Shimano SLX Drivetrain Review

XTR is Shimano's top of the line and XT follows closely behind and there was a time when the performance drop off below the XT level was severe, but it appears that's changing. Shimano has trickled down many of the features of the top two groups to the lower cost SLX group and much of the quality and precision of the top two groups are present here, with one modest upgrade. We’ll get into that below but after spending considerable time on a Shimano XT drivetrain and six months on SLX, I've been left impressed.

I’ve spent tallied over 700km of off-road use on SLX in everything from winter slop to dry, blown-out moon dust. I've had one derailleur mishap thanks to a root, bending the outer plate of the cage by the lower jockey-wheel. Thanks to the metal construction of the derailleur, it was quickly fixed and hasn't been a problem since. Line choice and trail obstacles are hardly the derailleur's fault.

Shimano SLX (M7100) Drivetrain

Before the 12-speed SLX group arrived I’d been happily riding the SRAM equivalent; GX Eagle. SRAM drivetrains once again found a home on my bikes when the 12-speed option was released and like many, I've been quite happy with the performance. Without beating around the bush, the 12-speed Shimano SLX drivetrain has features that I prefer over GX. The best for you will depend on how you weigh the importance of performance, budget, and weight.

Features:

• Hyperglide+
• 10–51T Cassette w/ alloy easiest ring
  • 510% range w/ 10-12-14-16-18-21-24-28-33-39-45-51
  • 10–45T Cassette also available
• Shadow RD+ rear derailleur
• Two-way release shifter
• Hollowtech II cranks w/ single ring setup
• 30, 32 (tested), and 34T size options
  • Steel teeth mated to an alloy 'spider'
• Three crank lengths options: 165mm (tested), 170mm and 175mm
• Weight: 1,589g (inc. gear cable, 73mm threaded BB)
• MSRP: 409.93 USD

Getting Set Up

12-speed SLX set-up and installation doesn't differ greatly from previous Shimano drivetrains and when stacked against 12-speed XT, it’s essentially identical. There are some subtle differences between the two tiers but they’re minimal. Looking at the cranks, there's a slight visual difference to the finish and the SLX weighs a few grams more than an equivalent XT setup (with similar crank length and chainring size). But we’re talking about a claimed ~10 grams. The SLX cranks tested were in the 165mm length and with a 32T chainring they tipped the scales at 625g. Their short 165mm length is worth noting too; I’ve previously had a difficult time finding this length with a 73mm BB, especially at lower price points, but it's now available in both XT and SLX.

I’ve always enjoyed the simplicity of the Shimano crank setup and it remains the same with the latest SLX. The cranks easily bolt together from the non-drive side and with the now common double pinch bolt securing everything in place, I’ve had no issues. There's no need for self-extraction or crank-pullers with everything sliding together easily with a few bolts. As with the XT drivetrain, the new chainring features coated steel teeth mated to an alloy spider that’s mounted directly to the cranks.

At the rear of the bike, the toughest thing was waiting for a Microspline driver for the Newmen A.30 wheels. More brands have Microspline drivers available now and even smaller outfits like White Industries have one for their XMR+ hub. The SLX cassette has more pieces than the SRAM GX, which is a pinned one-piece design, and that made getting it on trickier. Shimano includes a plastic carrier that simplifies things when mounting but it’s still relatively fiddly and less than ideal. Whenever removing the cassette from the driver I’ve attempted to slide it back onto the plastic carrier but it’s proven quite cumbersome.

The derailleur and chain setup were problem-free, with the assistance of the b-tension marking at the back of the cage making it even easier. I used my old chain length to set the SLX chain but for those building a new full suspension bike, Shimano recommends a full wrap of the drivetrain plus 5–6 links before the quick-link. Admittedly, I initially rode the bike with the b-tension set by feel before stumbling upon the marker on the derailleur. My initial setup was off and while it still performed great, I noticed a slight improvement once set using the b-tension reference marker.

Grinding Gears (At Least Trying To)

Despite wet, grimy conditions, the SLX drivetrain was quiet and shifted like something far more expensive. Compared to the GX drivetrain I’d come off, the shifts felt tighter and more precise. It remains that way to this day. Shifting down the cassette into harder gears, I found little difference between the two drivetrains but when moving to easier gears the more precise shifts of the SLX were obvious. It often felt as though the worse I shifted – under load thanks to poor timing or having to bail from a bad gear selection – the better it performed. I’ve been woefully unsuccessful in getting the SLX gears to grind or skip.

I’ve discovered that I prefer the gear ratios in the Shimano cassette. Shimano's four largest cogs are 33t, 39, 45 and 51, while SRAM's are 32t, 36, 42 and 50 (or 52 for new cassettes). It doesn’t sound like much, but in the four lowest gears I find things more comfortable with the Shimano gearing thanks to the more gradual steps. I can happily sit in each gear where I often find myself between gears with SRAM. Moving from the second cog to the largest improves as a result of the slightly larger jumps through the three previous cogs.

The SLX cassette jumps 6 teeth from the 45 to the 51 where the SRAM jumps 8 moving from 42 to 50 (and now 10 with SRAM's new 10–52T). The larger jump has always felt like too much to me, causing a more pronounced change in cadence and momentum. This is exaggerated by the tighter jumps leading up to it. Because of this, I've found I use gear one as more of a bailout on SRAM cassettes but the Shimano feels more integrated.

