The new sub-compact and the future of wide-range gearing
The next phase in road cycling presents new challenges. Riders are no longer sticking exclusively to smooth tarmac with their road bikes, and many are starting to expand their riding horizons onto the dirt and gravel paths. That new terrain is demanding more versatile equipment choices to match, and as the terrain gets steeper and the bikes get heavier, our gearing choices must adapt to suit.
One of the most interesting trends is “sub-compact” gearing, spearheaded in the mainstream market by companies such as Specialized and Felt. CyclingTips content strategist and tech writer, Dave Rome, investigates what sub-compact gearing is, the alternate wide-range options, and what the future of road gearing may hold.
Take the road out of a traditional road bike and you’re left with a number of compromises and considerations in traditional gearing.
For a start, higher-volume tyres are not just wider; they also come with a larger outside diameter, which changes your effective gearing. For example, the jump from a 25c to a 40c tyre effectively adds two teeth to your big chainring. In addition, average speeds are typically lower when you venture off-pavement, off-road climbs are often steeper than tarmac hills, and tyre traction generally isn’t as good, either.
As a result, stomping that 53/11T seems a little redundant at one end, and we already know that clawing your way up a steep gradient in a gear that’s too big isn’t the most efficient (or pleasant) way to gain elevation.
Recent times have seen many bike brands resorting to a compact crank and an 11-28T, 11-30T or even 11-32T cassette out back on all but their most race-oriented models. This would be considered generous gearing on the road, but the additional challenges of gravel and adventure-type riding is now forcing yet another reconsideration of what’s appropriate.
Enter the sub-compact crankset, which often uses 32/48T, 30/46T, or even 28/44T chainrings in lieu of the usual 50/34T, 52/36T, or 53/39T options. In general, all of those options provide gearing that roughly replicates the biggest gears used in cyclocross racing, but with much more total range, especially at the low end, to ease the sting of climbing.
For 2017, the Specialized Diverge and Felt VR bikes are being offered with this new gearing format. While the Diverge is a gravel bike, the Felt VR leans more toward the modern endurance road bike. In either case, the fact that sub-compact gearing is now being specified by two decidedly mainstream brands provides more than enough backing for what just recently would have been considered a radical idea.
“The idea to pursue sub-compact gearing came from a technical need and from anticipating the shifts in how and where road bikes would be ridden,” said Felt global road brand manager Hubert Otlik. “As road bikes move onto variable terrain, tyre volume grows and topography becomes more dynamic. With the need for larger volume tyres, we needed to provide gearing that normalised the gearing to the tyre volume, while providing an expanded range to tackle the more variable topography and surfaces that road bikes are now riding on and over.”
How do the ratios compare?
Rollout is a measure of how much distance is travelled by the rear wheel with a single revolution of the cranks, and it can change substantially with tyre size even without changing the chainrings or cassette. As compared to the chainring/cassette ratios that are usually referenced when discussing gearing (53-15T, 34-28T, etc.), rollout provides a much better indication of just how hard a gear will feel when climbing.
Point toward the sky and the smaller chainrings clearly hold an advantage. But just how much? The graph below looks at the hypothetical cadence required to ride at 11km/h uphill. It’s a simplistic view as the force required to maintain that speed increases as the cadence decreases, but it’s useful nonetheless.
The fact that lower gearing makes for easier climbing will come as a surprise to no one. But a primary limiting factor for the uptake of the regular compact has always been the compromise made in top speed on the flats and downhills. For example, a 48T big ring with an 11T rear cassette cog gets you to nearly 50km/h at 90rpm; under the same conditions, a 52T chainring gets you to nearly 53km/h. That’s a huge difference for racers seeking to gain every advantage over their competitors, but so many of us don’t ride in pursuit of the finish line.
The appeal of these new chainring and cassette arrangements, however, is total range: the ability to nearly replicate the top speed of traditional gearing, but with the added climbing prowess so cherished by mere mortals. The specific chainring combinations used by the new sub-compact cranksets also allow that expanded versatility without having to replace your entire drivetrain.
For front derailleurs, “capacity” refers to the biggest allowable difference in size between the inner and outer chainring, and most drivetrain manufacturers limit that jump to 16 teeth. Bigger gaps may be possible, but often with a degradation in shifting performance. This is why the new sub-compact gear ranges are the numbers they are, and why the traditional 50/34T, 52/36T, and 53/39T combinations are what they have always been.
Along with FSA, Praxis Cycles has been one of the earliest adopters of the new sub-compact concept.
“The reality is it’s just a new great gearing option,” said Adam Haverstock, Praxis Cycles’ director of marketing and sales. “Gravel/adventure riders can use it, traditional road can use it, leisure can use it, women’s category can use it. It’s just a great new option and it’s striking a nerve with consumers as it’s opening up the doors.
“It’s for sure going to grow as many are realising they aren’t really giving anything up on the top end,” Haverstock continued. “Look on a gear calculator at a 48×11, and then look at a 53×12: they are almost identical. So people are getting a new super low gear, and then they basically keep a good tall gear for the flat.”
