View unanswered posts | View active topics It is currently Thu Oct 18, 2018 4:36 am



Reply to topic  [ 12 posts ] 
 Discussion thread: Believeable/Realistic car physics 
Author Message
User avatar

GeneRally Carmaster

Joined: Tue Dec 29, 2009 3:55 am
Posts: 1121
Post Discussion thread: Believeable/Realistic car physics
Hi all,

Decided to start up this thread to get some discussion on "realistic" car physics. Even though GR isn't a sim at all, I wanted to bring car physics that were very different from the high-power and sliding physics typical on most user's cars.

Power
According to a carmaking tutorial on the F1Cup site, power is actually measured in kilowatts (kW) rather than horsepower (BHP/HP), the commonly agreed belief on the vast majority of carmakers. However, to me, using either BHP and kW would make cars accelerate very slowly, moreso for heavy American V8-powered muscle cars (which were known for at least respectable 0-60 times). Therefore, I used the SI unit measurement of torque (nM) for the power value on all of my cars.

Weight/Mass
Everyone thinks it's kg. I agree... except that with commonly used slowdown values, this makes cars again very slow. My common solution is to half the mass for the GR model's weight (this is the setup used for all of the FMGR cars).

Slowdown
Slowdown as its name implies controls how much the car's top speed is limited (some kind of magic value). I used to use the common slowdown value of 0.1 on tarmac, but 0.01 allows cars to go much faster. On dirt and ice, I use 0.02, and on sand and snow, I used 0.05.
Grip helps to counter the small slowdown values.

Grip
Used to be wild guessing.

Then I developed a formula (still in refinement) for tyre's tarmac grip, so that I would not have to guess the amount of grip.
It factors in three things:
1) Front tyre's width (A)
2) Rear tyre's width (B)
3) Compound from 1 to 9... (C)

- 1 being crappy gripping "Economy" tyres
- 2 being whateverish "Comfort" tyres
- 3 being mediocre "Road" tyres
- 4 being OK "Sport" tyres
- 5 being fair "Super" tyres
- 6 being good "Semi-Slick" tyres
- 7 being "Racing Slick Hard" tyres
- 8 being "Racing Slick Medium" tyres
- 9 being "Racing Slick Soft" tyres

The formula comes out like this:
(0.7+(C*0.1))+((A+B)*0.001)

...so if we use...

235 mm tyres front
275 mm tyres rear
Super road tyres


(0.7+(5*0.1))+((235+275)*0.001)

Our tarmac2 grip is 1.71.

For tarmac1, use this guideline if you are using my formula:
If the compound/tread type is less than 6 (road tyres): Tarmac2-0.1
If it's a racing tyre (compound value more than 5): Tarmac2-0.2 (it's because of "marbles" effect)
Historic tyres (pre-1980) have a -15% grip penalty.

Off-road values
- For racing tyres, the grip on any non-kerb or non-tarmac surface should not exceed 0.6, on kerbs, it should be the respective tarmac grip -1
- For road tyres, the values vary on the compound:
Gravels and Sand: 0.6 (Economy), 0.725 (Comfort), 0.85 (Road), 0.725 (Sport), 0.65 (Super)
Mud and Snow: 0.4 (Economy), 0.55 (Comfort), 0.7 (Road), 0.6 (Sport), 0.5 (Super)
Ice: 0.35 (Economy), 0.5 (Comfort), 0.65 (Road), 0.55 (Sport), 0.45 (Super)
RWD cars: -0.05 less grip on all off-road surfaces.
FWD cars: No grip penalties/bonuses.
4WD cars: +0.05 grip on all off-road surfaces.

Air Resistance
As a general guideline, if the real drag coeffiency is not availible, use a value that is somewhere between 0.28 and 0.5. Excepted are very large and normally non-aerodynamic vehicles such as 18-wheelers. Some futuristic automobiles also have drag coefficients that are less than 0.27. "Blockier" cars should have more air resistance, more round and "streamlined" shapes should have lower values.

Downforce
Downforce influences the cornering at medium and up speeds mostly, but mildly influences low end as well. Higher downforce increases the grip at speed and will not change if you, for instance, slide the car. This means you will always have a steady 'flow' of downforce, which can allow you to tune out bad sliding behaviors.

As a general guideline, refer to the table below:

No downforce - Most production cars. Examples: Your grandpa's station wagon.

5-15 downforce - Common sports cars with spoilers. Examples: Subaru Impreza WRX STi (all production models), Ford Mustang Cobra R, Toyota Supra, etc...

15-30 downforce - Mid-range sports cars with spoilers and/or undertray diffusers. Examples: Ferrari F430 Scuderia, Porsche 997 Turbo/GT2, Chevrolet Corvette ZR-1 2009, etc...

