John Cutler posted on July 15, 2010 17:14
It is a tempting trap. Your goal time for the bike portion of your event is 1hr. You know the bike leg is 40k. So, you reason, if you average 40k an hour you’ll be on your way to nailing your goal. This speed – 40k / 24.8mph in our example – becomes your barometer for judging your fitness and workouts. Your club segments its group rides based on average speed. Even when checking your previous results you can’t escape average speed. It’s listed right up there online with time per 100m (swim), and minutes per mile (run).
Using pace for swim and run makes sense. There are no hills in the pool and while running courses vary, wind is rarely a factor. Both disciplines challenge the athlete with more even resistance.
Triathletes obsess about average speed on the bike. And it isn’t a healthy obsession. Why?
Take the following example:
Rider A rides a 40km time trial with no headwind.
Time: 61:37.03
Average Speed: 24.18mph
Rider A rides the same time trial a week later with a 5mph headwind
Time: 70:28.33
Average Speed: 21.15mph
For the above example, we’re assuming a power output of 250w for each ride. But imagine for a moment that Rider A attempts to hold 24.18mph on her second ride? How much power will she have to generate? It’ll take 350w to go 24.18mpg into a 5mph headwind. It’s safe to say that if 250w was doable but tough, then 350w is way too tough. In fact, she’ll probably implode in less than 5 minutes (and forget the run completely!).
On the flipside, you might have an athlete who recently fine-tuned their riding position. Now they are more “aero” and cheat the wind more effectively. Imagine they go out determined to ride 24.17mph. Now, instead of pushing 250w, the rider will only need to generate 225w to maintain that average speed. That’s all well and good – their goal will be met – but how much faster could they have gone if they ignored speed and kept power constant? 59 minutes 47 seconds.
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The bike ride went great! The new machine just cruised and the miles flew by. It may be because the bike is my favorite event, or because the wind keeps you nice and cool - whatever it was, I pulled of a 1:12:59 25-mile course, with an average speed of 20.8 mph, the EXACT same average speed as I did in California six weeks ago. The big difference was how I felt afterward; in California my back and legs were trashed after the bike. In St. George, my legs and back felt like they were barely used and ready to run!
Consider the following:
- Maybe 20.8mph was too fast for the California race?
- Maybe he could have gone faster on the bike during his second race. Should your legs feel barely used?
Simply put: It is almost impossible to maintain the correct training / racing zones by riding based on speed. On an indoor track (assuming a consistent position on the bike), split times can be used as a proxy for power/pace, but outside, all bets are off.
So what’s the answer? Without a power meter, your best bet is to build an acute awareness of perceived exertion. What does your 40k bike leg pace actually FEEL like. Forget the computer for a moment. How do your legs feel? How about your breathing? How was the run? Many athletes obsess so much about the numbers that they fail to build solid body awareness.
Stop the obsession. Build that awareness. Consider a power meter. And nail that bike split!