Everything you need to know when buying an aero bike
Weight may have been the primary concern of bike manufacturers for much of the history of cycling, but aero has become the new big thing in the last few years. Every company going has an aero bike somewhere in its range, and casual flick through a race gallery is all you’ll need to see that the vast majority of pro riders are using aero bikes too.
If you’ve decided to join the growing number of amateurs with an aero bike in the stable, then what exactly should you be looking for and how much should you pay? Or if you’re still considering whether an aero bike is the best investment to make, then how much faster will one make you, and is it really worth the faff?
How much difference does an aero bike make?
Well that’s a very good question that, with Cycling Weekly wind tunnel still seeking funding from the powers that be, we can’t answer with complete scientific accuracy. However, we have conducted a couple of experiments that have compared the performances of aero bikes with non-aero bikes.
In the first of these, we put the two bikes to the test in what should be the aero bike’s home turf: the velodrome. We rode each bike (a Cervelo S5 and Canyon Ultimate CF SLX) for 10 minutes at 200W and 10 minutes at 300W, with the aero bike being 275m ahead and 1.7kph faster when ridden at 200W, and 435m ahead and 2.6kph faster when ridden at 300W.
In the second experiment we pitched an aero bike (again the Cervelo S5) against a lightweight bike (a Focus Izalco Max) on a climb, tackling Box Hill in Surrey twice on each bike, again at 200W and 300W, to see if the aero bike would still be faster even in the hills despite the Cervelo S5 being 800g heavier.
However, this time it was the lightweight bike that came out on top. At 200W, it took our test rider 9:24 to tackle the 2.5km climb on the aero bike at an average speed of 15kph, while the lightweight bike was 18 seconds faster with an average speed of 16kph.
At 300W, the lightweight bike was still faster, but the gap between the two was reduced, with the aero bike only being seven seconds slower with a 0.4kph difference in speed. This shows how much more important aerodynamics become at higher speeds, while weight is more of a factor at lower speeds.
The take home message then, is for most riders over most terrains, an aero bike will be faster than a lightweight bike. The only case where weight begins to become more of a factor is on steeper climbs where you’re travelling more slowly, and even then any time gains could well be balanced out on the descent?
What aero features should I look out for?
At a most basic level, all aero bikes should come with tubes that have been shaped to smooth airflow, meaning that they will have a slender front profile but being extended rearwards. However, manufacturers can’t go crazy if they want to see their bikes used in races, with the UCI’s 3:1 rule restricting the ways in which they can shape the tubes.
This rule means that the depth of a tube’s profile (or indeed any other part of a bicycle) cannont be more than three times its width. So if a bike’s down tube is two centimetres wide when viewed from the front, then it cannot be more than six centimetres wide when viewed from the side.
Watch: Cycling Weekly Aero Bike of the Year 2016
In an attempt to continue to improve the aerodynamics of their bikes while staying within this rule, many manufacturers now use kamm-tail tube profiles. This means that the tube retains a traditional aerofoil shape at the front, but with the back half lopped off to give it a flat back.
Integration is the latest big trend when it comes to aero bikes, with the latest aero bikes such as the Specialized S-Works Venge ViAS and the Trek Madone aiming to hide as much hardware as possible within the frame.
Key to this is cable routing. The sleekest aero bikes keep the gear and brake cables hidden for as long as possible, routing them through the handlebars, stem, and frame before they emerge close to their partner components, usually on the backside of the tubes to keep them out of the wind. At the next level down from this the cables are not routed through the handlebars and stem, but do at least enter the down tube behind the head tube to keep the cable entry out of the wind.
Integrated brakes are also found on many aero bikes. At the front, some manufacturers such as Look and Boardman position the brake within the fork, while the Specialized S-Works Venge ViAS puts them on the rear side of the fork. However, most aero bikes still come with the front brake mounted in the standard position on the front of the fork, although often with direct-mount brakes to bring the caliper closer to the frame.
When the first aero bikes emerged a few years ago, most manufacturers decided that the most aero place to stick the rear brake was by the bottom bracket, however the aerodynamic benefit of this this is questionable with that area having some pretty irredemably “dirty” air caused by the movement of the cranks and chainrings.