30-80 downforce - Moderately modified versions of the low-end sports cars, and supercars. Examples: MINE'S Skyline GT-R (R34), Mugen S2000, Lotus Sport Elise, Ferrari F40, etc... NASCAR falls under this group as well.

70-115 downforce - Ultimate track-day oriented supercars and racing-type touring cars. Examples: BMW Motorsport Team Germany 320si Touring Car, Ferrari FXX Evoluzione, McLaren F1 LM (road car), Edo Competition 997, HKS Evolution "Time Attack", etc...

100-140 downforce - FIA and ACO based GT2 and GT3 racing cars, and FIA's WRC rally cars. Examples: Flying Lizard Motorsport 997 GT3-RSR, Risi Competizione F430 GT, Spyker Squadron C8 GT2, Subaru Impreza WRC 2008, Citroen C4 World Rally Car, etc...

130-150 downforce - FIA and ACO based GT1 racing cars from after 2000. Examples: Vitaphone Racing S7-R, AF Corse MC12 GT1, Aston Martin Racing DBR9, Chevrolet Corvette Racing V6.R GT1, etc...

150-165 downforce - All JAF SuperGT/JGTC based GT300 racing cars and all DTM post-2000 and pre-1994 cars. Examples: ARTA/ASL Garaiya, Studie-Glad Asada Racing Z4M, Audi A4 DTM, etc...

155-175 downforce - All JAF SuperGT/JGTC based GT500 racing cars and all DTM cars from 1994-1999. Examples: Xanavi Pitwork Motul Z, Alfa-Romeo 155 DTM, Opel Calibra DTM, etc...

170-190 downforce - ACO based LMP (any class) cars. Examples: Audi R8 LMP, Audi R15 TDI, Peugeot 908 HDi FAP, Pescarolo C60, etc... Also, any of the GT1s from between the years 1994 to 1999 fall under this category. Most modern open-wheel cars that push beyond 400 bhp and do not compete in F1 will likely fall into this category.

180-200 downforce - All FIA based Group C (any class) cars. Examples: Mercedes-Sauber C9, Toyota Minolta 88C-V, Mazda 787B, Jaguar XJR-8, Nissan R89C, etc...

200+ downforce (Strava's editor) - Pretty much any F1 car after 1972. Modern-day Indy and Champcars will fall under this category, too. Other notable examples include the Chaparral 2J Chevrolet and the Porsche 917/30.

Sliding
I find sliding value not very useful. I almost always set it to zero since most of my cars have enough grip to slide on their own anyway.

Balance
Dependant on the weight and drive of the car - the heavier it is, the lower it should be...:
FF (front engine, front wheel drive) : 0.5 to 0.8
FR (front engine, rear wheel drive) : 0.5 to 0.9
MR and RR (mid/rear engine, rear wheel drive) : 0.6 to 1.0
4WD: 0.5 to 0.9

Other stuff
Y-value in "Car Data" influences the center of gravity.
Driver's head can be used to influence the center of gravity (thanks Krisu).
Try messing around with wheel placement to fine-tune handling (fictional cars).

Interesting stuff
Tyre width
- JGTC/SuperGT cars in the GT500 class will typically run 300 mm wide tyres on all four corners.
- FIA/ACO GT1 cars will almost always run 300 mm (front) / 330 mm (rear) wide tyres.
- FIA/ACO GT2 cars will almost always run with 290 mm (front) / 300 mm (rear) wide tyres.
- Typical production cars will run anywhere from 175 to 235 mm.
- Most sports cars will run 255 mm to 305 mm tyres, with exceptions of smaller cars such as the Lotus Elise.

Drag coefficents
- Typical examples
- Carfolio also has drag coefficients for several cars not covered by Wikipedia

Tyre grip and slowdown
- Because paint reduces friction of a surface, tyre grip worsens when driving on painted tarmac and/or trackside "kerbs". This effect becomes far worse if said painted surface becomes wet.

Hope this provokes some discussion.

Haruna.

_________________
"In my world, we don't have enemies. Only rivals.
In my world, our dreams become REALITY."

-- World Endurance Championship 2015 Promotion


Last edited by Haruna on Mon Mar 01, 2010 2:51 am, edited 5 times in total.



Mon Mar 01, 2010 1:34 am
Profile E-mail
User avatar


Joined: Mon Dec 28, 2009 10:26 am
Posts: 1117
Post Re: Discussion thread: Believeable/Realistic car physics
WoW!!!! Really better than the one I made some time ago! :wow: I'd suggest to put the tittles in bold though... :roll:

I'd have a try at some VB prog that could calculate the grips with your formula, if you agree that I use it, off course... :bg:


Mon Mar 01, 2010 2:15 am
Profile E-mail YIM
User avatar

GeneRally Carmaster

Joined: Tue Dec 29, 2009 3:55 am
Posts: 1121
Post Re: Discussion thread: Believeable/Realistic car physics
Hi TGF,

Of course you can write a program which does all of the "hard work".

