Seaboard CX03 Review: Steel Gravel Frameset Under $400

Almost everything I test on this site is carbon. That is where the AliExpress boom has been loudest: wheels, bars, frames, all chasing the lowest possible weight for the lowest possible price. So a steel frameset is a bit of a detour, and the Seaboard CX03 is the one that finally made me take it. It is a chromoly gravel and all-road frameset with modern standards: thru-axle, flat-mount discs, internal cable routing, and a steel fork included, all for less than $400. That is the number that makes this frame interesting, because a complete frameset with a fork for under $400 costs about what a single decent carbon wheelset does.

I built mine up as an everyday all-road bike: mixed surfaces, commuting, the sort of riding where a bike needs to be useful rather than fast. The short version is that the build quality genuinely surprised me, and the one real compromise is exactly the one you would expect from steel at this price. There is a full build and ride walkthrough in the video above if you want to see the frame in the flesh.

What you actually get for the money

The first thing worth knowing is where this frame comes from. It is made by Tsunami Bicycle, who also sell it under their WEAPON branding: a workshop with a real reputation in the steel frame world, particularly among fixed-gear and track riders. There is a brand name attached to it, and a shop that has been selling steel frames for years.

The specification is more modern than the classic silhouette suggests:

Tubing: triple-butted, heat-treated chromoly (CrMo) steel, TIG welded, with a conical CNC-machined head tube.
Fork: a steel fork is included in the frameset.
Weight: the quoted figures are 2,150 g for the size 50 frame and 850 g for the fork with an uncut steerer, both without thru-axles. So call it a hair over 3 kg for the frameset.
Wheels and tyres: 700c, with the listing quoting clearance for 42 mm tyres (the brand quotes up to 43 mm).
Standards: 142 x 12 mm rear thru-axle and flat-mount disc brakes. Both current, both what you would want on a bike you intend to keep.
Routing: internal cable routing for shifters and brakes, which is a big part of why the finished bike looks far more expensive than it is.
Mounts: rack and fender mounts, so it will take mudguards for winter and a rack if you ever want to load it up.

At the time of writing the listing sits at roughly $370, down from a list price closer to $470. Put that next to what you are getting: a triple-butted CrMo frame, a matching steel fork, thru-axle and flat-mount standards, internal routing, and rack and fender mounts, for less than $400 all in. A steel frameset from a Western brand with this spec starts at two or three times the money, and plenty of them arrive without a fork. That gap is the whole story of this frame, and it is why the value here is hard to argue with. AliExpress pricing moves constantly, so it is always worth checking the current price rather than trusting a number I typed weeks ago.

Where it genuinely impressed me: the build quality

This is the part I did not expect, and it is the reason this review exists. The frame is well made. The welds are tidy and consistent, the sort of even stacks you would hope for on a frame at any price. The alignment was right, which matters enormously on a steel frame, because a misaligned rear triangle is a problem you cannot fix with careful assembly. The dropouts and thru-axle interface are cleanly machined, the paint is evenly laid down, and the internal routing ports are properly finished.

None of that sounds thrilling written down, and yet it is exactly what separates a frame you can trust from a frame you tolerate. When people ask whether it is risky to buy a frameset from AliExpress, the honest answer is that the real question was always about quality control: whether the thing arriving in the box would be built to a standard you could safely bolt a groupset to. This one is. Building it up was a normal, unremarkable experience, and "unremarkable" is the highest praise you can give a frame during assembly.

The classic look is a bonus and, I suspect, half the reason people buy this frame. Thin steel tubes, a slim silhouette, no oversized aero shaping. It looks like a bike, and it takes modern components while doing it.

The honest compromise: stiffness

Here is the trade-off, and I want to be direct about it, because it is the one thing that might rule this frame out for you. It is one of the more flexible frames I have ridden. Put real power through it out of the saddle, in a hard sprint or on a steep ramp where you are wrenching at the bars, and there is noticeably more give than you get from a stiff carbon frame or a burly aluminium one.

That behaviour is normal for a steel frame at this weight and price, and it is the flip side of the thing steel is loved for. The same compliance that costs you a little precision under load is what makes the bike calm and comfortable over broken tarmac and gravel. You get one or the other. Every frame material is a negotiation, and steel negotiates in favour of comfort.

Whether it matters depends entirely on what you are doing with it:

If you sprint, race, or you are a heavier and more powerful rider, you will feel the flex and you may dislike it. Look at a stiffer frame.
If you are riding all-road, commuting, doing long mixed-surface days, or touring, it sits somewhere between a non-issue and an advantage. Over a four-hour day on rough surfaces, a frame that takes the edge off beats a frame that wins a drag race.

The weight belongs in the same category of honest compromise. Three kilos of frameset is heavy: you are carrying maybe 1.5 kg more than a comparable carbon frameset, and you notice it on long climbs. If your priority is a light bike, steel was never the answer, and no amount of value changes that.

Living with it as an all-road bike

The way I set mine up, as an everyday go-anywhere bike, is where the CX03 makes the most sense to me. Room for 42 mm tyres means you can run something genuinely comfortable and stop caring what the surface does. The fender and rack mounts mean it handles winter and hauling without any bodging. The internal routing keeps it looking clean. And because it is steel with proper rust proofing, it is a frame you can leave outside a supermarket, ride through a wet season, and treat as a tool.

That is a very specific kind of appeal, and it is one carbon struggles to offer at any price. A carbon all-road frame is a lovely thing that you worry about. This is a bike you use.

Who this frame is for

Buy the CX03 if you want a do-everything drop-bar bike with a classic look and modern standards, and you would rather spend your money on wheels and a groupset than on the frame. Buy it if you have a groupset sitting in a box and you have been looking for an excuse. Buy it if you like the idea of a bike you can use hard, in the rain, with a rack on it.

Skip it if you want the lightest possible bike, if you race, or if a bit of frame flex under hard efforts is the sort of thing that will nag at you every ride. Skip it if you need a shop to hand the bike to when something goes wrong: buying a frameset from AliExpress makes you the mechanic and the warranty department.

Verdict

The Seaboard CX03 is the easiest kind of recommendation to make, because it is honest about what it is. It makes no claim to be light, and it gives up some stiffness. In exchange you get a properly made steel frameset: good welds, correct alignment, real rust protection, thru-axle and flat-mount standards, a steel fork in the box, and clearance for 42 mm tyres, at a price that undercuts almost anything comparable from a Western brand by a wide margin.

I built it as an all-road bike and it is exactly what I wanted from that: comfortable, useful, quietly good-looking, and cheap enough that the money went into the parts that actually spin. For less than $400 it is the best value frameset I have bought, and the one I would point almost anyone towards who wants a steel all-road bike without spending four figures on the frame alone. If that is the bike you have been sketching in your head, check what it is going for today. The price swings a lot, and anywhere under $400 it is an easy yes.