Is it a drop-bar mountain bike? A gravel rig on ‘roids? Or a bike from another dimension? When it comes to codifying bikes these days, it’s really easy to get really lost (real quick). However, once in a while, a bike comes along that challenges the norm, flips the bird to conventional geo numbers, and stands alone: not as an outlier, but as an original. Sam Rice has been test riding Curve Cycling‘s long-awaited GMX+ and shares his thoughts on why it isn’t “just another touring bike” below, along with a look at their updated Seek 430 FM carbon fork.
During my test period, I’ve pedaled a massive array of mixed terrain routes in the UK, from the corrugated dirt roads, techy singletrack, and bumpy bridleways in the South West of England, to a rugged AF bike-rafting mission in the Lake District. Hundreds of miles later, I’m here to spill the beans on this gear-hauling, mile-munching, juggernaut of a bike.
Race. Ride. Seek: Introducing The GMX+ Platform
Originally released in 2020 and dubbed “the ultimate titanium bikepacking” rig, the GMX+ exploded onto the scene and quickly developed a cult following. Designed specifically for Race to the Rock – a harsh, remote desert race across the Australian Outback – its long wheelbase and chubby tires excelled across the corrugations, while its low stack produced a riding stance that’s both comfortable and performance-focused when racing off-road.
Fast forward three years and after some careful R&D, Curve has recently released the GMX+ Steel. Sharing the exact same geometry and DNA as its space metal cousin, the steel version features a blend of Columbus Cromor and 4130 Chromoly steel tubing, an all-new non-suspension-corrected carbon fork, boost spacing, and clearance for 29” x 3.0” tires. The result is a durable, supple, and rugged adventure rig that’s dripping with all the bikepacking features you could ever ask for straight-out-the-box.
Style For Miles: It’s All In The Details
If there’s one thing Curve is known for, it’s their attention to detail. They have a knack for eking out every available millimeter of space, performance, and style across their bikes, and the GMX+ is no different.
The frame itself is littered with mounting points, including rear rack mounts and an unprecedented seven pairs of bottle cage mounts: two in the triangle, one under the downtube, two offset toward the top of the downtube, and one on each chain stay. This enables riders to maximize the bike’s large front triangle with a full-sized frame bag, without limiting water-hauling capabilities. The prolific storage solutions is a crucial feature for both small riders, who constantly battle with space, and folks who ride in remote places where every inch of space counts.
A word of warning: the large front triangle does mean the GMX+ Steel has a high standover across every size. In the context of its intended purpose – overlanding across countries – that’s not a big deal and the space created in the frame is more than worthwhile. But, it does mean that across technical terrain some riders might find the high standover quite unnerving.
Follow the bike’s angles closely and you’ll also spot top-tube mounts, bolt-on downtube cable guides, a replaceable derailleur hanger, a threaded T47 bottom bracket, and a reinforced chainstay yoke with a horizontal brace to stiffen things up and maximize tire clearance.
I’m not a huge fan of running snack bags on my bars as I find they can hinder steering performance, rub the headtube, and damage paint. So being able to run 2x 1L bottles (offset) on the downtube whilst still retaining 100% of my frame bag capacity was a real game changer for me, and something I know I’m going to miss when I send the bike back.
GMX+ Steel Highlights (Size L)
- Frame: Columbus Cromor and 4130 Chromoly Steel
- Angles: 69° head angle, 74.75° seat angle
- BB Drop: 85 mm, approx BB height 292mm measured with 29″ x 2.6″ tires
- Boost Spacing: 148×12 mm
- Bottom Bracket: T47 BB (73 mm)
- Brakes: 160 mm flat mount
- Max Tire Size: 29” x 3.0”
- Frame Weight: 2.950 kg
- Price: USD $4,300 / AUD $6,649 AUD (for RivEagle build)
A Pioneering New Fork: Not a Carbon Copy
Alongside its steel frame, Curve has also designed a brand new carbon fork, dubbed the Seek 430 FM. Engineered to work in harmony with the GMX+ Steel frame, it builds on the success of the original Seek 430 fork. New dynamo and brake routing, plus the introduction of flat-mount brakes, brings it bang up to date. But the real shining feature is the all-new, quad-pack mounting system that is rated to carry up to a whopping 7 kg across each fork blade! Yes, you read that right: the new Seek 430 FM can safely carry a total of 14 kg without skipping a heartbeat. The secret to its Schwarzenegger strength? Reinvention, not replication.
