From Newsgroup: sci.physics
Christopher Howard <
christopher@librehacker.com> wrote or quoted:
(1) In pictures of sportcars (I can't afford one) the wheels are thin
and the body is very low to the ground. What is the reason for this? Is
there some inherent aerodynamic advantage to having the body of the
vehicle very low to the ground? Or are we just trying to keep the wheels >inside the body, so that we don't get additional air drag on the wheels?
A low-slung chassis chokes off the air flowing underneath.
Forcing that air through such a tight squeeze makes it speed up
and drop in pressure as it dumps out the back. That generates a
vacuum via the Bernoulli principle that literally glues the car
to the tarmac, giving you insane grip without adding dead weight.
Regular cars sit high, letting a ton of air underneath. At speed,
that air acts like a wing, lifting the chassis and making the
steering feel sketchy and washed out.
Slamming the car shrinks the frontal area, which is the total surface
cutting through the wind. Less frontal area directly cuts aerodynamic
drag, letting you hit higher speeds with less effort from the motor.
Keeping the heavy bits like the engine, transmission, and chassis
right on the deck keeps body roll to a minimum.
When a high-riding SUV takes a hard turn, weight transfers
violently to the outside tires, making the truck lean and
lose its bite. A low-profile sports car spreads those cornering
loads evenly across all four patches of rubber.
Those thin low-profile tires have stiff sidewalls. When you
turn the wheel, the rubber does not deflect or roll over,
giving you instant turn-in.
Mind you,
Speed bumps, steep driveways, and potholes will easily tear off
pricy front splitters and carbon underbody trays.
Since the sidewalls have no meat on them, they cannot soak up bumps.
Low-profile tires give zero cushion to the alloy wheels, leaving
them wide open to bending or cracking if you nail a pothole.
(2) Why is it that, in all the vehicles I've seen, there is an intake
for cooling air rCo pulled or pushed through by the radiator rCo but not >really an exhaust for it? I assume most of the incoming cooling air goes >through the radiator and then is bludgeoned down underneath the car. I've >read articles on careful management of cooling airflow in aircraft, but
this doesn't seem to be a concern for cars...?
Managing cooling airflow actually tops the agenda for automotive
engineers, though the hardware stays out of sight. You rarely spot
dedicated exit vents on daily drivers due to a blend of packaging
bottlenecks, design cues, and budget limits.
Hood vents or fender louvers let moisture, road grime,
and engine noise migrate to where passengers catch wind of
them. Plus, routing clean, ducted exhaust pathways eats up
prime real estate inside a packed engine bay.
To handle this air without glaring vents, modern rides count
on undertrays and active grille shutters. Active shutters seal
off the front inlets when the engine runs cool, forcing air to
sweep over the hood rather than crowd the high-drag engine bay.
When they snap open, the oncoming air hits the radiator and gets
channeled along the underbody by contoured panels. These trays
keep the air from pooling and generating lift, turning the
underside into a low-pressure zone that sucks the hot air out.
On high-performance builds and track cars, this aerospace-grade
thermal management breaks the surface. Race cars and track-focused
supercars regularly sport deep hood vents right behind the radiator.
This setup lets air pass through the front grille, exit straight
through the top of the hood, and wash cleanly over the roof.
By ducting the air upward, engineers wipe out front-end lift
and drop the drag coefficient, hitting the exact sort of
fluid dynamics you see in aviation.
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