Updated to include Force AXS Wide and Campagnolo EKAR 1x13 drivetrains.
Okay. Deep breath. Things are about to get technical.
After tires and wheel sizes, gravel bike drivetrain options are the biggest topic of our discussions with customers. And with good reason- there are a lot of technical aspects to consider. Add in personal preference, ergonomics, and past experiences and there is no one answer that will suit everyone. So at the risk of inducing analysis paralysis, let's dive in.
Let's start with a few terms (as they'll be used for this discussion) so that we're on the same page:
- Ratio: In short, it's the comparison between front chainring and a given rear cog. A 42t chainring and 21t cog will reduce to a 2:1 gearing ratio. It's not used much because the numbers rarely work out that cleanly, but as starting point, we tend to target somewhere in the neighborhood of 1:1 for a low gear for a gravel bike (42:42, 34:34, etc.). If you go much lower, traction and balance can become issues- as anyone who's struggled to stay upright at a walking pace will attest.
- Range: The difference between highest gear ratio and lowest gear ratio (high divided by low) expressed in percent. (I know- range should be [high-low]/low. But the bike industry collectively decided to apply its own definition.) For single-ring drivetrains it's straightforward: a 10-42 cassette gets you 42/10 or 4.2 or 420%. With a double, you'll need the highest and lowest ratios (as well as a pencil), but the idea holds: it's a single number that can be used to communicate breadth of ratios available to a rider.
For reference, a typical road drivetrain (Shimano Ultegra 50/34 x 11-32) has a 428% range, a SRAM Eagle mountain bike cassette 500%.
- Step: The difference, in percentage, between one cog and the next in a cassette. When shifting from cog A to cog B the step would be (B-A)/A. For example, a 15-to-17t shift would be a 13% step.
Why not just count teeth? Well, an 11-to-13 two-tooth step (18%) will have a much bigger impact on cadence and feel much bigger than a 25-to-27 two-tooth step (8%).
- Cadence: How fast the rider is spinning the pedals, in RPM. Generally, most riders are comfortable between 80 and 90RPM and can spin up towards 105 or more- but it gets awfully bouncy. 60-70RPM is a pretty slow cadence, seen standing on steeper grades.
How Gravel Bike Gearing Affects Speed
How do these things come together? Let's look at a few options, two familiar (Shimano Ultegra R6700 2x10 & R8020 2x11) and two newer gravel-oriented (SRAM AXS 1x12 and Shimano GRX 810 2x11), all with 700x40 tires.
A Shimano R8000 Ultegra group is a fantastically refined set of components. Designed for road riding and racing it has most of the performance of the range-topping Dura Ace group at a fraction of the price. The widest-range crankset is a 50/34, and with a the widest-range 11-32t Ultegra cassette you can approach a 1:1 low gear. Swap in a clutched Ultegra RX rear derailleur and chain retention is excellent too.
Shimano Ultegra R8000: Speed by Gearing Ratio and Pedal Cadence
Looking at the table above, you can see that our traditional Ultegra double can comfortably cover speeds from 5mph to over 40mph. Do you need to be able to spin happily at 37mph? If you do a lot of group rides with strong riders it could be nice- though if we're honest with ourselves 40mm knobby tires probably aren't helping you reach -let alone maintain- those speeds.
You'll see in the table above that a number of ratos and rows are greyed out. Those are basically redundant gears- somewhere around 2:1 most riders swap from one chainring to the other- and unless they're faced with an unusually flat and long road don't shift between rings to find the perfect ratio. It's no bad thing (we'll get to steps in a bit), but there is a fair amount of redundancy in most double- and triple-chainring drivetrains. Overall, the 11-speed Ultegra drivetrain has a 428% range.
For what it's worth, its 2x10 predecessor (Ultegra 6700) was available with a wide-range 50/34 crankset and 11-28t cassette. We'll save the table but that works out to a 90rpm speed ranging from 9mph to a little under 34mph. In terms of range that works out to 374% for 10-speed Ultegra.
Wide-Range Gravel Doubles
Now let's shift to the double-ring versions of SRAM's Force AXS and Shimano's GRX groups. Both are available in single-ring and double configurations, and both were made with gravel riding in mind.
Shimano's GRX is what most riders think of when it comes to gravel drivetrains. Borrowing from Shimano's road and mountain groups, 10- and 11-speed GRX groups use cassettes from elsewhere in Shimano's catalog, shifters that borrow heavily from similar-tier road groups, and derailleurs that draw heavily on the design of Shimano's 11-speed mountain drivetrains. Out of the box, GRX clutches tend to be on the light side (which helps with Shimano's trademark smooth shifting), but they can easily be adjusted, allowing you to find the right balance between shift quality, chain noise, and chain retention.
Shimano GRX 2x11: Speed by Gearing Ratio and Pedal Cadence
We generally spec a 46/30 crankset and the widest compatible 11-34t cassette on our GRX doubles. As with Ultegra there's a fair amount of overlap in the middle of the range, but all told GRX 2x11 has a 474% range and can comfortably be ridden from below 5mph to over 40.
