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by Dave Rome
April 4, 2018
Photography by David Rome
When Giant unveiled its long-awaited update on the Propel aero road bike, the curtain was raised with astonishment – but not because of the aggressive use of truncated aero shapes, staggered rim depths, or the clean-looking proprietary cockpit. Rather, it was because the race-focused machine was revealed with disc brakes and no alternative. Giant was putting all of its cards on the table.
It’s been several months since tech writer Dave Rome first test-rode the new Propel Advanced SL Disc at the launch in France. Stock has been slow to hit bike shop floors since then, but Rome nevertheless got his hands on a lower-level version of the bike and put some rubber down on his local Sydney roads.
We already covered how this bike came to be during our initial launch coverage of the Propel Advanced SL Disc, along with first ride impressions of Giant’s flagship aero road racer.. But as a refresher, Giant concluded during prototype testing at Aero Concept Engineering (ACE) in France that a disc-brake bike could not only compete aerodynamically with a rim-brake bike, but could actually be faster.
According to Giant, and with the help of a moving mannequin for more realistic testing, removing the clutter of rim brakes from the fork crown more than offsets the extra drag that comes from the additional hardware down by the hubs. No specific data has been shared, but Giant claim the new Propel at least “meets its direct competitors” in the wind tunnel. Compared to the previous Propel, the new disc version is claimed to save an average of 15 watts at 38.6 km/h (24 mph) when pedaling at 85rpm.
Giant Propel Disc 2018 first-ride review
Giant pushed aerodynamic UCI limits on the old Propel with long teardrop-like tube profiles, but those skinny cross-sections didn’t exactly make it the stiffest bike on the circuit. The new profiles are still deep and narrow this time around, but now have truncated tails like many other aero bikes, such as the Trek Madone. Switching to a truncated design effectively made all of the tubes wider and stiffer without increasing drag, and along with a new material lay-up schedule, Giant say the new bike is approximately 36% stiffer torsionally, and is now much better suited to strong sprinters fighting for the line.
The flat-backed down tube and seat tube are vastly different to the original Propel.
Further aero tricks include a horizontal top tube that tapers toward the slim seat tube, sleekly profiled dropouts at the bottom of a bowlegged fork, and a rear wheel cut-out wide enough to shield a 28c tyre. But according to the Taiwanese mega manufacturer, a key part of the wind tunnel time was spent looking at the bike as a complete system, rather than just the frameset.
The new cockpit was a big part of the aerodynamic puzzle, and like many in the industry, Giant realised big gains by cleaning up a key frontal component. Where many others have gone with one-piece handlebar and stem combos, Giant designed a two-piece aero system which allows for simpler size customising and servicing. The deep-drop bar pushes the UCI’s 3:1 aspect ratio rule to the limit, and the stem has a rounded nose up front. A separate bolt-on cover (which Giant state is UCI approved) hides brake hoses and gear wires (or cables) internally, shielding them all the way down the back of the fork steerer into the frame.
The Propel Advanced Disc offers a clean front end.
Lastly, the wheels were another point of focus. Giant found that deeper rims are faster to a point, but they also hold obvious compromises in real-world conditions when instability in crosswinds can effectively make them slower. To overcome this, Giant sacrificed some aerodynamic performance in favor of a staggered rim setup that uses a shallower 42mm-deep front wheel with the 65mm rear wheel. The mullet setup of wheels is far from conventional for an out-of-the-box bike, but it proves that Giant is willing to compromise wind tunnel numbers in order to create a bike that handles more like a bike should.
Giant produce the Propel Disc in two frameset variants: the Advanced and the Advanced SL. The latter is the company’s flagship offering, the product used by its pro riders and what was tested at the launch. That model offers a high-grade carbon composite for an improved stiffness-to-weight ratio, along with an integrated seatmast that Giant say reduces weight and improves ride comfort by promoting more flex on bumpy roads.
An adjustable seatpost is an often-favoured feature of the second-tier Giant road bikes.
The Advanced level frame tested here uses a lower grade of carbon fibre composite to help bring the costs down. There’s also a separate telescoping aero-shaped carbon seatpost, which uses an internal wedge seat clamp to hold it in place. Such a change is likely a blessing for those that wish to travel with their bike.
