Ground Clearance vs Aerodynamic Drag

[NeilBlanchard]

Right, and I thought that going too low increases drag? With the Pillbug, they did testing on this and they settled on ~6" of clearance as the lowest drag.

[freebeard]

Here's a visual on a Porsche 914 that was tested:

The first three look the same to me, that's why I have a 4" brass caliper right next to the monitor.

The fourth one looks like it's parked. It's laying frame.

IMHO a good ride height is with the rocker pointing at the bottom of the rim. That's the legal requirement (so you can have simultaneous flats on both sides and not run aground) and it will generally clear speed bumps.



Lower looks better though.

[aerohead]

Originally Posted by California98Civic

That's a really big reduction on the basis of ground clearance for that porche. But the benefit of lowering would be less significant if the car had first been fitten with an under tray and/or airdam, no?

*It's a good question and I have no way to answer it. Until we construct a larger data base,all we can say for certain is that this particular car,under these conditions,exhibited these results.
*The VW Flow body has a perfectly smooth belly and its drag INCREASES from Cd 0.913,to 0.10 as it goes from 0.04 L= G.C.,to G.C. = zero.A complete trend reversal!
*Ford provides us with zero data on the PROBE-IV,except in the lowered and raked attitude,with the deployable front spoiler extended.So in a sense,we've learned nothing other than the obvious.

[Cd]

Originally Posted by freebeard

The first three look the same to me, that's why I have a 4" brass caliper right next to the monitor.

The fourth one looks like it's parked. It's laying frame.

IMHO a good ride height is with the rocker pointing at the bottom of the rim. That's the legal requirement (so you can have simultaneous flats on both sides and not run aground) and it will generally clear speed bumps.



Lower looks better though.

Much like your avatar picture

[aerohead]

Originally Posted by Cd

Doing it wrong :
Still doing it wrong :

We now return to our regularly scheduled topic :

Thanks for the info Phil. Dropping a car real has a big difference in drag, eh ?

I keep thinking back on that Fusion that ran at Bonneville and the amount of drag that was reduced by the drop

Here is the image :

This is the kinda data we need. Wish they had included the contribution from the decklid extension.

[aerohead]

Originally Posted by ksa8907

So dropping the cts 1.5" all around may give a measurable gain?

We may want to wait and look at more comparisons.The VW is showing a trend reversal,so we have at least one example where lowering doesn't help a lot.

[aerohead]

Originally Posted by California98Civic

Here is the image :

I can't help but wonder if they tested this fusion's bellypan improvement after they had already lowered it all the way down to 2" GC. The bellypan benefit was less than mirror removal, which seems counterintuitive.[/QUOTE]

Yes,and until we find out,we're at a loss for information.
In the past,benefits accrued from mods were listed as a reduction to the base vehicle and were additive,not cumulative.
If this is true for the Fusion,then the bellypan is rated at full ground clearance and by itself would give Cd 0.33,a 2.94% drag reduction.That's on a underside which has already seen much detail optimization.

[aerohead]

Originally Posted by rollercoaster

I would think the combination of a full belly pan and lowering would increase drag because of the pressure differentials from top compared to bottom. In essence, you're creating suction -yes?

OP -Any data on lowering in conjunction with a full bottom pan?

The VW Flow body has a full,smooth belly and undergoes a 9.5% drag INCREASE when dropped to zero clearance.
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As to suction,I'm not sure.
The pan's job is to eliminate turbulence and deliver laminar flow to the wake,or to a diffuser,which can decelerate the flow and deliver a higher base pressure,cutting pressure drag.

[aerohead]

Originally Posted by Vekke

I have also studied this long time ago and if I remenber correctly if you go lower than 50mm clearance it does not help anymore :/.

You can try to find details of the Bugatti veyron as it lowers at high speeds.

50mm is an interesting animal.The PROBE-IV,with the front airdam deployed gives the car about 1.92-inches ( 48.76mm) actual ground clearance.Ford could have chosen any clearance.It's interesting that they ended up with around 50mm.

[aerohead]

Originally Posted by ennored

I've always though that lowering a car had more to do with lessening frontal area and hence drag than actual drag coefficient.

I know that when measuring small changes, like mirror removal, they don't recalculate the frontal area, just take it as an improvement in drag. Maybe that's what's going on here? Probably never know for sure, but anyone have any solid facts?

Recently,with the VW Jetta land speed record at Bonneville,it was mentioned that lowering the car probably did not affect the Cd so much as that it just reduced frontal area.So we have at least one confirmation to this idea.