As much as its use of existing Shimano cassettes is admirable, it does drive some compromises. The 11-34t cassette is the widest approved with a double chainring and it has wider steps than most road cassettes at the high end of the range (smaller cogs) and smaller steps at the low end. Its progression stands out on paper (see visualization below) but as a rule these differences are probably more noticeable from an office chair than from the saddle. The high gears are lower than most road riders are accustomed to, but so too are the low gears, which should make the 6.5mph @ 90rpm low gear welcome on steep climbs and for loaded touring.
With Force AXS from SRAM, we get into both 12-speed and electronic shifting. SRAM's take on electronic shifting includes wireless controls (reducing complexity and more importantly those wire rattles you just can't fix) and individual batteries for the front and rear derailleur. Roughly the size of a match box, AXS batteries can be removed from the bike for charging and even swapped mid-ride should you miss the low battery indicator. The brains of the system are in the rear derailleur and SRAM's AXS app allows the rider to customize shift behavior, update firmware, and even see time in gear for a given ride.
SRAM Force AXS 2x12: Speed by Gearing Ratio and Pedal Cadence
The wireless shifters use a single paddle on each brake lever and auxiliary "blips" can be mounted under or on top of bar tape, usually at the bar tops or ends of aero bars. Out of the box, left clicks shift to easier gears, right to harder, and both at once switches chainrings. If desired, the system can be set up to shift sequentially, with the front derailleur changing chainrings at optimal positions and adjusting the rear to accommodate.
With a massive 516% range, Force AXS Wide is the group that does the best job of straddling road and gravel use. A winch-like 0.8:1 means that even the steepest climbs are within reach- but so to are forty-plus mph descents. If you want one bike to do it all, Force AXS Wide should absolutely be on your list.
What About "One-By" Gravel Groups?
Here's where things get interesting. As mountain bikers have known for some time now, a wide-range cassette can deliver as much or even more range than a double, only with less weight, noise, cost, and complexity. Let's take a look at Shimano GRX, SRAM AXS, and Campagnolo's EKAR.
Shimano GRX 1x11: Speed by Gearing Ratio and Pedal Cadence
Shimano's GRX is our (and most riders') jumping-off point. While Shimano prefers to limit the cassette to an 11-42, it's widely understood that the 11-speed GRX 812 rear derailleur will quietly and precisely manage an 11-46 without blinking. What that nets us is a 418% range for 1x11 GRX. That's a fair bit down on the double but all of that comes out of the top end. The 0.9:1 low gear nets 6.4mph @90rpm (6.5 with the double) so it's actually better on climbs. It's coming down that the lack of a second chainring is felt most: sustaining speeds much above 30mph calls for some frantic spinning. Do you spend a lot of time above 30mph? If we're honest with ourselves most people don't- and the reduced noise and weight are enough to sell many riders.
Don't want to compromise? How about a Mullet? OK, it's a bit cringe-y but the name has stuck. Using the AXS wireless protocol, a Mullet build uses road brakes and shift levers with a mountain rear derailleur, chain, and cassette. That means that the meat of the drivetrain has been proven in some pretty severe conditions and parts are readily available.
SRAM Force AXS 2x12: Speed by Gearing Ratio and Pedal Cadence
SRAM's 12-speed (or "Eagle") mountain groups are available with 11-50t, 10-50t, and 10-52t cassettes. It's the 10-50 that's most common on gravel bikes, but the 10-52 is identical save for a "Hail Mary" extra-low gear. With a 500% or 520% range a 1x12 AXS gravel bike has wider gearing than a GRX double. It's easy to spec anything from a 28t to 48t chainring, but most gravel builds go with a 42 as it will handle everything from steep 4mph climbs to 35mph descents without issue. For loaded touring or more trail riding a 40t or 38t chainring can make sense while more road-biased riders have gone as high as 46t.
Not keen on electronic shifting? Of course it's Campy to the rescue. Historically the first to market with one more cog, the EKAR 1x13 group has three cassette options, with the 9-42 having the widest range overall.
Campagnolo EKAR 1x13 Wide: Speed by Gearing Ratio and Pedal Cadence
With EKAR's 467% range, Campy does come up a bit short of AXS- and just shy of a GRX 2x11. The group is relatively new, but Campagnolo has a history of supporting their drivetrains with spares for far longer than other brands. Unsurprisingly, being very Italian and very race-focused, Campagnolo's lever feel and shifting are solid and unambiguous. When you've shifted, you know you've shifted. What may be surprising, however, are its price and weight advantages. Priced closer to GRX than AXS, Campagnolo has a 3/4lb weight advantage over GRX 1x11 and takes 1/2lb out of a SRAM AXS 1x12.
While it gives up a bit to SRAM in terms of range, where EKAR pulls ahead is in gear ratio spacing. Which handily brings us to our next topic.
