Cupra R Downforce & Diffusers

[JamJay]

I had noticed in the past with an LCR, during a trip to mainland Europe (not mine, never leaves the garage ), that it became very light past a certain speed. This can be felt at the front end especially through the steering and at the rear when changing direction and braking. Stiffer, lower suspension, a R-ARB & spacers helped the issue second time around especially with the rear stability but the car still felt quite light.

I'm considering having a local plastic fabricator make up a rear diffuser for the LCR rear bumper. Firstly I like the sporty look that they give but in this case, it's a matter of function over form with the aim of sticking the rear of the car to the ground a little better at high speed. I'm also looking at generating more downforce at the front also.

The design I will be looking at will be similar to that of the Clio 197 or loosely the MK2 LCR which I think is for style:

Clio

Leon

It will be bolt-on, attaching to the underside of the LCR bumper in the 'black' cut-out area and widening if necessary, here:

...and not externally like this:

There are a few things to consider though.

- Is the design of the Clio diffuser functional or is it a show piece? This, I don't know.
- How much down force will it create?
- Will it create so much downforce at the rear that the front end lifts or will it balance the car? In the case of the former, will a larger (BTCC style) or addtional front diffuser need to be fitted?
- Will the BTCC style lip create any more downforce than OE? If not then perhaps some modification to the undertray?
- Is it possible to weigh the front down for track action? It's an idea but would be nicer to have a permanently balanced setup.

I'm sure that there are some more questions but my mind has gone blank. My main concern is that by sticking the rear down, the front will become lighter, obviously it should be front biased. The only way I will know for sure is either by wind tunnel which isn't going to happen or track testing. If by some miracle I got it right first time then great but that's not likely so I do need to realistically look at solutions for the front at the same time.

So what are your thoughts? Discuss.

 

[Mark300zx]

I have thought this and think it would make the car look better as well, would be interested to see the end product!

 

[Booya]

would make the car look better as well, would be interested to see the end product!

+1

If the cost wasn't too great I would defo fit one.

 

[sambryant]

This i would also like to know

 

[traumapat]

Will creating more downforce to the rear make the front lightness worse?
I think any weighting to the front would ruin handling at lower speeds.

 

[tyrer]

Not sure on the technical side of things...but would look tasty

 

[CupraTurbo81]

A diffuser like that will certainly serve a function but more in reduced drag rather than downforce. It will create some if designed the right way but not as much as a conventional spoiler which we can all agree look pants on the leons.

 

[traumapat]

A diffuser like that will certainly serve a function but more in reduced drag rather than downforce. It will create some if designed the right way but not as much as a conventional spoiler which we can all agree look pants on the leons.

I think the idea behind it is that the air moving under the car sucks the car down , rather than reducing drag but not certain.

Sierra Whaletail fabbed up from cast Iron would do it

 

[MrBen2k7]

From all I have learned and read from the years of F1 and the Scrabsf1 blog... I know that rear difusers give large ammounts of downforce and rear grip when designed well.

They will make the front end lighter at speed and understeer.

 

[paul26982]

do you really need this for rear end grip on a FWD car, fairt enough on 4wd & Rwd, if you said for looks then id be or ok then might look good.

 

[CupraTurbo81]

From what I can gather is that the diffuser diffuses the fast moving air underneath the car as it meets the area of low pressure air at the back reducing drag. Due to that fact it will create some downforce at high speed but not much. These things only really work at their best with a flat underneath on a car close to the ground. You may see some improvements on fuel economy but I doubt anyone fits a diffuser for that reason.

 

[JamJay]

Thanks for the input.

So far some points that I already knew i.e. increasing downforce at the rear only will lift the front. This just reinforces thoughts for something more substantial than the splitter and under tray at the front.

As far as I know, the fins on the rear diffuser are there to straighten airflow and help pull the car down although I'm not sure how...hence posting this up for some more info. I need to know whether the Clio version is functional really and it would be handy to have a thorough look but I know no-one with one of these cars. It could be that it's just part of a fancy bodykit to set the car apart from the base models, who knows but if that is the case, I'm going to have to do a lot more research into what actually makes one one these work and getting a moulding made up might prove tricky. Worst comes to worst then I might just end up with a nicer looking rear end.

Does anyone have any thoughts on increase front end downforce?

 

[seanaldo1987]

i was just talking to my mate at work about doing something like this, just for looks and not necessarily for downforce or what not

i'd be interested in one of these and also a solution to get more front end high speed downforce

 

[JamJay]

i was just talking to my mate at work about doing something like this, just for looks and not necessarily for downforce or what not

i'd be interested in one of these

I agree, it would probably look quite nice but if it's possible it would be nice if it worked also.

Someone mentioned above that there's little need in creating rear downforce for a FWD. Can this be backed up at all? We know that the LEON is light at the front at high speed so say a good front diffuser is fitted, what would be the implications of more downforce at the front and leaving the rear standard?

 

[Murdered LCR]

Some one has fitted one on the yellow Leon he wasn't from this country tho but he had a big turbo lol , looked quite good

 

[DJ-LIAMC]

May look a little like this?

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[JamJay]

That's brilliant Liam, just what I had in mind with four fins.

Would look good on a lowered LCR for sure.

 

[jonjay]

My thoughts:
Are you talking about your car or a standard LCR?

Doubt the diffusior will make any difference whatsoever. If you need stability at high speeds (we are talking about 120-130+ mph????) then a wider track and lower car will be more benificial. I would go as far to say that the BTCC front splitter will help.

 

[JamJay]

It will be going on my car, yes although I have not hit those speeds before in mine, this was based on a friends car which has since been sold but was of similar spec.

I'd like to take it to Europe next year and perhaps let it see some track action, this is why I am investigating.

I will look into getting the BTCC splitter in that case although will strictly only be fitted for the track, no way practical for the road/UK roads.

 

[Booya]

Looks great!!! I wouldn't be too bothered about whether it actually has an effect or not as I'm not a track user or autobahn user lol. It would be nice if it did work of course but I would be more interested in the fly looks