The next tuner challenge..

  • Thread starter Leonidae
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Again though - where is your data coming from? How do you know so concretely that an arbitrary figure of "6" is any more realistic than "10" or "15"? I can be convinced here, but I need real data, not arbitrary suppositions.

Downforce, throwing out body modification, is based on the angle of attack at which the air meets the downforce-generating surface. Theoretically, a tuner could adjust that wing to any angle of attack he desired. Just because most street tuners don't do it, doesn't mean that it can't or shouldn't be done. Also, given that the wings in GT4 add no noticeable aerodynamic alterations to the car's body, why is it so far out of the realm of possibility to assume that PD's scale of 0-30 is based on their interpretation of a car with a streetable wing like the ones available at GT Auto? This holds up to scrutiny when you consider the fact that GT4's racecars almost always are able to accomodate 1.5-2x the amount of downforce as its street cars.

As for weight - consider it this way. RJ, you ought to enjoy this one :sly: You have a powerful FWD car at the dragstrip. You break your tires loose at launch and lose traction after each change-up through third. You then add ballast weight above the front axle. You no longer break loose as easily at launch, and you now only spin after the 1-2 change-up. This works - try it. That's how PD handles weight and traction loss.
 
I can go either way on wings. I really do want to know, though, where you're getting your numbers, setsunakute - you've stated "6" as a hard ceiling over and over as if it's a fact - I want to know why we should consider it a fact.
 
CraftyLandShark
I can go either way
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Uh-oh. :P

CraftyLandShark
I can go either way on wings. I really do want to know, though, where you're getting your numbers, setsunakute - you've stated "6" as a hard ceiling over and over as if it's a fact - I want to know why we should consider it a fact.
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Methinks that he finds himself a better tuner than everyone else here, or am I missing something?
 
I don't mean to suggest he thinks that. If he really has data, or at least a convincing argument to back it up, I'm all for it. Like I said, I can be convinced. Just show me the numbers, Sam :sly:
 
CraftyLandShark
I don't mean to suggest he thinks that. If he really has data, or at least a convincing argument to back it up, I'm all for it. Like I said, I can be convinced. Just show me the numbers, Sam :sly:
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Well, it's just how his post came off on me...

And, in truth, I think that if a downforce limit was enacted, 13 front and 18 rear would be about right; Rally cars don't tend to have monster amounts of aero work, do they? In fact, the aero work done to them is entirely possible to be done to a street car...
 
Yeah, the more aero work done to a rally car, the more than can break off over a steep crest :sly:

I don't think they use much downforce either. Spoilers, yes. Wings? Not really.
 
Right, and in-game they're modeled as having 13 units of front and 18 units of rear downforce... If memory serves. Might be a good starting point, yes?
 
Sounds pretty reasonable, unless someone wants to do a massive Scaff-esque study in which we compare real life laptimes from a known track with and without downforce for a given car... LOL
 
I crashed the Koeniggseggaaahhhblablabla!

I don't know...

Anyone want to do a test, Lancer rally car with no downforce Vs with?
 
so far, i have read a lot of "debates" over matters here:

well, since you guys are having an argument over downforce, why don't we exclude it, just like what N4HS suggested..,

also, how about we only allow Weight Reduction Stage 1?? for those who really insist on getting their cars on a diet??

how about this for the tracks..,

Confirmed - Trial Mountain, Deep Forest, Autumn Ring (and Mini)

Pending - El Capitan, Citta 'di Aria, Nurburgring Nordschleife

feel free if you want to add some more..,
 
d24/7, the debates are part of life here.

If we didn't argue amongst each other, it'd be a big, fat, communist "You will do it this way, nothing else" party. Every tune would be identical, etc.
 
I think stage 1&2 WR and no wing allowed is a good idea. Weight Reduction stage 1 and 2 are both replacing parts with lighter ones like you can easily do in real life yes? Stage 3 is a full lightened racing monocoque, not so street car like.
 
On weight reduction, I tend to agree. Stage 3 is unrealistic for street purposes - as you said, it's a full monococque body.

