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The mkiv Supra Owners Club

Rear Downforce- Tech Opinions


Thor

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Guys, firstly I don't like the F&F look rear wings, but is there any real advantage on a fast RWD road car? If so which type. I have been watching the JGTC & they all use similar huge wings.

 

If there are any proven wings, are there any links to web sites?

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Thor,

 

To get one to work properly on our cars it would have to be mounted quite high and as far back as possible...

 

Having said that an APR (F&TF) wing is certainly more functional than the stock or TRD no.s. http://www.aprperformance.com/products_list_spoilers.asp

 

They certainly can work but to get the best out of them won't mean they are pretty....

 

One thing I've wondered is if a bootlid extension would help....ie the extension of the natural lip that is the end of the boot.

 

To get a bi-plane wing to work you need good (usually means large) endplates to force the air over the wing.

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I'm thinking of something similar to what the Elise uses....

 

All you need is a big piece of aluminium with end pieces welded on or just formed. Mount that to the bottom of the fuel tank from the rear subframe and neatly merge it into the rear bumper.

 

With the Supra being so wide would you need to sub divide this rear under tray (longitudinaly(sp?))

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To make best use of any wing you have to be doing over 60mph anyway.

 

They can help, even the stock one, when taking fast corners. Each and every kg of extra downforce makes a difference, maybe not to the everyday driver, but if you took two of the same drivers one in a winged car and one in a non-winged car, everything esle being equal, the one with the extra downforce will have more grip through the corners.

 

The stock and TRD spoilers have been designed by TRD themselves so they are effective when doing some speed.

 

The F&F style spoilers all seem to be the same shape and stlye so I can not say whether they will be in the effective airflow over the car to be very effective.

In the JGTC they will have been specifically placed so that they fall into the down-wash over the top of the car but without knowing their measurements I wouldn't like to just stick on a F&F style spoiler as you may even end up with 100% drag and 0% downforce wich would defete the object.

 

In some situations you can actually get -ve downforce if a spoiler has been positioned wrong.

 

But in the end if it is just cosmetics you are after then all of the above is not important.

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Guest Terry S

I would be very interested to hear CW's input on this.

 

Alex, I was looking at my mate new Elise's diffuser last Saturday. It is so simple. I think it's sheet Galv not Aluminium. I have thought about making one up as well but unless you flat bottom the whole car I am not sure what if any effect it will have. I have enclosed the front spoiler but the exhaust is in the way of everything underneath. I think the JUN car must have the exhaust either inside the car or the tray very low which would make it wholly impractical fro road use.

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Originally posted by Terry S

I would be very interested to hear CW's input on this.

 

Alex, I was looking at my mate new Elise's diffuser last Saturday. It is so simple. I think it's sheet Galv not Aluminium. I have thought about making one up as well but unless you flat bottom the whole car I am not sure what if any effect it will have. I have enclosed the front spoiler but the exhaust is in the way of everything underneath. I think the JUN car must have the exhaust either inside the car or the tray very low which would make it wholly impractical fro road use.

 

With a proper splitter at the front and a decent sized tray at the back I would guess you can make an improvement....though maybe it wouldn't be worth the effort if at the track you haven't got the suspension needed to drop the car low enough.....

 

I suspect you're in a better position to try due to your contacts at work.

 

Has anyone found any rudimenatary(sp?) air flow diagrams for the Supra? I think there is one in the owners manual but that is too dumbed down. Or failing that a generic fastback car's airflow diagram aka wind tunnel flow patterns.

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Forget rear diffusers and flat floors unless building a track only car. You need a maximum of 50mm ride height for these to begin to work. Front splitter will help stop air packing under the car though. Be aware that they may fail MOT and would certainly fail construction and use regs, or whatever they are called nowadays, as they would be a bit nasty to a pedestrian, even at low speed.

 

For sure a rear wing will help, but most of the ones in body kits are a joke. You need something big to have any real effect on a car as heavy as the Supra, and a big (properly made race type) wing needs STRONG mountings. They are also expensive, budget 1k on anything worthwhile, new, or 600 or so secondhand, without mounts. They won't do much under about 90 MPH though. There's also little point in gaining a huge amount of rear downforce if it unbalances the car, you need to add it in proportion, but having said that the rear is where it will be needed until substantial downforce at that end is achieved.