It should also be noted that the formula for tarmac2 grip can also easily be adapted into a formula that can be used in Microsoft Excel (works) and OpenOffice (untested).

Cheers!
Haruna.

PS.
I will upload a few cars demonstrating my physics setup later for those willing to try it out.

_________________
"In my world, we don't have enemies. Only rivals.
In my world, our dreams become REALITY."

-- World Endurance Championship 2015 Promotion


Mon Mar 01, 2010 2:20 am
Profile E-mail


Joined: Sat Jan 02, 2010 2:40 am
Posts: 1311
Location: Parallel World
Post Re: Discussion thread: Believeable/Realistic car physics
AWESOME!! SO INFORMATIVE :bg:

_________________
Hi! I'm Rendy, and welcome to GeneRally!

GeneRally Catalogue - [R]GARAGE - Twitter - Blog


Mon Mar 01, 2010 10:03 am
Profile E-mail YIM WWW
User avatar

GeneRally Trackmaster

Joined: Tue Dec 29, 2009 6:37 pm
Posts: 4725
Location: NRW in Germany
Post Re: Discussion thread: Believeable/Realistic car physics
I've got a short Question
Haruna Say wrote:

Grip
The formula comes out like this:
(0.7+(C*0.1))+((A+B)*0.001)


Is this for all cars the same or just for your formula?
And what about the topspeed? since now I used kph*0,277777777..... and I don't know if that is right
btw it seems to be great :woohoo: :bowdown: I'll just test it for my pontiac firebird ( viewtopic.php?f=7&t=3&start=80 ) :flip:


edited:
Now i've tested it and it's great :banana: My muscle car has got really great values!! :loveyou: (i'm not gay :lol: )

_________________
My e-mail-address:xyyverwaltung@googlemail.com
Last track: deRUkt89.-Z+ - Last car: Ford Falcon GTHO Phase III


Mon Mar 01, 2010 12:02 pm
Profile
User avatar


Joined: Fri Jan 08, 2010 10:38 pm
Posts: 694
Location: Finland
Post Re: Discussion thread: Believeable/Realistic car physics
Generally is science.


Mon Mar 01, 2010 1:35 pm
Profile E-mail
User avatar


Joined: Mon Dec 28, 2009 10:26 am
Posts: 1117
Post Re: Discussion thread: Believeable/Realistic car physics
Ok, so far, my prog can create grip values for all the surfaces, thanks to that wonderfull functions I found yesterday (y=(-1/16)*(x-4)^2+1.8)... I gonna have a try at doing some congruent Power/Mass values... Then the slowdowns will be tried... Obviously, copy/pasting this into CE would be quite painful so maybe I'll have a try a creating .CAR files with the informations in... I'll need help for that... :ugeek:

I'll first release the thing Friday :bg: I cannot actually upload it...

EDIT: All done but not the slowdown values...


Mon Mar 01, 2010 4:00 pm
Profile E-mail YIM
User avatar


Joined: Mon Dec 28, 2009 10:26 am
Posts: 1117
Post Re: Discussion thread: Believeable/Realistic car physics
:yummy:

Improved version coming someday...


Attachments:
HPC.rar [21.99 KiB]
Downloaded 194 times
HPC.PNG
HPC.PNG [ 16.05 KiB | Viewed 4172 times ]
Fri Mar 05, 2010 6:18 pm
Profile E-mail YIM
User avatar

GeneRally Carmaster

Joined: Tue Dec 29, 2009 3:55 am
Posts: 1121
Post Re: Discussion thread: Believeable/Realistic car physics
The Great Falcon wrote:
:yummy:

Improved version coming someday...


Thanks. Could use more refining though:
- All non-Slick/SemiSlick tyres have more grip in gravel than on road.
- Racing slicks + RWD generates negative grip in ice, which cannot be used in Juan's Car Editor (no problem with Strava's/Stephen's one but Juan's is more commonly used)
- Soft Racing Slicks' offroad grip is very low, while Hards have rediculous grip
- Semi-Slick has crazy high grip offroad except in ice.
- Tarmac grip is a little on the low side for non-slick tyres.

_________________
"In my world, we don't have enemies. Only rivals.
In my world, our dreams become REALITY."

-- World Endurance Championship 2015 Promotion


Fri Mar 05, 2010 8:30 pm
Profile E-mail
User avatar


Joined: Mon Dec 28, 2009 10:26 am
Posts: 1117
Post Re: Discussion thread: Believeable/Realistic car physics
Haruna Say wrote:
Thanks. Could use more refining though:
- All non-Slick/SemiSlick tyres have more grip in gravel than on road.
- Racing slicks + RWD generates negative grip in ice, which cannot be used in Juan's Car Editor (no problem with Strava's/Stephen's one but Juan's is more commonly used)
- Soft Racing Slicks' offroad grip is very low, while Hards have rediculous grip
- Semi-Slick has crazy high grip offroad except in ice.
- Tarmac grip is a little on the low side for non-slick tyres.

