By Tom Demerly
Cervelo’s S5 joins the growing aerodynamic road bike category with the new Scott Foil and Specialized Venge, a category already populated by the Felt AR series bikes, the Litespeed C1, Ridley Noah and others.
Unlike many recent aero entries the new Cervelo S5 is convertible from a road geometry bike to a steep seat angle/triathlon bike for use with aerobars. Of the recent introductions, only the Felt AR series shares this level of versatility.
“The Cervelo S5 is convertible from a road geometry bike to a steep seat angle/triathlon bike for use with aerobars.”
Cervelo waited to introduce their aero road bike until after Scott, Felt, Litespeed and Specialized introduced their interpretations of the category. There is something to be said for being last to the party- you know what everyone else is wearing. This is primarily a marketing advantage for Cervelo with the publicity of the Garmin/Cervelo team in the Tour de France and Thor Hushovd owning the yellow jersey during the opening week of the event. The engineering advantages built into the S5 started years ago at Cervelo and are part of their aerodynamic legacy.
Many of the aerodynamic cues from the S5 can be attributed to the development of the Cervelo P4 and P3. These developments go back years in Cervelo’s engineering DNA. The shared concepts are obvious: Cable routing, front wheel to down tube proximity, fork crown, seat stay/seat tube union, seatpost binder bolt, rear wheel cut out and even a minor inspiration in the bottom bracket. These aerodynamic details took Cervelo years to develop. While most other companies in the aerodynamic road category are newcomers to aero bike design, it is where Cervelo started. As a result, aero road bikes are a natural extension of Cervelo’s engineering specialty. They’re an aero bike company.
“While most companies are new to aero road bike design, this is where Cervelo started.”
Because of their engineering (not marketing) based product development Cervelo product introductions have historically been significant. When Cervelo introduced the P3 it touched off an entire generation of bikes from other brands that mimicked its appearance (if not engineering). The P3 established what a time trial/triathlon bike should look like for the last decade.
Cervelo’s success with an engineering approach to product development extended to their road line with the development of the “R” series ride quality bikes and “S” series aerodynamic road bikes. The “R” and “S” series are two distinctly different bike types with specific engineering features and benefits for specific goals. You either wanted an “R” series bike for its stiffness or an “S” bike for the aerodynamic benefit.
But what if you wanted both? In one bike? That is where S5 becomes significant.
Another noteworthy addition to the S5 is the BBright asymmetric bottom bracket. BBright uses a 30 millimeter oversized bottom bracket axle combined with a bottom bracket offset to one side of the bike resulting in greater frame stiffness and better aerodynamics. The bottom bracket on the S5 isn’t centered on the bike; it sits off to one side, making the bottom bracket stiffer and more aerodynamic. The bearings are housed entirely inside the frame making it more aerodynamic: No bearings sticking out. BBright is supported by SRAM, FSA, Rotor, Tune and others with the use of an adapter. In fact, cranks from Zipp, Campagnolo and Shimano also install on a BBright configured frame. Another benefit to BB right for 10 speed drivetrains is improved chain line. The chainrings are centered on the rear cogs better making your crossover gears work better. BBright is a seemingly subtle feature that offers significant benefits.
“BBright is a seemingly subtle feature that offers significant benefits.”
The aerodynamics engineered during the development of the P4 meet the frame stiffness features of BBright on the S5. While other brands have gone to much wider tubes for frame stiffness Cervelo has maintained wind tunnel and competitively proven shapes while integrating increased bottom bracket stiffness. It’s stiffer without being wider. Additionally, the bearings are housed inside the frame resulting in a measureable drag savings, one of five significant aerodynamic refinements unique to the Cervelo S5.
“The S5’s optimized aerodynamics from the P4 meet the frame stiffness features of BBright. It’s stiffer without being wider.”
The 5 Things.
Cervelo includes five performance features on the new S5 that are unique:
- Dropped Down Tube/ Fork Crown. The down tube and fork crown are closer to the front wheel, filling in the area between the front wheel and frame. This reduces drag by a measureable amount.
- Designed for Bottles. Cervelo pioneered the integration of water bottles on the frame to enhance aerodynamics with their P4. That concept is executed on the S5 with optimized bottle mounting including a specific provision for aero bottles.
