FAST BIKE FRIDAY – CERVELO S5 DISC ULTEGRA Di2

‘Tron called, he wants his bike back’ quipped one of my work colleagues when he first laid eyes on the Cervelo S5 Disc Ultegra Di2 aero road bike. It’s a fair comment; this stunning bike looks like something from a science fiction film. In the sea of aero road bikes that are out there now the Cervelo S5 stands out from the crowd with its unique looks which are a result of some very thorough design development and testing in the wind tunnel and in real world conditions. Over a short period of time the S5 has become an iconic bike with a very long list of race victories proving this bike is not all style and no substance, so let’s take a more detailed look at what makes this aero road bike so competitive…

With striking looks the unique Cervelo S5 Disc Ultegra Di2 is an aero road bike like no other.

 

If you’re looking for out-and-out speed from a disc brake equipped road bike then the Cervelo S5 marks the pinnacle of performance. The S5 has its sights firmly fixed on aerodynamic performance and stiffness making it the ultimate race weapon for sprinters and fast escapees. This has been brilliantly illustrated over the past few months with the S5 taking an iconic win on the Champs Élysées at the Tour De France piloted by Wout Van Aert. Wout’s Jumbo Visma professional cycling team had a whole fleet of Cervelo road bikes to choose from during the Tour De France campaign with each rider selecting a particular model to suit each stage. Young rider Jonas Vingegaard was seen on the S5 model during key stages where flat-out speed was required, helping to contribute to his brilliant final 2nd place overall at this iconic race; following on from the Tour Wout Van Aert showed his versatility by piloting his Cervelo S5 to a Silver medal at the Tokyo Olympics.

Wout Van Aert recently piloted his Cervelo S5 to a sprint victory on the Champs Élysées at the Tour De France as well as an Olympic Silver Medal in Tokyo.

 

2nd place overall Jonas Vingegaard chose the Cervelo S5 on the faster transition stages between the mountains of the 2021 Tour De France.

 

You’re excused if you skip this techy bit on aerodynamics and jump straight into the spec of the Cervelo S5! All you need to know is Cervelo have been VERY thorough in their research; for those of you who want to read more on the problems encountered in aerodynamics air-flow and the solutions that Cervelo have brought to the S5 then let’s dive in…

Cervelo are industry leaders when it comes to aerodynamics with the company founded with the goal of making cyclists faster and more competitive; they understand what a huge effect aerodynamics can have on just how fast a cyclist and their bike can go. Read through Cervelo’s own content on their website and you’ll quickly discover that their research and development is firmly centred on aerodynamics and it informs everything they do. Their own scientific testing has proved that aerodynamic drag is the major factor affecting a bike and rider, accounting for up to 90% of the overall resistance that a rider must overcome.

Cervelo identify a number of types of aerodynamic drag which effect the bike and its rider. The designers and engineers have spent endless hours focused on these factors, first getting a really clear understanding of the reasons behind each type of drag and secondly finding solid design and manufacturing solutions to negate the negative effects of aerodynamic drag as much as possible. Cervelo have focused on overcoming the following types of drag:

Pressure Drag

When bike and body pass through the air, the air molecules are quickly forced out of the way as we pass through. The air molecules push back on bike and body creating pressure; the pressure facing aft (to the rear of the bike and body) is referred to as ‘pressure drag’.

Friction Drag and Turbulence

Air has its own viscosity or ‘thickness’ and air molecules which come into contact with the rider and bike stick to their surfaces and stay stationary in relation to the movement of the body and bike. As they continue to move other air molecules pass the stuck molecules and flow around body and bike in layers following parallel paths, scientists describe this as the ‘laminar boundary layer’ within the process of friction drag. At some point, as speeds increase ‘laminar flow’ cannot be maintained and the air molecules begin to tumble and mix instead of flowing smoothly around the object, changing the boundary layer airflow from ‘laminar’ to ‘turbulent’ which then increases the thickness of the airflow increasing disruption within that boundary layer and causing more friction drag. The aerodynamic research boffins of the world even have their own scale for measuring this phenomenon; the ‘Reynolds Number’ indicates the point at which smoother ‘laminar flow’ becomes the more unstable ‘turbulent flow’ on a chosen object, this occurs at around 10,000 as shown in the figure below:

Stalled Flow Drag

Air has mass, so moving mass has its own inertia, that inertia cannot easily follow around the form of high-curvature surfaces and at this point air separates from the body and the bike. This in turn creates low-pressure areas that actually pull on the moving surface creating more drag; if the trailing edge of the bike isn’t shaped to pull that air neatly back together then there is a ‘stalled flow’ – a region of recirculating air with low pressure which pulls on the surface creating even more drag.

