Micro? Mini? The FSA SL-K Modular Crank

Micro? Mini? The FSA SL-K Modular Crank

I like going fast on bikes. I’ve written plenty about the rush that comes with zooming through some landscape. All those of us who have a taste for it know how effective it is at brightening the worst day. There’s a funny thing about speed, though: though Albert Einstein might not agree on a technical basis, speed is relative. Or perhaps, with due deference to constant—the speed of light, a whopping 186,000 miles per second—we should say the zoom is relative. So while 25 mph is 25 mph no matter where you do it, cruising at 25 on flat asphalt is good fun, but doing that speed on fall-line, winding singletrack would be terrifying. Not so much the zoom.

I mention that, because the more riding of drop bar bikes I do on unpaved surfaces, the more I have come to appreciate just how much lower my average speeds tend to be. Due to unforgivably steep pitches in the dirt roads around my home—very few trails ever get as steep as the steepest fire roads—I’m no longer surprised (or crushed) when I look down and see that I’m climbing at 6 mph.

Which brings me to the SL-K Modular crank from FSA. This is the crank that FSA created to go with the Felt VR, which, amazingly, isn’t a gravel bike, not in the strictest sense. What that bike is, or is not, doesn’t really matter here.

What does matter is this little thing that not everyone buys into, called reality. In this increasingly parallel universe, there are no unicorns and everyone with any taste still agrees that Wilson Philips is not good music. In reality, we look at the kind of speeds we actually ride and we make gearing decisions based on those speeds.

Sure, I see riders struggling up 18-percent grades with a 34×28 low gear. You’ve got to be going 8.9 mph to pedal a 90 rpm cadence with a gear that big. At 4 mph you have a cadence of just 53—less than a pedal stroke per second.

Now, compare that to what happens when you swap out those 50 and 34 chainrings for 46 and 30. Provided you’re running the same size tires, combine this crank with an 11-32 cassette and that low gear of 30×32 will let you go 6.9 mph with a 90 amp cadence. As useful as that is to people who live in hilly places, that’s really not what makes this subcompact crank so great.

As cassette have grown to include concave dinner plates, the jumps between cogs have at times grown to be excessive. And while double-chainring drivetrains can be criticized for duplicate gears, by shrinking the chainrings themselves, you end up with cassettes with a greater number of usable cogs. Forget that almost no one pedals around in a 50×11, let alone a 53×11, in an 11-cog cassette, how many gears do you typically use when in the big ring? Depending on where in the range of the cassette you are, that’s good for two more usable cogs.

And that’s really the argument for a subcompact crank—more usable gears at the speeds you ride.

I know that some riders will worry about running out of gear at the high end. If you can pedal 120 rpm, a 46×11 will carry you to 41 mph.

The SL-K Modular is the lightest of the subcompacts on the market, at 605 grams. It comes in four configurations; there’s a mid-compact 50/36, compact 50/34, and two subcompacts with either 48/32 or 46/30 chainrings. For gravel riding and for a great many road riders, the 46/30 makes the most sense. It comes in three lengths: 170, 172.5 and 175mm.

FSA is fond of the BB386EVO standard that they developed and there’s good reason: the BB386EVO will fit nearly any frame on the market. While there are exceptions, they are few. The spindle is forged aluminum for strength. The crank bolts (for the little ring) are chromoly so that they won’t strip; the big ring is splined and secured by a locking. Crank arm construction is hollow carbon fiber and they are secured with a single self-extracting bolt. Pins in the big chainring aid shifting and while the SRAM eTap front derailleur cage isn’t shaped for chainrings this small, I’ve yet to drop the chain even once.

I get asked about upgrades with the regularity of stock market updates. People invariably want to go faster. We all want to go faster. Other than aero equipment or full suspension, not much will make you go faster. What’s more satisfying most often is having a bike that better suits your needs. That’s bigger tires on rough roads, a better fit … and gears the fit the speed you ride.

Given how many upgrades can run upward of a grand, the SL-K Modular is a deal at $347.99. Honestly, I could see putting this on most of the road bikes I own.

Final thought: the beauty of a sandwich cookie isn’t what’s on the outside, it’s what’s on the inside.

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41 comments

  1. Lyford

    The “subcompact ” cranksets do make a lot of sense. I hope to see more of them. I’ll never be a wattmonster, and the ratios available with a 46/30 and 11-32 would work better for me.

    What’s missing right now are versions with shorter crankarms for smaller folks — who are often riders who would benefit from lower overall gearing.

  2. Nik

    Nice. I wish there was a cheaper version with aluminum crank arms.

    I know dozens of cyclists (all of my wife’s friends, and there are thousands more just like them at Cascade Bicycle Club) who would be better off with this gearing instead of 50/34 or larger, but don’t even know this exists. Some of them are probably riding around with 52/36 or 53/39 cranks and have no idea what that means, or think “bigger chainrings make you go faster”.

    I wonder what percentage of cyclists overall actually benefit from the 50×11 and 50×12 gears. I suspect it’s 5% or less.

