Can a single ring drivetrain really offer sufficient gear range and what are the advantages? We take a look at SRAMs Force 1 drivetrain to find out.
If you’re in any way familiar with the MTB scene, you’ll know that single chainring setups are currently de-rigueur— it’s fast encroaching on the cyclocross scene too. SRAM has championed this desire to simplify for years.
Back when Shimano was still peddling the virtues of the triple-ring drivetrain, SRAM was pushing 2X setups for mountain biking. Next they developed a huge 10-42, 11-speed cassette and ditched the front derailleur entirely. They’re clearly onto something, as Shimano is now offering wide-range 1X drivetrains too and very few high-end MTB’s come with more than one chainring these days.
So what does this have to do with road bikes? Well SRAM now offers a number of 1X11 road drivetrains and they’re not just pitched at the cyclocross and ‘gravel’ markets. SRAM believes the single-ring format offers real benefits on the road and bolstering this notion, we’ve also seen 3T release a 1X specific aero road bike – the Strada – that will ridden by the Aqua Blue Sport team in the pro peloton for the 2018 season.
In a traditional road setting, SRAM believes 1X offers a range of benefits. First up, it’s lighter; you’re not just eliminating the front derailleur, you’re also removing a chainring, one gear cable and the shift mechanism within the left hand brake lever. SRAM also claims improved chain security, quieter running, better durability and simpler more intuitive shifting. There’s certainly something appealing about the clean look of a 1X equipped bike, so we decided to put their claims to the test and build a bike with the Force 1 group.
While the Niner RLT RDO that we chose as a test platform is an adventure style ‘gravel’ bike, we’ve put it to task in everything from fast bunch rolls with 28c tyres fitted through to fat tyred dirt-road adventures. We’ve been running this setup for four months now—long enough to become quite familiar with its strengths and shortfalls, so let’s run through what we found and see if it stacked up to the claims…
You’d assume that weight loss is a given with the jump to 1X. It makes logical sense that removing components will lead to a lighter bike; however the gains on this front aren’t as great as you may think. The main weight savings come from removing the front derailleur and cable; this cuts just over 100g from the get-go. Single ring cranks are marginally lighter than their 2X counterparts; a saving of around 36g and a further 50g is saved in the single sided shift mechanism.
The flip-side to this is that you’re likely to run a larger cassette to gain sufficient gear range and SRAM’s clutch equipped 1X specific derailleurs are around 70g heavier—this certainly puts a puts a dent in the savings. All-up you can expect to save between 50 and 100g over an equivalent 2X compact drivetrain. It’s worth noting that SRAM’s 10-42 cassette is impressively light for its size; at 325g it’s actually lighter than the 11-36 version and only 25g more than an 11-32 cassette.
With a multi-ring setup, the teeth are cut down and shaped in a way that makes it easier for the chain to derail at certain points on the chainring. While this may result in smoother shifts between chainrings, it also makes it easier for the chain to fall off on bumpy roads or with botched gearshifts. Going 1X allows the use of full-size teeth on the chainring and they can be shaped with chain retention in mind. To complement this, SRAM’s 1X specific rear derailleurs feature a friction adding one-way clutch and a fixed upper pivot; these combine to reduce chain bounce and keep the chain right where it should be.
Anything that lessens the chance of chain loss is a good thing and I can certainly vouch for the chain security offered by the Force 1 drivetrain. One of my adventures took place over two days and covered 200km of dirt roads; it included some fast and rough descents that would have been better tackled on a MTB. Not only did the chain stay right where it belonged, the drivetrain also remained exceptionally quiet with no chain slap.
While the front derailleur has been refined over the years, it remains a problematic design; SRAM sees it as the number one weak link in the drivetrain. Where the rear derailleur guides the unloaded portion of the chain from one cog to the next, the front derailleur has to move the section of chain that bears all of your pedalling load—and forcing the chain to leap from one chainring to the next does impact on drivetrain longevity— especially if you shift under heavy pedalling load.
Eschewing front shifting entirely eliminates this wear factor and is bound to improve longevity. Running the chain at an excessive angle will also lead to accelerated drivetrain wear. On a 2X drivetrain, if you only use the top half of the cassette with the big chainring and the lower climbing cogs when in the small chainring, a traditional drivetrain will run within a relatively moderate range of chain lines.
The one-by drivetrain allows you to utilise the full breadth of an 11-speed cassette. While this does produce a fair range of chain angles, even the most indirect gears are far less extreme than what you get when cross-chaining on a 2X setup. Finally, the full size teeth of a 1X specific chainring provide more engagement with the chain and greater longevity than a chainring that’s built with cut down teeth and shift gates.
Shifting with a multi-ring drivetrain mightn’t seem a big deal to the dyed in the wool racer, but most newcomers to cycling will struggle with the finer points. With a 1X drivetrain you simply shift up or down to suit your needs and there are no idiosyncrasies; no redundant ratios, no cross-over gears and no need to back off on the power for certain shifts.
This even provides benefits for the experienced rider as there’s less to think about; something you’ll appreciate when fatigued or riding on the limit.
With fewer cables, chainrings and other moving parts, the bike looks cleaner and tidier. From a functional standpoint, it also frees up a number of other design elements. With only one chainring there’s more room around the chainstays. This vacant space can be used to create more clearance for wider tyres.
