Downforce / areodynamics

[malyon]

Right then I don't know how many of you guys have played with this subject but very interested in people opinions.

Long story cut short original plastic splitter was broken when I purchased the car.
I decided to upgrade to large cm composit splitter and possibly canards.

Now I know clios have a tendency to be a little light on rear with abit of lift off oversteer. Now as I'm now adding down force to front possibly exaggerating lift off oversteer dew to more weight pushing down on front.
Now my thinking is if I'm adding more downforce to the front comonscence tells me I should fit adjustable rear spoiler to add downforce on rear?

Opinions and experience will be apritiated.

 

[DannyR]

You could retrofit a 197/200 rear diffuser

 

[barnesautos]

I was thinking just this the other day , as I had an off at bedford , and we all know the rear of clios are bloody light [emoji35]

 

[alistairolsen]

Diffuser is pointless on a small FWD hatch unless it has a full flat floor and is run extremely low. Even if those things are true, the 197 item is almost certainly of no benefit whatsoever except cosmetics.

I'm not sure how true the light back end theory is, they're still fairly understeery in normal conditions.

 

[Goodj]

90% of aero mods only provide placebo downforce. But those affected will go ultra-defensive if you even begin to suggest it.
You're more likely to just create a whole load of drag that you are weight. This then makes people slower into corners and further compounds the placebo effect ("it's gorra be workin cuz im slower, so downforce")
As for the 197/200s, they had the diffuser as it was engineered to give downforce without the weight & drag of a wing. The later addition of stick-on rear wings was mostly a marketing piece..unless it's a bonefide Cup Racer wing.

That said, it's all pretty pointless because it's a nose-dragger so unless you replace the rear wheels with casters, after the limits of adhesion are reached all you'll get is understeer

 

[malyon]

I agree about the fact for a defuser to work properly it does require a flat floor to stop turbulence under the car.

I think the only way to sort this out is to experiment with subject.

 

[tom172cup]

Pure Motorsport have done a flat floor

 

[alistairolsen]

The problem is that to make it work it needs to run so low you can't get it on and off a trailer, jack, anything, its just a PITA. Also without MAJOR surgery, you're pretty much out of suspension travel and your geometry is ruined, which is too much compromise IMHO.

 

[malyon]

I agree the practicality of a deffuser with flat floor isn't practical.

I've been talking to a few motorsport buddy who run fwd with front splitters and adjustable rear wings and they say it dose improve lap times and a more solid feel to rear end in high speed corners. This is on VAG cars.
I think I might just make up a fully adjustable rear wing set up and have a play.

 

[Entity]

look up "nige" or nigel's MK2 Golf on northloop.co.uk for instance.

He runs a custom front airdam & splitter from plywood and a DIY rear diffuser. The practicallity will probably be a bit foregone but then again, if you worry about practicallity what are you doing considering a front airdam / splitter and rear diffuser ?

It's only "worth it" if you are either pretty hardcore into trackday driving, or are seeking the last seconds you can on track (and I don't know rules but doubt a lot of competitions allow aero to be run with the exception of TimeAttack)

 

[Goodj]

PLYWOOD?!?!!
seriously?

 

[Entity]

yhea, why not ?

not 3milimeters thick off course but probably more like 1Cm or such but ... it IS a composite afterall and pretty sturdy to boot ...

 

[Goodj]

Sounds like an amazing idea.
Did it get a TUV stamp?

 

[Entity]

Don't know if he's ever been TUV inspected at the ring but ... He's from the UK so don't think he's really worrying about that.

 

[mark123]

Most modern cars actually generate lift so countering that with a small wing and splitter can be beneficial. I don't know the specifics on a clio though.

 

[alistairolsen]

Plywood is fairly common to be honest, the planks under F1 cars in the 90s were ply! It's a nice, stiff, thin and cheap material. Alucore is also used, as obviously is foam cored carbon.

 

[mace¬]

My mate said he had a car built from wood once PMSL a Morman it was called.

 

[Entity]

Tbh, plywood is a "modern" material, lightweight, strong & cheap, easely replaceable (since splitters & airdams WILL take a hefty beating when you venture off-track / onto curbs) ... Makes total sense to me.

