Curve Cycling G4 55/70mm carbon clincher review

by Matt Wikstrom


Curve Cycling recently unveiled the fourth generation of its carbon rims. The new G4 hoops offer some nice updates, such as a wider rim bed, but it’s a change in materials and production processes that really count as major improvements. Australian tech editor Matt Wikstrom spent a few weeks riding a bespoke wheelset utilising 55mm and 70mm G4 rims for this review.


Curve Cycling is a small wheel brand that was born in Melbourne, Australia almost 10 years ago. Starting a small wheel brand is probably the second-hardest thing to do; keeping it is a much more difficult task. Nevertheless, Curve Cycling has managed to achieve the latter with a growing range of products and retail partners.

In the last 18 months, Curve Cycling has added steel and titanium frames to its catalogue along with a variety of carbon forks however wheelsets remain the company’s primary interest. Curve is now starting to roll out the next generation — the fourth — of its carbon rims, starting with road offerings.

“We had a long lead-up period — 18 months — to the actual release of these rims,” said Steve Varga, one of Curve’s co-founders. “First off, we wanted to make a better product than our G3 rims. G3 is a solid product, but not without its flaws. They fail under high heat loads like many other carbon rim brake products.

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“With the G4 we beefed up the rim profile to help dissipate heat build up,” said Varga. “We also introduced a high-temp resin throughout its makeup to create a more stable product and we’ve very happy with the outcome.”

Curve’s earliest rims were open-mould products, but once the company found a suitable production partner in Asia, the two started working very closely. “As with all of our products, we teamed up with our production partner of five years to develop this series of carbon rim and wheel products from the ground up,” explained Varga.

A variety of new features have been introduced with the G4 rims, some of which are related to materials, and others to the construction process. What the buyer will notice is that the price of Curve’s carbon’s rims has gone up a little but there is a greater range of rim profiles to choose from.

I recently spent a few weeks riding a 55mm/70mm “mullet-combo” created by one of Curve’s retail partners, Zak Smiley at Skunkworks Bikes. The presentation of the rims has changed, but the new G4 rims make for a stiff, race-oriented wheelset just like the previous generation.

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Before the ride

The introduction of carbon composites has had a huge impact on the bike industry, but the appeal of the material has always been undermined by its susceptibility to impact damage. Once composites were used to create wheel rims, a second weakness was soon uncovered, namely the susceptibility to heat build-up and damage caused by rim brakes.

There is, however, a third major weakness for carbon composites that hasn’t received the same kind of attention as the first two, and that’s the risk of manufacturing defects. As layers of carbon fibre sheets are bonded together, any voids and wrinkles that occur will undermine the strength and integrity of the final product.

“We had some ideas regarding the use of robotic automation in rim production as long as three years ago,” said Steve Varga. “This process was being used by several industries that required high consistency and higher tolerances, so we could see it had potential for our rims.”

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Curve took the idea to its Asian manufacturing partner with the result that all G4 rims are produced in single moulds by a semi-automated process. More time is required to create a rim but according to Curve, the new rims are lighter, stiffer, stronger, and the company expects fewer rim failures due to construction defects.

While Steve is pleased with the new rims, there was a limit to the amount of detail that he could offer on the manufacturing process as part of Curve’s agreement with its production partner.

Be that as it may, the G4 rims have a few other features worth mentioning. First, the rims are constructed from Toray T700 and T800 fibres with a combination of unidirectional and 3K weave. Second, the basalt brake track utilised by G3 rims has been replaced by a combination of 3K weave and high temperature resin to improve both braking and heat management. Third, rim width has increased to 25mm with an internal width (measured hook-hook) of 18mm. And fourth, where once Curve’s carbon rims were tubeless-compatible, G4 clincher rims no longer have this feature.

This is all in addition to the expanded range of rim profiles mentioned above. Curve’s G4 rims are available in a choice of 25mm, 35mm, 45mm, 55mm and 70mm profiles, and all are UCI-certified. Each rim has a rider-weight limit of 100kg except the 25mm version, which is 85kg. Maximum tyre pressure is capped at 115psi.

