Quote Originally Posted by Tombie View Post
A study tested it in a wind tunnel, the result was an improved cd with tyre on bonnet.

Study link here:

Wheel on Bonnet = Aerodynamic improvement
Yep, post 18 here...

I recalled reading that back in 2012 or so when he posted the link and anecdotally over the years have seen slight differences in fuel use over a long trip and it can mean the difference between 4th or 5th gear on shorter trips around here in our winds (Exhaust gas temps of 550 or 650 - tailwinds = EGT of 400 or less). Where I live, we are known for our winds and with the tyre bonnet-mounted, it can break up a bit of the head wind. Out where I spend a lot of time we average 6m/s along the ridgeline and 5m/s on the flats. A long stretch of road some 15-20km is slightly up hill all the way (40masl to 120masl over 15km) and into the prevailing wind direction.

The remaining 10km is crosswind or tailwind and the HCPU helps catch that...