Scott FOIL: Road Aero Redefined
While most makers of carbon bike fames have been building super-light and super-stiff frame sets in recent years, not many have taken up the challenge to create a road frame that is also more aerodynamic. Scott’s FOIL was one of the first to combine all three.
We met in Vegas, by the pool at Treasure Island.
By now you’ve seen these in the pro peloton, first under the Team Highroad riders (including Mark Cavendish who helped in the design process, and now under the Orica-Greenedge riders), and likely read a review or two. And while the frameset design itself has been extended across a variety of price points by Scott, the growing number of “aero” road frames from other manufacturers only adds credibility to what Scott was doing two years ago, when they launched the FOIL as an aero shaped road frame that was both very light, and very stiff.
And here’s Matt Goss’s Scott FOIL at the 2012 Tour de France.
Development on the bike began in 2009, when Scott was sponsoring Team Highroad, and was asked for a bike that had yet to be built – something that would be lighter, stiffer, and more aerodymamic than anything before – while of course adhering to the UCI’s strict guidelines for these parameters.
We talked at length with Scott’s chief engineer on the FOIL, Cyril Beualieu, who told us: “We tried to find a new concept to improve aerodynamics without using a complete aero profile, which is very bad for stiffness and weight.”
Building all three of these criteria into one frameset is anything but easy: there are plenty of light and stiff bikes, but these two parameters usually come at the expense of an aero shape. Giving up material to lose weight means you have less material to shape into anything ‘aero’, while shaping the tubes to counteract wind drag generally costs ‘stiffness’ at key places in the frame. Conversely, making the bike aero usually requires more material, which adds weight, or if done to keep the weight down, you end up with tubes so small they’re anything but stiff.
Make It Light, and Make It Stiff
The FOIL’s 840 gram frame is made from Scott’s proprietary HMX carbon – which they dubbed “high modulous extreme”.
It starts with carbon strands made to their own spec, designed with a very high tensile strength (they use a stiffer fiber so fewer strands are needed to achieve their desired tube stiffness) that results in a lower weight in the final product. An HMX frame can weight up to 100 grams less than a similarly sized FOIL frame made with their next best grade HMF carbon.
Like many of the top builders, Scott has developed its own process for forming carbon frame sections, and indeed whole frame sets. Scott’s integrated molding process (IMP) is their version of forming the tube sections under variables of heat and pressure to create very light, very strong, and very well shaped pieces that form the bike frame.
Cutaways of the frame reveal that the tube walls are a lot thinner than I expected, especially given the relative large diameter of the main tubes. Bottom line is that they started out with a lighter material, then used some smart shaping so that less material was needed for the overall frame.
The higher tensile strength of the fibers and overall tubes, combined with tube shapes that are anything but round, resulted in a frameset that comes in light, and is so stiff that the HTC boys actually asked Scott to dial back the stiffness on prototypes.
Ride quality is determined with a combination of their carbon choices, and how they choose to lay up the carbon sheets. Since they know the flexion of each fibre and in which directions they flex, so they can control the stiffness at any point on the frame.
Make It Aero
So the weight and stiffness issues were covered – but what about making the whole package more aero? Remember that a couple years back, many manufacturers were delivering TT bikes that the UCI deemed “too aero” for a bicycle. The UCI announced its version of what was legal, and the manufacturers were invited to work within these parameters – if they wanted the all powerful “UCI Approved” decal that would make their bikes race legal. Scott got on board immediately to work within the guidelines.
The engineering challenge was to take tubes with relatively small surface areas, and shape them practically for use on a road bike to direct airflow the way they wanted.
When looking at any aero-designed bike, it’s important to remember that real-world wind direction is anything but constant. Unless you’re moving in a straight line, riding with no wind at all, you’ll be subjected to wind angles that swirl from many directions, and these will impact how efficiently the bike & rider will move through the wind. So tubesets and frame designs need to consider wind resistance from various yaw angles to truly paint a more complete picture.
Scott provided the diagram below to show computer modeled airflow around a round tube, a fully ‘aero’ NACA tube, and a FOIL tube, which gives a good indication of how well the various tube shapes perform to wind coming from straight on.