Any tarmac grips are taken right from your definitions... up there... :sweatdrop:

Anybody can understand that negative value on ice means 0.1(lowest) in Juan's editor :bg:

And, yeah, maybe the grip is a bit high on dirt... :scratch:


Fri Mar 05, 2010 8:46 pm
Profile E-mail YIM
User avatar


Joined: Fri Nov 05, 2010 9:33 am
Posts: 432
Location: United Kingdom
Post Re: Discussion thread: Believeable/Realistic car physics
I wanted to post to say thank you, Haruna. This guide was a great point of reference for me when I was making my more recent cars(recent as in within the past two years.). Since I came back you've become my personal favourite carmaker.

I also came to post to ask- do you consider this guide relevant anymore? I notice in your released car threads, you state you keep refining your physics calculations and that you hate all your old physics.


Mon Nov 05, 2012 5:34 pm
Profile
User avatar

GeneRally Carmaster

Joined: Tue Dec 29, 2009 3:55 am
Posts: 1121
Post Re: Discussion thread: Believeable/Realistic car physics
ACM wrote:
I also came to post to ask- do you consider this guide relevant anymore? I notice in your released car threads, you state you keep refining your physics calculations and that you hate all your old physics.


In my opinion, the guide is now more or less irrelevant, at least to my physics calculation models. There's many more variables at play.
To say without spilling the "secret sauce":

Aerodynamics
Because the cars in Driving Passion (cars from Haruna's GT Carpack v2, V8 Supercars Cars of the Future, etc...) use actual dimensions and proportioning, we can assume that cars with a larger length and width will generate more negative lift (downforce) than smaller cars of the same aerodynamic style and tech.

Since cars have all sorts of aerodynamic configurations, technologies, etc., I created separate formulas for three components: the underside of the car (under-body, like diffusers, ground effect, etc.), front wings/splitters, and rear wings. Additionally, these are subject to "technology scaling" which is dependent on complexity of the car's aerodynamic tech: Le Mans Prototypes are considered more complex than a NASCAR stock car, which is more complex than a grandmother's station wagon, etc.

Additionally, it's not always possible to find drag coefficients for all vehicles ever made, so a reasonable approximation must be made: we consider the frontal area (length x height) and then use length as a multiplier. Longer cars are penalized less. If a real figure for the drag-coefficient is found, an additional scaling factor is placed to bring the car to that number.

Some figures from the Excel file I've created for all of the car settings:
(name), (lift @ 200 km/h), (GR value), (car type)
Peugeot 90X, -2160 lbs lift, 332 DF/W, Le Mans Prototype
Saleen S7-R, -1491 lbs lift, 229 DF/W, FIA/ACO GT1
Ford Falcon V8SC, -726 lbs lift, 112 DF/W, touring car
Koenigsegg CCX, -257 lbs lift, 40 DF/W, supercar
Nismo 350Z, -226 lbs lift, 35 DF/W, tuner car*
VW Lupo Cup Car, -37 lbs lift, 6 DF/W, hatchback*

*These cars should actually generate lift, but because of playability reasons, they simply have very little downforce instead.

Chassis and Tires
Here's a short section on how I arrive at my balance settings for each car.

It's determined by three factors:
- Frontal weight
- Curb weight
- Tread width

The last two are usually easy to find, the first one is almost always a ballpark figure if a real one cannot be found. Regardless, a lower frontal weight value will yield higher balance, as will lower curb weight. Increasing tread width also increases response (unique steering angle is not "simulated" in GR, so I use this).

More importantly, grip is also determined by frontal weight and tread width. More tread on the axle with more weight means more grip, of course. Some multipliers are in place for different surfaces (tarmac, worn-in tarmac, and off-road). Two separate multipliers for tire softness and tread amount determine the grip on each surface type.

Data Requirements for DP cars
    Peak power (break horsepower)
    Curb weight (kilograms)
    Drivetrain (if weight distribution cannot be found)
    Frontal Weight
    Tread widths
    Three-sizes (length x width x height)

_________________
"In my world, we don't have enemies. Only rivals.
In my world, our dreams become REALITY."

-- World Endurance Championship 2015 Promotion


Tue Nov 06, 2012 8:10 am
Profile E-mail
Display posts from previous:  Sort by  
Reply to topic   [ 12 posts ] 

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group.
Designed by STSoftware for PTF.