Designing a bike is an exercise in balance, engineers teetering back and forth as they plan and build, determining how much emphasis any single attribute deserves and positioning those values into the finished product. Within an aero road frame, this balance is even more precarious. Aerodynamic shapes don’t lend themselves to high stiffness or low weight — two qualities that we still find rather important in the evaluation of overall ride quality. There’s a reason why riding a time trial bike tends to feel a bit like someone has applied a tiny jackhammer to the bottom of your saddle, and why they don’t tend to be in any way light.
This article first appeared on our sister site, velonews.com
Current aero road options run the gamut from the thin, blade-like Cervélo S5 to the fat-tubed, Kamm-tailed Trek Madone and Scott Foil, and everything in between, reflecting the various approaches the industry has taken. Based on our VeloLab testing, the latter two ride stiffer and are lighter than the former, but the S5 is quite a bit faster against the wind. Each has tradeoffs.
Unsurprisingly, Giant says its new Propel Advanced SL doesn’t suffer from any of these tradeoffs, that it’s the lightest, the most aero, and among the stiffest. But we’ve yet to run into a manufacturer that doesn’t make similar claims, and they’ve all been easily disproved so far. Everything has its weaknesses, and its strengths. How does the new Giant stack up?
Frankly, we won’t really know until the Propel goes through the full VeloLab test procedure. I could wax moronic about “holding speed” and “cutting the wind” until my fingers fall off, but absent a portable wind tunnel to bring to Australia, it has thus far been impossible to confirm or deny Giant’s claim that the Propel is the fastest aero road bike on the market, faster even than the S5. Without a stiffness test, we can’t verify the impressive front-end deflection figures, either. And since Giant wasn’t keen on disassembling their bike, we don’t have anything but claimed weight (which is an impressive 950g for the frame). Alas.
However, Giant did allow VeloNews to hold onto a test bike built up with Giant’s own PSL1 wheelset and Shimano’s brand new 11-speed Dura-Ace Di2 9070 for a few days after the official launch in Adelaide, and I put in a total of four solid and diverse rides throughout last week on the same roads featured in the Santos Tour Down Under, including the climbs up Old Willunga Hill and the Corkscrew. Road surfaces varied from nasty chip seal to brand new, smooth asphalt, and though the climbs and descents were not particularly long, they were more than enough.
This rather long-winded synopsis is all completely subjective, of course, but we have had most of the industry’s aero road options through our door at some point in the last year and so have a few good benchmarks to which comparisons can be made. I can say with some confidence that I have a decent feel for the Propel, now.
How it rides
To simplify excessively, the Propel rides as a race bike should. It’s on the stiffer end of the spectrum, despite its narrower tube shapes, and the engineering team has avoided the wooden feeling found on other narrow-tubed frames — a feel similar to the carbon frames of a decade ago, which had to use thicker tube walls to maintain stiffness. The slim top tube and the down tube, which tapers relatively quickly from a thin profile to a water bottle- and stiffness-friendly Kamm tail, likely contribute to that feel.
Tall, thin seatstays, attaching low on the seat tube, result in a very compact rear triangle and make the back end quite stiff in every direction. Road buzz is not muted as it is on the new, aero Madone or the S5. The back end feels more akin to a Foil. It’s lively, a bit jumpy out of the saddle, and carries road vibration straight up the integrated seat mast and into the rider’s behind, particularly on the nastier road surfaces. This is no comfort machine; if you don’t want a frame that is tuned more for get-up-and-go than for plush cruising, look elsewhere. Even among other race frames, the Propel is on the firm end of the spectrum.
Front-end stiffness is impressive, aided by the Control SL integrated bars. Here, the parts spec does make a difference, as the whole system can be brought to its knees by a single weak link — put a noodle of a bar or stem on an otherwise stiff fork/head tube and steering and sprinting turn to mush. The Propel, as I rode it, steered and sprinted as precisely as anything available. The front end seemed to do a much better job than the rear of removing road vibration, too. Again, I wouldn’t call it overly comfortable, but certainly highly acceptable given the frame’s intended use.
The overall sensation is rather similar to a Specialized Venge. It’s less comfortable than top-tier, traditional road frames like the Specialized SL4, Cannondale SuperSix EVO, or similar. But while it fails to cut the buzz like these frames, it loses very little in pedaling or steering stiffness, which is rather impressive given the narrow tube shapes. It does not have that supremely crisp feel that the latest traditionally shaped frames provide — the only two aero road frames to maintain that sensation are the Madone and the Foil. But the Propel is extremely close. If it does turn out to test as well in the tunnel as Giant claims, that small sacrifice could well be worth it.
Beauty and beast in the details
The Propel jumps on the trend towards increased integration of both front and rear brakes, utilizing a TRP-built linear-pull brake system (identical in function to the old V-brakes on your decade-old mountain bike) instead of classic road calipers. BMC’s TMR01 uses a similar linear-pull design, and the new Madone uses Shimano’s new dual-mount units; both frames place the rear brake down near the bottom bracket, which looks great but is highly annoying when doing anything from a quick wheel swap to changing brake pads.
