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by Matt Wikstrom
June 6, 2018
Photography by Matt Wikstrom
When road disc bikes were first unveiled, Shimano was reasonably quick to bring suitable brakes and wheels to market, but none could be counted as high-end products. That all changed when Shimano unveiled the new Dura-Ace R9100 series for 2017 that included its vision for a high-end disc brake groupset.
The new ensemble of Dura-Ace components included a range of road disc wheels with a fresh pair of carbon rim profiles — C40 and C60 — that was studiously developed to suit tubulars and tubeless clinchers. In this review, Australian tech editor Matt Wikstrom takes a close look at what the new road disc wheels have to offer, paying particular attention to the mid-profile C40 for tubeless clinchers.
Shimano’s recent overhaul of its Dura-Ace components for 2017 was extensive, to say the least, with the company producing four discrete ensembles incorporating both mechanical and electronic transmissions as well as rim and disc brakes. The new R9100 collection also included a range of new wheelsets, and most notably, the company’s first all-carbon road clinchers. There was a catch, though: the new all-carbon clinchers were disc-only while the rim brake versions would continue with carbon-laminated aluminium rims.
Given the problems that rim brakes can create for carbon clinchers, Shimano’s steadfast devotion to carbon-laminated rims is understandable. If nothing else, the scale of Shimano’s production means that a tiny safety issue in terms of percentages would still have an impact on a significant number of cyclists and mar its reputation.
By contrast, Dura-Ace racing tubulars have featured all-carbon rims for several years, so it’s clear that Shimano is not wholly cautious with the material. Instead, the company’s approach appears carefully considered, so it’s really not surprising to see Shimano’s first all-carbon clincher rims being developed for disc-equipped bikes.
As reported in our initial look at the R9100 Dura-Ace range, there are four road disc wheelsets on offer, one pair to suit tubular tyres, and another pair to suit tubeless clinchers. All make use of the same hubs and spokes with a choice of two rim profiles for each tyre system, C40 and C60, which are 37mm and 60mm tall, respectively.
For the majority of riders, the tubeless-ready C40-TL will be the most alluring option in Shimano’s new range of Dura-Ace road disc wheels (all of which wear the same R9170 catalogue number). After all, tubular tyres are simply too inconvenient to use on a daily basis, and a mid-profile rim like the C40 is well suited to year-round use because it won’t be troubled by crosswinds like the taller C60 profile.
As mentioned above, all R9170 wheels feature the same hubs, straight-pull spokes, and external alloy nipples. Spoke counts and lacing patterns are also identical, and like all of Shimano’s wheels, they are manufactured in the company’s Malaysian facility. The tubular wheelsets are significantly lighter than the tubeless models, though: the C40-TU (tubular) is over 200g lighter than the C40-TL, while the C60-TU is 140g lighter than the C60-TL.
There is one other difference between R9170 tubeless and tubular rims, and that is the external width of each rim. The tubeless rim measures 24mm wide while the tubular is 28mm. Nevertheless, both rims share the same D2 rim profile that was refined with the help of wind tunnel testing. Shimano is not making any of this data public, so for those that need hard data, they will have to wait until independent tests are published.
The C40-TL and C60-TL are tubeless ready and arrive with suitable tape and valves installed.
Be that as it may, I suspect that the tubular rims are a little more aerodynamic than the tubeless equivalents due to a sleeker rim/tyre interface. And while the C40 may offer some reduction in drag, it won’t be in the same realm as the C60. If Shimano has done its homework, then the C60 should achieve the same performance (or better) than the C75 it replaces while offering the rider some respite from crosswinds.
Shimano has long championed the value of wheel systems, where the design of each component is diligently engineered to complement the others, and the result is a wheel that is greater than the sum of its parts. The downside of this approach is that it results in proprietary parts that cannot be replaced at short notice, however Shimano does make a range of spares for its wheels, includes hub parts and spokes.
The primary goal of developing these wheel systems is to create a reliable and safe product. Interestingly, there is no weight limit for any of the R9170 range, which provides some measure of the confidence Shimano has in the strength and durability of these wheels.
Halving the number of spokes on the non-drive-side of the rear wheel means more spoke tension is required, which is a better match for the high tension on the drive-side spokes.
One key aspect of this strategy is to address the imbalance in spoke tension for the rear wheel, which is always higher on the drive-side. This is where Shimano’s OptBal spoke system comes into play, which is simply a re-badged version of triplet spoke lacing (just like Fulcrum’s 2:1 spoke ratio and Campagnolo’s G3 lacing pattern). By using half as many spokes (eight) on the non-drive-side of the wheel, and employing a radial lacing pattern (which keeps the length of the spokes as short as possible), more spoke tension is required to match the drive-side spokes.
