Giant Propel Disc 2018 first-ride review

by Dave Rome


Giant’s aero road platform, the Propel, has stood mostly unchanged since it was first released back in 2013. Back then the Propel was rather revolutionary, making some bold claims on its speed and with some interesting brake integration and tube shapes to back it up.

In recent years the bike has arguably been screaming for an update as many of its competitors moved to more integrated approaches and refined tube shapes to further cheat the wind. Three years in the making, the 2018 Propel is now ready. It’s the same bike that Sunweb’s Michael Matthews showcased on his way to winning the green jersey at the Tour de France, but now it’s official.

Australian tech writer Dave Rome was last week sent to an unassuming country town within Nevers, France to find out more about this new speedster from the world’s largest bicycle manufacturer. Read on to learn how the 2018 Propel came to be, how testing was done, how it rides, and why Giant believes it’s the fastest bike on the market.


Three years in the making and a decision that’s still a risk today

giant propel and shimano dura-ace disc brake

The biggest story of the new Propel is that it’s only available with disc brakes. As of right now, there is no rim brake model. It’s a decision made even more interesting when you consider the development timeframe of this bike was three years.

Amongst all the uncertainty from the UCI and pushback from the professionals on disc brakes, it’s interesting that such a big company would put it all on the line like that. Giant’s senior marketing manager, Andrew Juskaitis, has long spoken strongly for disc brakes on the road and remains equally vocal when asked about the element of risk in such a decision years out.

“We’re still stressed out,” he said. “Three years ago we were really stressed out. The UCI was really waffling about the situation. But at a certain point we reached a go-no-go and that was based on initial testing we were able to do with CFD (Computational Fluid Dynamics).

“The computer was telling us that it was not only possible to make a disc-equipped road bike faster than the previous generation Propel, but also faster than our competitors. In the end, the decision back then was based on two things – science and gut. Those that have ridden disc-equipped bicycles, you just have to agree that the power modulation you get with a disc brake is just so much superior to a rim brake. Those of us that ride truly believe in disc brakes.

“We knew and still believe that it was the right thing to do.”

When asked whether sales of the TCR rim and disc-brake platforms gave some indication, Juskaistis proved the new Propel is a risk for the company. “We still sell more rim-brake TCR versions than disc versions. And it’s not a price issue, we’re selling top-end rim brake versions. It’s a traditionalist issue.

“I’ll tell you right now it’s a risk. We’re offering a brand new product for 2018 that right now is only available in a disc version. Some of our sales teams around the world are quite scared of our commitment (to disc brakes), to the point and to be frank, they’re carrying the old Propel for 2018 as well [ed: not applicable for Australia and North America].”

Aero elements

So why did Giant launch its new aero road bike in the quiet, rolling hills of Nevers, France? Quite simply, because its wind tunnel and aerodynamic experts, including former F1 racing aerodynamicist Xavier Gergaud, are found at Aero Concept Engineering (ACE), a former F1 aerodynamic testing facility that sits within the greater complex of the Magny-Cours race track.

ACE wind tunnel
A look inside the wind tunnel. The floor rotates between 0 and 30-degree yaw angles. It’s an impressive facility, a full steel closed circuit – allowing for reliable and consistent testing.

Giant has used this ‘low speed’ facility and the attached expertise for the past seven years, since work started on the first Propel project. Gergaud’s wind tunnel and CFD expertise has also been applied to projects from the likes of Bianchi, Lapierre, Shimano, Mavic and Look, an extensive list of WorldTour teams and many other industry applications too.

However, in the case of Giant, they have an exclusive (and arguably industry-first) testing protocol in use – a moving mannequin and rolling system to replicate a rider in motion on the bike. It’s something that creates a more real-world testing scenario that also overcomes the inconsistency issues found when testing with real people. This specific and extremely time-intensive testing protocol is a clear example of Giant’s development budgets.

With Gergaud’s help in computational fluid dynamics (CFD), Giant were able to realize that keeping the frontal profile as clean as possible, especially around the fork crown, offered greater aerodynamic advantage than that lost with discs. Additionally, it was discovered that the front tyre, rim, spokes and then fork blade are already creating enough “dirty air” that the addition of a disc rotor and calliper has a negligible effect on drag. Giant uses an asymmetric fork design to help shield and push air around the front disc-brake calliper too.

Beyond the discs, the new Propel doesn’t share a single tube shape in common with its predecessor. The new ‘AeroSystem Shaping Technology’ tubes use a truncated ellipse shape that’s similar to that found in a number of other leading aero road bikes. It’s a design that, while perhaps not the absolute fastest in cheating the wind, allows far greater engineering freedom in creating a frame that performs like any good road bike should.

propel downtube close-up
Giant’s new ‘AeroSystem Shaping Technology’ at work. The shape is a ‘truncated ellipse’.