Further adjustments to the frame are seen at the cockpit, and while the Advanced Pro Disc features the same carbon aero handlebar as its top-tier siblings, the matching stem is aluminium, not carbon.
With a full Advanced SL Disc frameset said to weigh 2,145g (including cockpit), the lower-grade Advanced frameset, with its separate seatpost and alloy stem, clocks in at approximately 450g more. Considering the Advanced Pro Disc (as tested) shares an otherwise-identical component spec with the Advanced SL 1 Disc (AU$7,999 / US$7,140), the AU$1,400 / US$1,325 price difference gives you some indication of what that weight is worth.
The rest of the build simply comes entirely from Shimano and Giant’s own house brand. Such a trend is increasingly normal, and certainly, the likes of Specialized and Trek can claim a similar feat. The pessimist in me sees it as a way for the big bike brands to ensure you can’t directly compare value for money, all the while offering said components for sale separately to establish said value. While that may be an element of it, in reality, it’s just smart business when a company can engineer and produce components that are competitive as name brands, but at a lower cost.
Two small bottles of tyre sealant is included with the bike. The sealant is made by NoTubes, but keep that a secret.
Like all of Giant’s performance road bikes, the Propel Advanced Pro comes straight out of the box set up tubeless, in this case with Giant’s 25c Gavia Race 1 tyres. All that’s needed to complete the setup (for the shop) is to squirt the included latex sealant through the valves. From there, the tyres inflate with ease.
Tubeless requires more maintenance than set-and-forget inner tubes, but remembering to top up the liquid tyre sealant every three-to-four months is a fair trade for the benefits. These include the ability to run a lower pressure without risk of a pinch flat, and reduced rolling resistance. The sealant also has some seal-repairing capability; as long as the holes aren’t too big, they’ll automatically seal on the move. In addition, the weight is similar (or sometimes even lower) to a tube setup.
The tyres are mounted on to Giant’s SLR 1 Aero wheels. Compared to Giant’s top-tier SLR 0 wheels, these feature heavier hub shells, lower-level DT Swiss hub internals, and heavier DT Swiss spokes. However, the tubeless carbon rims are identical between the two sets.
The out-in-front mount features a two-bolt mount beneath it, allowing the addition of lights or a camera.
Giant includes two bonus accessories, the first being an integrated out-in-front GPS computer mount that wedges between the stem’s two lowest bolts. This composite mount is stiff, but like the prototype I previously tested, the Giant Neostrack computer has the slightest amount of wiggle in it. Pucks for Garmin and Giant’s own NeosTrack computer are provided, but unfortunately, there’s no word on when a Wahoo Fitness puck will become available.
The second item is Giant’s wireless RideSense cadence and speed sensor, which bolts directly into the left chainstay and offers both Bluetooth and ANT+ communication.
The remainder of the build is a full Shimano Ultegra R8070 Di2 disc brake groupset. The popularity of this new generation of Ultegra has caused enormous supply issues for many bike brands, including Giant (hence us being halfway through the season and only just receiving 2018 bikes). It’s effectively a heavier version of Dura-Ace 9170, so there’s little to complain of here, especially considering the slender shape of the updated hydraulic lever design. Unlike the Advanced SL models, the Advanced Pro does not feature Di2 sprint shifters in the drops.
All up, my medium sample weighs exactly 8kg (17.64lb) without pedals.
Building up the Propel allowed more insight. It’s certainly simpler to adjust the handlebar position, or work on overall, as compared to the likes of the Trek Madone or Specialized Venge Disc. But it being a true aero bike means it’s still a more involved process.
An obvious departure from a regular bike is seen at the cockpit. Stem lengths (available in 80-140mm, in 10mm increments) can be changed with relative ease, as can bar widths (40-44cm options available), but you’re stuck with a single choice of compact handlebar shape and eight-degree stem angle. There’s also no way to adjust the bar angle.
Like all of Giant’s performance road bikes, the Propel Disc features Giant’s OverDrive2 1 1/4 tapered fork steerer and stem diameter. Compared to the standard 1 1/8in diameter, Giant’s design is said to be stiffer without weight gain. This typically means you’re locked into a limited choice of compatible stems, but given how the internal cable routing is setup on the new Propel, you’re effectively locked into the provided system regardless.