As to downforce, I'm a bit split. It's debatable in terms of degree, but it's also a tool used very often in touge-ish circles. I'm working on a method of getting a good limit based on RJ's suggestion last night, if we do decide to use it. I'll be running tests on that today and I'll report what I find here.
 
CraftyLandShark
I don't mean to suggest he thinks that. If he really has data, or at least a convincing argument to back it up, I'm all for it. Like I said, I can be convinced. Just show me the numbers, Sam :sly:
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If you can conceive a method of measuring downforce effects, then be my guest. It was a gut feeling. For example, why does it only take 3 downforce units to plant the rear of a wild MR2? So, what would interpret as a realistic value for road cars? Just because a car *can* achieve something, it should be obvious to you that they wouldn't implement it.
 
Rotary Junkie
Methinks that he finds himself a better tuner than everyone else here, or am I missing something?
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No.
Rotary Junkie
Right, and in-game they're modeled as having 13 units of front and 18 units of rear downforce... If memory serves. Might be a good starting point, yes?
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There's a major disconnect between rally cars and road cars. Rally cars do use high downforce, which is especially strong at the rear. The very high downforce at the rear prevents the car's nose from dipping when airborne. If you watch rally footage of contemporary cars, the rear will dip once the car leaves the ground.
nd 4 holden spd
I think stage 1&2 WR and no wing allowed is a good idea. Weight Reduction stage 1 and 2 are both replacing parts with lighter ones like you can easily do in real life yes? Stage 3 is a full lightened racing monocoque, not so street car like.
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Best-case scenario, you might be able to save 60-80kg by replacing parts with dry carbon or lightweight alternatives. That includes front and rear bumper, decklid, bonnet, racing seats, wing. But there's no way to reduce your car's weight by a consistent amount for every car; there's no control.
 
To quote Danoff from the Current Events subforum ... "I guess my gut is broken". Here's the way I look at it.

In GT4, fast racecars run approximate values in the range of 55F/75R

Rally Cars, according to most of what I've been able to find in some (admittedly limited) searching today, don't use much downforce - yes, they use more than a bone-stock road car. But relative to a full-blown racer? Nowhere in that league. In GT4, PD interprets this as 13F/18R

The very small wing on the bone-stock R34 makes 5R just by itself. No doubt a real tuner is going to employ a wing that produces significantly more than factory downforce when doubling, or in some cases, tripling the power of the car in question, ESPECIALLY if he's on street-compound tires.

All of this together suggests that figures of 6, 8, even 10, are probably on the low side.

<edit> Rally racing is a field of racing in which privateer teams are among the most profligate. It would then stand to reason that rally levels of downforce are easily acheivable on a realistic budget. After all, downforce is produced by nothing more than an airplane's wing turned upside down. They're not difficult to make or buy.
 
this bickering is pointless. there is a way to apply downforce on a car without that hideous GT-wing, atleast it works in real life. I've also tested it extensively recently, and it works in most of the cars. wingless car might not produce as fast laptimes as one with wing and max downforce, but atleast it'll let you feel and notice the hard work gone to the suspension tuning.
 
I don't think this is bickering - we simply want to find an acceptable range of downforce. I find it to be interesting - apparently so does setsunakute. If we use it for the challenge or if we don't, that's cool. Either way, it's one of the GT4 settings continuums that there's not a lot of concrete accounting for. Investigating it can't hurt 👍
 
CraftyLandShark
The very small wing on the bone-stock R34 makes 5R just by itself. No doubt a real tuner is going to employ a wing that produces significantly more than factory downforce when doubling, or in some cases, tripling the power of the car in question, ESPECIALLY if he's on street-compound tires.
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The rear spoiler of a BNR34 is fully adjustable; your value of 5 is mostly likely derived from the posterior flap adjusted to the maximum angle of attack. Using an aftermarket wing, double the downforce? yes. Triple? No. You need to understand the reasoning behind Japanese street tuners, first. A new rear wing helps keep the rear stable on mid-speed corners and, to some effect, low-speed sections by reducing the tendency of the rear breaking out. They don't install a new wing *just* to produce tire-crushing grip. 'Why?' Because they don't substitute slightly increased tire widths or suspension adjustments with downforce; it's a quick ticket out of perseverance and satisfaction behind working hard on building a balanced and competitive car. But I digress. I'm not offering a defense for my tuning belief in (relatively) low/medium aerodynamic aids and greater dedication in working with the rest of the car. But if you need evidence, question why a JGTC race car has such a hard time achieving 300km/h. Mechanically, the drive gears, powerplant and light weight are well capable of it in a flash. I don't have a PlayStation right here in front of me to validate their GT4 downforce units, but, scale back the numbers to about half that amount and you'll still feel a markedly heavy resistance to speed. That's something road cars (pro street or otherwise) avoid.
 
