Iban Mayo and Cadel Evans, among others, demonstrated some important aerodynamic concepts for us in the stage 13 time trial in Albi. Specifically, they showed us about what to do - and what not to do - with the knees and elbows. We learned a few more subtle lessons from Levi Leipheimer and from the Astana team, and we saw once again that a wet road does not slow a fast rider… well, except on corners.

Two distinct styles: Evans vs. Mayo
Long TV shots from the front allowed us to see how Evans maintained a compact, narrow position throughout his body, and how Mayo did not. Evans has wide, square shoulders, which is not optimal, compared to the smoothly rounded shoulders, of, say, a David Zabriskie, but there is probably not much he can do about that. Otherwise, though, his arm position and his pedaling style are optimized for good aerodynamics.

Evans pedaled the time trial with his knees passing so close to each other over the top tube that they almost touched. He also kept his arms in.On the other hand, Mayo’s elbows were very widely spaced, and, perhaps more importantly, he pedaled with his knees way out, almost bowlegged. If you are already a lightweight rider with not a lot of power and you present the frontal area of a Mack truck to the wind, you can’t expect to go very fast.

Evans and Mayo are similar in size and climbing ability, at least they were until Mayo had the stuffing whupped out of him in the time trial and folded in the Pyrénées. One could also surmise that they have similar power output at aerobic threshold. They also both had considerable motivation to do well in Albi, since they were in third and fourth place overall, separated by only two seconds, and were four and six seconds behind Alejandro Valverde, who occupied second overall at the time. And the good money was that the guy in first, Michael Rasmussen, would flail in the TT and lose many minutes, so the yellow jersey might have been there for the taking, too.

So what happened? Of Evans and Mayo, only one of the two did well, and it is obvious that a big part of that was the lower aerodynamic drag of the Australian.

Leipheimer
Lessons from Leipheimer were a bit more subtle. From the side, the Discovery captain has a very smooth aerodynamic profile, and from the front, his arms are in very close as well. But it is from the front that his most glaring aerodynamic weakness is apparent, namely knees that stick out far wider than his arms do.

Leipheimer’s super-narrow elbow position does not benefit him nearly as much as it could when he pedals with his knees out so far. His knees are not waving out in the wind like Mayo’s, but they are certainly sticking out further than Evans’ are. Perhaps the Californian’s relatively stocky physique combined with the fact that his time trial bike has such a high top tube relative to his knees prevents them from being able to come close to each other – and almost touch, like Evans’ do – when pedaling. (In order for the top tube on a time trial bike to be level – which it must be to minimize air drag, it cannot be dropped lower than mandated by the size of a 700C front wheel, the room required for the front brake and headset, and the length of head tube required to attach the top tube. And a top tube flared at the front like Leipheimer’s must sit up higher yet on the head tube to make room to join a tall, aero down tube. This means that a short rider will have very little seatpost extension, as Leipheimer has on his TT bike, and consequently, his top tube will be more up between his knees than would be the case for a taller rider.)

If Leipheimer cannot bring his knees in closer while pedaling hard, it is hard to imagine that he would not actually improve aerodynamically by spreading his elbow pads further apart so that his upper arms block a bit more of the air that is hitting his knees. And wider elbows usually results in improved breathing ability, improved leverage pulling on the bars, and better bike control in curves. Might as well take advantage of these things and get better aerodynamically, if he’s going to pedal with his knees out.

Astana’s fast guys
Yes, they’re now gone from the Tour, but there are a few lessons to be learned from the fact that Astana’s top three riders smoked the time trial. Vinokourov gave a demonstration of how to pump pure determination, anger - and, perhaps, a bit of somebody else’s blood – into the pedals and make them go around fast, while Klöden and Kashechkin demonstrated what clean aerodynamics combined with high power output can do.

However, while it probably made little time difference, certainly they were slightly slowed by those long floppy yellow straps “securing” their baby-blue Specialized helmets. It seems amazing that a team with that kind of budget, experience, and sophistication would allow its stars to ride with their helmet straps flapping like that. It is a simple thing to adjust a strap close to the ears and jaw and to trim off any excess with scissors.

Contador
Other than youth and inexperience, Alberto Contador does not have many weaknesses in the time trial. Indeed, Contador, Evans and Leipheimer have each shown that a great climber does not have to turn in a performance like Mayo did. However, they must have aerodynamics on their side, because their low weight and thin limbs means that they do not have the power of, say, a Fabian Cancellara.

Since wind resistance increases with the rider’s speed squared, the faster one goes, the greater the importance of wind drag. It goes up exponentially, and the flat course from Cognac to Angouleme on Saturday will produce high speeds. Also, a rider’s power is related to his volume (which varies with the cube of a body dimension), while his frontal area, and hence aerodynamic drag, varies with the square of a body dimension. This is why big strong riders generally do better in time trials, because their power increases with size more than their frontal area does.

Contador is a lightweight climber, but he keeps his thin legs tucked in nicely behind his arms and his shoulders nicely rounded. He probably has similar threshold power output to Evans, judging by their performances in the Alps and Pyrénées. With an aerodynamic profile almost as clean as the Aussie’s, I would not expect him to lose more than a minute on Evans, like he did in the first one.

Rolling resistance on wet roads
We saw how treacherous the rain made the cornering traction for many riders in the stage 13 time trial, taking down good bike handlers like Cancellara, Klöden, Gusev, and Popovych, among others. But many of the riders who did well in the Albi TT had wet roads. In many cases, the roads were wet and rain was no longer falling.

So when riders are not contending with curves, do their tires rollas well on a wet road as on a dry one? In my June26 Tech Q&A column on rolling resistance, one of the issues coveredwas whether a tire rolls faster on a wet road than on a dry road. I thinkit does, and that the rider can consequently go faster, at least as longas they are not plowing through raindrops in the air.
I received a number of responses to my theory, of which here is a sampling:Dear Lennard,
Certainly I have also always believed that rolling resistance is reducedin the rain. I had never considered that water filling voids in the roadsurface thereby smoothing the surface could be a cause. Instead I consideredthe following cause.A local segment of the tire obviously deforms from a round to a flatsurface when in contact with the road. I would assume during this deformationthat there will be sliding of the tire surface against the road. If true,there would obviously be dissipative losses. If friction were reduced duringthe deformation then rolling resistance would be likewise reduced. Giventhat static and dynamic friction is reduced when the road surface is wet,this mechanism for reduced rolling resistance is conceivable.
SteveDear Lennard,
I'm an engineer, and I just read your response on wet rolling resistance.
While there may be some truth to your "road smoothing" theory, I thinkit's more a result of shear. Water has low viscosity, and shears easily.The shear is much less in water than it is with rubber on a dry road.
JasonDear Lennard,
I just don't agree with you on the rolling resistance of bicycle tireson a wet road.
My experience has always been that it is much heavier going in thewet than in the dry. I'm prepared to accept that a large part of this maybe psychological - it's just plain miserable in the wet. Even so, considerthat on a wet road there is much more work to do:The tire has to push surface water out of the way.Water is carried up off the road on the tire, breaking contact against surface tension.Water on the tire is sprayed up into the air - more energy expended.Water on the tire increases the weight of the wheel.Armstrong & Ullrich may have gone faster in that 2003 TdF TT, but I think there were other overriding factors there.
StanDear Lennard
Any possible decrease in rolling resistance (negligible, if any) wouldsurely be more than offset by the pouring rain’s momentum effects on therider’s body. To illustrate the effect, imagine cycling at speed collidinginto a stationary mass – it would slow you down.
Rick