The original Propel was fast, but even its creator, Nixon Huang, Giant’s Road Product Manager, admitted it is now a dated design in real-world situations. “The original Propel tube shape design was strong at 0-degree yaw — at 5 degrees and beyond it, the trailing edge would hang up,” said Huang.

“The new Truncated Ellipse shape is superior to teardrop shaped tubes in multiple yaw angles. This new shape is used across the whole bike, stem spacers, fork blades, downtube, seattube, etc. The handlebar is the exception.

“The bottom line is that our numbers are really really close to these guys. In some cases it’s so close that it’s within tolerance of our wind tunnel, plus or minus one watt. Everyone is doing a great job, but we meet or beat our competitors with this new Propel.”

Giant now does its testing from zero all the way to 30-degree yaw angles and takes an average of these numbers (weighting unknown). This same testing protocol, with Giant’s own mannequin, is repeated to judge its competitors too, with the likes of the Specialized ViAS Disc, Trek Madone (rim brake) and Canyon Aeroad CF SLX being used as benchmarks. Giant claims the new Propel is on average 15 watts faster than the old Propel (at 38.6 kph/24 mph, 85rpm cadence).

“We do have numbers that prove ours is quicker than our core competitors. And I must say, all of these guys are doing a great job. When we first started our original Propel project, it was evident who was doing the aerodynamic testing for real, and who was just cheating,” said Juskaistis. “In 2018, you can’t make a bike and not have spent a lot of time in the wind tunnel. We know guys like Canyon and Trek are spending lots of time in the wind tunnel, because it shows when we test them.”

Aero x Stiffness / Weight = Propel

Giant aren’t making bold claims on how much faster the new Propel is in a wind tunnel, but they certainly aren’t shy to claim that it’s the most ‘efficient’ bike, with a claimed class-leading combination of aerodynamics, weight and stiffness.

For stiffness X weight, Giant puts itself at the top of the competitive test group.

Using the protocols established by Germany’s Tour magazine with size medium (or equivalent) framesets, Giant tested the overall stiffness of its and competitor frames. Of note, Giant did this with the actual fork in place, where others often do it with a steel bar instead.

propel frame stifness
Medium or equivalent frames tested.

Weights are a far less subjective measurement, and in Giant’s benchmark tests, the new Propel bests the Trek Madone and Specialized Venge ViAS Disc, but is beaten by the Canyon Aeroad CF SLX Disc. The new frame is 45g heavier than the old Propel, but still comes in under 1,000g. Actual complete bike weights (weighed by the author) are listed toward the end of this article.

giant-propel-sl-disc--frame-weight-chart

With all the talk of stiffness to weight, compliance was hardly mentioned and is rarely discussed in what’s effectively a sprinters bike. When asked about this, Juskaistis explained: “Compliance really comes from the layup schedule, and Nixon Huang, our road engineer is a master in that domain. Compliance was low on the list, but I think it’s a pretty comfortable bike.”

Talking along similar lines, Huang did admit that the integrated seatpost (ISP) found on the top-tier Advanced SL bikes does afford some more compliance than the adjustable post of cheaper Advanced versions.

Geometry is mostly unchanged since the last iteration, with only a few tweaks found in mostly smaller sizes. The new Propel Disc will be available in six sizes ranging from XS through to XL.

giant propel 2018 tyre clearance
A peek down the side reveals available tyre clearance. Giant claims the Propel Disc can fit a 28c tyre. A 25c is pictured.

Looking to the small details and the new Propel is not too different from the TCR Disc. It uses 12mm thru-axles, with 142mm spacing at back. Flat mount disc callipers keep things tucked and are matched with 140mm disc rotors front and rear. Without rim brakes in the way, the frame has plenty of clearance around its 25c tyres. Officially there’s room for 28s.

propel headtube
The headtube uses an hourglass shape, pinching between its oversized bearings.

The headtube sticks with Giant’s ‘OD2’ design, using a tapered design that sits at a larger 1.25in diameter where the stem is clamped. The bottom bearing is just shy of 1.5in. The bottom bracket remains with the Shimano-standard BB86 pressfit design, something Giant hasn’t swayed from since leaving threads.

System approach bike design – wheels and cockpit

Like so many other modern aero bikes, the Propel’s stem and handlebar move to an integrated setup that allows truly hidden internal cable routing. Instead of a one-piece system, Giant uses its own two-piece design that allows for arguably easier setup and greater control over mixing handlebar widths and stem lengths. Additionally, the two-piece design creates a nose-cone affect for a claimed improvement in aerodynamics.

The cable routing runs internally through the aero wing bar and then runs along the top of the stem, beneath a composite cover. The cables are then run behind the steerer tube, covered by flexible rubber before entering the back of the head tube. The only exception to this setup is seen with the base level model Advanced Disc, where its mechanical shifting doesn’t work with such a tight radius. In that case, the cable exits the bar and runs diagonally into the stem.

