Track car aerodynamics help

[1985michael182]

So... this is my car, Titanium silver 182ff

When I bought it, it had a plywood front splitter on attached to the subframe. It looked hideous just matt blacked and was heavy so I've removed it.

But now with no splitter on it doesn't look right.

So I've bought a skoda splitter off ebay that when fitted will look just like the standard cup one at a fraction on the price.

What I'm thinking though is was that splitter on to create downforce to stop understeer?
I've been looking at the Cm composites race splitter that I could fit under the skoda splitter which would make the splitter around 20mm lower than before creating a better vacuum at the front of the car i imagine. Using brackets made by a company called Back Yard Civic

http://bycdesigns.co.uk/index.php?route=product/product&path=67_17_64&product_id=104

The splitter would be mounted strongly to the chassis and the bumper would still pop of easily without having to remove the lot.

But...

What angle should the splitter sit at ?
Should it be flat when stationary or have a slight rake so under acceleration it sits flat?

Should the full car have a slight rake, higher at the back?

The rear bumper has been cut also which I'm assuming is to do with front to rear air balance?

I can always and a bit of angle to the rear spoiler with spacers if the rear becomes loose.

At some point I want to do a side exit exhaust, flat bottom underneath and a rear defuser, but with anything like this you need the scientific knowledge to make it actually work.

Anyone on the forum who might be an aero whizz any info would be greatly appreciated

 

[1985michael182]

@NorthloopCup

 

[1985michael182]

@bloke

 

[scotiamr2t]

complete waste of time, purely for visual effect. spend your money on more track time

 

[1985michael182]

It must do something surely? No?

 

[1985michael182]

@Tomotek our resident race engineer have you got and views?

 

[scotiamr2t]

Unfortunately not no. You would need a full flat floor, properly designed splitters front and rear and then a ride height that would make use of them. On a clio its a waste of time really

 

[Tomotek]

Splitters are great if you can make them rigid enough not to flex under the load they’ll see from driving at +100mph (where they will actually give you some downforce, by creating some high pressure above the splitter) a lot of the splitters I see on clios are just too flexible or too small for any noticeable aero benefits.. and as @scotiamr2t said you really need a flat floor under the engine bay to make use of it.. the flat floor allows the air to pass quickly with low pressure and the splitter creates high pressure air over the front of the car, if you have no flat floor the air is very turbulent under the car and doesn’t really travel much faster than the air passing over the top.. (with that said they’re not all bad)

One of the benefits to running a splitter even if it doesn’t extend that far back is that you’ll build up higher pressure around the grilles on the bumper and fog lights, which will increase the air flow through the rad and into brake ducts, if you have them, increasing cooling efficiency ( not all about the aero gains) [emoji6]

Canards or dive planes are a good aero component, they deflect oncoming air upwards which pushes the car downwards, with very little drag (depending on their angle)

I wouldn’t bother playing with the angle of the std rear spoiler, won’t do anything (unless u angle it at 45deg, but then the drag will hinder your top speed) .. if you want more grip at the back id go for a proper wing, with a decent aero profile.

Rake for aero purposes will be pointless unless u have a full floor and diffuser, and then they’re is a fine line between what is useful or not, if u can get big channels in the diffuser u don’t need much rake, F1 cars only use so much because the regs only allow relatively small diffuser sizes.. if u go to high with rake u end up pulling in air from the sides of the car which can reduce the diffusers effectiveness.. look at mid 90s F1 cars or current GP2 when they were/are allowed big Venturi tunnels, they hardly run any rake

Rake in a Clio is all about CG / roll centre heights for the suspension.. the higher you raise the rear the more it will roll, giving you an oversteery rear, helping to reduce the inherent understeer.. too much though and u start to make the car unstable under brakes, and will slow u through corners as you have raised the whole cars CG too much.

Rear bumper cut outs.. only worth scene points in my opinion [emoji1360] .. I’d only cut mine out if I was to put a working diffuser in its place, rather than leave a gaping hole at the back

 

[Tomotek]

Haven’t proof read that so may be utter jibberish lol. It is midnight after all haha

 

[1985michael182]

No it all makes sense.

