GT4 - Redline Specifications

[Tomte]

EDIT:

BMW M Coupe, BMW Z4 M, Nissan 350Z and Porsche 968 are now all v1.0, the Cadillac is probably coming tomorrow.

---

Texture files for the BMW M Coupe and the Porsche 968 are up (in Photoshop and Gimp format)
BMW_M_Coupe_GT4_Body.zip
Porsche_968GT4_Body.zip

I reworked both UV maps, they should now be slightly easier to work with....

----
here the links to the current versions:
BMW M Coupe GT4 v1.0
BMW Z4 M Coupe GT4 v1.0
Cadillac XLR GT4 v0.9
Nissan 350Z GT4 v1.0
Porsche 968 GT4 v1.0
----

As I wrote in that other topic somewhere here, I'd like to see some GT4 racing in Redline.
This tread should focus on the technical aspects of the cars, their limitations and how to balance the performance for close racing.
It looks like that the real GT4 class only contains of coupes and open two seaters (no Caparo T1 please ).

So the main aim is to have a class or group of cars which are balanced in terms of on track capabilities, but with different driving characteristics. The parameters I will outline here are only suggestions, nothing more.

In the spirit of the amateur GT4 races, we can only allow certain modifications to (already existing?) cars.
Proposals:

• Weight: Minimum weight is 1000 kg. If you find information on real GT4 cars (like in the source mentioned earlier), use that. It seems like GT4 cars have a power to weight ratio of about 3.2 to 3.6 (supersport like Lotus Exige not counting). Therefore, the cars will be quite a bit lighter than the stock cars. Add 100 kg for fuel and driver after the power/weight calculations.
  While in the real racing class exist additional balast weight for performance eqilibration, I'm not sure it would be good for Redline, as this would require refiddling the suspension settings (and inertia, but to a lesser extend).
  
• The body work remains unchanged, which leads us to the next point.
  
• Downforce No additional downforce enhancing wings, flaps, air dams, diffusors can be added. If the car has already some sort of wing, they obviously can be retained. Given that the TCC cars have a total downforce of about -0.2, I prefer to have no downforce. The cars can have as much lift as they want. We could use this parameter to balance the cars later.
  
• FrontalAirResistance: as we run the cars without additional wings, we can use production car values. Lowering the car won't make much of a difference I presume.
  
• Ground clearance: about 0.1m. We should try not to let the cars bottoming out, but neither do we need cars with SUV style ground clearance.
  
• CoG As with the TCC cars, the weight will be removed mainly from the interior and the rear of the car, thus the CoG should shift forward a bit. Body panels remain the same, but side and rear windows can be replaced, therefore I guess the CoG could be lowered slightly, but stay reasonable.
  
• Ride height: use what you think is all right, but don't lower the car so that it looks unrealistic. Think about the ground clearance when setting wheels.position. We could use this parameter to balance the cars later.
  
• wheels.stickyness: GT3 has 0.2, TCC has 0.13. GT4 race cars should use a value inbetween. I'd say we start with 0.15.
  
• Wheel dimensions should be close to original spec, Pirelli has quite a good list of available sizes here (pdf, page 7). Max rim width 11inch, max rim diameter 18inch. We could use this parameter to balance the cars later.
  
• wheels.loadsensitivity ±0.07, but try too keep the original driving characteristics. We used the same in the TCC class.
  
• engine specs: if you can find specs of your car on the web, use them (for now). Possible source:FIA GT4 cars. We could use this parameter to balance the cars later.
  
• wheels.friction could be set to 0.5 in order to slow down the cars a bit. For now, this is just an experiment.
  
• Gear ratios: free, maximum of 6 forward gears
  
• Gear Change times: sequential gearboxes are forbidden, so gear change time will be higher than in GT3. I propose 0.4s.
  
• Brakes: as we don't have a lot of downforce, I'd say limiting the brake force appears to be useless, as the Redline ABS happily interferes anyway if you use too high values. Still, given that we have sticky tires, I'd say we go with a maximum of 17000 for the total car, but I'm not to sure about that.
  

