AlgarveCycling

Really? What do think power is then?

Taking a 175lb rider pushing 300W with a W/kg of 3.75 and a 145lb rider pushing 300W with a W/kg of 4.60 as a baseline to start my thought process on this...

In this scenario where both are pushing the exact same Watts, the lighter rider has the clear advantage in terms of both Watts and, most often, Cda. If you do a Cda calculation on both, then the smaller rider will likely have aero gains, sure.

But you and another chap want to ignore W/kg to make the above true in all cases and focus only upon CDa. I'm not convinced because what happens when a rider has significantly more W/kg than another? Does CDa still win out overall? Or do the W/kg come into it? I think the W/kg come into it.

An excellent CDa is .19 - anything below .20 is fantastic. Larger riders do tend to have higher CDa's naturally than smaller riders, this is true. However, we have big units getting down to .20/.25 in the World Tour peloton and so pretty much negating the aero advantage of the smaller riders in a time trial position; hence large units like Ganna, Bisegger, Dowsett etc being so good.

Assuming both of my above examples are adopting a very good time-trialling aero position achieving a Cda of around .25 and .20 respectively to take into account an advantage for the smaller rider and pushing the same watts, yes the smaller rider has gains and wins - he/she will be able to push through the wind faster.

Now...if the larger rider is stronger as is most often the case at higher levels of the sport and has way more mitochondria in his bigger legs...

The 175lbs rider is now pushing 5 W/kg and still assuming a very good CDa of .25 and .20 for the smaller rider at 4.6 W/kg because they both have the best equipment and their coaches have them dialled in for position, the larger rider wins. W/kg trumps the CDa advantage.

There are other variables too. It isn't as clean cut as this in all cases - larger riders can still have lower CDa's than smaller riders depending upon physique. It does happen. But generally, we assume smaller riders have a better CDa albeit, as noted, this is not always the case. But they can be out-powered by the big units who have a greater W/kg. And then there are smaller guys with big W/kg, more than many larger guys, like Remco...so it's not straight-forward.

All that said! What happens in a sprint? Well, this is somewhat different to the very aero positioning of a time-triallist since now we are talking about standing up on the pedals...this is where the likes of Cavendish and Ewan can compete against the huge W/kg and max power that the larger units can achieve precisely because of a lower CDa. Larger guys stomping on the pedals struggle to achieve Cav's ultra-aero sprint style. Not all smaller riders are as good at this - Cav has a really aero sprint that he has perfected and larger guys would not be able to match it. Of course, Cav still needs plenty of watts too but can get away with less if he times it just right because for a short period, the big guys have to work a lot harder than he does.

The above outdoors in a typical road race, not indoors in a Velodrome where absolute power is what is required.

So yeah, aero and CDa is extremely important in cycling but so is W/kg and a host of other stuff too. While these two can make big differences, it is the sum of a total of many things that lead to the faster rider in all conditions.

I've focussed upon Elite athletes, at normal levels of the sport the variables are vast and so differences can be much greater. For example, larger riders can more easily have really bad CDa's and then smaller riders can push through wind far easier, if that's what you want to hear. Dialled in, strong big units can reverse that though.