SLX feels so similar to XT, I honestly couldn’t tell the difference. Or rather I couldn't once I switched out the SLX shifter for an XT. There’s no Multi-Release with the SLX and that for me was a bummer. Anyone who's spent time on Shimano in recent years should be familiar with the ability to shift two gears in one deep press of the release lever. When Shimano first presented the Multi-Release technology I remember scoffing that it was just a marketing ploy but in practice, I’ve grown very fond of it. So much that it's the feature I miss most when riding a SRAM drivetrain.

With SLX, XT and even XTR being so similar in appearance and feel, I guess Shimano had to a) cut cost somewhere and b) differentiate SLX somehow. I was bummed but that’s not where it ended. While the shifts on the SLX drivetrain feel tight and accurate through the pedals, the SLX lever lacks the feel and immediacy of XT. Shimano hasn't included Instant Release in the 12-speed SLX shifter and the result of the two-stage shift is a sloppy, less tactile feel. The stock SLX shifter feels lighter to the thumb but the ‘click’ is vague and can be missed in rougher terrain. With the XT shifter, gear changes were faster and tighter again, making the difference between the higher-priced XT disappear on the trail. This combined with the ability to shift to two higher gears at once makes the upgrade worth the additional ~30 CAD / ~21 USD.

Another subtle difference between the SLX and XT drivetrains is visible in the cassette. SLX includes one alloy cog – the largest cog – where XT includes two. The SLX weighs about 60 grams more but one less alloy cog should increase durability, with only the lowest gear using the faster-wearing metal. And while the closer ratios make the largest cog feel more integrated, I only find myself using it on hell climbs, or when I’m shattered. I could probably get away with the 10–45T cassette or as Andrew Major has suggested before, fewer gears. But of the Shimano 12-speed cassettes, there’s no question which one I'd run. Even if I could be convinced to fork out the extra money for XT I would still opt for the SLX cassette because only one cog is made of less durable aluminum.

Compared to the GX drivetrain the SLX replaced, the cassette carries the largest weight difference; 529g vs 450g for the GX. But as mentioned earlier, I also found the ride quality to differ significantly between the two. The SLX shifts are more precise than GX thanks to their new Hyperglide+ technology, which sees the inclusion of shift ramps that impact both up and downshifts. This also feels like something that will work better with eMTB’s thanks to the cassette’s ability to better manage shifts under load. On the topic of eMTB’s, the Shimano Microspline driver and cassette are optimized to work with the torque of an eMTB. (an earlier version of this article suggested that SRAM's XD driver standard and Eagle cassettes are not recommended for eMTB but this was not accurate - although SRAM recommends using their single shift shifter for eMTB).

I’ve ridden the SLX drivetrain with the supplied CN-M7100 chain for the duration of the review and it’s just getting to the 1/16th mark. I’ll be replacing this as soon as I can and will try a higher level option – XT or possibly even XTR – to see if that affects anything. The SLX chain retains the lengthened inner plates that make Hyperglide+ possible but Shimano claims the coatings aren’t as durable. If I get drastically more than 700km out of the next chain, I’ll be sure to write something about it.

Finally, the cranks and bottom bracket have been bombproof throughout testing. Until preparing for this review, I hadn't touched them at all and haven’t heard or felt anything to be concerned about. The cranks are visibly beaten, which I expect for this part of my bikes –a large part of why I opt for metal cranks. Aside from looking used, they’ve gone unnoticed, which is perfect and thanks to the steel teeth on the chainring, I don’t expect a need to change that anytime soon. Setup is dead simple, removal for maintenance equally basic, and they haven’t needed any attention after hundreds of kilometres of abuse. Win, win.

Can It Be Improved?

It’s hard to argue there’s anything wrong with SLX when considering value. That is with the caveat that I believe upgrading to the XT shifter is a must for any discerning or core rider. Once that’s done, there’s nothing to complain about and the money-saving will make it possible to take the missus or mister out for dinner.

Verdict

Testing the SLX drivetrain back to back with GX was an interesting process. Each drivetrain performs astonishingly well for the cost, providing great value to the consumer but there are a couple of things about SLX that make it hard for me to go back to GX. The shifting performance of SLX makes it feel like a much more expensive drivetrain and I find the gearing more comfortable. With the upgrade to an XT shifter, feel at the lever is better and I now have the ability to shift to two higher gears in one hit, something I find myself doing 95% of the time. Even with the shifter upgrade, the SLX drivetrain offers greater value. But if the weight were more important, then GX is the way to go, albeit only for 109 grams – 112 grams with the XT shifter upgrade.

Shimano 12-speed SLX provides ridiculously good shifting and performance for the money, making it hard to argue with. Toss an extra few coins in and you get all of the tech from the higher-priced Shimano siblings in a more wallet-friendly package. I don’t see any need to dig deeper into my pockets with the performance SLX provides and can only imagine it being a status move, a case of weight weenie-ism, or senseless spending to do so; it really is that good.

More information on Shimano 12-Speed SLX can be found on their website.