The time trial conundrum

[hazaran]

Solve a riddle for me:

Tour 2016 Stage 13 hilly 40k ITT: 0 Froome, +2:05 Quintana
Tour 2016 Stage 18 uphill 20k ITT: 0 Froome, +1:10 Quintana

Giro 2017 Stage 10 hilly 40k ITT: 0 Dumoulin, +2:07 Nibali, +2:53 Quintana
Giro 2017 Stage 21 flat 30k ITT: 0 Dumoulin, +0:54 Nibali, +1:24 Quintana

Vuelta 2017 Stage 16 flat 40k ITT: 0 Froome, +0:57 Nibali

It seems most noticeable in the Giro but why do riders that are more talented climbers than testers do so comparatively bad in the hilly time trials, and vice versa, comparatively good in the flat time trials? What is the missing predictive factor?

 

[del1962]

Quintana's 2016 tour form was poor

 

[Dekker_Tifosi]

In flat time trials the pace is high so the relative differences in time are little.

In hilly time trials, the speed is slower. And because the hills are usually shallow percentages, you need more pure power than climber. So the advantage of the time trial specialists among the GC men become even higher. Lower speeds = greater differences

 

[Gigs_98]

Wrong thread

 

[PremierAndrew]

Re:

In flat time trials the pace is high so the relative differences in time are little.

In hilly time trials, the speed is slower. And because the hills are usually shallow percentages, you need more pure power than climber. So the advantage of the time trial specialists among the GC men become even higher. Lower speeds = greater differences

This. All depends on the gradients of the hills. The time trial specialists are able to produce more power, but because air resistance is proportional to velocity^2, at 55km/h, a 20W difference will not make much difference in speed, whereas at 40km/h, it will make a much bigger difference in speed between a TT specialist and a climber.

A TT specialist will weigh more than a climber, and at high gradients, the extra weight that a TT specialist will have to overcome will outweigh the difference in power that a TT specialist has, but at shallow gradients, the extra difference in speed that 20-40W causes is greater than the effect of the extra weight

 

[hazaran]

Re: Re:

This. All depends on the gradients of the hills. The time trial specialists are able to produce more power, but because air resistance is proportional to velocity^2, at 55km/h, a 20W difference will not make much difference in speed, whereas at 40km/h, it will make a much bigger difference in speed between a TT specialist and a climber.

A TT specialist will weigh more than a climber, and at high gradients, the extra weight that a TT specialist will have to overcome will outweigh the difference in power that a TT specialist has, but at shallow gradients, the extra difference in speed that 20-40W causes is greater than the effect of the extra weight

Thats a great hint with the drag. If the course is flat => speeds are high there are dramatically diminishing returns on higher power.

 

[Brullnux]

Re:

In flat time trials the pace is high so the relative differences in time are little.

In hilly time trials, the speed is slower. And because the hills are usually shallow percentages, you need more pure power than climber. So the advantage of the time trial specialists among the GC men become even higher. Lower speeds = greater differences

Also both flat time trials listed have come in the final week of a GT, so pure TT ability matters less. And Tuesday's TT wasn't that anomalous, it was only 20-30 seconds out from what was probably expected (or at least what I expected).

 

[Pantani_lives]

A climber only has a real advantage on the portions that are at least 7% uphill. Most of those hilly time trials only have a small portion of those, if any. In an actual climbing time trial the climbers will be on top, but not in a long time trial with one or two gentle climbs. There's also the danger of giving too much on that small climb and then collapsing in the flat section against the wind.

 

[Parker]

Solve a riddle for me:

Tour 2016 Stage 13 hilly 40k ITT: 0 Froome, +2:05 Quintana
Tour 2016 Stage 18 uphill 20k ITT: 0 Froome, +1:10 Quintana

Giro 2017 Stage 10 hilly 40k ITT: 0 Dumoulin, +2:07 Nibali, +2:53 Quintana
Giro 2017 Stage 21 flat 30k ITT: 0 Dumoulin, +0:54 Nibali, +1:24 Quintana

Vuelta 2017 Stage 16 flat 40k ITT: 0 Froome, +0:57 Nibali

It seems most noticeable in the Giro but why do riders that are more talented climbers than testers do so comparatively bad in the hilly time trials, and vice versa, comparatively good in the flat time trials? What is the missing predictive factor?

They're fighting different enemies.

In the flat time trial it's air resistance, so aerodynamics is the key parameter

In the hilly time trial it's more gravity, so weight is the key parameter

 

[Red Rick]

Re: Re:

In flat time trials the pace is high so the relative differences in time are little.

In hilly time trials, the speed is slower. And because the hills are usually shallow percentages, you need more pure power than climber. So the advantage of the time trial specialists among the GC men become even higher. Lower speeds = greater differences

This. All depends on the gradients of the hills. The time trial specialists are able to produce more power, but because air resistance is proportional to velocity^2, at 55km/h, a 20W difference will not make much difference in speed, whereas at 40km/h, it will make a much bigger difference in speed between a TT specialist and a climber.

A TT specialist will weigh more than a climber, and at high gradients, the extra weight that a TT specialist will have to overcome will outweigh the difference in power that a TT specialist has, but at shallow gradients, the extra difference in speed that 20-40W causes is greater than the effect of the extra weight

Air resistance is actually proportional to the ^3. You have to accelerate the air, and you have to accelerate a greater amount. This gets more complicated with wind. 400W on the flat would be 45ish (I guess), for most riders. Sprinters can reach 1600+ (2^2 times 400W), but they're not near 90kph.

As they're climbing you basically get an equilibrium of air resistance and climbing resistance (linear). You'd think climbers would be favoured by going uphill, but on lower gradients, where air resistance is still very significant, the heavier riders will spend less W/kg on air resistance and so he will be spending relatively more W/kg on climbing resistance. The difference is probaly smaller than the difference in P/area, but this difference is affects speed linearly.

That's the physics.

The rest is purely form. Dumoulin was very tired at the end of the Giro.

 

[Escarabajo]

Re:

In flat time trials the pace is high so the relative differences in time are little.

In hilly time trials, the speed is slower. And because the hills are usually shallow percentages, you need more pure power than climber. So the advantage of the time trial specialists among the GC men become even higher. Lower speeds = greater differences

This.
The power climbs benefits the time trialists even more. Besides having flats after these climbs does not help the climbers.