Breaking Wind

I’m often irritated by reading some very uninformed & aggressive forum trolls ideas on what makes riders fast in a time trial, the bit that bothers me most is the complete lack of understanding of aerodynamic theory. This isn’t too hard to grasp, at it’s most basic, something small creates less drag, while something big creates more. But it gets complicated when we start looking at cross-sectional area & body lengths, here’s some busted myths…

I don’t go fast enough to use any aero kit.

Aye you do, even if you’re ground speed is low, you most likely race in winds blowing faster than you can ride, so you’re combined air speed is at a significant level where small aero advantages will make a big difference. It’s all too often you see riders off their aero bars while riding into a headwind, this is the worst thing you can do, this is precisely the point that you need to be the most aerodynamic, regardless of your overall average speed.

Get aero in a headwind, think about air speed rather than road speed for aerodynamics.

Why are pro riders going faster in time trials when they lose weight?

It’s not hard to understand, a smaller object requires less power to travel through air at the same speed as a larger object. A larger object has more wind resistance. So if we take one ‘sample rider’ weighing 80kg, then reduce his weight to 75kg, will he be faster on the flat? The answer is undoubtably yes. But you’re now thinking that it only counts if a rider reduces that weight as fat content, incorrect. The rider can reduce the weight as a mixture of fat & muscle, making their limb & torso cross sections smaller, while not reducing their overall fat percentage, here’s how.

Lets say this ‘sample rider’ is pushing 400 watts during a time trial at 80kg, 400W isn’t too much in muscular terms, but it’s a lot in aerobic terms. Your average skinny youth rider is perfectly capable of producing a wattage much greater than this in a sprint, so that in itself displays the required muscular physique to produce over 400W. So if our ‘sample rider’ reduces their weight to 75kg (for example if they were already at a very low body fat percentage), then they have lost 5kg but still have plenty of muscular power left to produce the required wattage.

Aerobic power output does not require big muscles, smaller muscles have less drag, an endurance rider can lose muscle and still go just as fast aerobically. Similarly, if you’re a chubby cyclist, you could record some much better results from eating less cakes & drinking less lemonade.

If I go as low as possible, I’ll be quicker?

Also not true.  As the hip to torso angle decreases, so does power generated, so a rider who’s front end is crouched as low as possible is losing power in that position. This results in a play off between power & aerodynamics, something that is going to be very hard to replicate unless you have access to the measurement resources of a pro rider, so you’re going to have to estimate it yourself. There’s also going to be physical limitations here, Jonathan Vaughters has said that his pro rider, Dan Martin, has bad hip flexion, so will be unable to attain a very aerodynamic time trial position, potentially ruling him out of winning grand tours with a large amount of time trialling in the future. There’s also the physical limitations involved here, get too low and your thighs will start to hit your ribcage. It’s all about finding a ‘sweet spot’ that is correct for you as an individual, a compromise between aerodynamics & power generation.

Low isn’t always best, everybody is different, so it’ll take a bit of work for each person to find their optimum position, don’t try to copy somebody else exactly, but certainly take some tips from photo’s & videos of pro’s with a similar body type to yourself who have access to wind tunnels.

I can go just as fast as somebody else who weighs the same as me with the same power output.

Maybe you can & maybe you can’t, some things are just down to genetics. If you are the same weight & height as somebody else, but possess a longer back & shorter legs, you may have a lower aerodynamic drag. A simple rule is that longer objects along the direction of movement through air cause less turbulence, so a rider with a long body like Wiggins for example has a genetic aerodynamic advantage, he has short arms relative to his size and can also tuck those away easier as everybody has to conform to the UCI positional rules which advantage & disadvantage certain body types. So if you have access to a power meter, you may be able to find your optimum position by doing some field testing, but it has to be very closely controlled, likely impossible to do the estimates on different days, or even different conditions on the same day, a very subjective & complicated area to step into.

