How to pace a time trial with power

A time trial is the purest test in cycling and the easiest to get wrong, because the mistake happens in the first three minutes when you feel excellent. Pacing is not a detail on top of fitness — on a flat 40-minute effort it is worth more time than most riders gain from a winter of training.

The good news is that with a power meter it is a solvable problem. You can know your target before you start, and you can watch yourself obeying it.

Three ways to ride the same course

The bars below are stylised, but the shapes are real. Each shows power across ten equal segments of an event, as a percentage of the target.

Why starting too hard costs so much

The underlying physiology is worth understanding, because it explains why the damage is not symmetrical — going 20 watts too hard early costs you far more than going 20 watts too easy early gains you.

There is a power at which your body reaches a genuine metabolic steady state, sustainable for a long time. It is often called critical power, and it sits close to what most riders think of as their threshold. Above it, no steady state exists. You are drawing on a strictly finite reserve of work, conventionally called W′, and the deeper you go above critical power the faster you drain it. When it is gone, your power collapses — not as a matter of willpower, but because the metabolic conditions in the muscle no longer permit the effort.

An over-hard start therefore does two things at once: it empties a reserve you needed for the finish, and it leaves you riding the rest of the event in a progressively worse metabolic state. Pacing research on athletic competition consistently finds that in events of this length, an approximately even effort beats a fast start.

Thinking of W′ as a budget

The practically useful framing is that you begin with a fixed number of match-equivalents above critical power, they deplete when you ride above it, and they partially recharge when you drop below. Models exist that track this in real time; you do not need one to use the idea.

The rule that falls out of this is simple. Spend above target only where the course forces you to, and only briefly. Every excursion above critical power is a withdrawal, and the recharge is slower than the drain.

Hills and headwinds: when variable is faster

Even pacing is optimal when conditions are constant. They rarely are. Modelling work going back to the 1990s shows that on a course with gradient or wind, varying power the right way beats holding it constant at the same average — because the time you save at low speed is larger than the time you lose at high speed.

The size of the sensible variation is smaller than most riders assume. Modelling of realistic courses suggests the gains come from modest swings — on the order of five to ten per cent either side of target for sustained features — not from attacking every rise. Large surges cost more in W′ than they return in seconds, and they wreck the second half of your ride.

Choosing the target number

All of the above is useless without a defensible target. The most reliable way to set one is from your own power-duration curve: the best power you have actually produced for a range of durations, drawn from your real ride data rather than from a formula.

• Estimate your finishing time first. Distance, profile and your realistic speed. This is the single most important input, and it is worth being pessimistic about wind.
• Read the corresponding point off the curve — the power you have held for about that duration before, in comparable conditions.
• Subtract a little for a first attempt at a distance you have not raced. Two per cent under is recoverable; five per cent over is not.
• Sanity-check against duration. Most trained riders hold something close to threshold for a 40-minute effort, somewhat under it for 90 minutes, and comfortably above it for 10.
• Do not set the target from a single indoor test. Outdoor power is often lower, and a hot, still day changes everything.

Moveee builds that power-duration curve automatically from your uploaded rides, so the number you race on is one you have genuinely produced rather than one you hope for. If your target event is in the plan, the taper is built backwards from its date — see the last two weeks.

Executing it on the day

• Use a longer power average on the head unit. Three-second power is noise; a 10- or 30-second average shows you what you are actually doing.
• Cap the first five minutes. Set a ceiling you will not exceed no matter how good you feel, and obey it. This one habit is worth more than any other on this list.
• Check in at a third and at halfway. If you are meaningfully over target and already hurting, correct now rather than at the point of collapse.
• Hold position, not just power. Sitting up to recover on a climb can cost more than the watts you save. Aerodynamics does not take a break.
• Empty the tank in the last few minutes. W′ has no salvage value. If you finish with something left, note it and raise the target next time.

Ride it twice on the same course with the same fitness, once too hard at the start and once with discipline, and the gap will tell you more about pacing than any article can. The discipline is the whole skill — a time trial rewards the rider who is willing to feel slow for the first ten minutes.