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All of Curve’s G4 road wheels are built to order with a choice of four hubsets (DT Swiss 350; DT Swiss 240; White Industries T11; Chris King R45). In every instance, the front and rear wheels are laced with 20 and 24 Sapim CX-Ray spokes, respectively, and alloy nipples. Prices range AUD$2,399-3,499 (~US$1,770-2,580) with forecast weights as little as 1,310g (25mm rims, DT 240 hubs).

There is a smaller range of disc-specific rims in the new G4 collection — 25mm, 35mm, 45, and 55mm — and a choice of two road disc hubsets (DT Swiss 350; DT Swiss 240) and two spoke counts (24 or 28). Prices range AUD$2,399-2,939 (~US$1,770-2,170) with wheelset weights as low as 1,385g (25mm rims, DT 240 hubs).

That’s not the end of the possibilities though, since Curve or one of its retail/wheelbuilding partners can supply a custom-built wheelset for those buyers with specific needs. This may include a different brand of hubs, spoke counts and/or lacing patterns, where the final cost will vary according to the options selected.

The wheelset sent for review by Skunkworks Bikes is one example of a bespoke G4 build, where the goal was to maximise speed and aerodynamics while making some concession to crosswinds. Thus, Zak paired a 55mm 20-hole front rim with a 70mm 24-hole rear rim and laced them to a set of Industry Nine Torch hubs (supplied by Dawson Sports) with Sapim CX-Ray spokes and alloy nipples.

A radial spoke lacing pattern was used for the front wheel compared to a two-cross pattern for the drive-side of the rear wheel. Zak opted to use radial lacing non-drive-side spokes to add a little extra lateral stiffness to the wheel for sprinting.

Total weight for this build was 1,641g (front, 720g; rear, 921g) at a cost of AUD$2,900 (~US$2,140). To put those numbers into context, Zak’s wheelset weighs 50g less than Zipp’s Firecrest 404 clinchers despite a significantly taller rear wheel and is 10% cheaper.

All G4 wheels are supplied with a two-year warranty, a pair of skewers, two pairs of brake pads and spare spokes. For more information, visit Curve Cycling and Skunkworks Bikes.

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After the ride

The first thing to stand out about Curve’s G4 rims was the new finish. Where once the company favoured the matte black finish of unidirectional carbon, now there is a wavy, almost psychedelic weave. The new finish clearly demarcates G4 rims from earlier generation rims while teasing the eye with what appears to be a subtle texture.

One touch is enough to break that spell though, since the rim surface is glassy under the fingers. At a distance, the weave isn’t obvious, so onlookers discovering the wheels for the first time are likely to be delighted when they discover the patterned finish. That Curve has elected to sticker the rims with large logos adds to the boldness of the presentation that suits the tall rims.

I reviewed Curve’s third generation 38mm clinchers about 18 months ago and the one trait that stood out for me was the amount of radial stiffness. It really marked the rims for racing purposes rather than all-day outings.

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That stout radial stiffness remains unchanged for the G4. On smooth roads, the G4s rolled smoothly and the firm feel of the wheels added a racy edge to the bike. The wheels were a little slow to wind up but the overall sturdiness was exactly what I’d expected from a set of race wheels, right down to the absence of brake rub.

That radial stiffness had an obvious disadvantage though. Any kind of sharp hit from a pothole, crack, or road seam was always harsh. I spent the entire review period riding Vittoria 700x25c Corsa tyres inflated to 60psi, a generous combination that I’d normally expect to provide a pillowy ride.

When paired with a stiff chassis — DeAnima’s Unblended — the G4s became tiresome on long rides. During the first hour, when my legs were feeling fresh, the bumps weren’t so troubling, but after a couple more hours, I started dreading level crossings and cracked sections of bitumen.

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That all changed for the better when I swapped the wheels to a more forgiving chassis (Baum Corretto). I was able to ride the same long route without any undue harshness from the wheels. The wheels were still noticeably firm, and indeed, added a racy edge to the feel of the bike, but I stopped dreading the cracks and bumps.

I’m sure the tall rim profiles added to the stiffness (and harshness) of the wheels. I have yet to experience Curve’s other G4 rim profiles but based on my experience with a low-profile (24mm) version of their third generation rims, I expect low-profile G4 rims (25mm) will be more forgiving. At the same time, the wheels will be lighter and more versatile than the 55/70mm combination tested here.