In the case of the C40-TL (and the rest of the R9170 wheel range), this spoke lacing strategy is complemented with carefully refined hub geometry that attends to the spoke tension while providing robust bracing angles for lateral stiffness. I found that the tension on the non-drive-side spokes of the C40-TL rear wheel sent for review was virtually identical to the drive-side of the wheel, which is something that is not normally seen for any rear wheel with an asymmetrical hub. Indeed, it trumps Campagnolo’s and Fulcrum’s best efforts, where non-drive-side tension is ~70% of the drive-side, and promises to further reduce spoke fatigue.
The OptBal system is not applied to the front wheel even though it also has an asymmetrical hub (the left hub flange is offset by the disc rotor). Instead, a conventional two-cross lacing pattern is used for the 24 spokes in the wheel, with the result that spoke tension on the right side of the wheel was two-thirds that of the left side. While this may seem like an oversight, I suspect that the extra forces associated with front-end braking and the disc brake played a role in this decision.
Like the rear wheel, 24 spokes are used to build the front wheel, but that number is evenly split, so 12 spokes are used on each side of the wheel.
The R9170 C40-TL wheelset sent for review by Shimano Australia weighed 1,566g (front, 705g; rear, 861g) with rim tape. Out of the box, the rims were ready for tubeless tyres with tubeless valves installed.
In the first instance, I was able to install a set of standard clinchers (28c Vittoria Rubino Pro) with inner tubes without any difficulty. The tyres were an easy fit without levers, and they were quick to seat once inflated. Installing a set of tubeless tyres (25c Schwalbe Pro One) was a little more difficult, but that’s the nature of the tubeless beast. With an air compressor on hand, the tyres were quick to inflate and seat with a few loud pops. After that, they stayed inflated and I was able to ignore the tyres.
The C40-TL and C60-TL rims have a 17mm rim bed, which has become the industry norm for modern rims. It’s a little wider than rims used to be, and any road tyre will puff up a little wider than usual (for example, a 25c Schwalbe Pro One measured 26.5mm at 70psi). With that said, other brands are producing rims with wider beds (19mm or greater) for road/all-road use, so Shimano is far from the cutting edge with its tubeless rims.
Shimano recommends tyre sizes of 23-32c for the C40-TL (and C60-TL), which will suit most road and all-road bikes in use today. However, the 24mm external width of the tubeless rims places a limit on the tyre size that can be used without interfering with the aerodynamics of the wheels. This is not a major restriction, but I can’t see any sense in a buyer opting for the aerodynamic appeal of these wheels and then fitting 32c tyres for extra comfort/traction.
The C40-TL hubs accommodate 12mm diameter thru-axles with 100mm and 142mm spacing for the front and rear, respectively. Both have become the default specification for road disc bikes, but it’s worth noting that it is not possible to convert the hubs to other sizes, such as a 15mm thru-axle for the front, or standard quick-release axles.
Both hubs roll on conventional cup-and-cone bearings with stainless steel balls. In a market dominated by hubsets with cartridge bearings, this may seem like a throwback to an earlier era, but Shimano (like Campagnolo/Fulcrum), believes in the traditional design. If nothing else, it is far easier to service and adjust the bearings; all that is required is a few oversized cone spanners.
Aside from accommodating a 12mm diameter thru-axle, the front hub is a conventional cup-and-cone design.
A pair of 17mm cone spanners is required to remove the lock nut.
Once the adjusting cone has been removed, the axle slides out. Bearing shields on each side of the hub will keep the bearings in place.
The bearing shield is easy to pry off with a flat screwdriver.
The ball bearings sit in a retainer that makes it easier to handle them.
Wipe out the old grease, smear on some new stuff, and the hub is ready for re-assembly.
Front axle assembly: note that one cone is fixed, which simplifies installation and adjustment.
Center Lock mount for the disc rotor and straight-pull spokes.
A two-cross lacing pattern is used for both sides of the wheel.
The assembly of the rear hub is largely the same as the front, however a combination of 17mm and 19mm cone spanners is required to undo the lock nut.
The lock nut is easy to unwind…
… as is the adjusting cone.
Once the axle has been removed, the bearing shield can be pried off.
The non-drive-side bearings are held in a retainer.
If the inner race is ever damaged, it can’t be replaced.
The drive-side bearings are not held in a retainer, so it’s more difficult to remove them and clean up this part of the hub.
The rear axle assembly is just as simple as the front.
The rear wheel makes use of straight-pull spokes with a three-cross lacing pattern on the drive-side…
… versus radial lacing for the non-drive-side spokes. Note also the difference in spoke count.
The freehub body also continues with Shimano’s sealed design, which cannot be serviced, only replaced once the internals become contaminated or degrade. The body itself is made from titanium, which will resist sprocket-bite, and is only available to suit Shimano/SRAM cassettes (up to and including 11-speed).