In short, sub-compact chainrings should offer a good solution for most riders looking for more total range, but that’s hardly the whole story.
The new sub-compact sizing is far from the only solution for those seeking a little more freedom on the hills, and many alternatives don’t require you to replace your entire drivetrain.
One such option is the Wolf Tooth RoadLink, a small aluminum link that installs in between your current rear derailleur and the frame. This effectively extends the length of the derailleur hanger to allow short- and medium-cage road derailleurs to handle far wider cassette ranges than what the manufacturer originally intended. Another Wolf Tooth product is the Tanpan, which allows a Shimano 11-speed road shifter to work with a Shimano mountain bike rear derailleur, and the vastly expanded potential gearing range that goes with it. All of sudden, the use of a 11-42T cassette on your road bike is possible.
“RoadLink and Tanpan demand has been strong,” said Brendan Moore of Wolf Tooth. “This is primarily driven by more and more riders using drop bar bikes for more than just pavement. I think that is driven by the sense of exploration and adventure that comes with mixed-surface riding and the safety aspect [of not sharing roads with motorised traffic]. Most drop bar drivetrains are not well suited for true multi-surface exploration. We are just now starting to see more demand for road 1x too.”
The old triple crankset remains another option for those seeking an impressive gear range, and one that still finds a surprising amount of use in the European market but lost widespread popularity long ago elsewhere. As compared to a wide-range double, triple drivetrains are heavier, the pedals are spaced further apart, they’re more complex, and there are more redundant (overlapping) gears.
Wide-range cassettes complement the argument
We’re in an age of cycling where a 11-23T or a 12-25T cassette is more often something you buy to restore a replica bike instead of using on your everyday machine. Much like the adoption of wider rubber, a peep into the pro peloton will reveal the majority of riders on 11-28T cassettes. Head to the mountains, and even some professional riders are having mid-cage rear derailleurs fitted to allow for wide-range cassettes that span 11-30, 11-32T or 11-34T. And for the non-sponsored rider, going even wider than a 34T is as simple as Wolf Tooth’s $22 part.
In many ways these mountain-bike sized cassettes are complementary to the adventure riding scene, and finding a gear that is sufficiently low is hardly the challenge now. Instead, it’s at the opposite end of the cassette that attention needs to be paid, and the limit of an 11-tooth cog may prove the deal breaker for those looking to use a 46 or 48T big-ring on the road.
It’s here that SRAM may hold the answer. When SRAM designed its 1×11-specific mountain bike drivetrain (XX1), the company realised that the current Shimano/SRAM splined freehub body standard limited the total gearing range. Specifically, it wouldn’t allow for a cog smaller than 11T. To remedy this, SRAM created its shortened XD freehub body, an open standard that was designed to directly retrofit on to the majority of big-brand sealed bearing hubs on the market (albeit with a few small part changes). This design provides space for a cog as small as a 9T, although SRAM stops at 10T on its current cassettes. At least in the mountain bike world, Shimano are now the only wheel and hub supplier to not offer compatibility with the XD design.
So by changing out the freehub body to an XD driver, a 10T small cog is a real option. However, all of SRAM’s 10T-equipped, wide-range cassettes are paired with enormous 42T inner cogs – a spread originally chosen with mountain bike needs in mind. Moreover, the compatible rear derailleurs are only designed to handle single chainrings.
Single-ring drivetrains have practically become standard-issue on modern mountain bikes, cyclocross bikes are rapidly following suit, and SRAM has even pitched 1x as an alternative to traditional two-chainring transmissions on the road.
Although these provide impressive flexibility, there is still slightly less total range than what most two-chainring drivetrains can provide, or a similar total range with very big jumps between each gear. You’ll also have to find your way across the cassette for larger ratio changes, instead of simply shifting at the front for a sudden jump (or dip) in speed.
Regardless, the potential exists for a very intriguing wide-range, two-chainring drivetrain that is ideally suited to the “new school” of road riding. For example, a road-focused 10-32T cassette could prove a perfect companion to a sub-compact setup, nearly replicating the top-end gearing of a traditional 53-11T combination but with the mountain-scaling 32-32T at the opposite end.
The battle of front and rear
SRAM is waging a war on front derailleurs with its 1x setups, and many, including our own Matt Wikstrom, are sold on the idea in certain applications. And while it hasn’t hit the road (and no word on it doing so), SRAM’s latest Eagle 12-speed mountain bike drivetrains offers a whopping 500% gear ratio coverage with a mega 10-50T cassette, all while fitting the same freehub as its 11-speed system. That 500% coverage may be a little too much for the road, but there’s nothing stopping SRAM from releasing a middle ground cassette, such as a 10-46T.
However, for Hubert Otlik of Felt, he doesn’t see 1x drivetrains taking over the road anytime soon.
“I may be a voice of dissent on the topic, but I’m a fan of 2x drivetrains. I’m certainly not opposed to 1x, but I believe that they are ultimately compromised. I admit that 1x drivetrains can offer extremely broad absolute range configurations, but they ultimately arrive at that on account of another limitation.
