Heading into stage 20, Primož Roglič (Jumbo-Visma) leads the race by 57 seconds over Tadej Pogačar (UAE Team Emirates), having led the race since stage nine.
There are still 36km of lonely road between the Slovenian national champion and his first yellow jersey, as riders race to the top of the 6km, 8.5 per cent average Planche des Belles Filles.
Pogačar may have hope however, having triumphed over Roglič in the Slovenian time trial championships on a similar, but shorter, course in June, taking the national title by nine seconds.
But what will be the deciding factors in this race against the clock to decide the 2020 Tour de France – will they ride TT bikes or road bikes, how many watts would Pogačar need to win the race, and could tyre choice make the difference?
We asked aerodynamics and time trial expert Xavier Disley to get his thoughts on this pivotal moment in the race.
Horses for courses
Firstly, which kind of ride does this course suit?
The stage is 36.2km-long and can be split into three distinct sections – the flat opening 14km a gradual climb on the Col de la Chevestraye in the middle 10km and the following descent, then the categorised climb to La Planche des Belles Filles.
The flat section should take riders around 18 minutes, the middle section about 23, while the final climb is 18 minutes straight uphill.
Disley said stage will be well suited to a rider with a strong aero pedigree, but who is slightly heavier than the pure climbers and can hold a high watts per kilogram – think Tom Dumoulin over Nairo Quintana.
He said: “They would then have an advantage over the very small riders on the first two sections and not lose as much time (or any) on the uphill if they can match their w/kg.”
TT or road bike?
On bike choice, Disley, director of testing, coaching and aero product firm Aerocoach, said: “They will choose a TT bike for the start line, and although we saw Roglič do a bike swap to a road bike for the final climb when he won silver at the Bergen World Championships TT in 2017, and Pogačar doing a bike swap at Slovenian TT nationals this year from road to TT bike after the first 7km climb, I don’t think it would be a good idea for this race unless the rider really isn’t comfortable climbing on their time trial bike.”
Disley said that there is a weight-saving opportunity in switching from an 8.3kg time trial bike to a 6.8kg-minimum road bike, but the change is still too much of risk.
He added: “The risk of a botched change is high – we’ve seen this before – and the bike would need to be quite a lot lighter to account for the lost time (over 1.5kg lighter), as well as having a perfect changeover.
“I don’t think it’s a good idea, but we will certainly see riders doing it.”
How many watts does Pogačar need to win the Tour de France?
But what kind of performance would Pogačar need to put in to overthrow the pre-race favourite Roglič?
Both are outstanding against the clock, particularly on climbing course, so it’s going to take a special performance to find almost a minute out on the road.
Disely said Pogačar would need 15 watts more than Roglič to gain 57 seconds, with most of that time being found on the final climb, where you could find 34 seconds with those 15w.
You could also pull out that kind of advantage by weighing 3.8kg less, but Roglič and Pogačar are very similar in weight (65kg and 66kg respectively, according to Pro Cycling Stats), and you can’t save that much weight on your bike or other equipment.
The gap equates to around a nine per cent decrease in aerodynamic drag, which Disley says is no small change.
Tyre choice is key
But there is one detail, often overlooked, that could be pivotal – tyre choice.
Disley said: “We do a lot of work both for the general public as well as for some of the WorldTour teams on tyre rolling resistance as it’s an often under-appreciated topic for performance, and most of the teams are well versed in the importance of TT tyres as well as road race tyres.”
Tubeless would be ideal in a situation like the Tour time trial, Disley said, as any punctures won’t cause problems as long as the hole seals properly, and you’ll avoid a very costly mechanical.
Both UAE Team Emirates and Jumbo-Visma are partnered with Vittoria tyres, which is great news for the teams as the Vittoria Corsa Speed had the lowest rolling resistance in Aeroach testing.
Disley said the tubeless version of the Corsa speed could be the ideal choice, but with both teams likely to have access to these tyres, the advantage could be neutralised.
So how will all this play out on the road?
“Add in a tyre choice (let’s say Pogačar chooses a faster tyre like a Vittoria Corsa Speed and Roglič a slower tyre like a normal Vittoria Corsa), then you can halve the gap immediately due to the differences in rolling resistance,” said Disley.
“Now you only need 7.5w more, or a 2kg weight saving or a 4-5 per cent drop in aero drag to overcome the deficit. Or you can combine all those savings, so better tyre, plus 3w more, plus 800g less, plus two per cent lower drag – now you’ve won the Tour de France.”
Of course it’s never that easy, as Jumbo-Visma have really increased their focus on time trials in recent years in pursuit of Grand Tour victories.
Disley said: “Don’t think that Roglič’s team don’t know this though! But you have to optimise your equipment to give you every best chance to win.”