This article first appeared in the July/August 2023 issue of Adventure Cyclist magazine.
British writer Graham Greene once wrote that he was attracted by the blank spaces on maps; those ambiguous zones, he said, inspired him to adventure further into “rough, unmapped country.” The allure of the unknown will be familiar to riders of Soma. The San Francisco–based bike brand offers options for riders who like to get far off the beaten path. Their all-steel lineup of frames skews toward all-road versus tarmac for road bikes, and includes everything from hardtails to randonneuring bikes. Now, the brand is filling in a blank space on their own map with the addition of the Jawbone, their new off-road touring frameset that slots in between their gravel and mountain options, promising versatility, stability, and adventure readiness.
The Jawbone is the beefiest dropbar frame in Soma’s lineup, surpassing their monstercross Wolverine in tire clearance, stability, stiffness, and potential for multiday escapes. With straight-shooting gravel geometry, tons of mounting options, and clearance for huge tires (29 x 2.25in. or 27.5 x 2.6in. with plenty of mud clearance), the Jawbone, which retails for just over a thousand dollars as a frame ($770) and fork ($270) combo, seems like a solid mid-range option for riders in search of fun and adventure. I set out to put it to the test in Soma’s home turf, the San Francisco Bay Area, and found the Jawbone to be a solid all-rounder for day riding on gravel and light singletrack that invites bigger adventures with its sturdy touring potential.
First off: the Jawbone is available in two versions, the A-Type and the B-Type. The A-Type frame, which is a bit more expensive at $1,176 for the frameset, is designed around modern standards like 142 x 12mm thru-axles and flat mount disc brakes, and comes with a 100 x 12mm thru-axle lugged fork. The fork borrows its design from Steve Potts, the legendary California framebuilder and Bay Area mountain biking pioneer who has been designing and building custom bikes for decades. The B-Type frame, like the Wolverine, features IRD Broski sliding dropouts, which allow riders to build it as a singlespeed, with an internally geared hub, or with a standard derailer. The sliding dropouts also, according to Soma, allow riders to fine-tune their ride by adjusting the bike’s effective chainstay length. The B-Type uses an old-fashioned 135mm quick-release axle in the rear, but that can be upgraded to a 142 x 12mm thru-axle with IRD dropout inserts, which are available through Soma for $73 a set. It also has standard IS disc mounts on both the frame and its accompanying fork, which is a unicrown, 100mm quick-release design featuring two sets of three-pack mounts on each leg for a total of four.
Soma says that the A-Type is focused on simplicity, durability, and modern standards, while the B-Type offers riders versatility, more build options, and backward compatibility with older components. The A-Type, then, is likely designed for weekend warriors, gravel day-riders, and folks with only one gravel bike. The B-Type is for parts-bin tinkerers, singlespeed devotees, and world tourers who may be attracted to the internal hub compatibility and the simplicity and worldwide availability of quick-release parts. Regardless, both iterations of the Jawbone are meant as a confidence-inspiring, stable gravel bike that can ride smooth-to-medium singletrack and tackle far-off dirt-road overnighters.
The Jawbone is available as a frameset only, which leaves build possibilities wide open for the rider. I opted to ride a tester bike that came in on the roadier side of potential setups, with a two-by crankset and 29er wheels. That’s not to say it wasn’t a capable build, though. With meaty 2.25in. Maxxis Rekon Race tires and a generous 36T cog on the cassette paired with a super-compact 46/30T GRX crankset, it was ready to spin up steep hills and grip the corners on loose descents. I found that the build was a nice match for the rutted, rocky dirt roads of Marin County, allowing me to ascend and descend with confidence.
The frameset itself is built from double-butted, heat-treated Tange Prestige chromoly steel with a butted chromoly rear end. Tange, a Japanese company with a long heritage of producing high-quality tubing for the bicycle industry, has the same primary distributor in the U.S. as Soma, the Bay Area–based Merry Sales company. According to Soma, the tubing on the Jawbone is stiffer than that of the Wolverine to offer more stability for loaded off-road riding, but not as stiff as that of their Juice or Riff, their trail-specific hardtail options. When I rode it, the frame felt responsive and pleasantly compliant under torque. The fork was a different story: with its straight blades and heavy tubing, and perhaps overbuilt to accommodate its abundant braze-ons (16 total!), it felt overly rigid on the descents. Even with 2.25in. tires at a relatively low pressure, I found myself with sore hands by the time I was halfway down the mountain. A stiff fork is exactly what you want if you’re going to load it up with serious weight for a long-distance tour, but for riders who are looking for a primarily day-riding machine, with occasional overnighters as a secondary function, the Jawbone A-Type, with its Steve Potts fork, might be a better choice. On the other hand, if I were looking to pack up the bike and head south to Argentina, I would probably appreciate the sturdiness of the B-Type.
Despite its burly tubing and touring-ready appearance, the Jawbone B-Type is reasonably svelte. My build weighed in at just 30.4 pounds, which slimmed down to 29.2 once I removed the Soma Lucas front rack and Shimano SPD pedals I was using. For a touring bike, the Jawbone climbs well. With high-volume 29in. tires, it felt playful on paved and unpaved climbs alike. It doesn’t accelerate quickly, but unless you’re talking ultra-high-end custom builds, few full-steel 29er bikes will. But once you get it going, the Jawbone is an enjoyable uphill ride. The bike’s relatively light weight and its comfortable tubing, coupled with Soma’s relaxed, upright geometry, make light, pleasant work of long climbs. You might not go fast, but you’ll have fun.