Cables run along the top of the stem, and sealing them from the wind is a composite cover held on with four small screws. Care is needed when using these as the screw heads are extremely shallow and the fine thread promotes accidental cross-threading. Use a high-quality hex key.
What the front end looks like with the stem lowered and steerer tube uncut.
Unfortunately, this cover only fits when the steerer tube is cut flush with the stem. As you can see in many of the photos, the Propel comes equipped out of the box with a huge stack of spacers. I typically don’t cut steerer tubes on bikes I don’t own, so much of my testing was done with the aero cover removed. Certainly be aware that you may need to resort to similar measures if dialing in the fit of your bike on the road.
Giant have been clever with its hidden cabling, and each headset spacer is given its own rubber shield. These stack together to create an evenly profiled cable cover from stem to frame. Removing a spacer simply requires unclipping the rubber shield from the respective spacer, and sliding the spacer off.
The composite stem cover incorporates small sprung wings at the rear, but unlike the wings on a Trek Madone that move as the handlebars are turned, these do nothing more than provide a window to access the clamp hardware. However, you’ll still need to remove the cover to adjust the headset preload.
The two-piece cockpit setup may be slightly easier to service than the fully integrated setups from other brands, but the internal cables still give you a short leash. If you plan on flying with the Propel Advanced, you’ll want a travel bag that keeps the handlebar in place, such as from Sci-Con.
The Shimano Di2 junction box sits at the end of the handlebar.
The Shimano Di2 hardware is well integrated, with the only wire in sight seen at the rear derailleur and the new EW-RS910 junction box tucked away inside the end of the handlebar. Wires do run outside of the bar and beneath the bar tape, though, from the drops to the shifters.
An expanding wedge system holds the Di2 battery in the base of the seatpost. The wedge uses a rubber sleeve, and I did suffer from the bolt pulling through the hole. A small washer quickly solved the issue, but if you’re ever having rattling issues, or the battery won’t stay in place, check this part.
Featuring a carbon shaft and with a bonded alloy head on top, the Giant aero seatpost features a reversible saddle clamp for variable set-back and infinite angle adjustment.
Both front and rear wheels are held by threaded 12mm thru-axles. The finishing angle of the axle levers can be adjusted with a hex key.
Lastly, the bike features a Shimano-standard PF86 press-fit bottom bracket, designed with 24mm-diameter crank spindles in mind. Press-fit bottom brackets get a consistent bad wrap, but my experience has been a pretty silent one with this system.
As the saying goes, first impressions last. My time riding this lower-level Advanced Pro has left me with much of the same impressions I got at the launch: the bike does everything you want from a race-specific ride, and it does it well.
But what I can’t comment on is how well it performs from an aerodynamic point of view. Like any good aero bike or a bike with aero wheels for that matter, it feels faster in a straight line than a conventional bike with round tubes and non-aero wheels. However, I’ll save the pseudo-science or regurgitating of marketing material and rather focus on how the bike rides.
That’s a whole lot of stack straight from the box.
The Propel may be designed for racers, but Giant have apparently aimed for those racers who also spend too much time in an office chair. The stack is a bit tall, there’s an enormous stack of spacers provided stock – far more than anyone actually racing would want to be seen with. The availability of long stems helps, but the single angle choice will mean that those seeking an extreme position will likely need to size down, much like many of the world’s top pro sprinters. With a generous handlebar reach, though, the actual reach to the bars is a tad longer than the geometry chart would have you believe.
The frame angles are fairly traditional, with 73-degree head- and seat tube angles in a medium. All frame sizes use the same 45mm fork rake, and Giant maintain a common 57mm trail figure in sizes medium and up. Likewise, the 405mm chainstay length is pretty average for such a bike.
The bottom bracket is relatively tall, sitting 67.5mm below the axles (70-72mm is more common these days). The Propel offers more pedaling clearance through tight turns when fighting for position in a crit because of that, but it comes at the cost of planted handling. Overall, the Propel clearly favours agility over stability, with a subtle feeling of tipping into corners as opposed to flowing. It requires very minimal input to change direction, but it’s also a machine that demands attention.