- Cut Out for Rear Wheel. Proven in the wind tunnel and competitively for years on the P3 and now the P4, the rear wheel cut-out goes to the road category on the S5.
- Shielding Seat Stays. The union of the seat stays to the seat tube is horizontal to the boundary layer of air and creates a fairing for the brake reducing drag.
- BBright Bottom Bracket. Improves bottom bracket stiffness and aerodynamics.
Cervelo is hanging their hat on the combination of these five things, and it’s a good hat rack. The other bikes in this category may have one or two similar ideas, but none incorporate all five. That is a strong engineering argument for Cervelo.
From an ownership perspective the Cervelo S5 appears to be an elegant and simple bike to own and maintain. The cable routing is clean and easy to service. The seatpost binder assembly is Cervelo’s best interpretation of this design yet- no slipping, good grip, easy to work with and modular.
The seatpost on the Cervelo S5 is a two position post, making this a more versatile bike than Cervelo is mentioning. With the saddle in the forward position a steep enough effective seat tube angle for aerobars can be achieved. That’s big news for many triathletes who may want a bike with a steep-ish head tube angle and a higher head tube.
The fit on the S5 is optimized for the most important aerodynamic benefit a rider can have: Good position. The S5 has a higher head tube than other aero road bikes. This is actually more aerodynamic for the majority of riders since the head tube of the frame reaches to the rider, not a stack of round headset spacers. This is also stiffer laterally and absorbs road shock better. Many riders will use the S5 with no spacers at all, the way we see most bikes be ridden by the top pros. The problem for us, the non-professional rider, is we couldn’t ride most other bikes without headset spacers under the stem- it would be too uncomfortable. On the S5 your set-up and mine will look just like the pros on Garmin-Cervelo.
“You are more aerodynamic on an S5 with no headset spacers than on a lower head tube bike with 4 cm of spacers.”
Another nice detail on the S5 is the option to mount your water bottles in the most aerodynamic place on the bike. This actually makes a measureable difference in bike aerodynamics amounting to more than a few seconds over 40 km. That advantage may be lost on you until you miss the last place in your age category at the local race by only 4 seconds. There are three bottle bolts on the down tube so a bottle can be mounted in the high position when two cages are carried or in the lower position when only one bottle is used in shorter events. The lower bottle mount is more aerodynamic with one bottle cage on the bike. For timed events an Arundel aero bottle can be installed on the seat tube (optimally) or the down tube for the best possible frame/bottle aerodynamics. Carrying the Arundel bottle on the seat tube mimics super-low drag numbers seen during the development of Cervelo’s P4, another lesson learned from that development process.
Rear brake mounting on the S5 is accomplished the same way Cervelo mounts the rear brake on their P3. The brake is mounted to a simple plate with an aligning pin and the plate/brake assembly mounts to the seat stay union. This area in front of the brake caliper forms the fairing that manages the boundary layer of air surrounding the brake. This is a strong design since it provides great rear brake performance while improving aerodynamics.
A final design theme from the P4 is the aerodynamic chainstays. A tremendous amount of work went into the wind tunnel development of the chainstays on the P4 so being able to use that theme combined with BBright is another technology dividend from the P4 development process. The chainstays mostly provide a smooth transition for low speed, turbulent air moving around the drivetrain.
Like all of Cervelo’s aerodynamic designs the S5 is a bike optimized through many small details. How much time does an aero chainstay save you? Realistically- not all that much. However, the cumulative improvement of all the aerodynamic benefits on the Cervelo S5 working together amount to a tangible performance benefit over bikes without this combination of features. It isn’t any one feature that optimizes aerodynamic performance; it is the combination of subtle features that provide a tangible benefit.
“It isn’t any one feature that optimizes performance; it is the combination of subtle features that provide a tangible benefit.”
