Hey guys,

Bit of a discussion here, be it if you like mpg or mph - aerodynamics are the goal. The little talked about low Cx is the holy grail, that's something like Cd x Frontal Area. I have been studying a 2001 Octavia brochure, and see the Vrs is 0.29 but the Elegance/L&K is 0.31, with the classic being 0.31.

I'm interested in how much the Vrs styling (as far as I can see, just front bumper - given the Estate matches Saloon in aerodynamics) lowers drag - especially as it has 205 wide tyres just like the Elegance which is 0.02 worse on drag.

Is it lower to the ground? I hope not as I struggle to get a jack under the Elegance/SLX and it won't go on ramps, lots of common underbody damage due to insufficient ground clearance, lowering that further must be a pain in the ***.

Comments please, Greg.

cant answer your question but i have the same problem with my elegance and ramps i have to use planks to lower the angle of the ramps

Yes it's very low ground clearance! Interested to see what vrs owners say, as I can't see theirs being much different other than the front bumper sends more air over and sideways.

What they quote in the brochure is the drag coefficient (Cd), to get an accurate idea of a cars actual drag it needs to be multiplied by the projected frontal area, wider tyres will increase this.

Drag force on a car is determined by the formula:

DF=1/2(pV*2CdA),

DF is drag force in Newtons, p is the greek letter rho which is used for air density at standard temperature and pressure which 1.226Kg per metre cubed, V is the vehicle velocity in metres per second *2 means it is squared, Cd is the drag coefficient (no units)and A is the projected frontal area in metres squared.

If you make the car higher you expose more of the front tyres to be taken into account for the projected frontal area (PFA), if you lower it you reduce the PFA but this can be counteracted with wider tyres giving more PFA.

For mpg, as the DF is proportional to the square of the velocity, if you double your speed you quadruple the DF, so your biggest gains in mpg would be made by driving slower.

If you're talking vRS vs other Octavia models then the main differences are front airdam, rear spoiler & lowered ride height.

I guess the front airdam & lowered ride height will combine to push air around the side of the car rather than under it; avoiding the 'messy' underside & reducing friction drag.

The rear spoiler doesn't look to me like it would produce any additional downforce as it's parallel to the bootlid, so I guess it's there either to help break the air away more cleanly from the rear of the car (thus reducing drag again) or it's simply an ornament.

Weighed against these advantages, the downsides of the RS bodywork would be extra cost & additional risk of damage from speedbumps, kerbs etc.

Of course we all know the main reason for the bodywork differences between the RS & the others - Marketing!

Sorry to be the anal engineer here but...

The rear spoiler is actually a rear wing. There is a difference in the fact that a spoiler is designed to create an area of turbulence (which may create downforce in a given situation), and a wing creates downforce using the wing effect.

The wing on the vRS may appear to be useless on first sight, as it's virtually parallel to the boot lid. But it does actually work. If you think about it the air flowing over the wing is not parallel to the ground/bootlid, it is parallel to the rear screen. Then imagine the angle between that air flowing down the screen and the wing, and you'll see that it does actually do a fair bit of work at speed.

That's why your vRS still sticks to the ground at 145mph!

People always dismiss things like wings and splitters as styling ad-ons. But somewhere in a cold dark room there's a team of engineers spending alot of time designing that little wing.......

Rant over!!

The vRS is definitely lower-set than the Elegance (I have an Elegance, and have a mate with a standard vRS). That could do it more or less by itself, since it will reduce airflow over the comparitively rough underside.

As to what the wing/spoiler does, on the hatch, and without actual tunnel data, I can't be certain, but I'd expect that it's working by increasing the depth of the stagnation zone on the rear screen to cut lift and parasitic drag. The edges are way too heavy to make it an aerofoil like Bodge suggests I think.

It's all getting a bit technical for me in here. It's just flown over my aerodymanic forehead

without actual tunnel data, I can't be certain, but I'd expect that it's working by increasing the depth of the stagnation zone on the rear screen to cut lift and parasitic drag.

:eek: blimey! My thoughts exactly

If we cared enough we could ask the skoda rally team for some comparison data! And they would ignore us!

At the end of the day the vRS is basically the best car ever made. I would marry my car if she didn't turn to heavy drinking every time I spank her!!

:eek: blimey! My thoughts exactly

Think of the back of the Octy hatch as an open V shape. On the "normal" models, when you get up to an aerodynamically significant speed, that open V is maybe half-filled with air that's not moving relative to the car (stagnant air), which means that you get a cleaner separation off the sides, and less air "sucking" on the rear window. What I think the rear spoiler on the vRS does is increase the distance that stagnant area lifts up the rear window at a given speed, thus reducing the amount the car is sucked up and back by the airflow.