Curve threw out everything they thought they knew about how mounts are added to a fork blade. They left the industry standard rivnut behind and instead, they developed their own unique thru-mounts made from 6061-T6 alloy. As the name suggests, the thru-mounts follow the same principle as thru-axles and are supported by both sides of the fork blades via a set of four reinforced M5 mounting points. With a larger surface area than a standard rivnut, the thru-mounts also give the fork a stronger and more durable mounting interface, all without increasing the weight of the fork itself which comes in at a scant 646 g.
These factors combined make the Seek 430 FM unlike any carbon adventure fork on the market and a truly unique component that I’m sure we’ll start seeing on other framesets in the near future.
Curve 430 FM Fork Specs
- All carbon construction
- 1 1/8″ – 1.5″ tapered steerer, 350 mm long
- 430 mm axle to crown
- 55 mm offset
- 15 x 110 mm (boost) spacing
- Brakes: Flat mount 160 / 180 mm
- 8 x M5 mounts (4 per leg)
- 7 kg load limit (across three mounting points) – 14 kg total
- Fork Weight: 646 g
You call that a ‘stock’ build kit?
When Sarah at Curve first reached out about reviewing the GMX+ Steel, she mentioned they’d be sending one of their “stock” builds for testing. I prepared myself for budget components, a heavy-ass wheelset, and an entry-level group set – ‘cos that’s what stock means in the bike world, right? WRONG!
Like us, the team at Curve are riders, racers, and tourers themselves. In their build offerings, this translates to thoughtfully-selected components based on their proven performance, quality, and reliability in real-life situations, instead of picking parts with profit margins in mind. Curve doesn’t skimp on the parts that you see a lot of brands save money on. For example, the SRAM AXS Rival/GX Eagle (RivEagle) build option that I’ve been testing, combines Curve’s own Walmer Bar, premium alloy Dirt Hoop wheels, an SP dynamo hub, a super reliable DTSwiss 350 rear hub, brass nipples, 29 x 2.6″ Mezcals or 27.5 x 3.0″ WTB Ranger tires, super reliable electronic shifting and a huge 10-52t cassette that will allow you to climb up walls.
The RivEagle stock build retails at USD $3,922 / AUD $6,649 AUD
But wait, what if electronic shifting isn’t your thing or you haven’t got that AXS mullah? Well, Curve also spec a SRAM Apex mechanical option, which makes use of the more budget-friendly Apex shifters and brakes, and makes sensible upgrades where they matter most. On this build you get a GX Eagle crankset and the improved XG1275 cassette (the new Eagle 10-52), rather than the Apex level options. Like its bougie older brother, the Apex build option also includes the Walmer Bars, alloy Dirt Hoops, SP dynamo hub, DT Swiss 350 rear hub, brass nipples, and the same robust tires (set up tubeless).
The Apex stock build retails at USD $3,333 / AUD $5,649 AUD
These build kit decisions combined mean that every GMX+ Steel stock build is ready for anything straight out of the box. No need to worry about upgrading tires or wheels, paying to get set up tubeless or putting up with sub-standard components. All you need to do is load it up and head to the backcountry!
Geometry & Sizing
I’m just going to come out and say it: on paper, the GMX+ shouldn’t work. Its lengthy wheelbase (1189 mm), long reach (466 mm), deep BB drop (85 mm), and low stack (637 mm) make for a perplexing set of figures. But, in my experience with this bike, it’s best not to get too wrapped up in the geo chart weeds, or caught up in a comparison vortex with what you’re used to riding.
The GMX+ is unique. Its stance is undeniably longer and lower than other bikes in its segment, like the Surly Grappler, Otso Fenrir, and Tumbleweed Stargazer. However, straight-up comparisons – even when using tools like bikeinsights.com – don’t reveal the true picture, as they fail to normalize their outputs for stem length. Yes, the GMX+ has a long reach when compared to other bikes, but this is a design choice: a feature, rather than a bug. The GMX+ geo is built around three core design tenets: a short stem, swept-back wide bars, and a steep seat tube angle (74.75°). All of these choices combined, shift the overall riding position forward, thus shortening the effective reach and balancing out the (at first glance) extreme geo numbers.
That said, I did choose to downsize from the XL (recommended for my height, 186 cm/ ~ 6′ 1″) to a size L so I could reduce my overall reach and bring it more in line with my other bikes. However, that doesn’t necessarily mean you should. After five years of touring around the world by bike, I’ll admit, I’ve become pretty accustomed to an upright “touring” position and tend to favor reach numbers in the 400cm-428 cm range. But with a 60 mm stem in the positive position, I found the 466 cm reach of the GMX+ (in size L) to be extremely comfortable and balanced, especially on multi-day off-road rides.