Like almost all of Cervelo’s designs the S5 is built on the principle that aerodynamics- of rider and of bike- are more important than weight or frame stiffness. Cervelo proved this in their famous “Col de la Tipping Point” presentation:
The premise of aerodynamics over weight was re-proven during the famous uphill time trial on L’Alpe d’ Huez in the 2004 Tour de France. How steep a climb has to be before weight is more important than aerodynamics depends on how much the rider weighs and how fast they are. A lighter, faster rider going uphill reaches the “tipping point” around an 8% grade. For a slower rider it may be closer to a sustained 5% grade. The change in overall time then becomes a function of how much climbing there is over the entire length of a given ride. For a rider climbing Mt. Lemmon in Tucson, Arizona- one of the longest paved climbs in the United States, it’s worth knowing the average gradient is 3.6% over 51.81 kilometers (32.19 miles) according to climbbybike.com. “Col de la Tipping Point” proves that for the average rider climbing Mt. Lemmon, body and frame aerodynamics is still more important than weight.
“Col de la Tipping Point” proves that for the average rider climbing Mt. Lemmon body and frame aerodynamics is still more important than weight.”
Old timers and light weight enthusiasts may doubt the findings of “Col de la Tipping Point” but the math can’t be argued away. Even on most climbs aerodynamics is still more important than weight.
I set up the Cervelo S5 in two different orientations for a test ride: The forward seat angle orientation with bolt-on aerobars and the conventional road position. In both set-ups I ran the stem on the head tube- no spacers under the stem. Road bike handling is predictably good, the tight rear wheel providing a nice measure of quick acceleration during the first few pedal strokes. I liked the rear end on this bike much better than Scott’s Foil which is very stiff in the front and trifle sleepy behind the bottom bracket.
The triathlon/steeper effective seat tube set-up on the Cervelo S5 winds up at 78.2 degrees using the forward saddle mounting position on the seatpost and a 30 cm long Profile Tri Stryke or Fizik Arione Tri Saddle. This is slacker than I ride on my dedicated triathlon set-up with a P3 by about 3 degrees. For the rider who may not sit at a steep seat tube angle with an open torso to leg relationship the S5 may provide as steep a seat angle as they will ever need for use with aerobars. Handling is responsive in the aero set up, more responsive than the purpose built steep seat angle bikes. For a triathlon with a lot of rolling hills and/or big climbs with technical descents the S5 would be perfect. Combine that with its great road set-up and this is two bike set ups on one good frame set.
The Cervelo S5 is sold in three different carbon lay-ups spread over five models. The difference in carbon fiber lay-up, or how the carbon fiber is placed in the mold, makes each successive frame level stiffer and lighter by approximately 100 grams of frame weight and 10% stiffness. I asked a Cervelo tech rep if a consumer would notice the difference between the three lay-ups during a ride, “Absolutely” was his response.
“The Cervelo S5 is sold in three different carbon lay-ups spread over five models.”
I’m a long torso rider with shorter legs. My favorite triathlon bike is Cervelo’s P3. It’s worth mentioning Cervelo has never given me a bike or compensated me in any way for a review, but I do continue to acknowledge their superb engineering compared to other brands in the areas of aerodynamics, fit and mechanical details. They’ve earned the acknowledgement.
During my ride of the S5 in both orientations I found the head tube as high as I would ever want on a bike in my frame size. I would normally ride a 54cm Cervelo P3 and R3 and have also used a 51cm frame size in some of their earlier road bikes and the aluminum P3 that pre-dated the carbon fiber P3. For riders trending toward a shorter torso and longer legs the S5 becomes an even more attractive option. It is a bike proportioned for the middle 80%. With my long torso and tendency to sit low, long and steep I become a bit of an outlier. I actually looked at the geometry chart on the 51cm S5 to see if I may be better off on that frame size than the 54cm test bike we received. Probably not. In the road orientation on a 54cm S5 I would make good use of the drop handlebars for hard solo efforts- and that is why road bikes have drop handlebars to begin with.
Cervelo new model introductions tend to be game-changers for the industry and the S5 joins that legacy. The five aerodynamic features combined with the unique, real-world “way we ride” fit and position on the S5 to make it a standout in the emerging aero-road category, a category Cervelo is an old hand at. For other bike companies trying to compete against Cervelo’s new S5 dual-position aerodynamic road bike they now have a very high bar to clear. I don’t see any other manufacturer with the same combination of unique features and benefits in an aero road bike. This is another aero category Cervelo owns.