Thread by @xavierdisley

It's the big one tomorrow for this year's @LeTour - Stage 16 time trial!

With the GC top spot of Jonas Vingegaard within 10sec of @TamauPogi, small differences in the 22.4km largely uphill test will add up!

Read below for my thoughts on what to expect 👇

1/20

#TDFF2023

The stage darts around Passy and finishes in Combloux.

It is 22.4km in length, with a tough short climb at the beginning (it's an uphill drag off the line before you even get there), and then the long >6km climb to finish at the picturesque centre of Combloux.

2/20

Weather wise it looks like it's going to rain 🌧 and not only that, riders will experience a slight headwind for the majority of the race. Tailwind to start, up the first short climb, but the wind is coming from the south west making the final climb a bit slower.

3/20

Let's look at the climbs in detail - here is the route profile but it's a little misleading as the 4.1km point is hard than it appears.

First 2.6km is 1.2% uphill (with tailwind), then it's a 1.7km climb at 7.8%, again with a tailwind.

4/20

This first 1.7km climb to Côte de la Cascade de Cœur will be <25kph and take around 4.5min for the top riders.

First question to ask is bike choice - these are relatively low speeds and it's a switchback climb, but I think a road bike would be the wrong choice here.

5/20

The main reason being that if you rode a road bike off the start line, you will lose 10-15sec in the first 2.6km compared with a TT bike at 20% lower aerodynamic drag.

Riding a TT bike up the first climb that's ~2.5kg heavier would cost around 8sec.

6/20

You have to make sure the gearing on the TT bike is correct, otherwise you lose more than 8sec compared with the road bike.

However - you absolutely need to be on a TT bike for the 11.7km central section, so you'd lose time swapping bikes at the top of the first climb.

7/20

This 11.7km section to the bottom of the final climb isn't all downhill - there's a short 1km 2% crosswind drag through Passy - but it will be fast and riders will need to be as aero as possible, especially with swirling/unhelpful winds.

8/20

Speeds will be well >50kph and this section will take around 13min to complete.

In my opinion we can largely ignore the first time check and instead focus on the second check at 16.1km as this includes the full downhill and the first climb.

9/20

If you're on a road bike during the 11.7km downhill section you will lose 50-60sec compared with someone on a TT bike so no one should be doing that, apart from the back markers who aren't that worried about bike changes during the stage.

10/20

We're now onto the final climb! A little bump up and downhill before the climb starts for real, and it's split into a steeper first part and shallower to finish.

2.7km at >8%, followed by 3.5km at just over 5%.

11/20

If we take the climb as a whole, it's 6.2km at 6.3%, and will take roughly 15min depending on the wind.

You don't have to swap bikes here, but it would be a good idea if you can get your bike swap time <15sec (very achievable). Gearing is again an issue on TT bike.

12/20

That 15sec is the penalty you'd have on a TT bike that was 2.5kg heavier but more aero. I use that example as there will be a few TT bikes approaching that kind of weight penalty - for the downhill you don't want to make your TT bike lighter/less aero for this stage.

13/20

The average speed on this final climb will be in the mid 20s kph, which is why using a heavy TT bike isn't actually that bad as aero still matters! But not as much as weight.

All being equal however, An extra 1kg on the bike/rider up the final climb will cost 9sec.

14/20

Last note on race modelling - tyres as always are crucial. Teams these days are all over it in terms of rolling resistance & are using time trial tyres not only on the hillclimb road bike TTs, but also on road stages where there's a tough final climb!

I approve of this 👍

15/20

If you use a normal road tyre rather than a TT tyre on the final climb alone, this would cost around 10sec - similar to adding 1kg to the bike! So don't do that.

16/20

What can we expect to see on the day? I think using the first time check as a benchmark will be a bit of a mistake - you may have people doing double bike changes, going too hard up the first drag, going too conservatively etc. so the second time check is more insightful.

17/20

I expect to see teams making the bike change at the bottom of the final climb.

As we've seen over a few recent World Tour TTs, organisers seem happy to add an extra element of drama into TTs by "forcing" a bike change. Maybe we'll see a gravel bike change one day 😅

18/20

10sec over the course of this race is nothing in terms of power output/aero drag/weight. All being equal, 10sec is the equivalent of:

3.9w
1.55kg
0.005m² CdA (<3%)

So recovery, kit selection, holding the aero position - get one of those wrong and you're out!

19/20

Hope everyone's looking forward to it as much as I am 😀 - see you on the other side!

20/20