In a heavy cross-wind, wind buffeting on the deeper frame tubes and deep rear wheel can be felt. Having the shallower front wheel absolutely makes a huge difference and rather than fighting the handlebars, the front wheel stays respectively planted, and your body weight is left to keep the deeper rear wheel in check. I’ve said it before, but I am a fan of the mullet wheel setup, and aesthetics aside, I’d choose to use a similar setup.
Even at my 69kg weight, the original Propel would flex through the top tube in a sprint. By contrast, the Propel Disc is certainly stiffer than I am strong, and absolutely no flex is evident when I’m doing a pathetic full-speed attack. This same stiffness reels back some love lost on the descents due to the high bottom bracket, with quick response and tactile road feedback.
Talk with any top-level sprinter and their opinion is that frame compliance is rarely a consideration, even if it keeps them fresher for the finish. The 25c tubeless tyres (measuring an actual 26mm) go a long way toward muting the smaller stuff and keeping the bike planted, and with room for 28s, a reasonable amount of comfort can be had. However, the aero profiles, oversized steerer tube and impressively stiff cockpit are clearly about power transfer before comfort. The Propel certainly shows its true colours and while the sound is turned down just a little, you can feel exactly what your wheels are doing on the road’s surface.
Keeping in mind that the initial test of the Advanced SL was months ago, in different conditions and with a different tyre setup, I do believe the ride of the flagship model was marginally smoother. I suspect the integrated seatpost does help to tone down vibration.
The limited choice in handlebar shape remains my biggest issue with the bike. The angle and general shape are good, but the deep-section tops present wrist clearance issues when your hands are in the drops. In a position where I can still reach the brakes, it’s near unavoidable. And given this is a bike for the sprinters, it’s not ideal that only those with wide elbows will find comfort.
Giant have definitely fixed the biggest weakness of the previous Propel. Those original linear-pull rim brakes were nicely integrated, but offered a vague lever feel and so-so modulation. The Ultegra hydraulic discs on the new Propel Advanced are at a benchmark level, however, and being able to brake late into a corner is definitely an advantage.
The Propel is set up to use smaller 140mm rotors, however, and while they’re lighter and more aero than 160mm discs, they also generate less raw stopping power (the latter being something you don’t really need with just a few millimeters of rubber on the road). An additional downside of the smaller rotors is heat management, but the three-layer Shimano Ice Tech rotors and matching finned pads help offset that.
The only trade-off to the superior brakes is the increased bike weight. While not an issue once at speed, the extra mass can be felt when climbing. It’ll get you to the top without fuss, but it lacks the eager jump of a lighter bike. Such a note shouldn’t be surprising given it’s a mid-tier aero bike with semi-deep wheels, but it’s worth mentioning nonetheless.
Helping scale those climbs is a reasonable semi-compact (52/36T) chainset that’s well suited to general training and racing. With an 11-28T cassette out back, the vast majority of riders will be happy with the versatile gearing.
Finally, aesthetics are such a personal point, but the Propel offers an appealingly slick profile (with the steerer tube trimmed). Particularly at the cable-free front end, it’s a bike that screams its purpose of going fast. However, the Aussie national champ colours of the Advanced Pro are certainly going to be polarising, to say the least.
A closer look at the truncated down tube.
Not a wire or brake hose in sight.
So much of that front-end stiffness comes from the wide down tube.
These wheels share the same carbon rim as the SLR 0 model found on the Advanced SL Disc 0.
The 42mm-deep front wheel gives an unusual contrast to the 65mm rear wheel.
One slippery profile.
The new Shimano R8170 shifters are a huge improvement to the previous Ultegra-grade offering. These share an extremely similar shape to the rim-brake equivalent.
The new Ultegra Di2 features a slimmer rear derailleur, so it’s less likely to get knocked about in a crash. Giant do not use the new direct-mount standard as of yet.
While technically a fairing, the stem cover is fully UCI approved.
Stem cover installed.
Don’t like green? Sorry, you’ll need to look to a different model.
Also from Giant’s component house is the Contact SL Forward saddle. It’s a minimal saddle, and pretty narrow by current standards.
The RideSense speed and cadence sensor is included with the bike. Its fitment is optional.
How that computer mount is fitted.
A special thank you to the Manly Warringah Cycling Club for hosting this bike shoot during its HART Friday night criterium. The weekly racing will be back next summer.