A key part of bike design for aerodynamics is shape of the bars that hold the bike together – completely circular tubes have more resistance than oval or squished tubes – but as you make the tube more squished it gets weaker – so its a difficult thing to balance.
The biggest problem with aerodynamics though isn’t the bike – its the rider! humans are big and blocky and it means we catch lots of air which makes it harder to go fast! some riders have special suits that reduce wind resistance!
If you’re gonna race o’brien – heres a top tip – don’t try and beat him for most of the race – ride just behind him for most of the race – this means he gets all the wind resistance (can be as much as 40% more at speed) – so he’ll get tired and you can sprint and beat him at the end! This arrangement is called a peloton – and thats why you see cyclists riding in groups! see more here: https://www.exploratorium.edu/cycling/aerodynamics2.html
Why not see if Cian will give you a race! Good luck – see if you can use science to beat him 🙂
hope this answers your question – let me know if you want to know more 🙂