" Aerodynamics doesn't begin to have an effect until 60 MPH "

[Blacktree]

Originally Posted by Gasoline Fumes

I assume the speed that aero matters depends on whether you're talking about drag or lift/downforce, right?

I think it's easier to generate drag at low speed than lift/downforce. So yeah.

But then you have the people who say "you won't make any downforce under 100 miles an hour", or something to that effect. That's not entirely true, either.

[kach22i]

Originally Posted by Gasoline Fumes

I assume the speed that aero matters depends on whether you're talking about drag or lift/downforce, right?

That might be an important part of the "seat of the pants" experience most likely responsible for someone's off-hand comment claiming 60mph is where aerodynamics takes affect.

On the aerodynamic experiments I conducted on my S10 pickup truck, some of the modifications could be felt starting in the 30-35 mph range.

This is the same range as feeling "a push" on my hand sticking out the window.

Below 30 mph hand out the window is perhaps a breeze, but above 30-35 it feels more like a "force".

Again, just "seat of the pants" subjective jargon where my 30mph is someone else's 60mph before they take notice.

I have to agree that in this context the wind noise issue, that is the flow coming into the vehicle at 60mph getting someone's unwanted attention might be a common experience, common enough to allow the 60mph comment to gain traction.

I mean how many people do you see driving down the road with their hand out the window measuring aerodynamic force using their hand as a diving and or lifting plane? Myself and maybe a couple of curious children not glued to their cell phones or TV's built into the back of their parents headrests.

[Piotrsko]

If low speed airflow had no effect then you wouldn't ever notice a light cross wind having an effect and the suspension would not move while parked on a pleasantly breezy day.

[Isaac Zachary]

There's probably someone out there that thinks aerodynamics aren't important until you hit 120mph.

[freebeard]

"Aerodynamics are for people who can't build engines." - Enzo Ferrari

[aerohead]

Originally Posted by Gasoline Fumes

I assume the speed that aero matters depends on whether you're talking about drag or lift/downforce, right?

* Since all-three would occur concurrently on any given vehicle, all three effects would be tracking simultaneously, along with identical air velocity, regardless of the indicated velocity.
* I agree completely that, individual priorities would dominate the narrative, and conclusions.
* Relativistic.

[Grant-53]

I measure differences in coast down tests for bicycle fairings at 13-15 mph.

[some_other_dave]

Originally Posted by Piotrsko

I believe the process is like the torque vs hp curve on an ICE. Max efficiency is supposed to be wheere the lines cross.

Where did you hear that? The lines cross at the same RPM, always! (Exactly what RPM depends on what units you use for power.)

In SAE units, HP is defined as (Torque * RPM / 5250). So those lines will always cross at 5250 RPM, assuming the engine was measured both above and below that RPM.

5200+ RPM is almost never the most efficient speed to spin your engine.

[Autobahnschleicher]

Originally Posted by Grant-53

I measure differences in coast down tests for bicycle fairings at 13-15 mph.

When I was a lot into road cycling, my topspeed used to be about 60 km/h.
That was in an all out sprint, I do not have a power meter but the Kreuzotter calculator says 1249 W of power are required for that on my roadbike in my sprinting position.
If I went with my most agressive TT position (Superman), I'd need only 570W for the same speed.
With a fully faired recumbent I'd be at a sustainable 180W.

Aerodynamics matter a lot even at that kind of speed.
And I love to show it to road cyclists by passing them on my rather comfortable and aerodynamic recumbent.

[aerohead]

Originally Posted by some_other_dave

Where did you hear that? The lines cross at the same RPM, always! (Exactly what RPM depends on what units you use for power.)

In SAE units, HP is defined as (Torque * RPM / 5250). So those lines will always cross at 5250 RPM, assuming the engine was measured both above and below that RPM.

5200+ RPM is almost never the most efficient speed to spin your engine.

Each engine BSFC map will show an island of highest thermal efficiency, spanning some rpm range.
If memory serves me, it has to do with mean effective pressure developed and coincident pumping losses.