers setup in the ideal position.

In contrast, the up-shift paddle is a pleasure to use, with a nice short throw and a more positive click compared to the SLX shifter.

Though SRAM’s GX Eagle trigger shifter also performs a similar job to X01 and XX1, the main shift paddle misses out on any angular adjustment. It’s still a big and easy to hit lever, but the shape is pointier and less comfortable on the thumb. In contrast, the up-shift paddle is a pleasure to use, with a nice short throw and a more positive click compared to the SLX shifter.

Ultimately, both shifters do what they’re meant to, and it’s only personal preference that will dictate a rider’s preference between SLX and GX Eagle, and for that reason these two are tied when it comes to ergonomics.

Winner: Tie

sram gx eagle shifter
The main paddle on the GX Eagle shifter is a little pointy, and you can’t adjust the angle like you can with X01 and XX1.
sram gx eagle shifter
Love the short throw and punchy action of the up-shift lever.

Shift Performance

On the trail, I have to say that the SLX drivetrain’s shift quality is nothing short of outstanding. In fact, there is really very little that separates the shift quality here compared to the thrice-as-expensive XTR groupset.

The shift performance it delivers under load is rather incredible.

Much of this has to do with the Hyperglide+ cassette. Hyperglide+ is Shimano’s name for the collection of shift ramps and pins that have been laid out in a specific sequence to reduce lag time as the chain shifts up and down the cassette. The technology first debuted on 12-speed XTR, but has now trickled down to 12-speed XT and SLX.

The shift performance it delivers under load is rather incredible. You can be out of the saddle, mashing on the pedals, and the chain will shift with little hesitation in whichever direction you want it to. This goes against everything I was taught when I got my first 21-speed mountain bike, and I’ll admit that it’s taken time with new Shimano drivetrains to trust that I can shift accurately under power, without fear of the chain exploding on me.

shimano slx m7100 10-51t cassette 12-speed
The new Hyperglide+ cassette provides incredible shift performance while under load.

In comparison, the GX Eagle drivetrain shifts just fine, though it isn’t quite as fast or as slick as Shimano’s latest 12-speed cassettes. It’s also a bit clunkier than an X01 or XX1 cassette, both of which are almost entirely machined from a single block of steel. The GX Eagle XG-1275 cassette uses individual steel sprockets that are pinned together instead, which in theory, allows for more flex under load. The result is less crisp shifting, particularly when you’re pushing hard. Yeah it’ll still shift when you’re hammering at the pedals, it just won’t do it as quickly or as reliably as the SLX drivetrain.

Cadence-sensitive riders may say otherwise, but the difference is small enough that realistically, I can get used to either one within a ride.

sram gx eagle 1x12 drivetrain
The GX Eagle drivetrain also shifts well, just not quite as smoothly as SLX.

Shimano also has SRAM beaten on outright range with its 10-51T cassette ratio, though it’s only by a small amount (510% vs 500%). There’s also a slightly different approach to the gear ratios between the two cassettes;

  • SLX: 10-12-14-16-18-21-24-28-33-39-45-51T
  • GX: 10-12-14-16-18-21-24-28-32-36-42-50T

SRAM keeps the ratios tighter for longer, before going to a big 8T jump on the last shift to the 50T cog. In comparison, Shimano’s cassette opens up a little sooner in the middle of the cassette, but never makes a jump higher than 6T. Is the difference noticeable between the two? In my experience, only on the last shift, which does feel bigger on a SRAM Eagle cassette. Cadence-sensitive riders may say otherwise, but the difference is small enough that realistically, I can get used to either one within a ride.

Overall, the SLX drivetrain is the smoother and quieter performer of the two. You’ll still get some crackly shift noises when the cassette is covered in dust (as has been the case on our local trails of late), but it’s not as noisy as GX Eagle. This is no doubt also due to the extended and chamfered profile of the inner chain links and the Dynamic Chain Engagement+ tooth profile used on the chainring, which allows for everything to mesh together smoothly and cleanly.

Winner: Shimano SLX M7100

shimano slx m7100 crankset 1x12 chain
The SLX chain uses extended and chamfered inner plates that mesh cleanly with the narrow-wide chainring profile.

Durability

While I’ve only had the SLX drivetrain for a couple of months, I’ve still managed to put several hundred kms on it so far. And aside from a few tweaks to cable tension as things have settled in, I haven’t had to touch any of the other adjustments – it’s been totally rock solid during that time.

Just like GX Eagle, the SLX cassette uses ten steel sprockets with the 51T being made from alloy. This of course makes it heavier than an XT or XTR cassette (the latter of which has three sprockets made from alloy, and five sprockets made from titanium), but it also means the teeth will be tougher and more wear resistant. I also like that Shimano hasn’t coated the steel sprockets, which means it looks fresher for longer.

The SLX chainring also uses steel teeth, which affords further long-term durability. In comparison, the GX Eagle cranks come stock with an alloy chainring. That said, the X-Sync 2 chainring design has proven to wear very well over time, and is a huge improvement on the original narrow-wide profile of the first generation X-Sync chainrings.

shimano slx m7100 crankset 1x12
The outer ring on the SLX chainring is made from steel, giving greater wear life to the teeth.

I’ve not encountered any issues with the SLX shifter or rear derailleur, though one thing I have (or more accurately haven’t) noticed is the slimmer profile of Shimano’s Shadow Plus rear derailleurs. When positioned in the 10T cog, the GX Eagle mech sticks out a full 10mm further away from the frame, putting it more readily in harms way.

It makes removing and installing the wheel a breeze

While we’re on the rear mech, I gotta say I still prefer SRAM’s Cage Lock button for locking out the jockey wheel cage. It makes removing and installing the wheel a breeze, and far easier than the SLX mech even with the Shadow Plus clutch turned off. That said, Shimano does allow the user to adjust the clutch tension internally, which means you can increase the tension it places on the chain for a tighter and more secure fit, even as things wear over time.

Winner: Shimano SLX M7100

sram gx eagle 1x12 derailleur
SRAM’s Cage Lock system makes it wonderfully easy to remove the rear wheel.
shimano slx m7100 derailleur clutch
You can adjust the clutch tension internally, and you can also flick the clutch off too.
sram gx eagle 1x12 derailleur
SRAM’s 1x mechs tend to stick quite far out from the frame.
shimano m7100 1x12 derailleur
You get an extra 10mm of clearance with Shimano’s Shadow Plus derailleurs, keeping them further out of harms way.

Shimano SLX M7100 vs SRAM GX Eagle – Overall

If you’ve been tallying up the results so far, then you’ll already know that Shimano has taken the victory here.

The Japanese brand may have taken its sweet time to deliver its first three proper 1x drivetrains, but it’s put a huge amount of consideration into creating a versatile, durable, and smooth-shifting system. With SLX M7100, the result is a tough 1×12 drivetrain that offers smooth, fast and accurate shifting at a rather incredible price point.

Providing you can fit a Micro Spline freehub to your existing wheels, this is the groupset is the practical choice for value-conscious riders who want XTR-like shifting performance, without the XTR-like price tag.

shimano slx m7100 10-51t cassette 12-speed
Shimano SLX M7100 wins this 1×12 drivetrain battle against SRAM GX Eagle.

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