The Propel keeps its rear brake on the seat stays and places the front behind the fork legs, the lines of each lining up nicely with the rest of the frame. Depending on how they’re set up, the brakes alternately offer up excellent power or modulation — finding the sweet spot between them requires a bit of experimentation, but is not impossible. Anyone who worked on mountain bikes in the pre-disc era will be familiar with the setup.
Now, allow me to nitpick a bit.
There is a bit of flex in the carbon brake arms, and if housing length isn’t absolutely perfect the curved noodle doesn’t sit perfectly in its slot, causing it to flop a bit as the brake is actuated. This adds a mushy feeling to the brake, a somewhat unrefined looseness, but can be mostly rectified with very careful installation. The contact point between the brake shoe and brake arm is similarly imperfect, causing the pad holders to squirm as they are tightened down. That makes achieving a perfect toe-in very difficult, but, again, not impossible.
Both of these contact points should be more precise, it would go a long way towards improving brake feel.
A few of the journalists attending the Propel launch, myself included, had issues with brakes coming off center mid-ride, rubbing the wheel and requiring adjustment of one or both tension screws to bring the pads back into parallel. The issue disappeared by the third ride, though.
There are a few other problems inherent in the use of a linear-pull brake. Primarily, there is no true quick release; the brake noodle must be detached from the brake arm itself. It’s a two-second process, but it’s also one more thing to screw up during a fast wheel change, and forgetting to re-attach results in zero braking. A Blanco team wheel change that occurred right in front of me during Tour Down Under took no longer than a standard swap, but the mechanic had obviously practiced the new procedure.
Adjusting the brakes for a wide or narrow rim requires the use of a spacer placed behind the brake shoes. It is obviously possible to adjust the brakes without it, via the cables, but that adjustment must be built into the housing and can only take up so much slack. Even if the cable itself is pulled tighter or let out, using the wrong shims will affect power or modulation, depending on the mismatch between shim used and rim width. The brake shoe shim is therefore required for any large difference in rim width.
The Blanco squad has actually engineered its own version of a short-arm linear-pull brake for the Propel, using custom-CNCed aluminum arms. The primary reason for the custom job, the team says, was to add an important feature: two slots for the housing to slot into, one for wide wheels and one for narrow ones, for quick and easy adjustment in the case of a wheel change. The brakes are set up for use of the team’s wide Shimano wheels, but allow the brake arms to be quickly pulled inwards for a narrow rim without adjusting the cable itself. That adjustment may not be perfect, but it’s better than no brakes at all. It’s a feature we’d love to see on the consumer version.
Despite these shortcomings, the Propel’s brakes aren’t all bad. Attention to some of the small details, like the inclusion of a small hole in which the cable end can be tucked away, is first-rate. And though the pads themselves are a bit of a pain to adjust, the arms are exceptionally easy to move about via a spring tension set screw on either arm. Once set up to one’s own preferences, they do feel quite nice; a good mix of power and modulation.
The brake integration likely plays something of a role in the bike’s excellent claimed drag figures, too, and their less-than-perfect performance may be overlooked for this fact. BMC’s own version of the same system has similar problems, and even the Shimano dual-mount brakes used on the new Madone have issues of their own (like not being able to adjust the rear brake when using a compact crank without pulling the entire crankset off). The kinks, it seems, are still being worked out of these more integrated systems.
Other than the brakes, the Propel is quite user friendly. The seat mast offers a decent range of adjustability, the internal routing can be swapped from electronic to mechanical relatively easily, and there are no other strange proprietary parts.
The Propel may have hit the sweet spot, that magical place between aerodynamics, stiffness, ride quality and weight, but until we see our own lab data it’s impossible to say just how close it has come. It is certainly light, falling right around 15 pounds with a rather heavy wheelset, and overall ride quality falls tantalizingly close to its round-tubed competitors. It feels stiffer than the Cervelo S5, particularly up front, and the tight, compact rear end is exceptionally solid under power. It’s not comfortable, but neither are the Scott Foil, the Specialized Venge, Ridley’s Noah or the BMC TMR01. And frankly, on a race bike, this isn’t really bothersome.
If the Propel proves to be as fast in the tunnel as Giant claims — and the company has made some awfully big claims, stating that its bike is faster than the venerable S5 — then it has a clear winner. But even if it were to be mediocre in the tunnel, it can stand quite well on its other merits. The bike is light, it corners, sprints, and climbs without issue, and the brakes are merely a mild nuisance; the tunnel data may be the final puzzle piece, but even without any aerodynamic benefit the Propel is a frame we’d happily throw a leg over on any race day. That fact alone places it in high company: the only other aero road frames we can say the same for are the new Madone, the Venge, and the Foil.