I propose to present the GT4 cars somewhere around here in the development section of the LoL forum. A officially appointed tester (C.P.Frost, are you there???) could make performance trials, we all could give suggestions as to how to balance the cars.
What we need now is a benchmark car. Anyone, anyone, Bueller?Nissan 350Z GT4GT4 Test pack containing the BMW's, Cadillac and Porsche

[NoNameBrand]

I'm in for the C6 and FR500C.

[DonaemouS]

Brakes: as we don't have a lot of downforce, I'd say limiting the brake force is useless, as the Redline ABS happily interferes anyway if you use too high values. Given that we have sticky tires, I'd say we go with a maximum of 17000 for the total car, but I'm not to sure about that.

17000 is a value really close to the same i needing to brake the sedans. But I think is proportionally to the weight right? (higher the weight is, higher the brakes values must be)

[Tomte]

Brakes: as we don't have a lot of downforce, I'd say limiting the brake force is useless, as the Redline ABS happily interferes anyway if you use too high values. Given that we have sticky tires, I'd say we go with a maximum of 17000 for the total car, but I'm not to sure about that.

17000 is a value really close to the same i needing to brake the sedans. But I think is proportionally to the weight right? (higher the weight is, higher the brakes values must be)

I'm just throwing numbers onto the wall and see what sticks.
I'm all in favor of less is more when it comes to braking. I would not want to let the cars brake worse than they could by limiting their brake force. As you said, weight will be a limiting factor as to how much brake force can be applied.

[slowDan]

how to balance the performance for close racing.

The most important factor for close performance is the tyre grip. Setting a standard size (and of course stickyness!) would be a pretty simple way to get everyone close, but it might not look so realistic on some cars. Perhaps a standard tyre width would be good enough?

[Tomte]

how to balance the performance for close racing.

The most important factor for close performance is the tyre grip. Setting a standard size (and of course stickyness!) would be a pretty simple way to get everyone close, but it might not look so realistic on some cars. Perhaps a standard tyre width would be good enough?

This is how they do it in touring car races (and one make series obviously, I agree), but in GT4 you have very different cars competing with each other. So limiting a say C6 to say 265 rear wheels might be a bit too much, but for a 350Z it might be well enough. I don't want to overcomplicate things, so for example a width by weight and power ratio might be very hard to determine.

Maybe we already get a good initial balance when we adhere to the specs provided on the FIA GT4 webpage. That's what I meant with staying close to the original specs: either from the GT4 site or the widest tyres a manufacturer was putting on the production model.

Of course, what works in reality must not necessarily work in Redline, thus I'm very open to suggestions.

[C14ru5]

we can only allow [...] (already existing?) cars

...but for a 350Z it might be well enough.

Well, the 350Z isn't "already existing", unless someone wants to make a .car file for this:

[NoNameBrand]

I have a modelled 350Z and Japanese Super GT350 350Z, along with preliminary .car files for each. Never finished it because I got bored with it.

[C14ru5]

Yes, I also find the 350Z pretty boring. That's why I really don't want to work on any GT4 car now. I'd much rather finish the RS200.

While I'm already posting pictures of possible GT4 cars:



A thomm-free Caterham, a VX220 Opel replacement, a Marcos Mantis Gillet replacement, and a Morgan Aero 8 Donkervoort replacement. The rear wings will have to go, of course.

[theSnail .@y]

Well - I dont know anything about .car development, but I've been thinking about it for a while … I'd like to learn and give it a try.
If you all think the 350Z is boring, maybe you will let me do it ? I'll do my best, and I know where I can find advice !

[Tomte]

Snail, you can certainly ask for help, I'd be glad to show you around. Next thing we know is you programming a script for some random cars. Brilliant!

Please, all, don't feel restricted by the cars I meantioned. I guess as long as it is a coupe, it is good to go. I was just looking at the models we already have.
Generally, I'd like to see another Cat, the VX220, the Morgan and many other cars as well. They could well create another, albeit very close, racing group.

When setting up the MX-5, I noticed that the car in itself is not very exciting, but races against other MX-5 it is great fun. This is what I'm aiming for, like an all Mini race, just with different cars.

[NoNameBrand]

Morgan Aero 8 would be very appreciated in GT3!

And Snail, just shoot me a PM/email if you know it. I'll upload the project folder for the 350Z.

[C14ru5]

OK, I'll prepare the models and make a new topic in this forum when they're ready.