    What’s most strange about all this is that except for this FSA crank and a couple of obscure, hard-to-find brands (Rene Herse, Sugino), no one even offers this choice. And FSA makes a dozen seemingly identical models, but only one of them offers the smaller chainrings.

    1. Nik

      Harris – thanks, but I don’t think I can put a square taper BB on my Specialized Diverge.
      If I keep riding the Diverge, in a year or two I’ll get the FSA SL-K crank or something similar.

  3. Quentin

    Given that there was a 52/39/30 tandem version of the SL-K in the past, I hope a tandem version of the 46/30 will be forthcoming eventually. Many of the available tandem cranksets on the market seem to be holdovers from the 3×10 era which is now several years behind us, and as far as I can tell nobody seems offers a tandem crankset, especially subcompact, with 2×11 in mind. On a tandem the 30 is much more important to me than the 50 or 52.

  4. Kimball

    I most definitely concur with this trend. Maybe its just another aspect of the general cycling population moving toward bikes that make more sense for them rather than just wanting what the pros ride.

    I was disappointed that my Niner RLT came with a 46/36 cycle-cross crankset and figured I would soon be replacing it with a 50/34 compact. But to my surprise, once I took my ego out of the equation, I found the 46 big ring plenty fast and instead swapped in a Sugino 46/30 subcompact and combined with an 11-32 cassette its been great. Absolutely no regrets. The Sugino is beautiful but pricey so good to see some slightly more affordable options with modern bottom brackets becoming available (nothing against square taper versions though and White Industries is another subcompact crankset option for those).

  5. Ben

    I’m also a big fan of subcompact gearing options, and put a White Industries VBC on my recent RLT commuter/gravel bike build. I went with a 50/28 to use the 50 as a 1x commuting and have the 28 as a bailout gear for gravel climbing, and have zero regrets.

    1. Ben

      Pretty well, honestly. It took a bit more fine-tuning than normal and I avoid shifting small-to-large under load, but it’s fine. The bigger issue, of course, is chain wrap; in the 28 the highest four cogs in the cassette are unusable, but I wouldn’t use them anyway.

      The other nice thing about the VBC, of course, is that I can swap either or both as much as I want without compatability issues, so if I get tired of the 50 or want a bigger small gear I can tune that how I like.

  6. Jeff

    Padarig, After you mentioned these in a previous post, I tried one on a BMC GF02 that I rode in Levi’s Gran Fondo, this year, vast improvement over the three previous times, a great choice for my 60 year old legs. I was disappointed though that this crankset would not fit either the Trek Domane or Boone I have because of Trek’s proprietary BB90 bottom bracket which requires a 24mm spindle. So I would take minor issue with your comment “While there are exceptions, they are few.” Hope to see more of these from the big guys like Shimano or Campy, they make all the sense in the world. Until then Rotor is rumored to be making one of these that will fit the Trek’s for next year, hope so. Thanks for keeping me informed.


    1. Author
      Padraig

      There really aren’t many bikes on the market that won’t work with BB386EVO, but the Treks are arguably the most prevalent out there, and the sheer ubiquity of Trek dealers goes to your point. Why they made their frames that way, I can’t say. So, yeah, you won’t be able to use the FSA, Praxis or Rotor subcompacts with it.

    2. Mike Jacoubowsky

      There is also the issue of front derailleur mounting; bikes with built-in front derailleur mounts have limited up/down adjustment and often won’t accommodate a low-enough position for the derailleur to match the smaller chainring size.

  7. Stefan

    I have this chainset on a 3T Exploro. Not only does it help on climbing (Campy 11/32 cassette) but at 46 mph, I can still stay on top of the gear. Great bit of kit.

  8. Chris

    I love these but almost none except Rotor and Sugino come in lengths of 165mm or lower. Shorter cranks are the next step in fixing cycling’s stupid fixation on tradition/pro builds that have kept gearing too high, tires too narrow, pressures too high, geometry too aggressive, etc, etc.

  9. TomInAlbany

    C’mon, Padraig. Sing along with me…

    Some day somebody’s gonna make you turn around and say goodbye
    Until then baby are you gonna let them hold you down and make you cry
    Dontcha know. Things’ll change. Things’ll go your way.
    If you ho-o-o-o-o-o-old on for one more day
    Things’ll go your way

    Not only am I that guy… I’m also that guy running 53/39 with 25/12 cassette. And, as you noted, i don’t use all of my gears.
    However, doesn’t it stand that you’re only going to use a few gears most of the time?


    1. Author
      Padraig

      If you’re happy with what you have, roll with it. That said, the number of gears you use can be a reflection of either a rider’s local terrain or their riding style. I use a lot of gears each and every ride because the terrain where I live demands it.

  10. Mike

    I am currently running a 44/34 with an 11-34 cassette and it works really well for me. To get this, I bought an aftermarket crankset and then purchased the chainrings I wanted. I have never been fond of the typically large jump with a front shift so a 10 tooth difference feels less extreme.

