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.