[theSnail .@y]

Ok NNB, PM sent

Tomte, a script is in the back of my mind of course - am I that predictable ? Hehehe …
But I want to write a .car for real before. This will teach me how things work before thinking of scripting them.

[Aleksi]

One question - is there any year limit (how old cars)?

[DonaemouS]

its just amazing reading all this involvement in the GT4 class...

let's see what will happens!

[Tomte]

One question - is there any year limit (how old cars)?

Screw age limits, it's the spirit that counts.

[theSnail .@y]

Did you know there's an official site with the cars specs ?
http://www.gt4cup.com/cars.php

See the presentation brochure in the download section too ...

[Tomte]

Yeah, I knew that page, one of my inspirations.

[Aleksi]

How to count power to weight ratio?

[Tomte]

How to count power to weight ratio?

you just divide the weight of the car (measured in kg) by the power (measured in hp). So a car with a weight of 1200 kg and a engine with 300 hp, it's
1200kg/300 hp = 4 kg/hp

Of course, you can use which ever unit for weight and power you want, kg/hp seems to be the norm in Europe.

[Tomte]

ok, question for the interested participants about 2 possibilities when it comes to gear ratios:
do you want free gear ratios or do you prefer stock gear ratios? I know of some cars who could really need some custom spec gears....

Now I know that we had a strict selection when doing the TCC cars, with GT3 cars doing with whatever seemed best.

I guess we have 3 options here:

1. We go custom spec with free final drive ratios and free gear ratios.
   
2. We use the production cars final drive ratio and free gear ratios.
   
3. We use the production cars final drive ratio and gear ratios from Hewland LSG-A gearbox: available in H pattern and it can hold up to 600 Nm (is that enought, NNB?). The gear ratios are a bit fuzzy to find, but this might hold it all. If somebody else figures out how to read this site, please say so. It's too late for me.
   
4. We use production car final drive ratios and gear ratios.

So that's 4 options. What will it be?

[NoNameBrand]

re: gear ratios

It's clear that a number of the cars in real life are using custom gear boxes. The C6 and Mustang both, for instance. I find it interesting that the C6 has a lower power/weight ratio than most of the cars and seems to be doing well this season. I guess handling counts for something...

[Tomte]

Ok guys, time for some action. I prepared a test mule for the upcoming GT4 class, a sort of benchmark car. The problem I'm having is that it is a bit too fast .

I used the old and trusted 968 platform, more specifically the 968 turbo S (without the R).

Changes from the road car include

• lower weight (-70 kg)
  
• slightly tuned engine (+35 hp)
  
• sticky tires (0.17)
  
• adjusted downforce (lowered from -0.125 and -0.15 to -0.04 and -0.05)
  
• new gear ratios using the Hewland LSG ratios and final drives (source)
  
• wheel dimensions close to road car (235/40 ZR18 and 265/35 ZR18 to 235/645 and 265/645)
  
• adjusted loadsensitivity to -0.015 and -0.025
  

Comparing to the qualifying times of this years GT4 round at Silverstone, the test mule seems to be some 4 seconds to quick. This year, a Ginetta G50 got pole position with a time of 2:02, I manage that time in just two laps and most of you are easily some 4 seconds quicker.

Important: You will find the car under "GT4 Test Mule" in the car selection screen.

I also started on a GT4 logo, an idea I briefly discussed with NoNameBrand. I thought we could all use the same door logo, with a space for the start number and a sponsor or team name.
Based on this logo, I also created a logo which we could use in front of the car names, for easier distinction.
All this is included in the zipped GT4 logo file. Of course, I'm no graphic designer, so don't expect beauty. If you come up with something different or you don't like the idea at all, just let me know.

And here we go:
GT4 Test Mule
GT4 Logos

Let me know...

[DonaemouS]

Thanks for the clarification, I feared that the car is just too fast. I had a look at what times we achive with the GT3 compared to real life qualifyung times.... we're a tad too fast there as well, as Dandy pointed out a while ago.
Now it's the question if we ignore it or if I slam the brakes on.

Well, I think, cause we are in early development yet, we can slow down the car. It's not a good start to have the Test Mule already breaking the "speed wall" of other real GT4.

[Sponsored content]