 

It's only when you start running a properly aerodynamically designed car REALLY low that you can use ground effects. Even a flat floor, decent splitter, some front tray venturis and a correct diffuser and proper rear wing can give awesome dowforce. the old true ground effect F1, F2 and F3 cars were sensational, but like all exciting things were banned. With development they would have been stunning to the point of people being unable to drive them due to the G forces capable of being generated.

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So Chris,

 

How does Thor or TerryS achieve an increase in grip?

 

On a road car can it only really be achieved by stickier tyres - ie more mechanical grip or should the suspension be more closely looked at? Will the TRD diff help them get out of slower corners and even off the line better? (The TRD Diff does reduce the top speed of the car but I'm more interested in its plate type design).

 

 

When quoting £600-1000 for a wing are we talking about BTCC ones or full blown GT1/2 rear wings?

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Originally posted by Alex Holdroyd

So Chris,

 

How does Thor or TerryS achieve an increase in grip?

 

Stop modding their engines as much would help

 

On a road car can it only really be achieved by stickier tyres - ie more mechanical grip or should the suspension be more closely looked at? Will the TRD diff help them get out of slower corners and even off the line better? (The TRD Diff does reduce the top speed of the car but I'm more interested in its plate type design).

 

 

When quoting £600-1000 for a wing are we talking about BTCC ones or full blown GT1/2 rear wings?

:baa:

Downforce will help at speed, but they'd need 100MPH to generate much. Better tyres, wider tyres, but LOADS of caveats there...

 

A tightly set LSD will help, but will cause corner entry understeer unless oother suspension mods are made to compensate. It would certainly help off the line for drag racing, but a pure drag race car would use a spool diff (no differential action at all, just locked solid). these are no use on the road, and only really useful for high speed ovals, or SERIOUSLY powerful cars with trick suspension geometry for road course work. Porsche made the 962 work well with a spool, but we race drivers hate them. If a driveshaft fails on a spool equipped car the other rear wheel is still driven with full engine torque and the car immediately and INCREDIBY violently turns left or right, far to fast and hard for you to do anything about at all. That's why FWD cars with tightly set LSD's pull violently from side to side under hard power. On FWD again suspension geo can help the torque steer, but I'm getting off the subject now...

 

This new thing i bought to race, that blew up, has a trick diff in it, but they take ages of playing around with to set up correctly, need constant maintenance, and, needless to say, are very expensive :(

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For ground effect to work don't you also need to keep the car completly level, if it rolls (like in a corner) then the effect is lost.

 

Chris, re LSD on FWD. My cousin rallied a mini many years ago and had an LSD in it for a while and as you say it's horrible/undrivable on tight corners. Didn't Clarkson say something similar about the new Ford Focus Cosworth?

 

A friend drove an F1 car in the wet and really felt the downforce working, the faster he went the more grip he had - took some getting used to!!

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Alex H: Current BTCC cars all have to use the same rear wings, a part of the TOCA package. It doesn't do a great deal. You'd need a proper big dual plane wing off a big GT1 race car for effective downforce on something like the MKIV. And no, you can't have the one off my Zeus... (It weighs 11 pounds complete with mounting, which i found kinda impressive).

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Originally posted by Chris Wilson

And no, you can't have the one off my Zeus...

 

:innocent:

 

it never crossed my mind!....

 

:innocent:

 

Do they sell replacements? They've got to expect you to stick it backwards into a tyre wall at somepoint....

 

Hmmm you might want to make sure the other half doesn't read that line!!!

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Originally posted by Alex Holdroyd

:innocent:

 

it never crossed my mind!....

 

:innocent:

 

 

Hmm, and it's unbolted off the car now, too (goes to check w/shop alrm is definitely ON....)

 

 

Do they sell replacements? They've got to expect you to stick it backwards into a tyre wall at somepoint....

 

Hmmm you might want to make sure the other half doesn't read that line!!! [/b]

 

They do, and she is already well annoyed about how much the engine will cost to fix, without her getting wind of body spares prices...:twak:

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Originally posted by John Packham

Chris: is that a supersports or what? I'm sure I've seen it Race Car Enginering, but can't find the copy. And is it one of Peter Sneller's designs?

 

Yep, a Sneller design, Supersports. Racecar Engineering ran about 4 articles on its development, I have got 2 of them, must ask Pete for copies of the rest. He designs some trick stuff, I hadn't realised just how diverse the stuff Zeus has done is.

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