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Road Racing

Gulo Composites GRX-SL wheelset review: carbon spokes for a pillowy ride

When it comes to wheels, fancy spokes aren’t everything

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Carbon fiber spokes have a long history in bicycle wheels, though with decidedly mixed results. One of the latest entrants is Gulo Composites, with a range of wheels all built around a uniquely “tri-axially braided” composite spoke design that’s not only barely half the weight of even premium stainless steel spokes, but also claimed to be stronger and more comfortable. The smooth ride quality claim checks out on the GRX-SL gravel wheels, but is that enough to justify the cost and some other key performance downsides? I’m not so sure.

[ct_story_highlights]What it is: A carbon fiber gravel wheelset that replaces stainless steel with fiber composite spokes ||Wheelset features: 23 mm-wide (internal width) tubeless carbon fiber rims, novel braided spoke construction, 7.5° rear hub engagement speed ||Weight: 1,289 g (589 g front, 700 g rear||Price: US$2,625 (pricing for other regions varies with exchange rates)||Highs: Buttery smooth ride quality, impressively low weight, good construction quality, easy tubeless setup ||Lows: Generic hubs and rims, convoluted truing procedure, expensive, warranty could be better[/ct_story_highlights]

Composite spokes — why?

Gulo Composites clearly believes wholeheartedly in the virtues of its proprietary fiber composite spokes seeing as how its entire wheel range is built with them. But whereas most attempts at rigid molded fiber composite spokes in the past have primarily used unidirectional fibers (perhaps with some sort of external wrap, like Mavic did with the R-Sys), Gulo’s G1 spokes feature a “tri-axially braided” construction that results in a sort of fancy woven cylinder that’s then compressed and cured like most other fiber composite structures.

Gulo is coy about the precise details of the construction, including what types of fibers are used. However, based on supplied images, it appears to be a mix of carbon, aramid, and some sort of long-chain polymer (possibly even something like Innegra). 

“We are not saying what the spokes are made of,” said Gulo Composites CEO David Watkins. “They are a true composite of multiple fibers to provide the strength and toughness we were after. The G-1 is the 52nd composite variant we tried before we got it right.”

Gulo Composites’ GRX-SL wheelset is impressively light and versatile, but wheels are complex items that are hard to get right.

Whatever the precise formula is, what results is a fiber composite spoke that’s not only barely half the weight of even a premium stainless steel spoke (like a DT Swiss Aerolite), but one that’s also supposedly less likely to break under impact and more resistant to stretching under tension — all of which are good things to have in a spoke for a high-performance wheelset. 

As you’d expect, such an unusual spoke requires a similarly unusual method of wheel construction. Both ends of the G1 spoke are bonded to threaded aluminum fittings, with one end threaded directly into the custom spoke flange in the hub, and the other one fed through the rim and secured with a proprietary nipple. 

The unique spoke design requires an unconventional style of wheel construction, too.

As for the hubs themselves, the specs are pretty straightforward, with oversized aluminum axles (17 mm front, 15 mm rear), sealed cartridge bearings throughout (two front, four rear), a six-pawl driver mechanism with a 7.5° engagement speed, interchangeable axle end caps, and swappable freehub bodies for use with Shimano HG or SRAM XDR spline patterns. Center Lock splined rotor interfaces are offered exclusively.

Watkins is evasive on the actual hub supplier for Gulo wheels, though, which isn’t all that uncommon. 

“At this time we are nor revealing who our hub suppliers are,” he said. “The hubs are designed by us specifically for the Gulo wheel system.”

Nevertheless, a few telltale features and markings strongly suggest they’re manufactured by Bitex, a popular Taiwanese OEM manufacturer (specifically, a custom variant of model BX312R). Bitex is hardly a household name and certainly not an aspirational brand, but it’s a reputable source nonetheless for those in the know with a pretty good track record for reliability (and armed with that data, it might then even be possible to mount a Campagnolo freehub body to a Gulo wheelset even though the company doesn’t offer the option).

The hubs are a custom variant of an off-the-shelf model made by Taiwanese brand Bitex.

Gulo incorporates all of this into six different wheelsets, all with tubeless-compatible carbon rims: three “PNF” models for mountain bikes, two “Parkway” models with aero-shaped rims for traditional road riding, and a single “Allpave” model called the GRX-SL that I’m reviewing here.

Of Gulo’s three drop-bar wheelsets, the GRX-SL is the most versatile with a 23 mm-wide internal rim width, 29 mm external width, and 28 mm semi-aero depth. The asymmetrical profile features spoke holes that are offset by 2 mm to help balance spoke tension from side to side, and claimed bare rim weight is 375 g. In keeping with the GRX-SL’s stated “road, gravel, trail, and everything in between” intent, Gulo anticipates those rims will “typically” be paired with tires around 33 mm-wide, although there’s obviously some wiggle room on either side of that.