Giant SLR 0 42 Disc wheel front
Giant chose a shallower wheel for the front to provide a more stable and easily controlled ride – even if it is slower in the wind tunnel. For this reason, you’ll find a 42mm wheel on the front, and a deeper 65mm profile on the back.

Giant continues its system approach with wheels too. In its wind tunnel testing, it found deep 65mm wheels front and rear were fastest, however, a compromise was made and the Propel comes with a 42mm deep front wheel, and a 65mm rear wheel. It’s a choice designed to make the bike handle better in windy conditions and help lighten the front steering.

All 2018 Propel Disc models will be sold as tubeless. In fact, Giant has made the huge step in making all of its 2018 performance road bikes tubeless. That’s not like other brands that supply you the valve and tape in case you want to ditch the tubes — Giant instead includes a bottle of sealant for the shop to simply fill the tyres with prior to handing over.

To this end, Giant is offering a full range of tubeless accessories for 2018, including tyre sealant, rim tape, valves, special tyre levers, inflators and even quick-fix patch kits. The last of those simply comprises pieces of new tyre tread and some fast-setting glue that covers a cut or rip from the outside to let you get home in an emergency.

Giant Propel computer mount

Included with each bike will be an optional out-front computer mount. It uses replaceable chip inserts, with mounts included for a Garmin or Giant’s own new NeosTrack (we’re working on a review) computer. Below the mount are two threads designed to work with common camera and light mounts. When asked, Huang admitted that the mount was not tested in the wind tunnel with the bike.

First Ride(s) impressions

Over two days I was given the chance to ride the range-topping Propel Advanced SL 0 Disc. The only pieces not stock were the missing Dura-Ace powermeter and the saddle that was swapped to remove a testing variable.

The first ride saw a select handful of media representatives roll onto the closed-circuit Magny-Cours racing track for two hours. Racing circuits built for motors are typically quite a drag on a bicycle, but this short and punchy course proved to be quite fun and even better for testing the handling and sprint-ability in a controlled environment.

Credit: Sterling Lorence

The following day saw the same group weave through 75km of local rolling hills in France’s summer heat. It was a chance to test just how the new Propel climbed, descended, attacked and cruised – all over an impressively wide variety of road surfaces, including gravel-littered farm tracks.

The testing was just enough to prove the ability of the new Propel. As a bike built for performance, especially in the final kilometre, it offered a noticeable improvement on the previous Propel. Actual aerodynamic performance isn’t something I can comment on, but how it behaved as a bike is.

For me the previous Propel always felt a little soft through the front-end. Throw your weight around and you’d see the bars twist with the top tube. Such a sensation was totally absent in the new Propel thanks to an extremely rigid bar setup matched with a much stiffer frame design. It’s something you instantly feel when out of the saddle or fully committing to tipping the bike over in descents.

Credit: Sterling Lorence

Put the power down in or out of the saddle and it’ll jump without hesitation. Hit a long or steep climb and it’ll get you to the crest, albeit with a little more effort than a lighter race bike specifically built for such situations.

Stiff axles and hubs means brake rub wasn’t heard, even in a monkey-armed sprint with the bike swinging from side to side.

I managed to test the bike side-on to some strong wind gusts and it handled amicably, the truncated frame and shallower front wheel being easy to handle with my lighter weight. I certainly wasn’t having to fight it.

Credit: Sterling Lorence

While the ride quality gave plenty of feedback from the road, it didn’t amplify anything and by no means was it unnervingly harsh. Bump-filled high-speed descents proved the Propel holds its line well, and I didn’t notice any skipping at the wheels. Keeping in mind this bike was built for sprinters who typically see compliance as power loss, the ride was surprisingly forgiving.

If I had more time on the bike, I’d be keen to test a different wheelset and see just how much of this was the tubeless tyres at work, though they were set up at a relatively high 100psi.

Looking beyond the frame it’s difficult to complain about the component specification. Shimano’s new Dura-Ace R9170 Di2 shifted exactly as expected and the ergonomics at the hoods were superb. The supplied sprint shifters make a great match for the bike’s purpose too.

The Dura-Ace hydraulic discs provided another level of control that would be impossible to match with any rim brake and carbon rim. With them, you’ll find yourself braking later into turns and with less effort required to do so. However, the brake pistons don’t always fully retract after using them and you’re left with the whisper of a rubbing disc. It’s not enough to slow the wheel, but is an annoying sound to hear. A quick tap of the brake was typically enough to solve the issue.