The solutions to Aerodynamic Drag

So what does this all mean when it comes to designing and producing an aerodynamic road bike and how have Cervelo applied their research to the development of the S5? To minimise aerodynamic drag Cervelo focused on two key parameters, the first is ‘drag coefficient’ a factor based on the shape of object and how the air flows around it. If you’ve managed to get your head around the factors behind aerodynamic drag which have already been described you’ll understand that an object’s shape has an affect on how air flows around it; for example a perfectly round bicycle frame tube has roughly 24 times the drag of a more aerodynamically-profiled tube such as Cervelo’s own TrueAeroTM profile. The most efficient angle of each tube shape on the Cervelo S5 is massively important too, elements of the frame such as the seat post and down tube are presented at an angle so that the air hits those tube profiles in an ellipse shape changing the coefficient.

You won’t be surprised that Cervelo have been very focused on the other parameter that they can control – the ‘Frontal Area’. This one’s a little more simple to get your head around; basically the larger the frontal area the bigger the aerodynamic drag. Cast your eyes over the front of the Cervelo S5 Disc Ultegra Di2 aero road bike and you’ll see that the designers have kept the frontal area to an absolute minimum with their fully integrated system giving maximum aerodynamic advantage.

Apologies if I’ve gone too deep on this, but I’ve come this far so we may as well include an equation from Cervelo too! The drag coefficient (CD) and the frontal area (A) are related to the total drag a bike encounters by the following equation:

The other parameters indicated in this equation are the velocity of the bike and rider through the air (V) and the density of the air (P) This is also the reason that many bicycle speed records attempts are made at high altitude, since the lower air density has a direct reduction on drag.

So let’s wrap this techy bit up by relating all of this information back to the S5 bike. The designers and engineers at Cervelo have taken all of their findings and applied it to a complete aero road bike and its components, minimising drag by focusing on CD and A. This is an efficient way of making the bike faster, however, also minimising the drag on the rider, through an efficient body position and paying the same amount of attention on component design all help to ensure the fastest overall result; that’s why real-world testing is such an important part of the design process at Cervelo.

The V-stem on the Cervelo S5 has quickly become iconic; there’s some solid stats backing up the science behind such a unique configuration.

 

The Cervelo makes the perfect race bike if you are someone looking for a super-fast aero-efficient road bike that can perform in fast, frenetic races such as your weekly crit, as well as the odd time trial or even triathlon. As Wout Van Aert has already proved it’s more than capable of winning bunch sprints and is super stiff and responsive under acceleration. Cervelo are quick to point out though, that this isn’t a one-trick-pony, despite its notable lateral stiffness the S5 gives a surprisingly comfortable ride and the ability of the Cervelo S5 to take 28mm wide tyres is another bonus.

There’s certainly been a lot of chat about the Cervelo S5’s iconic V-Stem; opinion is somewhat divided, but whatever your own thoughts the science behind the design of the cockpit cannot be disputed, with Cervelo optimising the shape to perform brilliantly in the wind with the minimal amount of drag. This configuration sees all of the cables being hidden inside the structure of the handle bar and stem with the cables then running into the frame and fork; it’s important to point out too that the designers have ensured there is plenty of scope when it comes to rider position and adjustability with enough bar / stem and stack options to fit anyone out there.

The Cervelo S5’s V-stem design has been optimised to deliver the best performance in the wind within real-world conditions.

 

Seen from the front it’s obvious just how aero the S5 is with those smooth lines and no exposed brake or gear cables at all.

 

The Cervelo S5 is pretty versatile when it comes to rider-position-adjustment, with multiple bar, stem and stack options to fit just about anyone.

 

That super-aero fork with its clever headtube-to-fork-configuration is designed to cut through the air; there’s tyre clearance for 28mm tyres too.

