6. Allowing split times to mentally affect your effort: I tend to avoid using split times unless it's a situation where it will really help. Just because you get behind on an estimated split doesn't mean the race is over. Concentrate on the effort. The very best riders will often ride negative splits and not let competitors' fast early split times affect their personal pacing strategies.
7. Not pushing hard enough from far enough out from the finish: The goal is to use every bit of energy you have and leave it all out on the course to get the best possible time. Learn when you can "open up the throttles" and sustain maximum effort to the finish.
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8. Being an absolute slave to the numbers: Power meters, heart rate monitors and cycling computers are all amazing tools that give us feedback about our performance. Don't allow the numbers they give to rule your riding completely. Learn what different heart rates and power outputs feel like. Do some of your interval training on perceived effort alone. Cover up the numbers on your monitors, go by feel and then look at the data later to see how close your estimates were. The most important heart rate and power zone to be able to "feel" for time trials is Lactate Threshold Heart Rate and CP30 power.
9. Not enough training time at Lactate Threshold/CP30 power: Training at or near this important point is essential to develop time trial fitness. The exceptions to this are extremely short (less than 5 km) and extremely long (more than 100 km) events.
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10. Going out too hard: This one is so important I had to list it twice.
Certainly there are many more subtleties that could be listed here, but this list should give you a few things to think about before you head to your next race against the clock.
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