Over the last few years the road bike market has become more competitive than ever. With constant innovation from manufacturers attempting to get an advantage over their competitors, The development of products to achieve greater performance is ongoing and seemingly never-ending. The ultra low weights of frames is something that the majority of major manufacturers appear to have mastered - so much so that many models are too light to meet UCI racing regulations. This led to the development of the aero bike, with the focus shifting to conquering of the cyclist's number one nemesis: wind - with up to 20% of total air resistance encountered on a ride attributed to the design profile of a particular frame. Research and development teams at some of the largest cycling brands claim that an aero-specific frame can reduce the aforementioned 20% to almost nothing.
An aero road bike is designed to feature enhanced aerodynamic features. The frames are often constructed with unique tubing that makes the bike appear stocky from the side but skinny from the front, whilst all parts of the bike are refined to keep the amount of wind resistance as low as possible. Think of the aero bike as the combination of the efficiency and speed of a time trial frame with the handling of a racing road frame, balancing weight and stiffness into a package that would appear, on paper at least, to be the ultimate choice for a speed-orientated road racer. Unlike a TT bike, aero bikes are safe to ride in a group - a big plus for those who ride with clubs or friends regularly.
Those chunky tube shapes usually conducive to lightweight, but the industry has certainly seen a shift in recent years to produce aero bikes which flirt with the UCI minimum weight limit with a combination of clever CFD (computational fluid dynamics) technology and wind tunnel testing, matched up with smart tube shaping and the impact of airfoil and kamm tail style tubing. Here, the trailing edge of a frame is effectively cut off flat to trick the wind into thinking that the tube is much deeper, mimicing the aerodynamic impact of a larger tube but saving a chunk of weight! Nearly all the major bike brands will have an aero bike in their stable these days with the latest models faster than ever without sacrificing rider comfort - something that had been a complaint about all-out aero bikes in the past. You're also likely to see integration of as many parts as possible as cleaner frames tend to perform better. This means that cables are more hidden that ever, with a spotless finish to some of the latest models.
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Geometry & Frame Material
When it comes to the frame material of your aero bike, quality carbon is by far the lightest and most compliant (comfortable) material. These qualities immediately put carbon at the top of the wish list for any aero riders as even the smallest of weight saving, efficiency-improving features can make all the difference to the performance on the road, especially on hills where heavier aero frames tend to come unstuck. Carbon can also be moulded into any shape - so it's the most popular when it comes to aero bikes as often tubes will be tapered or adjusted in gradient and design in order to make the bike as quick and aerodynamic as possible. To achieve the ultimate results in aerodynamics, Specialized has built its own wind tunnel and the majority of manufacturers are carrying out similar tests at other facilities. Each company has slightly different approaches to creating the best possible frame and geometry for aerodynamics but almost all aero bike models will be kitted out with aerofoil-shaped tubes, integrated brakes, aggressive geometry and internal cable routing. The tubing of the frame is specifically designed to allow air to pass over the frame with less resistance. This can be done in a variety of ways - with the most common methods being the construction of tubes with a teardrop profile or manipulating the airflow over high-resistance zones in order to provide an overall reduction in drag effecting the bike. When the unique tubing is combined with a larger diameter bottom bracket and oversized headtube, a stiff,aerodynamic frame is created and forms the basis of this category of road bike.
Aesthetically speaking, aero road bikes have a design that immediately appeals to those who love to ride hard and ride fast. The tube shapes go a long way to countering resistance to offer more speed but in terms of overall velocity, specific aero-componentry is the solution. Componentry to improve air resistance is often focused on the seat post, which is made to have the same flat profile as the tubing and is usually integrated in the frame. Furthermore, seat-clamps and internal cable housing/routing are often provided to reduce drag. Additionally, an oversized head tube is frequently fitted to improve the steering qualities of the bike.
The headtube on aero bikes is intentionally shortened to create a lower frontal profile and thus reduce the level of air resistance for the frame to overcome. The majority of aero bikes will feature headtubes below 140mm - when you can consider that endurance frames will normally feature 160mm plus headtubes it's clear to see the difference in terms of riding position. In addition to the shorter headtube, aero bikes tend to offer longer frame reach than endurance bikes, again promoting a tucked riding position to reduce drag. Approximately 80% of wind resistance encountered by a rider is due to their body, so by being lower and more compacted it means the rider's centre of gravity is lower and they'll have a much smaller head-on shape, making them more aerodynamic and allowing them to reach top speeds with less effort. The geometry of an aero bike will force the rider to push their weight low and forward, leading to less air resistance and more front wheel traction as the increased front-end mass puts more weight through the front tyre and directly increases cornering grip. For true comfort and maximum performance output there's really no substitute for a quality bike fit that will meticulously measure out your bike to your unique dimensions. It's critical to the point that even a budget aero bike that fits you perfectly is likely to give you far better comfort, performance and handling than a top of the range model that isn't fitted to you correctly.
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Aero road bikes normally have larger than normal gear ratios. This makes sense: aero bikes are predominantly designed to go fast and a large gear ratio will certainly aid this goal. In the past, the majority of road bikes came with a 53T large chain ring and a 39T small chain ring on the front crankset but over recent years there's been a definite shift towards 'mid-compact' cranksets, which offer a 52T large chain ring paired with a 36T small chain ring. Certainly for most aero bikes, you'll now see a 52/36 chainset specified as standard which allows you to keep the speed high but still provides a bail-out gear should you need it uphill! Cassette's will usually be a little different too, with most aero bikes coming with a lowest gear of 30t, rather than the 32t or even 34t sprocket you might usually find on a more endurance oriented bike.
Wheels & Tyres
Responsible for 7% of the total drag that a rider encounters while in motion, wheels are a vital piece of the aerodynamic puzzle. The solution to reducing wheel resistance is found in deep section wheels and it's pretty much gospel that aero bikes will always be paired with deep section wheels as they greatly reduce drag and directly enhance aerodynamics. Typically, deep set wheels will be between 40mm and 80mm deep with the downside of running this type of wheel being the potential handling issues in windy conditions and the additional weight to add to the frame - again, technology is starting to save us here, with specially developed rim profiles designed to better handle gusty crosswinds. Tyres on aero road bikes are fairly standard, but with the influx of aero bikes built around disc brakes and the wider tyre clearances which they allow, we now see much wider tyres specified as stock which can also help out in the comfort stakes.
Much like the wider road bike market, aero bikes have succumbed to disc brakes too! Previously believed to be less aerodynamic than the hidden brake set ups which were prevalent on early generations of aero bike, the latest disc brake models prove to either match or better the performance of their rim brake siblings with bikes like the Specialized Venge, Giant Propel and Trek Madone build from scratch with disc brakes in mind. So not only are disc brakes aero bikes more efficient in the wind, they now also have more predictable performance in all conditions, better modulation, and more stopping power allowing you to brake later, corner fast and descend quicker.
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