“More philosophically, however, I take the point-of-view that I want our riders to feel empowered and given the changing attitudes toward where a road bike should be ridden, I believe 2x drivetrains are more capable of inspiring the exploratory spirit and riding habits that today’s riders have embraced.
“Does this mean that we’d never consider a 1x drivetrain? Absolutely not. Again, our primary objective will always be to pair the correct spec to the application so we’re also open to new and emerging technology 1x or otherwise.”
Unrealised benefits and a couple of considerations
There are a number of benefits to the new sub-compact concept yet to be realised, but also a number of things you need to consider before looking to make the swap.
Tyre clearance is already a design issue in current frame designs, and short of going wider at the cranks, space is limited. As seen on mountain bikes, smaller chainrings provide space on the outside of the chainstay, therefore allowing for tyre clearance to be boosted. That’s not to say we’re at a point in road gearing where brands can commit and limit such choices, but it does reveal future possibilities.
Another benefit is potential for weight savings. The use of big chainrings accompanied by a wide-range cassette makes for a heavy setup. For sub-compact, the chainrings themselves are lighter, the cassette cogs can be smaller, as can the rear derailleur and even length of chain.
However, those smaller chainrings may require cranksets with smaller bolt circle diameters, as even the common 110mm BCD compact standard only allows for chainrings down to 32T in most cases. Brands have had to look at different methods in order to fit 32 or even 30T rings, and so far there’s no agreed upon standard for how to achieve this.
FSA is likely the largest original equipment manufacturer (OEM) currently offering sub-compact cranksets. Even within FSA’s range, there are multiple methods of achieving the new gearing, including a four-bolt 110/80BCD for cheaper options, a four-bolt 120/90BCD on mid-range options and a direct-mount big ring with a four-bolt 90BCD smaller ring for the premium models. The use of a 120BCD on some models is due to the more common 110BCD size causing overlapping issues with the chainring bolts. Models which use a 90BCD are said to be able to handle as small as a 28T ring, if or when the market demand arises.
Rotor, having first been asked by Felt to offer the sub-compact sizing, went the route of integrating both chainrings into a direct-mount spider for its cranks. David Martíne, head of engineering at Rotor explained that such a design “fixed clearance issues they ran into with using bolts and existing BCDs, all while allowing a healthy reduction in weight”.
Praxis Cycles, on the other hand, managed to maintain the standard 110mm BCD but machined a small step into the chainring spider arms and complemented that with an offset, threaded bolt hole in its forged chainrings to fit a 32T. Such a design aspect is now fitted to all its road cranks moving forward for compatibility with the new chainring sizes.
For those really not keen on a new crankset and not wanting the lowest gear possible, French company Specialites TA offers a 48/33T setup for use on a standard 110mm BCD compact crank.
Once you’ve got the gearing selected, then there’s the consideration of frames using a braze-on style front derailleur and that they may not allow the derailleur to sit low enough for reliable shifting. Keeping the derailleur high may work, but it’s not ideal.
And then if you do get it all working, then perhaps the most notable downside appears – increased drivetrain wear. Smaller cogs offer less load distribution and so the drivetrain will wear at a faster rate compared to larger cogs. With less chain wrap, small cogs also won’t be as tolerant of wear, and if you really want to nitpick, the smaller chainrings and cassette cogs generate a little more friction, too. For many riders, though, it’s a small price to pay for the benefits.
Is this the new compact?
So the conversation around these new gear ratios is based on adventure road riding, but what about the rest of us that stick to the tarmac? For many living in mountainous areas or perhaps just lacking the fitness or youth of others, this new sub-compact gearing could spell a real alternative to the current common compact setup, or perhaps put the final nail in the triple’s coffin.
Yes, some top-end is lost, but there are more than a few riders who rarely find themselves in the 50/11T of their compact setups.
“Our goal generally is to arrive at a 1:1, or lower, climbing gear for bikes like the VR and I think that will continue as we anticipate new needs and as gearing options develop,” said Otlik. “Personally, I’ve been riding a Praxis 48/32T crank in combination with a 10-speed 12-30T cassette and for how and where I ride it’s an ideal combo for rides that are a mix of 60-70% on-road and 30-40% on dirt, gravel, and fire road.
“What I’ve found is that up to a 7% gradient I can adjust my output by sweeping across the cassette and staying in the big ring. Once the road goes past 7% or I get onto dirt, the 32T is a wonderful driving gear and as pitches increase to nearly 20% the 32/30 gear combination is great, although 1:1 would be ideal.
“As I mentioned previously, our general guideline is 1:1, however, with how quickly things are changing, I can only say that what’s perfect today is only good for today, but that’s a good thing as I’m excited to see where we go next.”
Personally, the perfect road setup may just be my dreamed 10-32T cassette mated to a sub-compact. However, even if such a thing does become reality, it’s likely that the special freehub body and cassette means it’ll remain at a premium price for many, many years to come.