 

The Cervelo CS028 Carbon V-Stem forms a smooth junction between the frame, fork, stem and handlebar with all cables internally routed.

 

The smooth, aerodynamic profiling continues at the rear of the Cervelo S5’s frame.

 

Each tube-profile on the Cervelo’s S5 carbon frame has been carefully designed to be efficient at cutting through the air.

 

The cut-out downtube around the front wheel and curved portion of the frame around the rear wheel further-enhance the S5’s ability to cut through the wind.

 

This Cervelo S5 model features Shimano’s excellent Ultegra Di2 electronic groupset; this 11-speed drivetrain is activated by digital buttons on the brake lever / shifters rather than being cable-activated like conventional mechanical shifters. The benefits of this system are that every single gear selection is crisp and precise regardless of whether you’re in or out of the saddle or are selecting gears in the heat of a race; this reliable performance takes some of the mental pressure away when you’re riding hard and it’s flawless performance means that you actually feel encouraged to change gear more. Another benefit is the light-touch action required to change gear – you’re pressing a button rather then pushing a lever; this is an advantage for smaller hands or for when you’re hands a particularly cold and wet.

As its product name suggests this model of S5 features a precise-shifting Shimano Ultegra Di2 electronic groupset.

 

Both the front and rear derailleurs are really neat and compact, you almost have to look twice to notice they are electronic rather than mechanical. If you’ve not used a Shimano Di2 electronic groupset before they’re a real revelation, you can tune the gears exactly to suit you and your riding and once they are set they perform consistently regardless of riding conditions or longevity of use – there’s no cables to stretch here. A nice detail is the automatic front derailleur adjustment which eliminates any potential for chain rub as you move the chain up the rear cassette, if you’re moving up the block but still in the big chainring then the front derailleur automatically moves inward a small fraction, eliminating any unwanted chain rub.

The 11-speed Shimano Ultegra Di2 electronic groupset featured on the Cervelo S5 includes a 52/36T chainset upfront combined with an 11-30T rear cassette giving you a good spread of gear ratios that are perfectly suited to competitive cycling disciplines such as road racing, triathlon and even time trials. A premium race bike like this is aimed squarely at high performance and continuing personal development as a competitive cyclist. With this in mind Cervelo have included a 4iiii Precision Dual Sided Power Meter integrated into the Ultegra chainset; the power meter is powered by a 100+ hour coin cell battery and measures your power and cadence with 4iiii’s 3D technology, measuring tri-axial crank strain to produce super-accurate data from both legs. The 4iiii Precision Dual Sided power meter is compatible with ANT+ and Bluetooth smartphones as well as GPS cycle computers.

A nice extra addition to this Ultegra Di2 equipped road bike is the 4iiii powermeter allowing you to train more effectively.

 

When it comes to hydraulic disc braking on road bikes Shimano are leading the way; over the past half decade the Japanese component manufacturer has really refined their disc braking system, made specifically to meet the unique demands of road riding. The Cervelo S5 Disc Ultegra Di2 is fitted with their super-light, powerful Ultegra 8070 hydraulic brake callipers which are particularly neat and unobtrusive thanks to their flat-mount configuration. These brakes are matched with 160mm diameter SM-RT800 disc brake rotors which have been designed specifically to prevent excessive heat build-up by featuring a profile that includes fins designed to cool the rotor when you’re braking continuously on long alpine-style descents.

Flat-mount Shimano Ultegra 8070 brakes with 160mm rotors are neat and powerful in all conditions.

 

A super-aero road bike like the Cervelo S5, built to perform at high-speeds and designed to cut through the air needs a fast pair of wheels to really bring out the best in the chassis. With this in mind Cervelo have spec’d a pair of Reserve 50 carbon wheels to help you accelerate immediately when you stomp on the pedals in a mid-race attack and will then hold their speed as you ride up the road thanks to their lightweight carbon rims and deep 50mm rim profile. It’s interesting to note that the Reserve rims feature a 21mm inner-rim-with which helps to create a nice wide tyre profile with the tyres sidewalls not being excessively pinched-in, leaving more tyre surface in contact with the ground. The Cervelo S5 Disc Ultegra Di2 comes fitted with 25c wide Vittoria Corsa tubeless -ready tyres; it’s worth pointing out too that Cervelo state that the S5 will take up to 28mm wide tyres with no problems and this will increase your tyres footprint on the ground even more for enhanced traction and control.

