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Gravel bikes aren’t one size fits all and there’s a lot of diversity in how they can be specced for different objectives. One of the largest decisions is whether to fit a double chainset or go one-by. Here’s what to consider.
As gravel bikes have developed, there’s a range of bikes to suit different off-road uses. That’s reflected in our range of adventure bikes, with the carbon On And On geared more towards fast gravel and coming complete with aero tube profiles and the option of either 35mm or 40mm tyres on 700c carbon wheels. Compare that to the Around The Outside with a titanium frameset, the space for 650b wheels with 2.5 inch tyres and loads of mounts for expedition rides.
Gravel bike gearing options are also diverse to suit the different gravel ride styles, with a wide range of different options from all the main brands and including single and double chainring configurations.
The arguments in favour of a two chainring set-up centre on the larger number of gears available - double that with a single chainring. But that’s not all it seems, as there’s considerable overlap between the gear ratios that you get between the large and small chainrings’ ranges. In practice, the number of discrete, different gear ratios provided by a double chainset with a 10, 11 or 12 tooth cassette will be significantly fewer than the hypothetical 20, 22 or 24.
You may get greater overall range with two chainrings, although even that isn’t guaranteed (see Mullet Builds below). It’s also possible that you’ll get smaller jumps in the mid-range with the narrower range cassettes used with double chainsets, so you can better match your cadence to the terrain.
Again that’s not guaranteed: an 11-34 Ultegra cassette for use with a double chainset has nine two tooth jumps, whereas an 11-42 for 1x has six two tooth jumps. The larger differences are at the lower geared end of the cassette, so across the mid-range where most riding takes place there’s no difference in gear spread.
For a single ring groupset with a larger number of gears, there are even fewer large jumps: Campagnolo Ekar 13-speed cassettes have six single tooth jumps at the top end of the cassette, a SRAM XPLR 10-42T 12-speed cassette seven one or two tooth increments.
Riding off road can be tough on your bike’s mechanicals, particularly in the UK where “gravel” usually means “mud” for much of the year.
That mud has a tendency to accumulate behind the bottom bracket, where it can rapidly clog up the front derailleur and, for a mechanical system, its cables. Without a front mech, that’s not a problem with single ring systems.
The clutched rear derailleur used with single rings helps with chain retention and reduces chainslap too, although shorter cage derailleurs designed for 2x gravel riding will also have a clutched mechanism. More important is the chainwheel design. The deep teeth of a single chainring mesh more securely with the links in the chain, while you can add a chain retention device if you’re worried about dropping the chain. The wide/narrow alternating teeth of the chainwheel also help clear mud from between the chain links.
On the other hand, if you do drop your chain, it’s easier to get it engaged again if you have a front derailleur. With a single ring, it means a stop and manhandling the chain back into place with the concomitant oily fingers.
A big advantage of single ring groupsets for gravel is the increased clearance that they can offer for wide tyres, as the chainring is mounted more outboard than the inner ring of a double chainset. That clearance is often added to with a dropped drive side chainstay, which avoids interference with the chainrings. Some gravel bikes are designed to be single ring only to ensure maximum clearance.
Recognising that clearance is an issue with double chainsets and wide gravel tyres, SRAM introduced its Wide gearing at Force and Rival level, which shifts the chainline outboard by 2.5mm for, SRAM says, clearance for 47mm 700c and 2.1 inch 650b tyres.
SRAM Force Wide is an example of another trend in double chainsets for gravel bikes: supercompact ratios. Force Wide has a smaller bolt circle diameter than SRAM’s chainsets designed for road riding and uses 43/30T chainrings. Paired with SRAM’s 10-36T cassette that gives you really low gearing that most single ring configurations won’t allow, while still giving you a reasonably high top end gear.
Shimano too has supercompact gravel options in its GRX groupset, in its case 48/31T or 46/30T 11-speed or 46/30T 10-speed. With an 11-34T cassette you’re going to get good low range. You’ll compromise a little on high ratios for fast riding, but unless they’re riding their gravel bike a lot on the road most people probably aren’t going to miss the higher gears as much as they’ll benefit from the lower ratios off road.
One-by goes one better
Supercompact double chainsets best the lowest ratios available in most single ring groupsets - unless you go for a mullet built. Here you mate a road-going chainset and shifters with an MTB rear mech and cassette. SRAM’s electronic groupsets are the masters at this, as its Eagle eTap AXS MTB derailleurs and its road-going Red, Force and Rival shifters use the same wireless protocols.
That lets you pair, say, a 38 tooth chainring with a 10-52T MTB cassette for a huge gear range that should almost let you pedal up a brick wall.
A cheaper option
As well as the mechanical simplicity, single ring configurations are usually cheaper than two rings, as you have one less derailleur to buy, the chainset is simpler and there’s one less shift/brake lever, with the second lever being a “dumb” brake lever only - at least in mechanical shift options, although you need the second electronic shifter for SRAM and Shimano doesn’t sell a brake-only GRX lever to go with a Di2 groupset.
That’s opened up another opportunity with single chainring groupsets though, as the left hand lever can be used to operate a dropper seatpost - the latest must-have component on high spec gravel bikes.
Here at Pearson we’re fans of one-by groupsets and all our gravel bikes come specced as standard with single chainring Shimano GRX gravel groupsets. But two ring groupsets still have their place if you’re looking for maximum range while keeping close ratios across your high and mid-range gearing.
If you want to combine the best of both worlds though, have a look at our latest Classified x Pearson Powershift gearing option. You get all the benefits of a single chainring, but the Powershift hub means that you get the range and close ratios of a double chainring configuration. We’re one of the first brands in the UK to offer it on our bikes.