Friday, July 12, 2013

2013 Tour De France Stage 17
Light or Aero?

Coming up this Wednesday is my favorite kind of time trial. One that goes up big mountains and back down again. Inevitably we see a wide array of differing equipment choices. TT bikes or road bike? Light wheels, or aero wheels? The decision actually ends up quite complex and some teams have better options than others. This stage features two category 2 climbs with grades of around 6% for a total of 32 kilometers, almost none of it on the flat:




Modeling the Course


We can turn to our trusty equations of motion for a cyclist to get some insight into the complexity of the equipment choices faced on a day like this. We can model the course with a decent approximation on the  website at Analytic Cycling. By inputting the average gradient and distance of the two climbs and two descents we have a pretty good model of the course.  The power and mass of the cyclists will vary but we can use some average cases to see how a TT setup vs road bike setup might compare for a hypothetical pro badass. If you want to play at home you can use the code below in the free-form data entry box (click advanced) to use my course model, and tweak it to your own liking:

{ {0, 5500, 6.3 ,0,.004,0,0,0}, {5500, 6500, 0.0 ,0,.004,0,0,0}, {6500, 13000,-6.0,0,.004,0,0,0}, {13000,22000,6.3 ,0,.004,0,0,0}, {22000,31000,-6.3,0,.004,0,0,0}, {31000,32000,0.0 ,0,.004,0,0,0},}

TT BikeRoad BikeRoad Bike w/ Clip Ons
Mass74kg73kg73.2kg
Watts395400400
CdA.25.32.29
Predicted Time50:2852:1251:16
Uphills Only34:0534:1633:59
Uphills Only +10% Power31:0331:2331:04

We assume a 5 watt power less on the TT bike. Some riders suffer no power loss at all, while others suffer a bit more. We also assume around a 1kg weight penalty which is typical, though some teams may be able to hit the UCI minimum with their TT setups for some riders.  We then use average CdA values for TT vs "Drops" positions.  With these inputs you get a predicted time savings of 1:43 for the TT bike over the road bike, a huge advantage.  But things are not so simple. The descents are not straight lines, the turns and switchbacks will discount aerodynamic savings on the way down the climbs.  Athletes will likely pace themselves with higher power outputs on the climbs and less on the descents.


Since the downhills introduce a lot of complexity, we can also look at just the uphill sections of the course. In this case the road bike with clip-ons has a slight advantage.  But if those uphills are paced with 10% more power than the downhills, the gap narrows to almost a tie. In fact a slight tweak to any of these inputs could change the order around completely.  So  you can see there is a delicate balance at play.  An athlete who is not comfortable descending on their TT bike, and who makes more power on the road bike, might want to opt for the road bike with clip-ons.  An athlete who has TT expertise and has prepared and ridden the course ahead of time may be confident enough to tackle it on a time trial frame for the best overall time. You can also expect various hybrid options to be employed, such as road bikes with clip-ons and road frames with full aero cockpits.

#SecondGuessingPros


One of the best parts about being a fan is you can second guess the pros decisions. Whether it is tactics or equipment we can use our imperfect knowledge to have some fun and play armchair Directeur Sportif! What equipment will teams use on Wednesday, and what equipment should they use? Expect many pros who have no GC ambitions to be on road bikes. They find them more comfortable, and safer, and time is not a big concern for them.  For the GC contenders I think we will see a mixture of approaches.

Team Sky

Team Sky has no aerodynamic road bikes at their disposal, and their road frames are also the heaviest road frames in the tour.  I also expect that Froome has spent plenty of time preparing for this particular course and will be prepared to ride the TT bike on it. That should be the fastest option for him, though he may be the favorite on this course no matter which bike he chooses if he stays on his current form. 

Movistar

Movistar faces the same bike choice as team Sky, a heavy road bike or the new Pinarello TT bike. Their only GC contender now is Nario Quintana, who may not have enough experience with time trial bikes to make that choice on this stage. We may seem him on a road bike trying to make up the time on the uphills.  I expect this to cost him time, but his excellent climbing should net him a decent placing nonetheless.

Saxo / Astana / Omega-Pharma

These teams have two excellent choices from the Specialized stable of bikes, the Shiv TT, and the Venge.  Depending on the weight of various builds and the fit needs of their riders, we may see Venges with clip-ons, or Venges with aero cockpits, or Shivs in action on these teams.  Smart choices will be critical for Contador, Fuglsang, and Kwiaykowski. Anyone opting for bullhorn bars and STI shifters will likely give up time. 

BMC

Cadel Evans at BMC will face the same choice as the specialized teams, an excellent aero road bike or an excellent TT bike. Cadel has very...unique... TT fit needs, so there is no telling what will go down here. This course should suit him though, and the choices and results will be interesting. 

Radioshack-Leopard

Andy Schleck will have a choice between an excellent time trial frame in the Speed Concept, and the new semi-aero Trek Madone.  Look for him to be on a road bike given his complete lack of interest in riding TT bikes, ever. Perhaps a good battle between him and Nairo Quintana!

Garmin-Sharp

Garmin has three choices here which will no doubt have team tech gurus and riders scratching their heads. They could ride the super aero but slightly heavy Cervelo P5.  Or, as they have done in past uphill TTs, they could equip the S5 road bike with a TT cockpit to get very nearly the same aerodynamic prowess at a lower weight.  Lastly, they could use the new Rca frame, which is among the lightest frames in the tour, and semi-aero as well.  This might give them a weight budget to use deeper wheels and still hit the UCI minimum weight limit.  Dan Martin and Andrew Talansky will be the guys getting the best setups, look for them to be on either the S5 or the Rca, possibly with an all out TT cockpit.





1 comment:

  1. One situation where a road bike may be better for handling reason on that descent, although a light pair of clip ons would probably still be of advantage. All depends on what I could get inside the weight limit for wheel choice. teams with di2 have an advantage in that they can put satellite shifters on their clip ons, or shifters on their aero base bars.

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