setsunakute
The rear spoiler of a BNR34 is fully adjustable; your value of 5 is mostly likely derived from the posterior flap adjusted to the maximum angle of attack. Using an aftermarket wing, double the downforce? yes. Triple? No. You need to understand the reasoning behind Japanese street tuners, first. A new rear wing helps keep the rear stable on mid-speed corners and, to some effect, low-speed sections by reducing the tendency of the rear breaking out. They don't install a new wing *just* to produce tire-crushing grip. 'Why?' Because they don't substitute slightly increased tire widths or suspension adjustments with downforce; it's a quick ticket out of perseverance and satisfaction behind working hard on building a balanced and competitive car. But I digress. I'm not offering a defense for my tuning belief in (relatively) low/medium aerodynamic aids and greater dedication in working with the rest of the car. But if you need evidence, question why a JGTC race car has such a hard time achieving 300km/h. Mechanically, the drive gears, powerplant and light weight are well capable of it in a flash. I don't have a PlayStation right here in front of me to validate their GT4 downforce units, but, scale back the numbers to about half that amount and you'll still feel a markedly heavy resistance to speed. That's something road cars (pro street or otherwise) avoid.
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I referenced using more downforce to compensate for double or triple the power - not doubling or tripling the downforce - and I understand the purposes and effects of a wing beyond producing grip.

Yes, you're looking at insane amounts of downforce in a JGTC car. As such, in GT4, they're significantly higher than the "30/30" values allowed for road cars. This is only because they are bigger. In the formula for downforce, wingspan, wing height, AND AoA are parenthetically factored together as equally important values, which gives me an idea, actually. The R34's wing is adjustable, yes. The most downforce it will produce in GT4 is '5'. It's also small. This won't be strictly scientifically accurate, but using the formula for downforce, it may get us in the ballpark we're looking for.

The formula for downforce (ignore, for now, velocity, air density, and drag coefficient as they'll remain constant) is as follows:

Downforce (in newtons) =1/2(span*height*AoA)*CoD*density*m/s^2

We should be able to find this data for the R34. From there we can determine what an R34's wing set to maximum AoA will produce, in newtons, at a given speed and air density, using the R34's actual drag coefficient, and call that figure "5".

Things get unscientific here, but it should be accurate enough for our purposes. We have to estimate the height and span of a GTAuto wing on the R34. Span is no problem - should be the same as the stock unit, perhaps with another cm or two on either end. Height we'll hazard a best-visual-guess at. Assuming that the maximum AoA of the stock wing is the practical maximum of AoA one would want to use on the aftermarket wing, we then run the equation again. This gives us a figure in newtons that should be in the neighborhood of the practical limit of downforce used on the larger wing. Using the Newton:GT4 Unit scale we determined from the stock wing, we convert the GTAuto wing value from newtons into GT4 units, and we have, if not a strictly scientific answer, at least a good ballpark figure for rear downforce. From there, we derive the corresponding front downforce by observing the gap GT4 suggests in cars that have both stock F and R downforce values.

Worst case scenario: GT4 has the whole scale severely generalized, the GT Auto wing's assumed size has no bearing on how PD measures downforce, and the formula proves to be of no value.

Best case scenario: We find a good correlation, that yeilds useful data on how downforce operates in GT4. Nothing ventured, nothing gained!

<edit> with great thanks to Greycap, I've now got AoA, height, span, and breadth measurements for the R34's factory wing. It's likely that this is a vain effort as PD has probably oversimplified downforce, but we shall see!
 