Cyril told us: “In our first study, we wanted to find out which shape would be the best to optimize our three parameters: stiffness, weight, and aerodynamics. So, I simulated a round tube, a complete NACA profile like in the Plasma, and then I tried to analyze the barrier of the airflow on the tube and the separation. On the round tube, you can see the flow creating a lot of turbulence and separating quite early. Early in this case is in the middle of the tube. That creates a lot of negative force and a big tail with some turbulence. On the complete NACA profile, you can see that there is a very laminar flow around the tubing, which stays attached for a very long time to the tail. The separation is very narrow. That reduces the negative force on the back of the tube.”
Note how the rear surface of the FOIL tube is flatter – almost like the base of the triangle. This semi-triangular shape is really the heart of how these tubes are both aero and stiff.
As part of my due diligence, I called the Dave Salazar at A2 Windtunnel, who confirmed the Scott’s diagram is on the up. Dave also confirmed that the least aero of all tube shapes is in fact the ‘round’ tube – which generally causes air to separate sooner than a foil shape as it flows past, thereby creating more turbulence and a larger wake which will add more drag.
The diagram shows how Scott’s design takes a traditionally shaped aero tube and effectively uses only the leading edge of a full NACA tube to create the tube itself – removing the 3- to 4- times longer trailing edge altogether. This gets rid of all that extra weight, and offers up a tube that still directs air around it like a much larger surfaced tube would. It also allows for shaping that increases stiffness to Pro Tour levels.
Important to note is that the whole of these tubes are greater than their sum – While individual tubes are designed to be aerodynamic, the way they force airflow past the entire bike is also part of what makes this bike drag less than more traditional designs. Once the tubes are connected and a frame is made, the intended airflow (from the front) around the bike looks something like this:
The blue bands show airflow direction (assuming it is from straight on), while the red bands show how the tubes would look if built to full NACA aero specs.
More Than Your Average Tube Shape
Although the straight length tubes may look conventionally shaped to the casual observer, this tube set is anything but. Cyril designed specific curvature of the edges to optimize air flow around the tubes and also direct it to specific points around the bike.
The basic tube shape was applied to virtually every tube on the bike – head-, down-, seat-tubes and seat- and chain-stays too. Close inspection of each of these tubes shows the leading edge is wedge shaped while the back edge is almost squared off. Of course it helps that Scott has painted these flat sections on the back of each tube red to help illustrate such a unique difference of this bike.
The red areas on back of each tube help show off the unique tube shapes.
While Scott’s early carbon bikes were tube to tube construction, the FOIL has evolved to really make the most of use the advances in carbon moldings. The head, top and down tubes are created as one piece in proprietary molds, and using proprietary layups of Scott’s proprietary HMX carbon.
The junction at the head-, top-, down-tube may look like a massive chunk of carbon, designed to anchor the front end, but in reality there’s a lot more – and less – to it.
While the outside surface area has been maximized to accept the big 1.5 inch bearing at the headtube bottom, and also to allow what Scott presents as the biggest acceptable area to join the toptube and downtubes to the headtube, it’s also been designed to:
• transmit the loads and forces of the road, (so stress and break points are reduced or eliminated),
• channel the wind around this junction, and
• still be as light as possible.
A cutaway of this section shows just how thin these tubes really are. Note the curvature of the transition from the top tube to the downtube – which has been designed to do a lot more than simply join the tubes together.
The red outlines on this diagram from Scott show how a fully-shaped NACA tube would look if used for the head tube.
Cable routing is neat and tidy – with some nice attention to detail on the internal routing.
The down tube uses Scott’s proprietary shaping, and from the headtube gets even wider to almost full width of the bb, where the staunch seat tube is wider than a lot others too – helping to fight those lateral forces guys like Mark Cavendish can torque up.
Here you can see the tapered leading edge of the seat tube, and the flat trailing edge of the down tube (painted red.)
This cutaway of the bottom bracket shows just how little material there is here – critical to keeping weight down, but also shows the large diameter of the downtube/BB junction – essential for adding stiffness to the area.
Moving to the rear of the frame, both the chainstays & seatstays have been designed to channel air in a more efficient way. The seat stays follow the same design as the down- and seat-tubes – (curved front & flat back edge), the chain stays have been shaped to both tune the ride and direct airflow, while also…
… being shaped to counteract the twisting forces your big-watt gear grinding will surely produce.
