How much time each corner costs you in an urban time trial, and how much sprinting out of it is worth

At 300 W, the example rider cruises at 43.3 km/h. If a corner forces them down to 25 km/h, it takes 61 seconds and 670 metres to get back to 99.5 % of that speed, and over that stretch they lose 5.6 seconds compared with riding it at cruising speed. On a 20 km urban time trial with twelve such corners, that is 67 seconds: more than a skinsuit is worth.

How much does a corner cost depending on cornering speed?

The loss is not linear: dropping from 35 to 25 km/h in the corner doubles the cost (from 2.6 to 5.6 seconds), and a hairpin at 10 km/h costs 9. The reason is kinetic energy: regaining speed costs more the lower you went, and while accelerating you still have to beat air and rolling resistance.

Rule of thumb: every extra 10 km/h you can carry through a corner saves about 2 to 3 seconds. Knowing the line is worth more than almost any component.

Is it worth pushing out of the corner?

Yes, but less than it seems. If you ride 400 W for 15 seconds out of a 25 km/h corner instead of 300, the loss drops from 5.6 to 3.4 seconds: you get 2.2 seconds back. The cost is 1.5 kJ of W′ per corner, which is rebuilt on the cruising stretches below critical power³. With 450 W for 10 seconds the result is the same, 3.3 seconds, at the same cost.

With twelve corners, pushing out of all of them saves about 26 seconds and spends about 18 kJ of W′, almost the whole reserve of many riders. So choose: push out of the slow corners, where each extra watt yields more⁴, and ride calmly out of the fast ones.

• Slow corners (under 25 km/h): a short 10 to 15 second sprint on the exit.
• Fast corners (over 35 km/h): they cost little; not worth spending W′.
• Reserve: if the time trial ends uphill or into the wind, keep W′ for that; it buys the most time there.

What is known and what is not

The cost of accelerating is straightforward physics and the power model reproduces field-measured accelerations well^1,2. What the model does not know is how late you can brake and how fast you really take each corner: that depends on the line, the tarmac and your technique, and it is what changes from one rider to another at the same power.

Frequently asked questions

How much do I lose on each corner of a time trial?

Between 1 and 9 seconds, depending on how fast you take it. At 25 km/h, about 6 seconds for a 300 W rider.

Should I sprint out of every corner?

Only out of the slow ones. You get about 2 seconds back per corner for 1.5 kJ of W′; on fast corners it is not worth it.