Quote:
Originally Posted by jimepting
It does look to me like there is adequate clearance on the torsion beam rear axel to use one large coroplast sheet to cover up everything remaining open, but JMO.
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Jack the car up, off its rear wheels, to find out what the suspension looks like near maximum deflection. Options include a flexible panel spanning the axle, or an underbody panel mounted to the axle.
As to whether the performance improvement would be measurable, well, how good is your measuring technique?
Also, a boat-tailed Insight is more sensitive to airflow at the aft underbody than most cars.
On the subject of diffusers, MetroMPG posted a promo video a while back that accompanied the release of the Insight. It was not written for a technical audience, but the voiceover guy mentioned that "the coefficient of drag was reduced by keeping frontal area to a minimum"*, and the (7° by my measurement) slope behind the rear axle "reduces turbulence underneath the car".
*Not as bunkum as it sounds. Keeping height to a minimum improves fineness ratio and Cd, not just CdA.