This view of chainstays shows off their flowing curves, and also where shape has been used to ensure lateral stiffness is high. The shape does double duty though, also directing lateral airflow, which is easier to see in the cutaway below…
This cross section of the chain stay shows how shape has been used to direct airflow coming from the sides.
Close inspection of the rear dropouts reveals the acute shaping of both stays, and also the exit point for some tidy internal rear derailleur cable routing, which runs neatly inside the drive side chain stay, and exits almost un-noticed just above the drop out. The derailleur hanger is replaceable.
Moving back up, the seat tube–seat stay junction shows off Scott’s attention to every single section of this frame adhering to its aero-shaped design.
The seat tube junction is also wedge shaped, formed to hold Scott’s Ritchey-made similarly shaped seatpost. The triangular shape is also applied to the seatstays, illustrated by Scott’s indication of how air should flow past this rather turbulent area of the bike.
The carbon fork is Scott’s own design, and also features a tapered leading edge, and flat back edge.
Ritchey bar, stem & seatpost combine with SRAM gruppo and Zipp wheels for a top level all-American build-up.
Even the bottle cages were integrated as part of the overall aero-shaping, with the downtube shaped to “hide” a mounted water bottle from frontal wind.
The Arione saddle by Fizik remains a popular choice.
My test bike was built up with SRAM Red – always a good call.
The FOIL design is offered on a variety of models across a lot of different price points.
Scott had a reputation for building stiff riding bikes at least two models before the FOIL came to life, and I concur with other reviews out there – this bike gives you all the feedback needed to race at the highest levels.
Unlike some other bikes I tested, the FOIL just doesn’t need a lot of words to describe how it rides – there’s no way to interpret what they’ve done here in any other way – it is stiff.
After my somewhat simplistic evaluation of the ride, I asked our Tech Editor Charles Manantan for his take: “The feedback is exceptional and there’s a great connection to the tires and traction (and more importantly, knowing where the edge of that traction really is). Like most high end race equipment, loads of stiffness and feedback might not be for everyone, but the more people find themselves genuinely pushing the edge of performance / traction / handling, feedback is a big plus. For example, if you’ve ever had the chance to go really fast in a GP 2 car or an Indy ride from the last decade you would never be satisfied with anything else for all out speed and handling – but only for all out speed and handling.”
One thing that stood out was how all this feedback translated into the sensation of speed – everything felt fast. Cranking the pedals forward resulted in immediate and urgent movement in the desired direction – enough that I not only noticed, but noted that it would be a key part of my riding impressions in this review. Even when rocking the bike side to side while I accelerated out of the saddle, or stood while climbing seemed to propel the bike forward more quickly than other bikes I’ve ridden.
I could feel every bump in the road – this is not a comfort bike, and the only thing I’ll say about vertical compliance here, is that there’s not much (that my 140lb corpo noticed anyway).
This bike is made for racing and the geometry suites this ride quality. There’s no reason at all to try and tame the foil with a slack front end or longer stays or wheel base. It’s pedigree in Grand Tours and racing at the highest level is all you really need to know – if it’s good enough for a pro to ride 8 hours a day, it’s probably good enough for you too.
If your prefer slightly less ‘feedback’ from your rig, try a great set of tubeless tires at lower pressures and / or a fatter section 25 tubular pumped 15 PSI or so less than you would normally run your 23’s (if you normally run your 23’s at 110 or more). A set of “training wheels” wouldn’t help a GP car, but they will surely melt the high frequency vibes and take a big chunk of the edge off the ride (and making it a snap to go “full ape” when angry riding is on order).
I can’t say I noticed the reduced drag of the frameset, but when we’re talking tiny increments – like 30-40 seconds in a 40km time trial, I suspect even the most acutely aware of you will only really see a difference when your time is posted at the end of the long ride. But it is nice to know the engineering makes sense and is there to help you go faster.
I’ll admit there is something comforting knowing the bike underneath you is slicing the wind better than the next guy’s, and seeing more big brands introducing their own versions of aero-shaped road bikes simply adds credibility to what Scott did two years ago.
• Get more info on the Scott FOIL Team Issue here