So with a front splitter is there a point where it becomes too long or not long enough. I think I can get it rigid enough and follow back under the car and was hoping for a side exit exhaust to give free space for a diffuser.

 

[JB21]

Pointless on a Clio as mentioned aero only really starts to work at 100+ and I cant think of a track in the UK where a standard engine Clio would be moving through a corner at 100+ for aero to work. If anything adding aero will make you slower as it just adds drag.

Just an observation on your avatar and the lean angle you have through that corner spend your money on suspension.

 

[1985michael182]

Pointless on a Clio as mentioned aero only really starts to work at 100+ and I cant think of a track in the UK where a standard engine Clio would be moving through a corner at 100+ for aero to work. If anything adding aero will make you slower as it just adds drag.

Just an observation on your avatar and the lean angle you have through that corner spend your money on suspension.

Hi JB, no that's the old the 172cup. The silver 182 is the new motor.
On 48mm jenvey bodies
Gen 90 ecu
182 mani
@NorthloopCup 's Group N timing tool
Full SS slip jointed race exhaust
Gaz full coil overs
Hc brembos
CL brake pads

Running 197.3bhp and 171.8lbsft
Mapped at EFI

It's not sluggish by any means.
But I get your comment on the roll of the cup.

 

[JB21]

Hi JB, no that's the old the 172cup. The silver 182 is the new motor.
On 48mm jenvey bodies
Gen 90 ecu
182 mani
@NorthloopCup 's Group N timing tool
Full SS slip jointed race exhaust
Gaz full coil overs
Hc brembos
CL brake pads

Running 197.3bhp and 171.8lbsft
Mapped at EFI

It's not sluggish by any means.
But I get your comment on the roll of the cup.

Similar power to what my 182 was running but with AST's and other handling mods and there was still no way it was going through a corner at 100+ not with a noob like me driving anyway, lol.

 

[1985michael182]

Cadwell at the end of the start stop straight big sweeping left hander going up hill 100+.
Obviously if you have a load of power the drag from the aero on straights trades off against corner grip.
I'm just trying to find out the full truth about it all, what it does and doesn't do.
If the extra weight involved in fitting it is worth the trade off for less power to weight.

Would a basic air dam like the standard splitter but deeper be more beneficial or is it all just "MaxPowe" points and probably make the car handle worse ?

Obviously once you have your fast flowing air under the car you want to keep it there and stop air creeping in from the sides, so you'd need deeper skirts to trap it there ?
Then your diffuser at the rear to vent it out.

All sounds like it would need to be CAD designed using a wind tunnel to perfect and test it for it to actually gain grip.

 

[JB21]

Cadwell at the end of the start stop straight big sweeping left hander going up hill 100+.

Haha rather you than me attempting this in a Clio, lol.

 

[Tomotek]

There are a few corners +100mph .. Croft -Jim Clark esses, Dono - Craner Curves , Rockingham - Banking ... but we can take them flat with our car so adding aero won’t help (no issue with tyre wear either, which is another benefit of aero loading)... obviously if you’ve got more power you’ll start to need it as you’ll be going faster

And yes there will be a point u can have too large a splitter.. all dependant on speed of vehicle and shape of front bumper .. you can only create so much high pressure with the speed and geometry of the car.. the faster I go the more air u can trap above it, or if you have a bumper the size of a Bentley continental or a Nissan GTR you can certainly trap more air infront of it. If that makes sense

I’d love to be able to create a CFD model of the car and test all these things out, or get into a wind tunnel.. that’s the only way you’ll know

 

[JamesBryan]

Haha rather you than me attempting this in a Clio, lol.

It's like Island bend at Oulton, but up hill. I can say it's pretty quick!

 

[James H]

Not a Clio, but relevant...

 

[1985michael182]

I've done the cadwell corner at 100 and Croft esses. So it can be done. Think what I'll do is buy the cmcomposites splitter and the BYC mounting brackets and I'll test it on stack. With and without. See what happen eh ?

