Chasing Aero!

If you’re reading this article in a café or bike shop, have a look around you right now and check out the bikes closest to you. Do they look super aero? Chances are that most of the machines you can see are sporting slammed stems – in other words, any spacers between the dust cover and the stem have been removed, so that the stem has been lowered all the way down to the headset bearing cover. Take an even closer look – in all likelihood the stem has been flipped over too, providing an even lower and more aero riding position. 

Slamming your stem is a very trendy thing to do right now, and in theory it makes pretty good sense as it definitely sets the rider into a more aero position on the bike – and aero is good, right?

Well, yes – aero IS good, but only when it doesn’t come at the expense of anything else. Have a chat to any good bike fitter and they’ll tell you that there are four things that come into play when striving to get the perfect union between bike and rider: safety, comfort, power and aerodynamics.

Occasionally a pro rider or hard-core amateur will insist that power output is more important than safety, or that comfort really doesn’t matter much to them as long as they’re getting the results they want. But nobody who knows what they’re doing puts aerodynamics as the number one item on their list of priorities. There’s just no point – you really need to be able to go fast, and go fast for a while, before aerodynamics even matter.

You may or may not consciously consider many aspects of the activity of cycling; things like yourself, bike safety, comfort, power, aerodynamics, environment (wind, incline, road surface etc)

If you approach your riding and your bike as a whole system, rather than all these aspects separately it’s much easier to appreciate the trade-off between some of these factors. For example, a rider who lacks flexibility can force themselves into an aero crouch over the bars, riding in the drops and presenting a nice small frontal area to the wind – but they can’t do it for long. Almost immediately they start to feel uncomfortable, their breathing starts to suffer and their power output starts to decline. As long as they can maintain their original position they’re still pretty aero, but it’s almost pointless.

Now consider the same rider taking a broad critical view of his or her bike fit. They are safe and comfortable on the bike – the points of contact (pedals, handlebars and saddle) feel natural, the chest feels open and breathing is no longer laboured. The power they are able to develop translates directly into forward movement – the position they are in is not necessarily the most aerodynamic, but it works well for them and they are able to maintain that position for long periods of time. When the environment changes they can climb without major adjustment, descend quickly and safely and negotiate obstacles with confidence.

The same approach can be narrowed down to focus solely on stems. If everything else remains equal or is improved, then slamming your stem is definitely the way to go. Don’t rush into it, though. It’s a simple process – just pull those spacers off and chuck them away – but it can have complex consequences.

By dropping your bars only a centimetre or two you change your entire body position on the bike. Here’s a great self-test developed by Joe Friel, a pioneer in the fields of power training and bike aerodynamics: imagine that your pelvis is a bowl of water. Now picture yourself on your bike in your normal riding position. Water should be spilling from thefront of your ‘bowl’. This means that your hips are tilted forward, your neck and spine feel ‘long’, your back is straight, your chest is open and your vision is clear and unimpeded. Now, to provide some contrast, picture your bowl again: this time imagine trying not to spill any water. By focusing too much on keeping your hips level, your back becomes rounded, your chest becomes concave and therefore breathing becomes laboured. Due to the rounded position of your back, your head and neck are held in an unnatural position and the only way to see where you’re going is to lift your head extra high and curve your neck. Additionally, the lack of forward tilt at the hips reduces the potential to develop power through the legs and makes you feel as if you need to reach for the bars, even though the distance from saddle tip to handlebars has not changed.

What’s all this got to do with slamming your stem? If you can ride comfortably in this spilled-bowl position, with its improved efficiency, power and engagement of the core muscles, andrid your stem of a few pesky spacers then go for it. However, if it changes the way your sit bones connect with the saddle and robs you of power and comfort then forget it – it’s just not worth it.

Ever seen a rider sporting a super-slammed stem who alwaysrides on the hoods or up on the bars? The best way to get yourself into a more aerodynamic position without spending a cent or changing anything about your bike is to get used to riding in the drops. Even during races there are plenty of riders sitting up and effectively acting like human parachutes… they would save so much energy (or alternatively, use the same amount of energy but go faster) by riding in the drops. A rider in the drops has their torso much closer to the horizontal position, which of course results in presenting a smaller frontal surface area. If you’re still familiar with high school physics, you’ll remember that the air resistance of an object increases by the square of its velocity – this means that small aerodynamic improvements can pay big dividends. And the faster you ride, the greater the payoff.

It’s an easy theory to test in the real world. If you’re fortunate enough to have a power meter, find a flat stretch of road and ride with your hands resting on the hoods at a constant speed at a constant power output – for the sake of simplicity, let’s say it’s 30kph at 180 Watts. Now keep your power constant but move your hands down into the drops – check out your speed now. In most cases you get about a 1kph increase for no extra effort. If you don’t have a power meter you can still do the test – just keep your effort consistent and swap between the two positions, keeping an eye on your speed fluctuations.

So before you slam your stem, get used to riding in the drops for long periods on varying terrain. You may find that you’re not quite as flexible as you thought you were, or that the layer of winter padding you’ve developed around your waistline is slightly thicker than you realised! These are obvious areas for improvement – there are lots of great diet and stretching routines in Bicycling Australia magazine, so get to work!

Once you get to the point where you can complete your long rides comfortably in the drops and you still feel the urge to slam – take baby steps! Take out your smallest spacer, drop your stem and put the now unused spacer on top of the steerer tube. Don’t do any cutting just yet – there’s no going back once you do! Be honest in your self-assessment. How does your back feel? Are you putting too much pressure on the bars through your hands? Is your power output bleeding away? If you are absolutely confident that your core strength, power, flexibility and bike skills will allow you to go even lower, then give it a try, but don’t beat yourself up if you need to lift your bars back up to achieve maximum comfort and power. There’s a fine line there somewhere, and it’s in a different place for everyone – you just need to experiment a bit to find where yours is. 

So what’s the final verdict? In my opinion there’s way too many riders out there just slamming their stems for the sake of it, or because it looks cool; and lots of them are probably doing themselves a disservice in terms of back pain, power loss and poor bike position. For those few who can handle it without compromising comfort, power or performance then it’s actually a pretty good idea.

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