In terms of durability, the rims have “reinforcement where needed to enhance impact strength,” but otherwise don’t seem to be anything unique to Gulo.

Like the hubs, the rims themselves seem similarly generic.

Twenty-four spokes are used per wheel in a two-cross pattern throughout, and Gulo suggests a maximum rider weight of 125 kg (276 lb).

Claimed weight for the GRX-SL is a scant 1,275 g, which agrees well with my measured weight of 1,289 g (589 g front, 700 g rear, SRAM XDR freehub body, 12 mm thru-axle end caps, with valve stems and tubeless tape installed). 

Retail price is US$2,625 in the United States (roughly AU$3,420 / £1,913 / €2,165). Actual retail price will vary with current exchange rates, and shipping costs and applicable duties and taxes will vary with location as well.

Gulo has a decent warranty policy for all of its wheels, with five years of coverage on the rims to the original owner for “defects in materials and workmanship”, and a US$350 charge for rim replacements (including labor), whatever the cause. Gulo also provides five years of no-questions-asked spoke replacements, and two years of coverage on the hubs (with free bearing replacements within the first year). Claimed turnaround time for any repairs is 2-4 days, not including transit time.

And by the way, if you’re wondering where “Gulo” comes from, Watkins is an alumnus of the University of Michigan (which also happens to be my alma mater). The school mascot is the wolverine, and its scientific name is Gulo gulo.

Are my tires going flat?

Looking at the specs of the GRX-SL, the rim isn’t anything terribly unique, and as I’m already pointed out, the hubs aren’t, either. As such, what sets these wheels apart are its braided composite spokes, so naturally, the question is whether those impart enough of an effect on the performance to justify their existence.

And the answer is… sort of?

Gulo’s marketing spiel on the GRX-SL describes them as being the “lightest, yet stiffest race wheels ever produced.” Without question, they’re remarkably light for a disc-brake wheelset with rims that offer such generous width. And on the road (or trail, as the case may be), that feathery goodness is noticeable.

The rims are appropriately wide and set up tubeless fairly easily.

As many notably light wheels do, they make whatever bike they’re attached to feel nimbler and more maneuverable. They’re fun and flickable, readily tossed about when the path gets tight and twisty, and combined with what seems to be very good torsional stiffness, yes, they seem quite eager to accelerate when you ask them to.

What I found far more striking, however, was the wheels’ surprisingly cushy ride quality. Gulo doesn’t make much mention of this in any of the marketing materials I found, but back-to-back rides (with the only variable being the wheels) confirmed time and again that these things are wonderfully smooth-riding. I’ve ridden quite a few wheels at this point with carbon fiber spokes and carbon rims, and for the most part, they feel like conventional steel-spoked wheels, but with a chunk of weight lopped off.

The freehub uses a conventional pawl mechanism, with six pawls and a 24-tooth ratchet ring. The pawls are arranged in two offset trios, though, so the actual engagement angle is 7.5° instead of 15°.

Given that the GRX-SL rims are quite straightforward, that only leaves me to believe that there’s something to whatever secret sauce Gulo is using to construct these G1 spokes. It’s not a particularly subtle thing, either. In fact, it was so obvious my first time out on them that I rolled back to the house to double-check my tire pressures. 

Comfort isn’t the only benefit to the softness, either. On rough terrain, the GRX-SL wheels lend a confidently quiet and settled feel that hugs the ground instead of chattering about, as compared to stiffer wheels that rely more on the tires to help conform to the ground. Now, I know that the rims themselves aren’t actually moving here, so my only conclusion is that the spokes are squelching vibrations before they get to the hubs. 

It’s a weird feeling, but I like it.

Lingering concerns

Rarely did I finish a ride on these wheels feeling anything but impressed with the ride quality. But less confidence-inspiring was what I perceived to be mediocre lateral stiffness, particularly up front. It wasn’t very noticeable when riding on dirt or singletrack (where there’s a fair bit of sliding going on, at least around here), but it was more obvious when switching between different wheels on paved surfaces (again, using the same tires and inflation pressures)

If you take Gulo’s claims at face value, the issue shouldn’t be spoke rigidity; if anything, they should be less prone to bending than conventional stainless steel spokes. However, much of that may have been squandered by the disappointingly narrow spoke flanges, and the poorer bracing angles that result. And unfortunately, the way the G1 spokes are constructed may inherently limit how much Gulo (or, rather, Bitex) can widen the base of that triangle. 

Plenty of wheel brands use straight-pull spokes and star-type flanges like the ones on this Gulo wheelset. Bontrager is one notable example, and to solve this problem, its engineers “stacked” the opposing spoke heads nearly on top of each other so that the “pulling” and “pushing” spokes have nearly identical effective flange spacing. 