A time-trial bike is quicker than a road bike.

Again, this statement isn’t true in itself. The statement should be, ‘a correct position on a time trial bike is faster than a correct position on drop bars.’ I’ve been really shocked by the awful positions of some riders on tri-bars from early season Scottish race photos, some actually assuming worse positions on tri-bars than holding the tops of the bars, yet they assume they are ‘aero’ as they are using aero kit. What people forget is that aero kit in itself isn’t aerodynamic as such, it is used as a tool to get YOU more aerodynamic. You can spend all the money you like and bolt on all sorts of stuff, but without some thought & correct positioning, you could be better off without it.

Spend some time to get your position correct, don’t just bolt on kit & hope for the best.

A constant heart rate gives the fastest time.

As far as heart rate goes, it’s a historic measurement, it measures the effect on your body of what you did to it a few minutes ago, so in short time trials it is virtually useless for the first few minutes until you reach a plateau. At that point, if you encounter a headwind and you maintain the same speed, your heart rate monitor will tell you all about it, just a bit too late. Another effect is something called cardiac-drift, where your heart rate rises over time with a constant power output, so if you maintain a constant heart rate over a time trial, your will be producing less & less wattage as time goes on.

Heart rate isn’t an ideal guide to riding a time trial, but can be used wisely if you’re aware of its limitations.

A constant power output gives the fastest time.

You’ll not be happy about this if you’ve just bought a power meter & you think that if you find your FTP (Functional Threshold Power) and ride at exactly that then you’ll produce the fastest time possible, that’s not what will happen.

Every race will have slightly different gradients, slightly different wind conditions, different weather, traffic etc, there’s plenty of variables. It’s been shown that if there is a small hill with a subsequent small descent, then it’s best to power over that slightly and recover on the downhill (you’ll always find it much harder to maintain high wattage downhill, so it’s almost an enforced rest). It’s also been shown that the differences in power outputs when riding in a tailwind are much smaller relative to the difference in speed you gain, so shoving out a load of watts in a tailwind won’t necessarily gain you that much time. The opposite is true in a headwind, where large time gains can be gained through smaller changes in wattage.

So for those using power meters there are some very specific strategies you could use to achieve the fastest time possible by varying your wattage throughout your ride depending on gradient & wind conditions. An absolutely constant power output is never likely to give you the best result, it’s worth experimenting to see what works best for you.

Aerodynamics is irrelevant when climbing.

Take the Tour of the Campsies time trial as an example, the fastest riders can be seen climbing ‘The Crow’ on the tri-bars, Arthur Doyle is a prime example of this, look over some recent photo’s if you don’t believe me. If you require heavier aero kit for the rest of the ride, you may as well use it on the inclines. We can also see that pro riders like Richie Porte used tri-bars during Paris-Nice to win the Col d’Eze time trial. Porte opted for this setup over the lightest possible bike he could use, he did this because it proved faster, I trust Sky’s boffins to be able to calculate this kind of thing correctly.

Again, there’s more to this than meets the eye, pro riders are climbing significantly quicker than amateur riders, so there will be a larger effect the faster the climbing speed. Any rider will gain an advantage from using tri-bars & aero kit on anything but a straight out hill climb.

Conclusion

Hopefully I’ve given some riders something to think about, I really hope I don’t see those kinds of photos from early season again, with riders who look like they’ve not even spent 20 minutes setting up their TT bikes correctly. Put you bike on a turbo trainer, set up a mirror so you can see your position and aim to get ‘in the tube’, i.e. everything apart from your legs into an imaginary horizontal tube. The smaller the imaginary tube you can fit your body head & arms into, will generally prove to be the most aerodynamic, but remember not to go too extreme or you’ll reduce your power output too much. It will take some time to perfect, but it’s worth much more time to you than buying the next very expensive bit of aerodynamic kit and not using it optimally, or even worse, it slowing you down through poor setup.

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