 

[1985michael182]

Track*

 

[bloke]

from my experience/looking at the idiots, most aero mods that are available/that idiots fit are pretty much pointless. it's something i've never really got involved with as there are loads of dead hard sums to do and it gets mega expensive to do properly.

not an aero mod but my pet hate is bloody bonnet vents ?

 

[1985michael182]

from my experience/looking at the idiots, most aero mods that are available/that idiots fit are pretty much pointless. it's something i've never really got involved with as there are loads of dead hard sums to do and it gets mega expensive to do properly.

not an aero mod but my pet hate is bloody bonnet vents ?

Bonnet vents to let cold air in or hot air out?

 

[Tomotek]

not an aero mod but my pet hate is bloody bonnet vents [emoji35]

Haha I agree when they’re not functional, I’ve seen a lot that are just imitation vents with no actual holes in.. functional vents are good (all race cars vent the engine bays) , I’m considering fitting some to ours to help keep the engine bay temps down and help the cooling out, sucking hot air out the vents allows more air to be pulled through the radiator

Just don’t put the vents so water can drip all over the electronics!

 

[Vaughan]

Aero is not intuitive. A witches hat has less drag with the pointy part facing backwards...

http://illumin.usc.edu/252/drag-reduction-the-pursuit-of-better-fuel-economy/

 

[Vaughan]

An article about an intercooler bonnet scoop that didn’t work

http://www.autospeed.com/cms/article.html?&title=Optimising-TopMount-Intercoolers&A=112920

 

[Steven103]

Good topic but I think people massively under estimate how sensitive aero devices are.

Diffusers literally have a few degrees within which they work before you get flow separation meaning no downforce at all and a real possibility of increased drag. A splitter is a really fine balance between feeding or choking the underbody. Small things like vortices from mirrors or dive planes are the difference between sealing the low-pressure underbody or delivering a big patch of turbulent air right onto the the outer 1/3 of the rear wing. Gurney flaps ffs, 5mm doesn't do much, 15mm adds loads of drag but 10mm increases the efficiency of the wing.

FWD hatches are one of the worst starting points too. Weight distribution versus centre of pressure. Geometry and packaging that's terrible when lowered by 100mm. Already the worst type of car for pitch control (stable aero platform) made worse by the bonkers rear spring rates needed to compensate all the other fundamental flaws to get it to turn in.

Will you lap 1 second quicker - yes, because you'll be 1 second braver in the high speed stuff because you've seen a big wing ?

Undisputed proof is a coast down test. Expensive but actually cheaper than CFD or wind tunnel time. Log damper displacements and calculate lift and drag coefficients from change in ride height and deceleration as you coast down a disused airfield from 100mph to zero sort of thing.

 

[Vaughan]

 

[bloke]

Just bonnet vents in general but especially when people think they get extra cooling from them...oh and bonnet raisers at the rear!!

That one really makes me laugh especially when you point out to people what happens to rain on the bottom of the screen when you're driving along ?

 

[numbers_]

Should point out what happens to that bonnet in a head on accident.

 

[PhillipM]

As someone else said, rear bumper cutouts are a waste of time without fitting a flat floor and diffuser - it looks like you're dragging a parachute around, but because there's no flow path through there you actually end up with a stagnant pocket of air in front of it around all the rear wheel well, exhaust, suspension, etc, and the air flows underneath that - it actually ends up with less drag than a cutout bumper with air flowing through all the components at the rear.
Manufacturers aren't daft.

 

[Tomotek]

@PhillipM, I made the exact same comment on a post on Facebook the other day.. you’ve explained the physics very well [emoji1360]

 

[Kev@KAM]

Focus on mechanical grip. Get the car professionally set up suspension wise and get out and drive. Get a feel for how the car handles in different situations and then look at what can be done to change the dynamics of the chassis.

Some of the fastest Time Attack cars have very little aero. I think thats mainly because it is so hard to get right.

