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stage 12 TT is tomorrow over 33.7km. Comparisons to the final Tour de France TT are obvious given the route profile (finishing with a climb) but it's going to be quite different for a few reasons, and maybe this time a bike change is essential (thread) 
1/16
stage 12 TT is tomorrow over 33.7km. Comparisons to the final Tour de France TT are obvious given the route profile (finishing with a climb) but it's going to be quite different for a few reasons, and maybe this time a bike change is essential (thread) 1/16
Firstly although the profile appears flat then climb, the Tour TT was more consistent before the climb whereas after leaving Muro the loop round the coast consists of a series of short undulations to really throw the rhythm of already fatigued riders.
2/16
2/16
There is also going to be a large headwind from the north for the majority of the ride. This will really drive down the average speed for the flat section compared with a still day, & mean that riders who can't maintain a good aero position into the headwind will struggle.
3/16
3/16
On main roads for the first 32km, it is a non technical TT so riders will be able to focus on holding their position and getting the power out. This section will take the better riders <45min to complete.
4/16
4/16
A drop in power over the first 32km of 10w is the equivalent of a 31sec penalty. So two identical riders, one at 390w and one at 400w will see a 31sec gap between the two before the climb.
5/16
5/16
A 2% increase in CdA (badly pinned number, wrong front wheel choice) is a 12sec penalty here. Remember the gaps on GC are currently relatively tight and the lead is continually changing hands!
6/16
6/16
1kg of extra mass is a 5sec penalty over the first 32km of the stage. Aerodynamics is far more important than weight for this initial section, and a 10% increase in rolling resistance (choosing a slower tyre) will cost 14%, making Crr also more important than weight.
7/16
7/16
But then there's a climb - to Ăzaro - and it's steep. So steep in fact (well over 25% in the middle section) that riders have been forced to walk up it in previous races. This is something that will making maintaining stability tricky, especially on a TT bike.
8/16
8/16
Normally I'm against bike swaps in TTs, due to the risk of losing more time completing a change than you would gain by staying on the bike & maintaining your rhythm. However in this situation it is pretty much obligatory. Some will do the stage entirely on a road bike.
9/16
9/16
The climb is 1.8km long with an average gradient of >14%, and will take the better riders around 8min to complete. On this climb 10w is worth 12sec.
10/16
10/16
1kg on the climb is 6sec - and given team TT bikes can often be 2kg heavier than the road bike, a 12sec change at the correct location (when speeds are low) will be worth it. Especially from a gearing perspective as riders will need to swap to very low gearing.
11/16
11/16
Aero drag is not important on the climb, but a rolling resistance penalty of 10% would be worth 2sec.
12/16
12/16
If we add everything up, the 33.7km stage will take around 50min for the faster riders, with 10w power output being the equivalent of 43sec, 2% aero drag penalty 12sec, 1kg additional mass 11sec, 10% worse Crr 16sec.
13/16
13/16
The temptation will be to ease off on the initial flatter section in anticipation of the climb, but given the headwind for the majority of this part riders could lose a significant amount of time as everyone will be out on course for longer.
14/16
14/16
Holding a strong aero position is going to be key, as some of the less TT focused riders could lose a lot of time before you get to the climb, which they may not get back given its relatively short duration.
15/16
15/16
Top tip 
don't mess up your bike change. No-one wants to lose a grand tour podium on a bike change, and it may well come down to that.
16/16
don't mess up your bike change. No-one wants to lose a grand tour podium on a bike change, and it may well come down to that.16/16
