canards and rear diffuser

[patrickg293]

do canards and rear diffusers really make an aerodynamic differnce on the car or do they just look cool?

[AtomicRex]

Canards will make a very big difference....they are one of the cheapest forms of downforce available......if done right!
 
Diffusers on most of the cars are pointless, as they are designed to slow the air down from having been forced under the car.....seeing as 99% of cars aren\'t running flat floors the turbulence generated underneath completely negates the use of the difusser....hence it is there for looks.
 
Front splitters, once again if made correctly, are a good way of getting downforce....not such a cheap option though....and dont mount them directly to the bumper...as it is a good way of losing your bumper if you dig in with the splitter!

[m1tch]

I think if you want to put aero packages onto the car they need to be a whole package, not just bits a bobs, most of the aero mods seen on a lot of cars are just for show and just add weight!

[Nik da Greek]

I think I might have to half disagree with Jon on the subject of diffusers. Whilst I agree that they may not usually provide any great amount of downforce, I don\'t see how they can fail to have a positive effect on how the air passes under and away from the car. If you\'ve ever looked up the rear end of your FD from underneath (Oooer, matron! and lets be honest, who hasn\'t lol) it\'s obvious at a glance that the rear bumper cover is basically a massive parachute. There\'s nothing to stop air blowing up inside from the front of the car and then it has nowhere to escape, thus creating drag. I think that a diffuser that extends far enough forwards to stop this happening can only be a good thing, provided the front lip is not hanging down and exacerbating the effect.

You can see where in the early days of RX-7 tuning before diffusers became widespread how some tuning shops had twigged this and tried various remedies, usually no more complex than dremeling holes in the rear cover (the famous Knight Sports "Bomber Harris" handlebar moustache look, for example, and similar attempts from eg R-Magic and AbFlug). Sooooo, whilst I agree that a diffuser may not have a benefit in strict downforce terms through speeding airflow under the car, I think it must do in terms of keeping turbulence and drag under the car to a minimum. As always, I stand to be corrected if I\'m spouting abject borrocks :yes.

Some diffusers even look cool, which is a bonus. Canards, however, always look shlt and are named after a French duck, which is inexcusable. Don\'t do it :rollin

[SiH]

I\'ve always been told by people in the know that Canards are more of a tertiary device for fine tuning the car\'s balance, rather than a solution. I also personally think they look a little ridiculous on a road car.

Experience on my car = MS rear diffuser doesn\'t really make a tangible difference at the speeds I\'ve had the car at.
Front lip - definite difference to front end stability at speed.
Front undertray, however, makes a huuuuuuuuge difference to higher speed stability, turn in, and cooling.

If you\'re after more than just looks, I\'d go front undertray before anything else. I\'m not talking splitter here, just undertray.

[DrDan]

Let me preface this post by saying my knowledge is mostly theoretical, so this is what I *think* happens
[I did spend about three years of my life solving complicated equations use hard maths, and computers to model fluid flow, :Typing but I\'ve forgotten a lot of it ]
 

Diffusers on most of the cars are pointless, as they are designed to slow the air down from having been forced under the car.....seeing as 99% of cars aren\'t running flat floors the turbulence generated underneath completely negates the use of the difusser....hence it is there for looks.

I agree that without a completely flat underfloor and good "sealing" around the wheels wells, a diffuser will have limited benefit (see below also), but the way I seem to remember it is that the diffuser is there to speed-up air-flow. In fact to cause the "compressed" air from under the car to "expand", thus causing a low-pressure area in the area between the diffuser and the road, doing two things - increased downforce at the rear, and extracting air out from under the car - fast moving air is at lower pressure => causing the whole (flat) underfloor of the car to be "sucked" down onto the road.
 
If you want to confirm this (Bernoulli princple), try holding up two sheets of A4 paper a few cms apart and blow inbetween them, and they will move *together*, rather than apart as you might expect.
 
 

Front splitters, once again if made correctly, are a good way of getting downforce....not such a cheap option though....and dont mount them directly to the bumper...as it is a good way of losing your bumper if you dig in with the splitter!

Splitters are critical from an airflow perspective, but will achieve maximum return if designed with a flat under-floor and diffuser, etc., as I\'m sure that some of you will remember from the beginning of this years\' F1 season. For most benefit you need to match the aerodynamic properties at the front of the car, with the rear, as well as keep the flow along the length of the underside nice and "clean".
 

I think I might have to half disagree with Jon on the subject of diffusers. Whilst I agree that they may not usually provide any great amount of downforce, I don\'t see how they can fail to have a positive effect on how the air passes under and away from the car. If you\'ve ever looked up the rear end of your FD from underneath (Oooer, matron! and lets be honest, who hasn\'t lol) it\'s obvious at a glance that the rear bumper cover is basically a massive parachute. There\'s nothing to stop air blowing up inside from the front of the car and then it has nowhere to escape, thus creating drag. I think that a diffuser that extends far enough forwards to stop this happening can only be a good thing, provided the front lip is not hanging down and exacerbating the effect.

From a road-car perspective (i.e. <=70mph for most of the time :yes ) this is probably the biggest factor. A similar thing happens in the wheel wells... which is why those super-high MPG endurance cars have enclosed wheel arches - to minimise turbulence and drag, but let\'s face it, we all like to see our cool rims :Giggle And besides, if the wheels were covered, SiH would be out of a job commenting on wheel fitment :rollin
 

You can see where in the early days of RX-7 tuning before diffusers became widespread how some tuning shops had twigged this and tried various remedies, usually no more complex than dremeling holes in the rear cover (the famous Knight Sports "Bomber Harris" handlebar moustache look, for example, and similar attempts from eg R-Magic and AbFlug).

Actually a pretty good way to reduce this kind of drag, and again, a lot of road-going performance cars (Porsche 911s, etc.) have slits cut *behind* the wheel arches to allow air to escape from the wheel wells; if done properly this also has a side-benefit of drawing air over the brakes for added cooling. Take a look at the front wings of an FD
 

Sooooo, whilst I agree that a diffuser may not have a benefit in strict downforce terms through speeding airflow under the car, I think it must do in terms of keeping turbulence and drag under the car to a minimum. As always, I stand to be corrected if I\'m spouting abject borrocks :yes.
 
Some diffusers even look cool, which is a bonus. Canards, however, always look shlt and are named after a French duck, which is inexcusable. Don\'t do it :rollin

Turbulence and drag are not your friends for high-speed, obviously, but turblulence (vortex shedding) is *necessary* for down-force from spoilers, and drag is an unfortunate side-effect. ISTR an article on t\'Internet somewhere comparing the aerodynamic efficiency of an FD with and without rear-spoiler (92-95 style spoiler), the outcome was that the drag was increased (no surprise), without an appreciable increase in down-force; so it appears that you should go bare-arsed FTW.
 
Fo\' sho\' diffusers look good, especially when made of Carbon Fibre :Thumbsup!
 
DrDan.