Overall, I’m happy with the size I chose, but if you’re unsure, on the fence or, downright confused, I’d seriously recommend getting in touch with the Curve crew to discuss sizing and what will work best for you. Liege and the team were fantastic at understanding my preferences, taking into account my individual biometrics to dial in a fit specific to me. Thanks again Liege!
For more info on the GMX+ geo choices, check out this useful blog post from Curve.
Ride Quality, Sizing + Suppleness
When I first received the GMX+ Steel, I was living in Cambridgeshire, UK. I’d just returned from a three-month Euro-grav tour with my Singular Peregrine (a 27.5” short wheel-base gravel bike) and was chomping at the bit to start testing the GMX+ Steel. Coming from the Peregrine though, when I first got on the GMX+, I honestly didn’t know what to make of it. It’s a big bike by anyone’s standards and on the gentle countryside gravel and serene English laneways surrounding my house, it felt a bit out of place.
I decided it needed a real test. So I loaded it to the brim and went in search of the kind of terrain it was designed for. Eager to unlock the bike’s true potential, my first proving ground was the beautiful, but challenging Isle of Purbeck in Dorset. Despite its modest proportions, Purbeck is a bikepacker’s paradise. Its terrain ranges from brash, bumpy bridleways, drovers roads, and woodland single-tracks, to rutted, sandy two-tracks and steep, off-camber climbs to open ridgetops.
On this terrain, the GMX+ came to life. Stable, sure-footed, and predictable (especially while loaded down), the combination of wide-ass bars, a long wheelbase, and a low stack produced a distinctly “in the bike” feeling. Locked into the drops, low to the bar, and poised for anything, I felt invincible as I hit the tech sections of the trail, launching over fallen trees and flying down the steep drop-offs.
I found I was climbing on steep, technical terrain more proficiently on the GMX+ than on other bikes I’ve ridden, too. The long wheelbase meant I didn’t need to ride on the tip of the saddle or lower my chin to the bars to keep the nose planted. So gaining traction was a breeze, even on the 20% climbs I’d usually push. However, as a counterpoint, it does mean that climbing on the GMX+ isn’t as exciting or as lively as a bike with short chainstays. But for the riding I like most, the extra stability and grounding were definitely a worthy trade-off.
But it’s not all sunshine and rainbows with the GMX+ on tight technical terrain. Set up with the stock 29” wheels, 2.6” Mezcals, flat pedals, and 175 mm cranks, the BB drop is very low: 85 mm on the size L I tested. In real life, that means the underside of the pedal is just 3.5 inches or 90 mm from the ground, making pedal strikes on rocks and roots a real nuisance. Something to bear in mind if you’re planning on using the GMX+ on technical terrain.
Was this a show-stopper for me? Did the low BB height ruin the GMX+ experience overall? Hell no! Sure a 50 mm higher BB would help with pedal strike, but then the GMX+ would lose a ton of its hallmark stability, surefootedness and “in-the-bike” feeling I’ve come to love. Realistically, no bike can tick every box, and adjusting foot placement and line choice to compensate for the low BB wasn’t a huge issue overall, for me.
- Steel makes this GMX+ platform much more affordable than ti
- Endless mounting options, including dual offset mounts on the down tube across every size
- Next-generation “stock” build kits in which thoughtful, real-world upgrades are standard
- A huge main triangle across all sizes means everyone can enjoy a full-size frame bag
- Climbing technical pitches is a breeze thanks to the long wheelbase
- The new Seek 430FM carbon fork can carry 14 kg of gear.
- Once dialed, the long reach and low stack make for a very comfortable and fast riding position
- The huge tire clearance and steel construction delivers a super supple ride
- The low bottom bracket can make riding in rocky terrain tedious
- Hard to determine one’s size with the combo of a long reach and low stack
- In some environments, you can feel “overbiked”
- The long wheelbase can take some time to get used to
The GMX+ Steel is Curve’s bottom-up redesign of an off-road bikepacking platform. It isn’t just another gravel bike with big tires or Australia’s answer to an upright tourer like the Salsa Fargo. Nor is it designed to be an outright, race-first gravel gremlin. The GMX+ is spliced with both gravel bike and mountain bike DNA, and as a result, excels as a super capable, long-distance bikepacking rig that can handle a range of terrains with speed and comfort.
After a few rides, my initial hesitancy about its bold geometry choices faded away, leaving me with a bike that I grew to learn and love. I’ll miss riding this juggernaut of a bike, and I’d wholeheartedly recommend it if you’re looking for a mega-capable adventure rig, fit to take on the world!
Do you have any questions about the new steel version? Or a GMX+ of your own you’d like to share a photo of? Drop them in the comments and I’ll answer them as best I can!
Thanks to Curve for loaning me such an awesome bike. And a huge thanks to @becbycycle for the riding shots.