    1. Mike

      I should add that I am a relatively large rider on a not-lightweight bike. That 1:1 gear is important because I refuse to walk hills (not that I have never done it!).


    2. Author
      Padraig

      You know, every time I ride a bike with a crank with a 10-tooth difference between rings, I really love it and remember how much I miss that.

    3. Mike

      I find myself not shifting nearly as much when there is a 14-16 tooth difference. It feels like such a big “whump” that my rhythm is thrown off. With my current set-up, I can drop down to the little ring and not feel like I’m a hamster on a wheel.

  11. Louis Sarok

    Subcompact cranks are a great development, but I wish they made a 48/34 or 46/34. It would tighten up the jump between the rings and allow for much more time in the big ring.


    1. Author
      Padraig

      Depending on the crank, you should be able to order a Praxis 48t chainring and simply replace the 50t ring on a standard compact.

    2. Louis Sarok

      I checked with Praxis. They say that the shift ramps would be misaligned so a 48/34 or 46/34 would shifty poorly.


    3. Author
      Padraig

      They work really hard to make sure their shift ramps are well-placed and deserve credit for the effort they put in. That said, it’s not like going against their recommendation will result in something that doesn’t work at all.

    4. TomInAlbany

      So, I’m running old-school Ultegra 9-speed. 53/39. Usually, when I shift chainrings, I simultaneously shift up one on the cassette to minimize the huge change in force required to keep momentum. I wonder if the 10 tooth jump is a solution to my ‘not’ problem.

      Friends have said I’m nuts for moving both at the same time. It’s never been an issue.

  12. Andrew

    Help me out, since I am clueless on these things.

    My gravel bike is Ti Warbird. Originally spec’ed with a PF30- I changed that out for a Wheels MFG PF30 screw together BB. I’m currently running an Ultegra 50/34, with a Tiagra RD and an 11-32. If I wanted to switch to this up front (probably the 48/32- I use my 50-11), could I get a BB that would work with this?

    BB are such a PITA.


    1. Author
      Padraig

      The short answer is yes. The longer answer is that your shop can order the BB you need along with the crank. Given the creak issues that surface sooner or later with all PF30 BBs you’ll want them to do the installation.

  13. David B

    Wow. This is exactly what I’ve been riding for decades on four of my bikes. Except for some reason they left off the big (52t) chainring. Is this progress?


    1. Author
      Padraig

      Half-step triples never made sense to me. And I had one. As to the notion of progress, this crank is lighter, stronger, stiffer and works with indexed shifting systems, unlike a square-taper triple. That said, not all of us define progress the same way.

  14. Kimball

    Somewhat related (the quest for lower gearing on road bikes) is this new 53/34 chain-ring set from Wickwerks. I know at least two buddies who have nice older steel frames that they have not been able to convert to 50/34 compact cranksets because the front derailler mount is brazed on and will not allow the derailler to drop low enough for the big ring. Despite the 19 tooth jump Wickwerks claims excellent front shifting.

    https://wickwerks.com/products/road-bike-ultra-wide-53-34/


    1. Author
      Padraig

      I’ve heard of it, and while I don’t begrudge them producing it, as a couple of commenters have noted, a 10-tooth jump between chainrings is a really lovely shift. The 19-tooth jump would demand an immediate shift of three to four cogs, which is decidedly inelegant. But I suppose not all solutions are ideal.

  15. hiddenwheel

    I’m all for sub-compacts. They extend the range at the bottom end and don’t overgear 99 percent of riders. But they do tend to put you in cross-over gears when spinning along (e.g., a 30×12 at 80 rpm will put you at 14-15 mph). The little ring sweet spot for road bikes is 36-42. Wouldn’t it be great if the big players (SRAM, Shimano) made cassettes that started at 12 and 13 (and went to 32 or 34)?

  16. Jim Smith

    I ordered one of the FSAs about a year ago. It’s supposed to arrive soon. I’ll put it on my gravel bike I guess. I’m on vacation now with my S&S coupled Moots. Since the FSA didn’t arrive, I put a White with 46/30 on the Moots for my trip to Europe in the summer. It worked pretty well there (ramps aren’t quite as good as the Chrous crank it replaced) and was great going up the wall on the west Maui loop the other day. 300 metres with the Garmin showing 19% whenever I could get enough breath to look down means that 30 front, 32 rear is much appreciated by this 67 year old. I can even go down to a 44/28 as I get even older.

    I wondered a bit about the 46-11 as my high gear. It took about three seconds to realize that it was a bigger gear than the 52-13 high gear on the Marinoni that was the first good bike I ever owned when I was half the age I was when I installed the White. As others have said, I’m just waiting to see when Shimano and Campy get with this program. Maybe not since one by seems like the coming thing.


    1. Author
      Padraig

      It doesn’t really make sense to try, at least, not to me. Upon purchasing the crank you’d immediately have to remove the two chainrings and then mount a 1x-specific ring. It would be simpler (and less expensive) to buy a 1x crank with the correct ring on it. Aside from the tooth profile of 1x chainrings to consider, there are other issues such as chainline to consider.

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