The calculations, bearing in mind some of these values are reasonable estimations, not hard measurements:

I used an '02 R34 Skyline GTR V Spec II Nur. When referring to the "GTAuto" wing, I'm referring to the 3D Type B family, as it seems to represent a good "median" in the size ranges of the GTAuto wings.

Based on the dimensions of the car, the relevant measurements of the downforce-generating surfaces of each wing, excluding the strakes, and with height measured from the ground, appear to be approximately the following:

OEM Wing: 1.5m wide x 1.2m high - the car's width measured across its widest point, the rear fender flares, is quoted in the game as 1.785m. The OEM wing spans only from approximately taillight-to-taillight. The height of the car quoted by the game is 1.360m. The OEM wing surface falls approximately 3/4 up the rear glass.

GT Auto Wing: 1.775m wide x 1.360m high - it spans very close to the entire width of the car, quoted in the game as 1.785m. The height from the ground of the tallest point of the wing surface excluding the strakes falls nearly dead even with the roofline - car height quoted in the game is 1.360m.

The approximate angle of attack of the OEM wing surface at its most extreme setting is 30 degrees.

Air denisity at 20 degrees celsius, at sea level, measures 1.2 kg/m^3
For our calculations we assume a speed of 150 kph, or 540 m/s

Finding the correct CoD values for each side of the equation is tricky, and inexact. I typed out my entire justification (concerning relative surface areas of the the wings at their given AoA, and the effects of such on CoD) for my estimation, and re-read it to find it was nearly two pages long. If anyone is curious or questions its (semi)accuracy, I'll be glad to provide the justification by PM. Sufficed to say for now, the coefficient of drag with the GT Auto wing seems highly likely to increase by approximately .10.

OEM wing:

D(n)=1/2(1.5*1.2*30)*.40*1.2*540

This gives us (rounded) 6.739 kN. We now liken this to the effects of a GT4 value ("GT4d") of "5" given our constant atmospheric conditions and speed.

GT Auto Wing

D(n)=1/2(1.775*1.360*30)*.50*1.2*540

This gives us (rounded) 15.642 kN

As 6.739 kN : 5 GT4d; 15.642 kN : our final estimated value, which is...

8.7 (rounded), which is near enough to 9 in GT4 terms to round to 9.

So in the case of the Skyline, assuming that the measurements used are relatively accurate, 9 is the approximate amount of downforce you'd get out of a GTAuto wing assuming it used the exact same Angle of Attack as its OEM counterpart.

Real-world tuner cars often operate on higher angles of attack, however. Let's assume we bump the angle of attack on our GTAuto wing up just ten degrees, to 40, which produces a coincident increase in drag coefficient. I won't retype the formula for the sake of brevity but feel free to check my calculations. This puts you at 11.6 GT4d.

Here's the most important bit:

Now, we check the relative validity of what we've done. Using a realistic maximum practical AoA, 70 degrees, and accounting for the coincident increase in drag, we should come out close to 30. When I run the numbers, I get 28.435.

While this is certainly not definitive since so many of these figures are estimations, they're educated estimations. This tends to give the impression that the wing adjustment range in GT4 operates on relatively sound aerodynamic principles, unless I've just produced an off-the-wall coincidence.

As such, it seems that if we use downforce in the upcoming Touge Challenge, we can feel safe setting a cap based on research we do as to actual A'soA and wing sizes used in real-life builds similar to what we want to produce.
 
Thanks man! But like I said, it's pretty inexact... in particular, I had trouble properly quantifying the change in the car's overall CoD from one wing to another. The justification for that came in the section I had to omit for length, but to very briefly outline it: I ended up basing it on comparisons between the R32's single-plane wing and the R34's double-pane wing at different AoA from some Best Motoring test data, applying that to GT4's "3" for the R32 wing and "5" for the R34 wing, taking the rates of change derived from that, and applying it to the change between the R34 wing and the GT Auto wing... so if there's a really serious error, that's where it's going to be. There's a lot of steps there with a lot of room for error, especially in calculating the relative surface areas of all the wings.
 
Yeah, but it's still beyond me to do any of that. Sounds like a pretty good thing you did though, it can't be that far off.
 

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