The Reserve wheelset features 50mm deep carbon rims with an internal width of 21mm for a nice wide tyre profile.

 

Those fast rims are laced to durable, smooth-rolling DT Swiss DT 350 thru-axle hubs via aerodynamic butted flat-blade straight-pull spokes with 20 spokes upfront and 24 on the rear. The hubs feature easy-to-replace sealed hubs and really stand up to the test of riding and racing in less than perfect weather. The DT 350 rear hub features a superb Ratchet System consisting of 36 ratchets in the freehub body to ensue that there is direct power transmission every time you press down on the pedals.

The excellent Reserve wheelset includes durable, smooth DT Swiss DT350 thru-axle hubs.

 

The Reserve wheels feature aerodynamic butted flat-blade straight-pull spokes with 20 spokes upfront and 24 on the rear.

 

Rounding out the excellent Cervelo S5 Disc Ultegra Di2 is a Prologo Dimension Nack saddle which is perfectly suited to just how the S5 will be ridden – fast and in an aggressive low-profile position. There’s been an influx of stub-nosed saddles in recent years, made popular thanks to their enhanced comfort and more supportive profile. The shorter nose prevents the potential for pressure build up and the Prologo’s cut-out area in the centre of the saddle further negates the potential for unwanted pressure points; Prologo call this their P.A.S. – perineal area system.

The Prologo Dimension Nack saddle is a sensible width and boasts a short, stubby profile that has become popular in the last couple of years.

 

10 years ago the bike industry and road cyclists themselves, regardless of whether they were professionals or amateurs, were obsessed with the weight of their bikes. At that time the performance and the efficiency of a road bike was measured on just how light and spritely they were on the hills with very little attention focused on aerodynamics and how a road bike performed in that regard, particularly when minimal effects of aerodynamism or lack of are multiplied over longer distances. Take a look back at images of the Tour De France and similar races from a decade ago and the difference in bikes, clothing and equipment are stark with little or no consideration of aerodynamic performance. Things have changed significantly since then with brands like Cervelo leading the way when it comes to the design and production of road bikes that are super-aero and capable of shaving off big chunks of time; the Cervelo S5 looks fast just standing still and even to the untrained eye it’s obvious that this bike is built to perform at speed. Take a deeper look into the almost endless aerodynamics research and development that goes into the S5 and it’s clear that there’s some solid science backing up every curve and line of the Cervelo S5 Disc Ultegra Di2.

The Cervelo S5 Disc Ultegra Di2 is a true off-the-peg aerodynamic race machine.

 

Click the link above to find out more about the S5’s aerodynamics, explained by Cervelo’s designers and engineers.

 

The Cervelo S5 Disc Ultegra Di2 RRP £8,779.00 is available in-store and online now.

 

Full Specification:

• Frame: Cervelo S5 All-Carbon, TrueAero tube profiles, integrated head tube to fork configuration, integrated headset 1” x 1-3/8”
• Fork: Cervelo All Carbon, Tapered S5 Fork
• Headset: FSA IS2 1 x 1-3/8
• Shifters: Shimano Ultegra Di2 8070, 11-speed
• Rear Derailleur: Shimano Ultegra Di2 8050, 11-Speed
• Front Derailleur: Shimano Ultegra Di2 8050
• Cassette : Shimano Ultegra CS-R8000, 11-Speed 11-30T
• Chainset: Shimano Ultegra 8000 52/36T with 4iiii Precision Dual Sided Power Meter
• Brakes: Shimano Ultegra 8070 Hydraulic Disc
• Rotors: Shimano SM-RT800, 160mm
• Wheelset: Front – Reserve 50mm DT350, 20h, 21mm IW
• Wheelset: Rear – Reserve 50mm DT350, 24h, 21mm IW
• Front Tyre: Vittoria Corsa TLR G 25c
• Rear Tyre: Vittoria Corsa TLR G 25c
• Stem: Cervelo CS028 Carbon V-Stem
• Handlebar: Cervelo AB08 Carbon
• Seat Post: Cervelo SP20 Carbon Aero Post
• Saddle: Prologo Dimension Nack

 

Written by Johnny Dodgin

Photos by James Vincent

 

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