 

[getikte]

id tend to agree with utterly pointless on a clio.... as @Tomotek says if you are flat out then adding aero wont help. Much better off focusing on mechanical grip. However after my recent ring trip i did wonder how much aero work would change the characteristics of my m3....

 

[1985michael182]

When you look at the clio cup cars of 182, they actually don't have any aero at all and they will have looked into everything

 

[Steven103]

Not really. Think you’ve got the wrong end of the stick. It’s a spec series that needed to be affordable for those coming out of karting and sit below touring cars in terms of laptime. Depending on the era the Clio cup cars also needed to be slower & cheaper than the V6 Trophy and later Megane Trophy race cars that competed in the Renault World Series. All of the cars are identical and Renault aren’t competing against another manufacturer so there is no need for Renault to design a lot of pace into the car through very very expensive aero. Plus marketing wise it’s in their interest to make the race cars look not dissimilar to the road cars.

Current WRC is probably the best example of what works on a hatchback. Like a 182 track car they are relatively slow in a straight line with a relatively high ride height, compared to say a WTCC spec TCR touring car.

 

[1985michael182]

Ok makes sense

 

[Vaughan]

When you look at the clio cup cars of 182, they actually don't have any aero at all and they will have looked into everything

They have a front splitter and rear spoiler, and a flat front undertray -- that's about all that can be done with the packaging. The factory spent a lot of time reducing drag around the mirrors and wheels for the production models: increasing the track and sticking the wheels out of the guards can increase drag significantly, and a poor choice of wheel design can cause additional drag too.

 

[Vaughan]

However after my recent ring trip i did wonder how much aero work would change the characteristics of my m3....

Awesome.

A deeper front splitter might be a practical start, and have a reasonable chance of being successful (ie, providing a benefit and not just causing drag) while remaining street legal.

 

[Hoofy]

This is one of the most interesting threads I've read in a long while!

We run a pretty high spec NA Clio in CSCC Tin Tops and I have long contemplated what could be done with regards to aero. I think a very good indication of how far you would have to go to make a difference is that of the WRC, but those guys have spent millions developing those cars in a wind tunnel, something I don't think work will let me do for free.

As Tom has suggested and thanks to one of my best mates also being an Aerodynamics engineer, we realised that the best course of action for our clio was to focus on the cooling efficiency. We have fitted a composite front splitter, which fills in the gap between the front lip of the bumper and front edge of the subframe, where it is rigidly mounted. Along with the wide alloy radiator, we get great cooling performance, so much so that we are revving it to nearly 8k, pushing out nearly 230bhp, without an oil cooler and engine water temps rarely get past 85C, with oil temps not even breaking 100C.

Our priorities for the car are to keep the mechanical grip it has, whilst getting the weight down as far as possible and finding ways to increase engine power and especially torque reliably. I don't feel that a full flat floor and rear diffuser would give us an increase in corner & straight line speed to offset the additional weight of the parts required. At Spa this year, with a more driveable, torquey engine (similar peak power vs last year), we actually hit a top speed of 137mph vs 128mph from the previous year. Our best lap went from 2.55.7 down to 2.53.9 as well and I don't think we would've done that if we spent the same time and money on aero!

So, in conclusion, it's a really interesting topic, but for Clios, it's just not worth doing anything drastic. Perhaps a few little things here and there, but you won't make major gains and more likely, you could face major losses.

If you're interested to see our car in action, loads of videos on my youtube channel - https://www.youtube.com/channel/UC1HxV8GlsxjpokFXIrM9WVQ and somewhat of an extensive build blog on our website - http://chaseracing.co.uk/ And of course, we're on facebook and instagram, just search for Chase Racing.

 

[Kev@KAM]

The main issue for me with our chassis was getting the car low enough where undercar aero could be put on and work properly. We aimed for an 80mm ground clearance as lower was a massive compromise in suspension geometry. Even this is not really that low and we had to tub the arches and do many more chassis mods to get this rideheight. This is a 205 but I'd imagine not many people are getting their clios really close to the ground without a mechanical compromise.