Vuelta Stage 18 – Course Preview

Every grand tour used to contain a long flat time trial but these days they’re becoming more and more rare. Truthfully, we miss them and the organisers of the Vuelta must have been reading our minds because they’ve bought it back, though we’d prefer for it to be 50km like the good old days.

After making their way out of El Puerto de Santa María, riders will sette into their pace for a prolonged high-speed effort. There are a few twists and turns in Lomopardo and Estella del Marqués, where there’s also a time check. The route is tailor-made for pure time trial specialists so look out for big performances from Küng and Hayter.

The course map

The course is pretty simple, there are around 10 corners that will cause the riders to have to take some kind of action, be that get off their aero bars or slam the anchors on, but in general it’s a flat TT that goes from one town to another – the kind we’ve seen a million times.

The wind map and surface friction

Anyone who’s ridden their bike in coastal European towns will be familiar with the wind. We’ve all left a town into the open areas and found ourselves suddenly being thrown around by the wind between hedgerows and buildings. That’s why we developed the surface friction mapping at myWindsock.

The myWindsock surface friction plot displays the area’s topology. Shaded areas are where the wind will move slower than forecasted due to buildings, trees or other physical features of the landscape. As it happens, for this particular time trial the wind is relative mild but we can still see areas of the course where buildings slow the wind down around the start and finish towns. The wind is forecasted to be around 5m/s (18kph) for the time around which the GC riders set off.

The race is forecasted to be majority tailwind which means that the windiest part of the day is actually the fastest.

As you can see, the wind adjusted elevation plot shows the course to be effectively net down hill, despite finishing at a higher altitude (slightly). Essentially, riding the course will feel “down hill” as riders are pushed along by the wind. Especially in the middle section between the two towns.
Riders will be setting off between roughly 2pm and 5pm for this time trial. Broadly speaking, conditions get slower throughout the afternoon giving the time trial specialists who are a long way down on GC even more of an advantage against the GC riders. The only GC rider who has a track record of beating the TT purists is Roglic, who will be setting off during the slowest part of the window.

There’s a ten second difference between setting off at 15:00 compared to 17:00, so there’s not a lot in it but we’ve seen world tour time trials of this distance won by smaller margins.

How hard is it to gain two minutes?

To have any chance of winning this Vuelta, Roglic will have to ride this TT about 2 minutes faster than Mas. Given this will be the target, how good a performance is actually needed to pick up two minutes on a “bad” time trialist?

A bad time trialist in the Vuelta is a pretty good time trialist:

Enric Mas will probably not mind us saying that, relative to other riders at his level, he’s never been the best time trialist. Reportedly, he weighs about 61kg and has a sustained 40 minute power of around 370W. Let’s say he’s about 4% lower power on the TT bike than the road bike (this is the upper end of “average”) then we can guess he will ride around 355W for this TT. We’ll assume his cda is 0.2, it’ll likely be a little lower but as he’s not a TT specialist he will also sit up a bit, so that’ll drag his average cda up slightly. We will assume his mechanics have him on fast tyres and a fast drive-train.

Plugging all of these assumptions into myWindsock gives Mas a predicted (but large error bars here as this estimate really was a bit of a guess for things like power and cda) of 40:29.

In order to challenge on GC, a top GC rider will need to produce a time of 38 minutes and 30 seconds. What kind of performance does this require? Let’s go back over some of our assumptions and put them into “peak TT Roglic” mode.

Back in the day, Roglic wasn’t just a ‘good for a GC guy’ time trialist, he was great. He’s reported to be at a weight of 65kg, which is a couple of kg heavier than Mas. During this Vuelta, he’s been climbing at a similar, but slightly slower, rate as Mas. Based on his track record though, we can estimate him to be slightly more aerodynamic as well as have a slightly lower power loss in the TT position.

We will assume his sustained 40 minute relative power is 1% lower than Mas at the moment, based on their climbing performances so far during this race. This gives him an estimated 390W to play with, but we’ll assume he loses only 2% of this relative to Mas in the TT bars instead of Enric’s 4% drop off. That means our estimated TT power for Roglic during this TT is 383W. We will also assume a cda of 0.19, we could be more aggressive with this estimate but he’s currently struggling from the impacts of a crash in training before the Vuelta started.

All of these assumptions lead to a time of 38:56, about a minute and a half faster than Mas.

Now, in order to get that two minute gap back, he will have to take some risks on pacing. Let’s now assume he’s magically slightly more aero at 0.18 and loses no power in the TT bars. This is essentially the best possible day that Roglic could conceivably have…

This would give Roglic just over 2 minutes back. He needs a generational day, but it’s within the bounds of possibility.

This blog scratches the surface of how World Tour Cycling Teams use myWindsock to prepare for time trials. If you want a detailed look at Stage 18 of the Vuelta – you can check out the forecast here.