In terms of geometry, the Jawbone is fairly standard for a gravel bike of its class, comparable to bikes like the State All-Road 4130, the Kona Sutra, and the All-City Gorilla Monsoon, though a few things stand out. At 594mm for the 54cm frame I tested, the Jawbone’s stack is high, but not so high that you couldn’t build it with a fair amount of saddle-to-bar drop if you chose. On the other hand, the bike’s reach is agreeably short, offering a fairly upright position that allows you to open your chest. The short reach makes the bike comfortable, and riding it feels more like walking than running in terms of both cardiovascular discomfort and the machine’s natural speed. One potential downside of the relatively short reach is the potential for toe overlap, if that’s something that bothers you. Another interesting feature of the Jawbone’s geometry is its adjustable wheelbase. The bike’s horizontal dropouts allow you to adjust the chainstay length from 455mm, the longest, most stable setting, to 435mm, potentially fine-tuning its stability and acceleration for the ride you’re setting out on.
While the Jawbone’s longer wheelbase, stiffer tubing, and sloping top tube make it more trail-ready than the Wolverine, it’s not quite a dropbar mountain bike. Soma describes it as a “gravel bike that can fit mountain bike tires,” and that classification is borne out by some of their design choices: eschewing dropper post routing, for example. The Jawbone isn’t compatible with most aftermarket suspension forks, either, and Soma cautions against trying to fit it even with a 40mm travel gravel fork. The Jawbone is definitely a sturdy bike, and it can handle gravel roads and light singletrack, but it’s not built for anything much rowdier than that.
When ridden unloaded, the Jawbone was comfortable and pleasant to ride on uphills and flats, but less stable and confidence-inspiring on descents than I had expected. Part of this likely has to do with the bike’s relatively high bottom bracket height. With 29er wheels and 2.25in. tires, I was sitting high above the ground. But it also has to do with the steering on the Jawbone, which, while not exactly twitchy, wasn’t planted either. A bike with fast steering unloaded will feel perfect when the front end is loaded up, but a bike with slow steering will feel sluggish once you put some weight on the front end. A quick test confirmed this: when I strapped a six-pack of La Croix to the front rack and loaded up my rear seatbag, the steering settled into a comfortable middle ground.
Like the bottom bracket height, which is designed to accommodate a range of wheel/tire combos from 650b x 47mm to 29 x 2.25in., the skittish unloaded steering of the bike has to do with the fact that the Jawbone is designed as a true do-it-all machine, for touring and day riding, big wheels and small, on dirt and pavement alike. Any jack-of-all-trades will be a master of none, but the Jawbone definitely skews toward a specific kind of riding. The ideal environment for the bike might be the Tour Divide: a long-distance route, not especially technical, where riders are carrying their own gear over thousands of miles of dirt roads. If the Jawbone could do something like that — and I have no doubt it could — then it makes sense that it would be good, but not great, on day rides. On the other hand, if you’re looking for a faster gravel machine oriented towards lighter loads and gentle dirt roads, the Wolverine might be your best bet.
Finally, about the build. My Jawbone came built up with a wide-range 2x Shimano GRX groupset, which allowed me to carry my momentum on the flats and downhills and still spin up steep, rocky slopes. The hydraulic disc brakes performed far better than rim brakes or mechanical discs would have fared in the same conditions, especially once things got wet. The wheels felt relatively responsive, which is saying something considering they were clad in huge mountain bike tires. On the other hand, the stiffness at the rear end wasn’t quite what I would have liked, especially when I was standing up and applying heavy torque. Personally, if I was going to build up the Jawbone B-Type as a geared gravel bike with a standard, external derailer, I would probably shell out for the thru-axle dropout inserts, which would allow you to run a more modern wheelset and add some stiffness to the back end. If you were going for a more off-road specific build, a wide-range 1x groupset would offer more simplicity and fewer parts to break. And for a world-touring machine, I could easily see the Jawbone built up with a retro bar-end shifter setup, which would allow you to run a mountain-bike rear derailer for a huge gear range without the fussiness of indexing or brifters.
The Jawbone is a bike that, 10 years ago, would have been radical: with huge tire clearance and dropbar-specific geometry, its design is a result of the bigger-tires arms race that’s been going on among gravel bike manufacturers over the last decade. The problem with making and selling adventure-touring bikes like this one is that, ultimately, the market for them is pretty small. The number of people who take out their bikes for an afternoon gravel ride or a morning singletrack spin will always be far greater than the number of people who do the kind of multiday adventure rides that the Jawbone is built for. But whether you’re a member of the former or the latter camp — or if you, like most of us, do a little bit of both — the Jawbone is a solid middle-of-the-road purchase, good for riders with limited garage space or folks who want one bike that can do it all. It’ll be a reliable companion for spins around your local trails, and it’ll really shine when you have a chance to sink your teeth into a big, multiday ride.
Best uses: Gravel, easy singletrack, loaded multiday bikepacking
Price: Frame ($770) and fork ($270) only
Weight: 29.2 lbs. (without pedals or rack)
Available sizes: 50cm, 52cm, 54cm, 56cm, 58cm, 61cm, 64cm
Size tested: 54cm
Frame: Soma Jawbone B-Type
Fork: Soma Fork for Jawbone B-Type (QR) Black
Handlebar: Ritchey Butano, 440mm
Stem: Ritchey 4-Axis, 90mm
Rear derailer: Shimano GRX 11spd
Brifters: Shimano GRX 11spd
Brakes: Shimano GRX hydraulic disc
Rotors: Yokozuna, 180mm and 160mm (6-bolt)
Bottom bracket: IRD, 73mm BSA
Head tube length: 155mm
Head tube angle: 70.5°
Top tube: 553mm (effective)
Standover height: 805.3mm