Aero-bars are an easy topic. Use them when you can, even in training. A flat back with a slight skiers bend to the bars is probably the most efficient general rule, but, comfort is more important. A lighter pair is good if you can afford them. There, done with aerobars.
Wheels on the other hand are much more complicated. I have spent the past year relearning basic physics, reading rants on the internet, technical articles by engineers, and muddling through manufacturers' claims. The real-world decision in wheel choice is aero-dynamics versus weight. The greater the rim profile, usually the higher the aero-dynamic advantage at the expense of higher weight. As a cyclist, considering four (often ignored) principles is paramount to making a smart wheel choice:
1. Moment of Inertia (MOI) - This is the amount of force required to get a wheel rotating. The heavier the wheel, the more force (i.e. energy) needed to get the wheel rotating. And the further out from the axis the weight, the more energy required. Rim and tire weight are much more important than hub, skewer or cassette weight. Also, MOI is a good place to talk about pace. A cyclist that rides at a steady pace (speed, watt) is going to need far less energy (ie, not get tired so fast) than a cyclist that has an oscillating speed. Their average speeds might be the same, but, the amount of energy that riding an unsteady tempo is huge. To illustrate, I did a simple calculation assuming a flying start: a rider at 40km/hr for one hour at a fixed pace versus a rider averaging 40km/hr, oscillating between 38km/hr to 42km/hr. To make this a fair race, the steady rider would need to tow a Mini Cooper as far as energy is concerned!
2. Gravity and friction (rolling resistance) are real forces - I lumped these two together because they are the unseen forces holding you back. (Although, most celebrate on those fast descents when their wheels don't slide out, the other spectrum of these forces.) Gravity on a flat to uphill slope actively slows you down. The question becomes, at what grade does weight take precedence to aero-dynamics? There is no definitive answer, but when the slope starts to hit 3% or greater, a lighter wheel-set makes sense. Conversely, heading downhill, a heavier, aerodynamic wheel-set would be in order. Some people might argue that heavier wheels have a fly wheel type effect - that they store rotational energy. While there might be a small advantage, most of it would be negated by friction and gravity unless you are riding on a pancake flat or downhill courses. Tire choice, tubular versus clincher, is a great place to bring up friction. (We will ignore bearings except to say that sealed are more efficient than cartridge bearings, assuming that sealed bearings are dirt free.) I don't think there is enough data to declare one more advantageous over the other, if you are comparing top of the line clinchers to tubulars. Tubulars have the edge in cornering and possible weight savings (MOI advantage), but as far as rolling resistance goes, I really don't think one is better than the other. Often people claim that tubulars can take more tire pressure, which decreases rolling resistance. But, tires are like a non-compliant balloon - that is, more air pressure, at a certain point, will not help a tire deform less. Tire manufactures know this and design the casings and such to reflect this fact.
3. Variable winds - Most studies are done in a wind tunnel with a head on wind. Great for marketing, not so great for making wise decisions on the road. Even in the best of circumstances, there is no real advantage in rim profile until it reaches 50mm or more. 80mm and tri-spoke style wheels are close to a disk wheel as far as aero-dynamics. Also, there is not much advantage in spoke count or shape. Depending on wind speed and direction, larger profile rims and disks can make your bike unsteady and may even slow you down. If you are shopping for wheels, I would choose rim's less than 50mm in profile by weight, lighter being better, assuming a reasonable durability. As to wheels above 50mm in profile and disks, weight should be a consideration, but your are really looking for an aerodynamic advantage, which can be significant as your speeds increase. I would choose the largest rim profile without giving up bike stability.
4. Cyclists are not infinite energy sources - You are going to get tired riding a bike. And those heavier aerodynamic wheels are going to make you legs feel leaden after awhile. This is where you have to know yourself. Lance could push just about any wheel all day with no problems. However, if you are pushing your limits distance or climbing wise, lighter wheels will win out over heavier wheels.
So how do you choose which wheel is right? Just consider the four principles above. If you are racing a tight criterium with frequent accelerations or a mountainous course, a light set of wheels are in order. If you are racing a flat time trial with a headwind, dual disks would be in order. The in-betweens are the harder choices. If you have rolling hills, are feeling strong, then aerodynamic wheels would probably benefit you. Conversely, if you just hope to hang on, lighter wheels would be the option. I think the ideal stable of wheels (should budget allow) would be a really light box-rim tubular set, with a 28/32 spoke count and a 50mm front/80mm rear wheelset. And remember, the best wheel-set is the other riders you are drafting.
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