Vehicle Physics and Tire Dynamics in Just Cause 4

In this 2019 GDC session, Avalanche Studios' Hamish Young explains how Just Cause 4 copes with a wide range of vehicles and player styles though thoughtful design of its tire dynamics and how these relate to the overall vehicle gameplay experience.
Register for the all-digital GDC 2021: gdconf.com/pas...
Join the GDC mailing list: www.gdconf.com/...
Follow GDC on Twitter: / official_gdc
GDC talks cover a range of developmental topics including game design, programming, audio, visual arts, business management, production, online games, and much more. We post a fresh GDC video every day. Subscribe to the channel to stay on top of regular updates, and check out GDC Vault for thousands of more in-depth talks from our archives.

[@dbaron-gamedev]

Amazing talk, I'm working on a racing game prototype, really helps break down the math I needed.

[@bzdirt]

Nice talk! I only wish there were more video examples :) (and syntax highlighting in the code snippets)

[@DrTheRich]

It sounds like they ended up overcomplicating the fake physics in an attempt to make a simplified alternative to the real physics...

[@DigitalContentNetwork]

Wow. Very interesting, thank you for all your insights. Avalanche worked with ID or vice versa about RAGE 2. Great contributuon for that OpenWorld and its physics.

[@LB14745]

Just too bad that JC4 had the worst damage model in the series.

[@John_Conner_]

That and the physics despite what this guy said were pretty lack luster

[@DrTheRich]

@@John_Conner_ Sounds like in their attempt to circumvent proper physics, they created a more complicated fake system...

[@mmankt]

Great talk, was there live on this talk :)

[@sharikobe]

Isn't that Mad Max on the thumbnail? 🤔

[@AngleSideSideThm]

Nope it’s Just Cause, look at the rocket launcher on the character

[@DigitalContentNetwork]

Mad Max drives awesone.

[@LB14745]

Nah, MM didn't have such car.

[@PlebNC]

A wheelie good talk.

[@cgpilk]

It will really help accelerate your learning.

[@robertmcdowell6084]

It definitely steered me in the right direction.

[@BrightBitGAMES]

Regarding 12:48 Isn't total_wheel_load the same as vehicle_mass?

[@DrTheRich]

only in (vertical) rest, because it takes gforces into account, if the car drops down on it's wheels the wheel load is higher than the mass. if the car is flying through the air the wheel load is zero while the vehicle mass stays the same.

[@hakanviajando]

Thanks for the info, I wish I could understand that math

[@x-cry1036]

jc4 has some of the worst car physics. idk how to feel about this.

[@DrTheRich]

Sounds like in their attempt to circumvent proper physics, they created a more complicated fake system...

[@haha71687]

How does this system handle being stopped if all forces require slip?

[@borzonstudios8638]

When braking you generate slip, thus a braking force. That will slow down your vehicle until it stops

[@haha71687]

@@borzonstudios8638 I mean when parked on a hill. No movement, but still needs to generate force to keep from sliding. How do you handle that?

[@borzonstudios8638]

​@@haha71687 Phsysics explanation (1) and a game implementation (2). 1. On a hill, the car is tilted. This means you have a component of the force of gravity which acts in the longitudinal direction of the car. This wants to pull the car down the hill, but the static friction between non-moving tyres and ground generates elastic deformation on the tyres themselves even when you are standing still. Just like how you would deform the soul of your shoes if you tried to slide it. This elastic deformation generates a force. 2. In a game, I guess you would probably set an if statement. If the car is going less than a certain speed (say speed < 0.5 kph), then apply the static friction formula to the car/tyres. See Coulomb friction on wikipedia. I would probably do it like this.

[@ほしかわつくる-s7x]

I was waiting for the video of this session!

[@Allstreamer_]

Good talk but he says ahh a lot

[@kidShibuya]

This guy is why I get bored driving in most games. For a start everybody drives real cars while distracted, they are very easy to drive. The more sim the easier a car should be to drive. Give me understeer and oversteer FFS, keep it fun.

[@kubamax9kubowski176]

It’s different when for the most part most people will drive 50-60km/h on a normal day, while in most open world games players would easily push 200+ km/h on tight roads with lots of traffic. More realistic doesn’t make it easier, but there definetely has to be a good balance between realism and gameplay.

[@RocketPunches]

You know, you don't have to post something wrong in the comments of a video you didn't understand just because there's a field for it. You can, and should, just do something else with your life. You heard one line at the beginning of the talk about balancing the driving complexity with the gameplay complexity in Just Cause, a game with a high degree of freedom of movement that often interacts with vehicles, and decided this guy was making a boring driving system - while in reality most of this talk is about how to make a system that allows for developer control, solves for complex problems, and fits within a reasonable computational budget. You do not, in fact, have to be an asshole for no reason.

[@thatemocat]

Coping lol

[@latbat58]

Shouldve paid more attention to physics maths n geometry at school

[@windy3935]

Best _Just Cause_ entry in the series. Don't @ me.

[@jesustyronechrist2330]

This stuff requires way too much math and physics knowledge than my brain could ever muster. Cool stuff! (I guess?)

[@Nick-kb2jc]

But it’s all basic math and physics….

[@LB14745]

All these calculations didn't actually bring amazing and realistic vehicle physics to the game. That's all that matters at the end.

[@anonymouseovermouse1960]

​@@LB14745I do think that these explanations are a good resource for eg. hobbyists or indie devs looking for an example of how driving physics can be set up... but, yeah, it's just important to keep in mind that no Just Cause game has good vehicle physics, they're all just awful lmao

[@ECfuckingW22]

Jc4 handling sux

[@fuckugplus]

yeahhhhh.... like I care... i am flying