Ideal car rear roofline angle and shape for low drag?

[Fluido]

What is ideal car rear roofline(rear window and trunk) angle and shape(straight line, curve ..etc) for lower drag? Keep in mind if you increase angle, you reduce butt area / wake, but induce low pressure at rear window/trunk , if you decrease angle you increase butt/wake but increase pressure at rear window/trunk.

What car aerodynamics theory says about this?

[Greg Locock]

I suggest you get hold of a copy of Hucho "Aerodynamics of Road Vehicles" or start with https://en.wikipedia.org/wiki/Automobil ... oefficient

[MadMax]

Isn't this a classic "how long is a piece of string?" question?

[feni_remmen]

The answer is 11

[Stu]

A lot depends on what is ahead of and behind (and above & below) in terms of required airflow.

Race-cars tend to look like they do because of regulations, road cars tend to look like they do because of comfort/carrying requirements.

[Andres125sx]

What is ideal car rear roofline(rear window and trunk) angle and shape(straight line, curve ..etc) for lower drag? Keep in mind if you increase angle, you reduce butt area / wake, but induce low pressure at rear window/trunk , if you decrease angle you increase butt/wake but increase pressure at rear window/trunk.

What car aerodynamics theory says about this?

I think this is the only car designed to lower drag as much as possible even if it ruins practicability, comfort or aesthetics

[Stu]

Looks A LOT like something I drew up when I was at Uni 30 years ago!!
Mine had three seats and was intended to be powered by a flat twin BMW motorcycle engine.

[Rodak]

Here in the US a three wheeled vehicle is classed as a motorcycle in most states.......

[Greg Locock]

That's the Aptera, their early estimates of Cd (0.06) were hopeless. The interference drag between the front wheel pods , the suspension arms, and the body were totally ignored. Judging by the wild claims, they'd assumed laminar to 60%

Current estimate is 0.15, which is almost down to solar car numbers, and better than GM Impact, so that's a pretty incredible outcome given that it has physical rear view mirrors.

[Neilwade]

What is ideal car rear roofline(rear window and trunk) angle and shape(straight line, curve ..etc) for lower drag? Keep in mind if you increase angle, you reduce butt area / wake, but induce low pressure at rear window/trunk , if you decrease angle you increase butt/wake but increase pressure at rear window/trunk.

What car aerodynamics theory says about this?

For optimal aerodynamic efficiency, the ideal rear roofline angle for a car is typically around 15 to 20 degrees. This angle strikes a balance between reducing the wake area and minimizing low-pressure regions at the rear window and trunk. A smooth, gently curved shape rather than a straight line helps maintain laminar flow and reduces drag according to automotive aerodynamics theory.