Is aero everything?
The new Specialized Shiv is making its debut at Kona this weekend. To say that the design is polarizing is an understatement.
I remember when Cervelo revealed its P5X and Diamondback came out with Andean. Those bikes had their aesthetic critics. The new Shiv is something else. With ‘my eyes!’ and ‘fugly’ comments aplenty and complaints of violent gastric reflux at the sight of leaked photos, the bike sure has its critics.
You can see for yourself in this bikerumour.com article. It has the new Shiv in all it’s ocular-assault glory.
The element that most folks take issue with is the eye-sore of a rear fin cum water bottle. It’s likely the first thing you saw! Now, while I am not wild about its aesthetics, I’d like to talk about four design considerations of that fin that are worthy of note.
- Delaying flow separation
The fin is likely an excellent add from an airflow perspective. As an object moves through a fluid – and unless that object is a perfect airfoil – it will at some point begin to generate speed-sapping, turbulent wake drag. That’s where an areaof low-pressure air in the wake of the object effectively pulls on it, thereby slowing it down. The mission for bike designers is to push the formation of that turbulent air as far back along the bike plus rider as possible. Now I cannot be certain without testing the new Shiv, but I strongly suspect that the fin does just that. It delays flow separation – at least along the bike frame – and improves the frame’s aerodynamics. The image below illustrates how a more aerodynamic object (lower Cd) experiences a later flow separation and a smaller wake.
- Adding side surface area
That same fin adds side surface area and it does so well behind the steerer axis of the fork. Many top-end bikes add frame material to turn their steeds into wheeled sailboats. Integrated front end hydration systems are one example. Yet many of these – think Plasma Premium, Giant Trinity among others – have that side area AHEAD of the steerer. This matters! Anything in front of that axis contributes to steering input from side winds. Put another way: the more ‘stuff’ you have in front of the steerer, the more side winds affect steering. So, if a twitchy front end is not your jam, it’s smart to keep that are minimally busy.
- Improved weight distribution
I cannot say this with any certainty because I have not ridden the bike, but I suspect that putting some mass behind the seat post helps distribute the load on the bike. I’ve seen a trend in recent years to push saddles and front ends forward. I’ve participated in that trend too. I do like it from an aerodynamic and ergonomic perspective, but I am a little wary of the effect of front-loading a bike on its handling. Adding some mass to the tail end of a bike – such as a 1.5kg (when full) water bottle may help.
- Two Bottles’ Worth of Fluid Out of the Wind
This point needs little elaboration. 1500mL is more than two standard 24oz (710mL) bike bottles. That’s valuable fluid storage designed to improve aerodynamics. That’s a big win-win!
Now if we can accept that the new Shiv is both very aero and rides well, are those two factors enough to overcome its unorthodox aesthetic, or is that a deal breaker?