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Hello.

I am currently working on simulating an R34 as a free mod for the commercial racing simulator Assetto Corsa.

The engine is capable of simulating MacPherson strut, Double Wishbone and live axle natively. Of course, very similar performance can be achieved with DWB if one wants to simulate a trailing or semi-trailing arm, multilink in the front or rear etc. so the engine should have no problem at all simulating the geometry of the GT-R. The front end looks tricky due to the camber links but I think I can do it with enough data. The rear is essentially a DWB if the engine is concerned.

At the end of the post is a picture of what the suspension looks like in the dev tool, and the current properties. Also some ingame shots, just so any R34 or GT-R owner in general can spot if anything is terribly wrong. I am going on very limited data here: some scarce measurements I found and one or two pictures. Not very ideal at all.

Despite that, because most of the rest of the car is very well simulated and accurate, it handles and feels a lot like a GT-R with very similar performance and characteristics. It's just not quite there yet. Plagued by a tad bit too much natural understeer, and considering my aerodynamics are 98% accurate or so and everything that affects the handling of the car is pretty much as close as one can get it, it has to be the suspension geometry.

I have compared real life wheel cam videos and the simulator, and the wheel movements are pretty close, but I can clearly see some differences, and I am sure this is where the real GT-R's superior handling comes from. I cannot just simply go and change values as I please to achieve the handling because utmost realism is of concern here, so any measurements and GOOD pictures of the stripped suspension in neutral position is very appreciated.

I cannot record a lap in the car right now for reference, but it is *reasonably* close, but not quite there.

INSTRUCTIONS FOR MEASUREMENTS:

The suspensions.ini for this sim is a text file which the game then reads to place the pivot points of the suspension and does the simulation on those.
Camber, caster, toe etc. is calculated based on the physical locations of the steering and control linkages and camber and toe can be adjusted individually of the steering itself. You don't need to adjust the tie rod positions every time, the game does that for you, you just feed the correct numbers in. thus producing the ability to change toe and camber in-game. Caster is not adjustable outside the dev tool due to the complex nature of the simulation.

In the dev tool, the red lines are upper wishbones, and yellow lines are lower wishbones.
The long, vertical red line is the strut in the MacPherson strut. The blue lines are tie rods/steering linkages.
The circular things are a rough representation of the wheel + tire.
The arrow is the CoG of the car, base of the body and the direction indicator as well.
The blue crosses are the instant centers of the suspension, and bumpsteer is removed,with my method, by lining up a ruler to the screen and adjusting until your steering linkages point at the IC's. :chuckle: The front IC is outside the wheel, very uncommon to cars like this, so I am very sure my front end geometry is not right, I might need to simulate the camber links with DWB.

Links cannot be added as one wishes, only STRUT and DWB are valid in this case.

The way the engine calculates the positions of the links is simple:

You input in a wheel + tire diameter and CoG, and you then "draw" the linkages from the very center of the wheel in the Y, X and Z axis. Connection points to chassis and the wheel are indicated, obviously.

It goes as follows, for example: 1.0, 0.1, 0.01. This would mean that the pivot point of that particular link is ONE METER towards the INSIDE of the car from the wheel in the X axis ONLY (This is not lenght!), it is at TEN CENTIMETERS of HEIGHT from the wheel's center (Height in 3D space, not above the wheel) and it is ONE CENTIMETER in front of the wheel towards the front of the car.

You input in the position of a pivot point in 3D space, not the length or anything. Those are useless here.

So to measure the X axis, you would:

Line up your measuring tool with the middle of the wheel and pull HORIZONTALLY towards the inside of the car. Then with the measuring tool extended, you pull another straight object, like a ruler, 100% vertically down towards your measuring line, and if you did it right, you get the distance from the middle of the wheel to the position of the linkage in the X axis only.

You DO NOT measure the straight line distance from the middle of the wheel to the pivot point of the linkage.

Width, stiffness etc. of linkages is not desired and not even needed or simulated. They are represented as straight lines made of indestructble material, basically.

INSTRUCTIONS FOR PICTURES:

Please provide pictures directly from in front, behind, top, under if possible and the sides if there are visible wishbone or strut angles. Very good pictures can provide a reasonably accurate simulation.

NEEDED MEASUREMENTS:

Beginning and end of upper and lower wishbones to the pivot points. Beginning and end of strut. Beginning and end of tie rods/steering linkages. That is all needed to simulate the car as far as the engine will take it.

As accurate measurements as possible, but we can get away with even 1cm of inaccuracy, but 1mm would be pretty much ideal.


Thank you very much to anyone who contributes. Assetto Corsa is getting the Nissan GT-R very soon, with ATTESSA ET-S simulation, so this will be even better, then. HICAS is not currently supported, but I do not believe it has that much of a profound effect.

The 3D model is not mine, I am just making the physical model for the car.

(Once I have 3 posts, I will post an image album with pictures of the suspension in the viewer and the game.)
 
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