Anyone experiment with spring heights to change aero?

[2TonJellyBean]

I'm curious about the affect on aerodynamics on many vehicles by playing around with the front dan rear ride height differentials. I wonder if there are some cars that would be way if the bumpers weren't so level whether they tilted the vehicle forwards or backwards.

[2TonJellyBean]

Cars are often tilted down for down force. I wouldn't be surprised if some cars worked better with the butt dropped instead... but I know that dropping the nose would be a common situation. Still, it would be fun to have numbers for how many cars do and what the ideal front rear ride heights are.

[Danronian]

An oft quoted optimal ground clearance is 3.3"- I don't know the source or the validity of that.

If there was a gain from loweriing my car, it's damn small.

So it's desirable to have some air flowing under the car? I have my VX very low, and I wonder if that is worse aerodynamically.

[thisisntjared]

So it's desirable to have some air flowing under the car? I have my VX very low, and I wonder if that is worse aerodynamically.measure it on level ground. i bet you still have at least 5 inches. my civic rides at 8 inches and it is lowered :rolleyes: a lot of people think their cars are a lot lower than they really are.

[trebuchet03]

So it's desirable to have some air flowing under the car? I have my VX very low, and I wonder if that is worse aerodynamically.

Yeah, you get a ground effect which produces extra down force which increases rolling resistance. This is caused by higher velocity air moving under the car which means lower pressure (Bernoulli) - so low pressure under the car, high pressure above the car -- net downward force. Useful for high speed cornering and traction, not so much for P&G.

I suspect there's head and nozzle loss too along the leading edge of the portion of a car very close to the ground.

One F1 car used a fan to actively increase ground effect pressure http://en.wikipedia.org/wiki/Brabham_BT46.


I actually need to do research on this very thing for this year's human powered vehicle... When I eventually find some numbers where height becomes a factor, I'll report my findings :)

[01_fast_ride]

I thought I read somewhere that lowering the rear helped out (simulating a heavy load) by minimizing the effect of the windshield angle. Dropping the nose down seems like it would increase downforce but also increase windshield angle (increasing drag). An airdam in the front would keep airflow under the car to a minimum.

[thisisntjared]

adjusting the rake of a car for fuel economy really depends on the car. the bottom line is that you do NOT want to increase the frontal area.

[ezeedee]

measure it on level ground. i bet you still have at least 5 inches. my civic rides at 8 inches and it is lowered :rolleyes: a lot of people think their cars are a lot lower than they really are.

i got about 8 inces of ground clearance and i have taller tires than stock on my explorer, id feel like **** if a civic was that high. ive seen plenty of civics that were less than a coke can off the ground.

[ezeedee]

Tempos are pretty tall stock and they are only 5.something off the ground. Where are you measuring to come up with 8?

the ground to the lowest point of my vehicle (rear shock mounds in my case)

[thisisntjared]

Tempos are pretty tall stock and they are only 5.something off the ground. Where are you measuring to come up with 8?
hmm... i dont remember honestly... i thought i remembered measuring my old 4 door civic when i first lowered it. but now i realize that was over about 7 years ago and i bet my memory is shot.

when i measured it was from the bumper to the ground.... i will have to measure where my civic rides now...

also where the shock mounts to the control arm is not a good place to measure ground clearance because it is unsprung. i would measure the lowest part of the sprung chasis to the ground. this would probably some cross member or something.

[ezeedee]

also where the shock mounts to the control arm is not a good place to measure ground clearance because it is unsprung. i would measure the lowest part of the sprung chasis to the ground. this would probably some cross member or something.

i have a solid axle in the rear, so ground clearance doesnt change until i air down the tires and the sidewalls get some noticeable flex.

[2TonJellyBean]

or the differential in ezeedee's case

- a range rover would make it simple to test if it has manual control for fr/rr ht
- dunno if it does

[thisisntjared]

hmm i didnt think of the rear axle as the point of measuring ground clearance.... i dont know what the standard is, but i wouldnt count it. if you do then a lift kit will not get you more ground clearance, only larger tires would.

[2TonJellyBean]

sorry, that's just the way the industry measures it... lowest point

people looking into lift kits will see a change in the angle of approach/departure and breakover

[oneinchsidehop]

http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/index.html

Good article in parts. the gist of it: dropping the car is good for about a .01 improvement for every inch dropped. (I've heard that number a lot)

Dropping the front keeps air out and gives it a large space to expand: lower drag and squirrelly rear end.

Dropping the rear increases the venturi effect under the car (duh) so any belly pans become more valuable. Also creates (a lot) of lift in the front end. AKA suicide at speed. That would include 65mph with a gust of 50mph headwind.

Springs and ride hight effect the air under the car so much more than the air above that the changes in roof plane become almost unmeasurable.

Dropping works.
Air Dams work. if they're done right.
trunk extentions work
shaving works
chopping/channeling/sectioning works big time (reduction in frontal area)

Seems to make sense to me.

Oh, and no one at Bonneville (in the classes that allow it) run boat tails it seems. I wonder why? they do kamm backs though.

[theclencher]

1L doesn't have boattail either.