Climbs & Time Trials

Every year the presentation of stage races courses bring discussions on whether the path is more suitable for pure climbers or rouleurs-climbers. 

In an attempt to propose a criterion based on numbers and not just opinions and clichés, I would like to express some considerations. 

Most of the route of every stage race takes place on the flats and relatively easy hills (with average slopes of less than 7%): drafting gives significant advantages in both cases, advantages that are difficult to quantify and that differ from rider to rider (athletes of small size, in any case, have a greater benefit than bigger athletes). 

I shall therefore compare typical time trial courses with climbs of an average gradient superior to 8%, where speed is reduced, making the advantage of drafting of little significance. 

I calculated the difference in speed, on flat course and uphill, corresponding to a difference in required power equal to 5%: 

- pedaling at 51.2 km/h on the FLAT requires 5% more power than pedaling at 50 km/h 
(2625 vs 2500 are the square speeds): the difference between them corresponds to 1.7”/km, equal to 1.4”/min of effort. 
The same happens even at lower speeds: pedaling at 41 km/h requires 5% more power than at 40 km/h (1681 vs 1600 are the square speeds): the difference corresponds to 2.2”/km, equal to 1.5”/min of effort. 

- pedaling at 20km/h UPHILL requires 5% more power than at 19 km/h: the difference between the 2 speeds corresponds to 9.5”/km, equal to 3”/min of effort. 
The same happens at lower speeds: 15.8 km/h and 15.0 km/h present a difference of 5% in required power output, corresponding to 12"/km and 3"min of effort. 

Therefore, it is more difficult to make the difference in a time trial event than on a climb: a 5% gap between 2 athletes will be half as advantageous on a flat course compared to a climb. 
In other words, an uphill finish (with an average gradient higher than 8%) of more than 30 minutes in duration is compensated by a flat course time trial of 60 minutes.