Only thing I've seen done is add metal "wear bars" to the underside of the splitter so that if you bottom out it grinds the wear bars and not your splitter. So you at least have a bit of longevity out of it instead of wrecking it in one trackday because you where bottoming out / ride height too low and running curbs like the BTCC cars of the 90's

 

[Goodj]

My mate said he had a car built from wood once PMSL a Morman it was called.

I bet a Morris Traveller is the most motorsporty of car ever then.

I can see the reason for using a thick, heavy lump of ply on your front bumper. Even if it generates absolutely no aero benefit, you'll have added "downforce" directly to the front end even at standstill. Except it goes by the less technical term "weight".

My main thought it that it does sound overwhelmingly pikey though. As you said though, if you're going to just smash it to pieces the first time you go around Karussel, then yeah, better a sheet of ply than some $$$$££$$£$£$£$$£$$ carbon job.

This guy has totally got it sussed though, all that plywood downforce is clearly forcing the wheels into the ground.
h

 

[Entity]

Nigel's front airdam:

and @Goodj I think you overestimate the strength to weight ratio of plywood (unless your having a laugh... Internet does not convey sarcasm.)
a 1CM thick piece of ply covering the front of the car and giving an airdam / Splitter lip weighs in at ... a total of what 5 kilo ? Perhaps 10 including mounting bracketry and all ?

The added benefit it gives at high speed vastly outweighs the 5-10 kilo you might be gaining.


His rear-diffuser:

IF you google "Nige MK2 Golf" you'll find loads of pictures of his car including build-threads. Defenitly worth a read !

 

[Entity]

Another popular technique btw (and a lot prettier) is to use Balsawood to make the shape desired and then cover it with Carbon (and wear-bars)...

Light, strong, not flappy due to the Balsa core and "fairly" sturdy. Although, again, if you're going to be riding curbs like your in the BTCC, its a waste of effort imo.

 

[Sam@NP]

Aero is a hugely complicated field. The vast majority of downforce or Negative Lift is generated underneath cars. The airflow off the back of a clio will be so dire that it will create nothing but drag. It's certainly not clean enough for an aerofoil unless it's mounted seriously high and a long way back.

The MK2 Clio was designed back when aero was nowhere near as extensively researched and implemented in road cars as it is now. Literally pissing in the wind unless you have access to a very accurate CFD model and software. TBH sorting out the aeroflow under the car would be far more beneficial. I'm talking flat floors, wheel gerny flaps etc.

A little fact for you, front canards are mainly implemented to help maintain the negative pressure under the car created by the splitter and flat floor.

 

[scooby-93]

I bet a Morris Traveller is the most motorsporty of car ever then.

I can see the reason for using a thick, heavy lump of ply on your front bumper. Even if it generates absolutely no aero benefit, you'll have added "downforce" directly to the front end even at standstill. Except it goes by the less technical term "weight".

My main thought it that it does sound overwhelmingly pikey though. As you said though, if you're going to just smash it to pieces the first time you go around Karussel, then yeah, better a sheet of ply than some $$$$££$$£$£$£$$£$$ carbon job.

This guy has totally got it sussed though, all that plywood downforce is clearly forcing the wheels into the ground.
h

I bet a Morris Traveller is the most motorsporty of car ever then.

I can see the reason for using a thick, heavy lump of ply on your front bumper. Even if it generates absolutely no aero benefit, you'll have added "downforce" directly to the front end even at standstill. Except it goes by the less technical term "weight".

My main thought it that it does sound overwhelmingly pikey though. As you said though, if you're going to just smash it to pieces the first time you go around Karussel, then yeah, better a sheet of ply than some $$$$££$$£$£$£$$£$$ carbon job.