The fat aluminum ends of Gulo’s G1 composite spokes present some challenges in terms of how close opposing pairs can be placed to each other. Where Bontrager (at right) “stacks” the spoke heads in order to push the effective flange spacing further apart, it’s not quite as easy to do so with the G1 spokes. That said, it shouldn’t be impossible, either; it just might take more development effort than just requesting a modification of an existing hub from a third-party supplier.

Compared to the skinny stainless steel spokes Bontrager uses, though, Gulo’s G1 spokes have big aluminum ends that are more than twice as thick, which inherently limits how closely they can be placed to each other. As a result, half of the spoke heads are pushed far out to the edges of the hub shell, but the other ones sit almost a full 6 mm further inboard (and that’s per side, not total). In other words, while one half of the spokes on the front wheel have spoke heads sitting 60 mm apart, the other ones have a far less favorable bracing angle with an effective flange spacing of just 48 mm — and when you narrow up the base of a triangle that much, it’s a lot easier to push it over.

Riders concerned about aero drag should also be reminded that Gulo’s G1 spokes have perfectly round cross-sections measuring a relatively chunky 2.3 mm in diameter. In fairness, riders primarily spending their time on gravel likely aren’t going to care about this a ton. But ones who put a higher priority on efficiency, in general, won’t take a liking to having 24 little air brakes per wheel. 

At the rim end, the flats are there just to keep the spoke from rotating during building or truing. The nipple is hidden away inside the rim.

Watkins says bladed spokes are currently in development with a projected release in late 2021 assuming all the testing goes as planned, which will certainly help on the aero front. But that, unfortunately, won’t change the fact that these wheels are a major pain to true. Not only are the nipples proprietary, but because they’re hidden inside the rim, you also have to remove the tire and rim tape. Even ignoring the hassle factor, that means any minor tweak will likely require you to re-tape the rim (with fresh tape), replenish the sealant, and bite your tongue.

“We use external nipples so a spoke wrench goes on the ferrule next to the rim to hold the spoke and keep it from turning while the nipple is adjusted from the outside of the rim,” Watkins explained. “It is important to not wind-up the composite spoke by twisting. Through rigorous testing, we have found that our wheels rarely need re-truing like wheels with steel spokes do.”

Great wheels are more than just great spokes

Ok, so where does this leave us then? I absolutely love the ride quality of these wheels, as well as the weight, and while I never smashed the spokes into anything during testing, Gulo’s toughness claims are believable enough in that respect.

However, the GRX-SL still feels like to me like something assembled around a novel spoke technology using off-the-shelf hubs and rims, rather than a wheelset that was engineered in a more holistic fashion. They’re good, but not as good as they could be given the performance potential the spokes seem to offer. 

Then again, maybe all of this is how we should have expected it to be. Although Watkins is apparently an avid cyclist who has “enjoyed many years of tour cycling with friends,” the bulk of his professional experience has been in high-tech manufacturing, not the bike industry, and certainly not wheels specifically. Case in point, I asked him if these rims conform to the most recent ETRTO guidelines for tubeless compatibility, and he said he’d have to confirm and get back to me.

“[I’ve spent] the last 38 [years] as president of KEIR Manufacturing, which developed the Gulo Composites brand and product line,” Watkins said. “KEIR started as an advanced ceramic manufacturer making custom parts for various industries worldwide out of ceramic materials with unusual physical properties. We began developing our own products about 30 years ago and now have 23 patents. Eleven years ago, we got into the composites industry with the purchase from Kaman Aerospace, with a product line of strong yet lightweight industrial rotating parts for machinery. We developed many of our own proprietary manufacturing processes, which led five years ago to an exploration of which consumer markets could best utilize the advantages of these developments, which led to the launch of Gulo Composites in April 2020.”

These wheels have a lot going for them, but it’s hard for me to justify the price given what they’re lacking.

I personally am a big fan of fiber composites from an engineering perspective given the wealth of design flexibility they provide, and if you take Gulo’s claims at face value, there’s legitimately something to that G1 spoke — plus, I can’t ignore the GRX-SL wheelset’s distinctly buttery ride quality.

But that said, it also feels like Gulo could — and should — do more here to more fully eke out that potential. 

I’d like to see a more purpose-built hub with a dedicated flange design that pushes the spokes further apart, for example. A nipple design that doesn’t require tire and tape removal for even minor truing would obviously be preferred. I’d argue that the warranty needs to step up to the more comprehensive packages offered by major brands. And given that these wheels are supposed to play in the premium high-performance end of the market, those bladed spokes can’t come soon enough. Last but not least, I’ve no doubt that it costs a fair bit to make these spokes, but given that the matching rims and hubs are pretty generic, I can’t help but feel like Gulo is being more than a little aspirational with its pricing.

Is all of this asking too much? Perhaps, at least if Gulo is just a side project of a massive composites and ceramic tech company with a CEO that has a personal interest in cycling. But it’s not if Gulo is in it for the long haul and legitimately wants to make some killer wheels.

Time will tell which is closer to reality.

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