Installing the disc rotors was quick and easy thanks to Shimano’s Center Lock design. For the uninitiated, any Center Lock rotor simply slides onto a splined core and is held in place with threaded lockring that resembles a cassette lockring (it also requires the same splined tool as Shimano’s cassette lockring).
I’ve already mentioned that the C40-TL is delivered with tubeless rim tape installed, but in the event of a broken spoke, owners will have to contend with a unique requirement. That’s because the rim bed is not dotted with holes for the spoke nipples, but larger rectangular openings, which creates a challenge for sealing the rim for tubeless use. For this reason, Shimano created a special “stainless steel tape”, and panels of the stuff are used to cover each opening. These adhesive panels are single-use items, so owners will need to have a replacement on hand should they ever need to replace a spoke or nipple.
With a combination of all-carbon rims, high-end hubs, and the Dura-Ace label, the R9170 C40-TL promises to be an expensive wheelset, and it is: AU$2,400/US$2,000/£2,000/€2,200. However, it’s not as expensive as some brands that offer many of the same features, but it won’t catch the eye of bargain hunters, who will be more impressed with cheaper offerings (such as the Prime RP-38 road disc wheelset).
I had a fuss-free experience from the moment I pulled the C40-TL out of the box, and while the wheels never managed to dazzle me, they lived up to expectations for a mid-profile carbon wheelset.
To start with, they were versatile performers. They were light enough to take into the hills and I could attack valley descents without fear that a sudden crosswind would blow me off-course. That’s not to say that the front wheel was completely untroubled by crosswinds, but it remained quite predictable in windy conditions.
The C40-TL was reasonably responsive, too. As a sub-1,600g wheelset, they were light enough to spin up pretty quickly while offering a certain amount of agility, but they couldn’t match the performance of a lighter wheelset with low-profile carbon rims (e.g. the Hunt 30Carbon Aero Disc). For those riders looking to trade up from a heavier stock alloy wheelset, I expect the C40-TL will impress, which is what I found when I fitted them to Trek’s Emonda SL 6 Disc.
The ride quality of the C40-TL was unremarkable, which is to say they weren’t overly stiff in any regard. The wheels never felt harsh when hopping curbs and they never created any unnecessary vibrations on uneven surfaces. When it came to sprinting out of the saddle, they felt sure and robust under load instead of flimsy and uncertain. Of course, these impressions are subject to all sorts of caveats, including tyre size and pressure along with the stiffness of the bike, but after experimenting with a couple of different tyre sizes and bikes, I can say I was never disappointed by these wheels.
The wheels always rolled nicely, but if the 37mm rim profile helped my efficiency, then it was too small to notice. In this regard, the best any rider can hope for is a nuance. What I find is more significant is that the sight of a taller rim often helps me find a more aggressive frame of mind for my cycling, and I will go faster, but only because I’m inspired to drive the bike harder. As such, I don’t expect the C40-TL will overhaul the capabilities of any buyer, but they will probably have a good time using them.
After putting the C40-TL to use for a month, it was that enjoyment that proved to be the most consistent feature of this wheelset: a versatile pair of wheels that was easy to use and always a pleasure to ride. The rich gloss finish always looked classy, too, and I can imagine that having spent the money, I’d feel quite pleased with my purchase.
Over the longer term, though, I expect the C40-TL will really start to shine thanks to Shimano’s considered approach, the robust build, and the balance of spoke tension for the rear wheel. Strictly speaking, these are all aspects that remain unverified, however the potential is there. And without brake pads constantly scrubbing away at the sidewalls, the only part of these wheels that will suffer wear and tear are the spokes (provided the hubs are serviced at regular intervals).
Needless to say, the wheels did not come out of true during the course of the review period, neither hub developed any play, and there were no issues with tubeless tyres leaking air. As for the sound of the freehub, it was as quiet as any other Shimano freehub, generating a gentle click that often went unnoticed.
In the past, I’ve often described the rims on a road bike as a consumable product because it was inevitable that they would have to be replaced as the brake track was rubbed away with use. The introduction of disc brakes changes all that, and while a crash can still ruin a wheel, road disc wheelsets should enjoy a significantly longer service life than their rim brake equivalents.
As such, I find it much easier to justify the extra expense of a high-end carbon wheelset like the C40-TL. That this wheelset ticks a lot of boxes — versatile performer, classy presentation, easy to service hubs, reasonably light and responsive, tubeless-ready, and highly enjoyable — adds to its appeal, and the asking price is not too bad, either. I would prefer wider rims, though, and have a feeling that 17mm rim beds will soon become outdated as wider versions become more widespread.