This guy has totally got it sussed though, all that plywood downforce is clearly forcing the wheels into the ground.
h

Take a look at Andy forests impreza that thing is crazy! It also handles aswell as it goes and he has a ply wood front splitter/flat floor set
Up

 

[pure-motorsport]

Our hillclimb and sprint car has a full flat floor and rear diffuser, as in photo above. I planned to test it last year with a 'set a time then take it off and see' approach but never got around to it. The theory on our car was to reduce drag than to provide any real 'downforce'. The diffuser is possibly too aggressive and we'll try a new version this season. I'll do some wool tuft tests on the diffuser until we get the angle right and keep the airflow attached.
I think it should definitely make a difference but some real testing this season will see if the effort was worth it! The first splitter we had was ply covered in ally but it got damp and warped! The new one is made of sign writing board - really thin aluminium sandwiching some sort of plastic. It works really well, very stiff and seriously light. Only £60 a sheet as well compared to the £500 a sheet for aluminium honeycomb I was going to use!
The splitter is really low and can't get the car on the trailer without taking it off, so we have some locating pins underneath and on the bumper to just slot it on and put in some R clips to hold it in place.
One comment that a spectator said to me is that in the wet, it seems to kick up the spray out of the diffuser much more than the other tin tops.
Whether the weight penalty is worth it in hillclimbing is to be tested, but I think it should be worth it as we are often near or over 100mph.

 

[...]

did a fair bit of thumb in the air work on my carbon westfield , lift is a major issue on them and creates understeer on initial turn in on high speed corners like pohon at spa , and russell at snet ....

combination of flat floor , cannards , rear diffuser and a small lip and chin made a huge difference basically smoothing airflow


no ply used as i had access to lots of carbon , rear difuser was kept very very simple and was not extended much

 

[Goodj]

For Caterhams, don't you just slice a load of louvres into the cycle-arches at the front?

 

[JoeMarano]

I heard the Clio 197/200 diffuser generates 40kg of downforce at 120mph. So it does something....albeit not a lot.

 

[...]

For Caterhams, don't you just slice a load of louvres into the cycle-arches at the front?

No you square the tops

A 7 is as aerodynamic as a brick

 

[Goodj]

An right, cool.
Just thinking of all the super-hyper-mega-no-weight-busa/v8/cosworth 7-alikes, and I just remember the wings having more louvres than an Astra GSi bonnet at a max power show

 

[Steven103]

LMP square-relief arches y0...

 

[JoeMarano]

I don't know why people haven't covered the rear wheels. Thats a huge aerodynamic benefit right there provided the brakes have ducts.

I think spoilers and diffusers usually just complete a "look" a bit like how a 172 has massive arches that are bigger than they need to be tk fit the wheels in.

 

[Steven103]

I don't know why people haven't covered the rear wheels. Thats a huge aerodynamic benefit right there provided the brakes have ducts.

06 Ferrari F1 car
Some late 90s/early 2000s BTCC cars
Some 80s/90s Group C sports cars
Honda Insight (90s eco warrior thing, ahead of it's time!)
Blood hound etc

Can you think of any more road cars? That's all the mainstream stuff I can really think of. The fact that those are all very extreme cars chasing the very last fractions of performance, probably suggests there's not as much benefit as you think?

IMO probably the most important thing to grasp about aero is its not about one individual feature in isolation, it's about how one little feature interacts with a massive cluster f**k of other surfaces and features and phenomena that make up a car body.

Perhaps covering the face of the rear wheels is completely pissing in the wind, given that you'll always have a significant part of rotating tyre sticking out, it's right next to a huge wake coming off the C pillars & boot, turbulent air coming out from the back & side of the underbody and basically exposed to all the mess created by every single detail in front of it?

 

[JoeMarano]

In a nutshell Cliosport needs to start taking donations for a wind tunnel of our own lol

 

[Entity]

It's all about how far you want to take it, and how far your budget goes I guess.
One of the maddest things I've seen is a "Venturi Tunnel".

This means:
Behind the rear seats you create a tunnel from the floor to the boot which will, while driving, use the drag / low pressure area behind the car to lower underbody pressure.

example:
http://www.langracing.com/bmw-race-...users-rear-wings-venturi-tunnels-underbodies/

 

[JP83]

06 Ferrari F1 car
Some late 90s/early 2000s BTCC cars
Some 80s/90s Group C sports cars
Honda Insight (90s eco warrior thing, ahead of it's time!)
Blood hound etc

Citroen DS!

 

[Steven103]

In a nutshell Cliosport needs to start taking donations for a wind tunnel of our own lol

Stand on the gate at CSS with a "collections" bucket? xD


A splitter, flat floor & diffuser IS a Venturi.