The tops of the bars are left unwrapped for aerodynamic advantage and were large enough to provide a comfortable surface to grip. A subtle upward angle is given to the tops which helped perch my hands up without having to grip too tightly. I found the handlebar top set further back than what I’m used to, and as a result was bumping my knees on it at first – I soon adapted to sprint a little more centrally on the bike, however.

As a performance bike, it was really hard to fault the new Propel. Clearly Giant has been patient with its design and it showed. However, it’s when you start looking at your options to personalise the bike that negatives start to appear.

giant propel 2018 handlebar shape
The compact handlebar shape is the only option for the new Propel. The tops are set relatively far back.

The most obvious example is seen with the handlebars. Despite the two-piece design, the tilt of the bars is not adjustable. And while the compact shape, its chosen angle and large flat top surface was pretty comfortable, it may prove to be the maker or breaker of this bike.

If for some reason you don’t get along with the shape or profile of this handlebar, you’re out of luck. To overcome this, you’d need to swap out both the bar and stem, and then deal with the unsightly cable routing. This is a bike that was never designed to be used with anything other than its own bar and stem combo, and the fact that the entry-level Advanced model uses the same cockpit design is strong proof of this.

Like so many other modern aero bikes, setup is always going to be more painful. For example, adjusting stem height will always mean having to eventually commit to a cut steerer tube. You can install a regular 1 1/4in spacer on the top of the stem to play with going lower, but you won’t be able to fit the stem’s cable shield while you do this.

I walked away from the test impressed with how versatile the new Propel is. It’s light enough to not be a burden on climbs, it descends with a match of both control, and crazed speed and sprints without a hint of wasted energy.

Regardless of whether you believe in disc brakes or not, Giant has done a very good job with this new race bike. Just be sure you get along with that handlebar shape.

Model prices, specification, and actual weights

In the biggest markets, the Propel Disc range will consist of four models. The top two models (with ‘SL’ designation) share the same Advanced SL grade carbon frame and fork with Giant’s integrated seatpost (ISP). These two bikes also feature Contact SLR (carbon) versions of the integrated stem and handlebar.

All four models come stock with 25c tubeless tyres from Giant featuring Silica-infused dual-compound tread. All bikes use 52/36T front gearing combined with a 11-28T cassette. All but the base Advanced model will include a ‘RideSense’ Bluetooth cadence/speed sensor and bottle cage.

As tested, the Propel SL 0 Disc (US$11,300 / AU$11,999 /£TBC) is equipped with Shimano Dura-Ace R9170 Di2, including sprint shifters at the drops. Production versions will include the Dura-Ace powermeter. Rolling stock comes in the form of Giant’s new SLR0 42/65 wheelset, setup tubeless with Gavia Race 0 rubber. Using a trusty set of scales, a medium sample weighs 7.33kg with a standard set of Dura-Ace R9100 cranks fitted (no powermeter).

Sharing the same frameset, the Propel Advanced SL 1 Disc (US$7,000 / AU$7,999 /£TBC) greatly reduces the price by first dropping the power meter, and then moving to the new Shimano Ultegra R8070 Di2 groupset. Additionally, the wheels are swapped to the SLR 1 Disc, something that share the identical rim as the SL 0s, but move to a lower grade Sapim spoke and swap the hub internals from Swiss-made DT Swiss 240 to cheaper DT Swiss 360 internals. All up, a sample of this model (in a medium) weighed an actual 7.57kg.

The lower-priced Propel Advanced Pro Disc (US$5,700 / AU$6,599 /£TBC) moves to an Advanced grade carbon frame and fork, with an adjustable aero seatpost in place of the ISP. It features a Shimano R8070 Di2 groupset, Giant’s own SLR -1 wheelset and Gavia Race 1 tyres. The handlebar is still carbon, however the cost means the stem moves to an aluminium version – something that’s said to be heavier, but otherwise the same. A medium sample of this weighed 8.12kg.

Update: We’ve now reviewed the 2018 Giant Propel Advanced Pro Disc. Click through to read this in-depth review.

Sitting at the bottom of the Propel range, the Propel Advanced Disc (US$3,700 / AU$4,999 /£TBC) shares the same Advanced frame as the Advanced Pro model, but uses a heavier alloy fork steerer. This model is the only in the range to use mechanical shifting (Ultegra R8020). The bend is apparently too tight within the handlebar and stem for the mechanic shifting, and so this bike moves to an alloy Contact SL handlebar that has small exit ports for the cable housing to briefly pop out of the bar and into the side of the stem. It may not be as visually appealing, but it’s still hidden from the wind.

The wheelset is the same as that on the model above: the SLR 1 42/65mm combo. With the alloy handlebar and heavier fork, a medium sample of this model read 8.37kg on the scales.

Credit: Sterling Lorence

Disclosure statement: Giant Bicycles provided accommodation, meals and flights for Dave Rome to attend this launch event.

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