Steps and Progression Are Equally As Important When Considering Gravel Bike Gearing
Have you ever been in a car with a poorly-calibrated automatic transmission and overworked engine? One that hunts between gears, revving frantically in the lower and gutlessly lugging in the higher? That's an extreme example of what we're talking about here. Now, just like some motors are perfectly happy working across a broad range of speeds, some riders can easily adjust their cadence or speed by 5-10%. Others find larger steps jarring and prefer to keep their pedals turning within a narrower band. While most of us have a fairly narrow preferred cadence (somewhere around 80RPM), recent studies suggest that most of us are pretty far off the lower cadences thought to be most efficient, so conventional wisdom may be due an update. Even so, muscle memory is a powerful thing.
So where do our gravel drivetrain options land? Let's have a look:
Taking a look at the drivetrains we've discussed, given that many riders have experience with one or the other the two Ultegra groups can serve as baselines. Range is OK in both cases but the average step between adjacent cogs is 10%. Because we can only work in whole teeth, not all steps can be the same and there will inevitably be some variation. Some brands like to put the steps at the low end of the range (left), others at the high, and others push the big steps to the ends. Keep in mind that tooth counts can be misleading: a 9% 11-12 step is the same in terms of cadence impact as a 22-24.
On average, the groups with the largest steps have cadence impacts 40% larger than the traditional road groups. But getting into gravel, the difference is 27% from largest to smallest average. What that means is that a typical downshift at 75rpm in a GRX double will put you at 83rpm; a typical downshift in a Force AXS 1x12 will net 86rpm. Riding an Ekar 1x13, you'd end up at 85rpm.
But there are some big steps, right?
Sure, but not where you might expect. That 20% step at the low end of a GRX 1x11 or wide AXS 1x12 would take you from 75 to 94rpm. When faced with an extra-steep climb most folks will happily take a lower gear over a smoother shift.
So How Should We Build Your Gravel Bike?
Let's start by saying that no one company or drivetrain has found a magic bullet- just as no one is missing anything obvious. Drivetrains reflect a combination of company philosophies, engineering strengths, and market demands. Shimano favors smaller steps and more gradual progression at the expense of range (single chainring) or redundancy & complexity (double chainring) while SRAM generally prefers simplicity and range at the expense of step size.
Who Might Like a 1x11, 1x12, or 1x13 Gravel Drivetrain?
Gravel riders with a background in mountain biking, where 1x drivetrains have firmly taken hold, will probably find a single chainring setup more natural. Additionally, people relatively new to cycling tend to find the simplicity of the 1x setup appealing. And it's hard to argue against the clean aesthetics and lighter weight of a single chainring.
Riders from areas with more sustained climbing and longer, steeper descents are less likely to notice the larger steps of a 1x system. This terrain often requires more time in a few low gears on the climb, and more coasting than spinning on descents. Plus, the chain retention of a well-designed single-ring drivetrain is unmatched on steep, bumpy descents of mountainous areas.
Interested in a 1x setup? We currently spec Shimano GRX, SRAM Force AXS, and Campagnolo Ekar on our titanium gravel and adventure bikes. We don't have a lot of flexibility with Shimano chainring size, but SRAM and EKAR lend themselves to changes to tailor a build to their terrain.
Who Might Like a 2x Gravel Drivetrain?
If you're coming to gravel riding from a background road cycling, then you'll probably appreciate the smaller steps of narrower-range cassettes paired with multiple chainrings. You might also like the ability to find the "perfect" cadence when riding in a pack or on long, flat smooth or pavement stretches.
Flatter or more gently rolling terrain also lends itself to 2x gravel drivetrains. The smaller steps will allow you to maintain your preferred cadence through more subtle changes in the terrain. With less runoff scouring the road, surfaces tend to be smoother and you'll be able to keep up with the pack when the hammer drops. And as noted above, a 2x system -and Shimano GRX in particular- is a great choice if your ambitions include loaded touring.
The most road-biased riders will also love SRAM's AXS 2x12groups. They shift beautifully and have plenty of low end for all but the steepest dirt climbs. With twelve closely-spaced cogs to choose from, the perfect gear is always within reach.
No matter where you fall, we're happy to work with you to create a bike tailored to your terrain, riding goals, and personal preferences. Feel free to contact us to start the process.
Still having trouble pulling the trigger on a drivetrain? Know that no matter the manufacturer or model, there will probably come a time when you can't find the perfect gear—but we're fortunate to live in a time where the options from most major players work very, very well.
- To the extent that I was able to keep this simple, it was necessary to limit the discussion to mainstream options and manufacturers' recommendations. Yes, it is possible to exceed most companies' recommendations, but there are always caveats (and some even require the sort of modifications or adaptations that we have designed for others). So as fun as they can be we'll save the frankenbuilds for the time and desire to tinker.
- Speeds are based on our most common configuration: 700C wheels with 40mm (as measured) tires.
Last update: December 12, 2020
Want to go even deeper into technical gearing specs? We did even more math. Read our article, There's No Free Lunch in Gearing.