Wider tyres can always be used to improve the comfort of any wheel. I didn’t test 700x28c tyres on the G4s, but based on my experience with other wheels, this will be a sound option for any racer worried about suspension losses during a long race on dead roads. The wider tyres will create more aerodynamic drag but I suspect the penalty will be easily offset by the gain in comfort (and perhaps improved rolling resistance).

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I compared the weight and price of the G4 wheelset with Zipp 404s above, so what about the ride? I expect most riders will be able to tell the two apart, since the G4 is considerably stiffer than the 404, which I’d characterise as compliant and forgiving. Deciding between the two is unlikely to be a simple matter but in terms of ride quality it’s really a matter of matching the stiffness of the wheel to the rider in question. Big, powerful riders are likely to revel in the firm ride offered by 55/70mm G4s; small, light riders, not so much.

The question of aerodynamics always arises for wheels with high profile rims; similarly, the susceptibility to crosswinds. I have no data for the former (nor does Curve), however the modern toroidal rim profile combined with a generous rim bed promises at least a measure of the gains offered by a recognised aero wheel design like the 404.

As for crosswinds, the 55mm front rim was no better or worse than similarly sized rims. Thus, light-moderate winds were rarely a problem but strong, gusty conditions demanded extra vigilance and effort to keep the bike on line. Interestingly, I’ve noticed that I’ve become far more forgiving of the instability of tall wheels in crosswinds, which I presume is a by-product of familiarity. If that’s the case, then any rider can expect to find it easier to handle the bike once they become accustomed to the behaviour of the wheels.

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Another familiar topic of discussion for a carbon wheelset is the quality of the brake track. In this regard, the G4s were strong performers, and yes, the improvement in the quality of braking was tangible when compared to Curve’s previous generation of rims.

Zak supplied Swissstop’s Black Prince pads with the wheels, and the quality of grip on the rim was sure and even — until it rained. Then there was far too much slip for me to feel any kind of confidence when braking at short notice, so I was forced to ride defensively and allow for significantly greater braking distances.

This was my first experience with Industry Nine hubs. The deep colours and classic shape of this hubset recalls Chris King’s R45 hubs, yet there is none of the associated complexity. With simple precision-machined end-caps, the hubs are easy to pull down (no tools are needed) and service, while the freehub offers a rich buzz.

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Finally, a note about Zak Smiley’s wheel-building skills: he pays close attention to the components that he uses for a custom build along with the final spoke tension. As a consequence, I wasn’t surprised when I didn’t have any problems with the hubs or the rims during the course of the review period. His level of diligence is not something that can be immediately felt when riding his wheels, but it will be appreciated many months down the road.

Summary and final thoughts

Curve Cycling’s G4 rims boast a number of refinements, so while the company may be asking for a little more cash for the new rims, buyers are getting an improved product. The increase in the number of rim profiles for both rim- and disc-brake users has to count as perhaps the biggest appeal, though the latter may be turned off by the absence of tubeless compatibility.

If it wasn’t clear from my comments above, the 55/70mm combo tested was a stiff wheelset, and one that will be best suited to racers rather than enthusiasts. Compared to other high-profile wheelsets that I’ve reviewed recently, such as Boyd’s 60mm carbon clinchers, Irwin Cycling’s 58mm wheels, and Wheelworks 50mm Maker, Curve’s G4 55/70mm is easily the stiffest (and harshest).

But are they too stiff? I’ve yet to sample Curve’s entire G4 range but the stiffness of the 55/70mm combination does limit the versatility and general appeal of the wheelset. Some wheelbuilders might suggest a change in spoke tension to alleviate some of this stiffness, but I think there is room for some rim manufacturers to offers different amounts of radial stiffness for any given rim profile.

Ultimately, the suitability of any rim depends upon how wheel it meets the buyers needs. In this instance, Curve’s G4 rims are perhaps the best choice for any large, powerful rider seeking an especially stiff and robust wheelset for racing. For those riders outside of this category, high-profile G4s may still be a good choice depending on the combination of the chassis, tyres, and tyre pressures that are used with the wheels.

 

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