Increasingly we are seeing company’s go back to positioning the rear brake on the seatstays, but again using direct-mount brakes to bring them closer the the frame to smooth airflow, although Specialized has again chosen to do things a bit differently, giving the Venge ViAS a rear brake placed on the trailing edge of the seat tube.
However, possibly the most important part (or parts) of a seriously sleek aero bike are the wheels. According to Kevin Quan of Knight composites, a 95mm deep rim (which is admittedly incredibly deep) will save a typical rider 35 watts compared to a standard box section wheel at time trial speeds. That said, it is also important to consider the weight of deep section wheels and their effect on handling, particularly if you live in a hilly or windy part of the world.
Other than this, many aero bikes will also come with other aerodynamically engineered components, such as aerofoil-shaped handlebars or seatposts, and even, in the case of the Look 795, and aero crankset.
How easy are aero bikes to live with?
Yes, for most people on most terrains, an aero bike will be faster, but if you’re considering buying one, you also have to weigh up what day-to-day life will be like with your new pride and joy.
Unfortunately, the more aerodynamic the bike, the more difficult it can be to live with. No more so is this the case than with integrated cabling. Yes, this helps you cut through the wind just that little bit easier, but for the home mechanic (and even for a few WorldTour professional mechanics that we’ve spoken too) they can be a nightmare. The cable routing is often complicated and if you do have a problem with your shifting or braking, then the cause could well be hidden somewhere within the frame.
The integrated brakes on aero bikes can also be a bit of a faff. The traditional positioning of brakes on the seatstays and the front of the fork makes maintenance and adjustment a doddle, but once you move the brakes to within the fork and beneath the bottom bracket, then the extra time you take doing simple tasks like changing brake pads will be much more than the few seconds you can save in the local time trial.
Finally, if you’re going to get the most out of your aero bike, then you might occasionally find yourself riding in the dark. In this case, aerodynamic seatposts and handlebars can make it a little tricky to fit lights, while the seatpost design may also limit the saddle bags you can use.
How else can I be more aero?
Before you rush, wallet open, to your local bike shop in search of the latest aero bike, it’s worth considering that there are plenty of other much cheaper ways to make some aerodynamic gains.
The vast majority of the wind resistance that you have to overcome while cycling is caused by, well, you, so your position and clothing choice can make a big difference to your speed. Riding in a low, crouched position with your hands on the the hoods is roughly 20 per cent more aerodynamic than riding upright with your hands on the tops.
Similarly, tight-fitting aerodynamic clothing and an aero helmet can also make a significant difference. The benefits might not be as stark as with changing your position, but if you’re riding along with a bag raincap unzipped and flapping in the wind, then you can wave goodbye to any gains that you might have got from your expensive aero bike and flash deep sections wheels.
Our pick of the best aero bikes
How much should I pay?
With aero bikes now being available at almost all price points, it’s more a case of how much can you afford to pay rather than how much do you need to pay.
At the top-end of the scale, it’s not unusual to see aero bikes pushing hard against the £10,000 barrier, which should be enough to get you a cutting-edge frame matched with some pretty tasy components and deep section wheels for a seriously aero machine.
However, for a fraction of this price, you will often be able to pick up a bike with a frame that might not have the same high-quality carbon-fibre (so will be usually be less stiff and heavier), but will at least have the same shape tubes which will still be subject to the same laws of physics.
Wheel choice is also important when considering how much to pay for an aero bike. If you already have aerodynamic, deep section wheels, then there’s no point in paying more money for a an aero bike that comes with similarly posh wheels. Instead, buy the bike with the cheaper wheels, take these off to use as training wheels, then put on the deep section wheels that you already own for race days.
How we score
10 – Superb, best in its class and we couldn’t fault it
9 – Excellent, a slight change and it would be perfect
8 – Brilliant, we’d happily buy it
7 – Solid, but there’s better out there
6 – Pretty good, but not quite hitting the mark
5 – OK. Not much wrong with it, but nothing special
4 – A few niggles let this down
3 – Disappointing
2 – Poor, approach with caution
1 – Terrible, do not buy this product