Evil Twins, Triathlon’s Draft Box, and Race Day Interval Workouts

In this post on draft-legal triathlons, we learned that the triathlon rulebook specifies an unnecessarily wide gap between two triathletes riding their bicycles.

Science talks about things in terms of space and time, and so does the rulebook. To avoid penalties in a no-draft race, you have to overtake your competitor within 15 seconds of initiating a pass. Otherwise, you’re compelled to give up the chase and back off 7 meters again. Let’s examine what happens.

Consider the following example. Two triathletes, a competitor and her evil clone, are racing down the road on identical bikes. They start out of the transition area with exactly seven meters between them per USA Triathlon regulations on a totally windless, flat stretch of road, travelling at 20mph. Evil clone is leading and our friendly, law-abiding triathlete is second out of transition. Our law-abiding triathlete’s immediate desire is to pass her doppelganger.

Triathletes, triathlon, race, draft-box, passing

At 20mph, the evil twin will cover 134.1 meters in 15 seconds (sorry for the unit-swapping, aerodynamics works best in metric). To put her front wheel ahead in that same time, our heroine will have to travel 141.1 meters. When you back out from that number, you find that she has to move at 21mph to get ahead. In fact, no matter what initial speed the two competitors start at, the passing athlete has to put in an extra mile per hour to be legal according the USA Triathlon’s drafting rules. Simple enough, right?

Not quite. Our law-abiding triathlete needs to put out the necessary power to pass her leading evil clone, but she can’t accelerate to that speed instantaneously. So the question becomes how much more power is required to pass legally? To figure that out, we use a rather complicated equation:

Faster Jim Gourley passing formula

What this essentially says is that power is based on acceleration, velocity, mass of rider and bike, the coefficients of both air and rolling resistance, and the gradient of the road.

(There is actually a much more enjoyable and informative way to experiment with this and other physical factors of cycling. Check out the website www.analyticcycling.com for great “calculators” that graph performance and offer invaluable nuggets of wisdom about aerodynamics.)

Courtesy of math, we learn that at 20mph our 130-pound triathletes riding 17-pound bikes need to sustain an approximate output of 138 Watts. But to accelerate and cover the greater distance necessary to legally pass in fifteen seconds, our fearless rider will have to ramp up to around 185 Watts! That’s an extra 47 Watts.

And 47 Watts is kind of a big deal.

For heavier athletes at higher speeds, the increase is even more dramatic. But when you allow the trailing rider to close the gap by those two-and-a-half meters that don’t give any draft advantage, it reduces the power output needed to pass to only 168 Watts. That’s a major savings in terms of effort.

triathlon, triathletes, passing, draft box, cycling FASTER

The USA Triathlon drafting rule requires triathletes to put forth gargantuan exertions to bypass a non-existent “cheating zone.”

We’ve all felt the consequences. What should be endurance races are at times turned into fitful sprint intervals workouts coming out of transition followed by an exercise in mind-over-lactate buildup.

Race officials could still make the argument that the draft box promotes safety by avoiding collisions, but my counterpoint would be that safety would be improved if races had more course marshals to better enforce the rules.

It’s my suspicion that accidents often happen as a result of someone trying to “equalize” what they view as someone else’s cheating. In the meantime, cutting the draft box would at least put those who play by the rules on a more equal footing with those that don’t. It’s simple math and common sense.

Does the science of speed interest you? You’ll be fascinated by Jim Gourley’s new book FASTER: Demystifying the Science of Triathlon Speed.

Jim Gourley is an astronautical engineer and triathlon journalist. His new book FASTER takes a scientific look at triathlon to see what truly makes you faster—and busts the myths and doublespeak that waste your money and race times. With science on your side, you’ll make the smart calls that will make you a better, faster triathlete.

FASTER is now available in your local tri shop or from these retailers:

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