Alternately, the frame designer can tuck the back wheel in closer to the bottom bracket if they want to have shorter chainstays. With no need for a front derailleur mounting point, there’s greater flexibility with shaping the seat tube. Manufacturers such as 3T say they’ve achieved better aerodynamics due to the simplified drivetrain and the uncompromised seat tube profile. In short, 1X drivetrains free up frame designers and allows them to become more creative—who knows where it may lead in the future.
Hitting the road with 1X
The simplicity of the Force 1 drivetrain made the initial setup a breeze. Shifting was solid and consistent across the entire width of the cassette. All 11 gear options are accessible and run efficiently; there’s no feeling of chain line related inefficiency or drivetrain rub in any gear combination—something you won’t find with a regular 2X drivetrain.
SRAM Double Tap shifters have their own unique feel. One lever is used for both up and downshifts; a short push drops you into a bigger gear while a longer throw takes the chain into an easier gear. The lever action is reasonably light and it’s backed by a pronounced click. For me SRAM’s shifting strikes a nice balance; it’s smooth enough under power while still offering good rider feedback.
Aside from the shifter action, the lever hoods have a really nice feel. The front of the hydraulic lever stands quite tall, offering a secure grip with loads of support. We also ran the matching Force hydraulic disc brakes with tidy looking flat mount callipers. They were smooth and offered good modulation, although their ultimate power seemed slightly lower than their Shimano counterparts. Bleeding and initial brake setup was also trouble-free, so no complaints here.
Range to roam
Of course the main fear with running a 1X drivetrain is that you’ll run out of gears—it’s only logical to expect a narrower gear range if you’ve only got a single chainring. To tackle this potential issue, SRAM has a couple of extra-wide range 11-speed cassettes; there’s an 11- 36 as well as a huge 10-42. The 10-42 cassette requires a special SRAM designed ‘XD Driver’ freehub body—a regular freehub body wouldn’t permit the use of a 10-tooth cog. These are now common in the MTB world and most brands offer an XD Driver option.
If you’re sceptical about the gear range on offer, take a look at the gear ratio charts. When combined with a 44T chainring, the 10-42 cassette just about matches the total spread provided by a typical compact 2X drivetrain (34/50 chainrings with an 11-32 cassette). The lowest ratio is basically the same while the top gear is only the tiniest bit lower (119.9 gear inches versus 116.1). It’s a 430% total range on the 2X system versus 420% with the SRAM 1X setup. To put this in perspective, a compact double with an 11-28 cassette only provides a 375% gear range—the range offered by SRAM 1X really is huge.
I never ran out of gears and the 10-tooth cog makes a big difference. With a 44 or 46 chainring up front, there’s plenty of top end for descending or fast-paced bunch riding. Swap to a 42T chainring and you’ll have a super low gear for dirt road adventures in the hilliest terrain. Look at the gear ratios on the 2X setup and you’ll see that many of ratios cross over between the big and small chainrings. Over half the cassette overlaps; the small chainring only delivers three gears that are distinctly lower than what you can get from utilising the big ring alone. When viewed in this light, 1X really starts to make sense.
That’s not to say that 1X is free from compromise—it clearly does and that compromise comes with the jumps between some gear ratios. Again using the common 11-32 compact drivetrain as a benchmark, six of the 11 gear steps are closely comparable (between 12 and 17% variation). The main difference is found in the top-end of the gear range; here the 2X drivetrain has finer jumps of between eight and nine percent while the 10-42 cassette has jumps of 14, 17 and 20%. The impact of these broader gear steps really depends on the riding situation and individual rider preferences.
It did become irritating for me when trying to maintain a high tempo on flatter ground, especially when rolling through in a bunch. In this situation, the 16-20% jumps between the top couple of gears made it harder to find a comfortable cadence; the 12 cog would have me spinning a little too fast for comfort and jumping to the 10-cog would have my legs screaming as it was too big to push.
If you’re keen on 1X for road racing and high-paced bunch rides, I’d opt for the 11-36 cassette with a bigger front chainring to make up for the lack of top end. It still offers a reasonably healthy 347% total gear range (versus 375% with an 11-28 compact setup) but retains relatively normal 8-9% gear steps at the top end of the cassette. As an added bonus, the 11-36 cassette fits to a standard cassette body, so it’ll mount straight to your existing wheels.
Despite what many think, 1X is totally viable for traditional road applications and offers a range of advantages. According to SRAM it actually saves you watts; this comes from the improved chainline and the tooth profile on the 1X specific chainrings which reduces friction. I can’t say I noticed any ‘free speed’ but the drivetrain was certainly smooth and silent no matter what the road surface threw my way.
It’s also worth noting that it’s still relatively early days for 1X on the road. You only have to look to the latest MTB offerings to get an idea of where things may go. On the dirt, total range trumps close gear steps and they now have a massive 10-50 tooth 12-speed cassette—that’s a 500% gear range! Adapt it for the road and you could reduce the total range but gain close step ratios that would silence my only real criticism of the Force 1 setup.
In the meantime, I think that SRAM has a very handy drivetrain on their hands, and if the Force groupset is too spendy for your budget, the Rival 1 and Apex 1 parts offer the same basic function at more manageable price-points. Watch this space as we’ll undoubtedly be seeing more 1X action in the future.