You’re sitting in your living room, controller in hand, and you just slammed the gas pedal in Forza Horizon 5. The G-force (or at least, the visual sense of it) presses you back into the virtual seat. The engine roars, the tires scream, and the speedometer climbs. It feels heavy. It feels real. Then you switch to Mario Kart 8, hit a blue shell, and your kart goes from zero to “I am the lightning bolt” in the time it takes to blink, while drifting around a corner that defies geometry.
What’s happening under the hood? Why do some games make cars feel like they weigh ten tons, while others make them float like they’re in the moon? And why do even professional sim racers sometimes get the physics wrong in their heads?
Let’s rip the engine bay open and look at the math, the code, and the magic tricks game developers use to trick your brain into believing you’re driving a vehicle.
The Foundation: It’s All Just Numbers Fighting Each Other
First, let’s debunk the biggest myth in gaming physics: Cars don’t naturally want to stop. In the real world, friction, air resistance, and engine braking slow things down. In a raw physics engine without corrections, an object in motion stays in motion forever unless a force acts on it.
Game developers have to simulate these resistive forces because real cars are complex machines with thousands of interacting parts. Instead of simulating every piston, gear, and bearing (which would melt your CPU), they use simplified physical models that approximate reality.
The Core Equation: F = ma
At the heart of almost every game’s physics engine (whether it’s Unreal Engine’s PhysX, Unity’s PhysX, or proprietary engines like those used by Forza or Gran Turismo) is Newton’s Second Law:
\[F = m \times a\]
- F is Force (Newtons)
- m is Mass (kilograms)
- a is Acceleration (meters per second squared)
But here’s the thing: Games rarely use real-world units. Why? Because “real” numbers are often too small to matter.
In a real car, accelerating at 1 G (9.8 m/s²) feels intense. But in a game, if you’re simulating a car going 200 mph, you need to convert that into the game’s unit system. Most games use metres per second (m/s) internally, even if the UI shows MPH or KM/H.
The Speedometer Lie
Let’s say your game shows a top speed of 200 MPH. But internally, the car is moving at roughly 89 m/s. The physics engine doesn’t know what a “mile” is. It only knows that every frame (1/60th of a second, or ~16.6 milliseconds), it needs to update the car’s position based on its velocity.
\[Velocity_{new} = Velocity_{old} + (Acceleration \times deltaTime)\]
\[Position_{new} = Position_{old} + (Velocity \times deltaTime)\]
This is called Euler integration, and it’s the simplest way to move things around. But here’s where players get tripped up: deltaTime is not constant.
If your game runs at 30 FPS, deltaTime is 0.033 seconds. If it runs at 120 FPS, deltaTime is 0.0083 seconds. If the physics engine doesn’t account for this correctly, your car will move faster on a high-refresh-rate monitor than on a low one. This is why fixed timestep physics is crucial in racing games. The physics runs at a set rate (e.g., 60 times a second), and the rendering runs as fast as it can.
How Acceleration is Calculated: The “Fake” Forces
Now, let’s talk about what makes a car feel like it’s accelerating. In a real car, you feel G-forces because your body has inertia. In a game, you don’t have a real body. So, how do they fake it?
1. Screen Shake and FOV Changes
When you accelerate hard in Forza, the camera might shake slightly, and the field of view (FOV) might narrow. This is a visual cue that tricks your brain into feeling speed. It’s not physics; it’s psychology.
2. Tire Slip Angles and Grip Models
This is where it gets interesting. Games don’t simulate tire deformation pixel-by-pixel. They use Pacejka “Magic Formula” curves. These are empirical formulas that predict how much grip a tire has based on:
- Slip angle (how much the tire is pointing compared to where it’s going)
- Slip ratio (how much the tire is spinning compared to the road speed)
- Normal load (how much weight is on the tire)
- Surface friction (wet, dry, gravel, etc.)
The formula looks something like this (simplified):
\[F_y = D \times \sin(C \times \arctan(B \times \sigma - E \times (B \times \sigma - \arctan(B \times \sigma))))\]
Where:
- \(F_y\) is the lateral force (grip)
- \(\sigma\) is the slip angle
- \(B, C, D, E\) are empirical coefficients tuned for each tire type
Developers like Polyphony Digital (Gran Turismo) and Playground Games (Forza) have spent years tuning these coefficients to match real-world data from test tracks. That’s why Forza feels so real—the cars aren’t just “sliding”; they’re losing grip in a way that matches reality.
3. Aerodynamic Downforce and Drag
At high speeds, air becomes a solid wall. Games calculate aerodynamic drag like this:
\[F_{drag} = \frac{1}{2} \times \rho \times v^2 \times C_d \times A\]
- \(\rho\) (rho) is air density
- \(v\) is velocity
- \(C_d\) is the drag coefficient (how aerodynamic the car is)
- \(A\) is the frontal area
Notice the \(v^2\)? That’s why going from 100 to 200 MPH requires four times the power to overcome drag. Games that ignore this (like many arcade racers) will make cars feel unnaturally fast at high speeds because there’s no “air resistance” slowing them down.
The Two Types of Racing Games: Sim vs. Arcade
This is the biggest divide in gaming physics. Let’s compare them.
Simulation Racing (Forza Motorsport, Gran Turismo, Assetto Corsa)
- Goal: Replicate real-world physics as closely as possible.
- Physics Model: High-fidelity tire models, suspension geometry, aerodynamic downforce, and weight transfer.
- Input Handling: Direct mapping from controller/steering wheel to tire forces. No assistances unless you enable them.
- Speed Perception: Slow. It takes 5-6 seconds to go from 0-60 MPH in a real supercar. In a sim, it takes that long.
- What Players Get Wrong: Many players think they’re driving fast, but they’re actually driving slowly. The lack of visual speed cues (like screen shake or rapid background movement) makes it feel sluggish. But if you look at the telemetry, you’re doing 120 MPH. Your brain just isn’t used to the visual language of sim racing.
Arcade Racing (Mario Kart, Burnout, Need for Speed)
- Goal: Fun and accessibility over realism.
- Physics Model: Simplified. Cars often have “infinite grip” when not drifting. Acceleration is exaggerated. Top speeds are high but feel fast due to visual effects.
- Input Handling: Often includes “auto-steer” or “magnetic roads” that pull the car toward the optimal racing line.
- Speed Perception: Fast. The camera is close, the world moves quickly, and there are constant visual cues (speed lines, screen flash) that tell your brain “you are going fast!”
- What Players Get Wrong: Players often think these games are “realistic” because they feel fast. But in reality, the physics are floaty. A car can drift around a corner at 200 MPH without sliding off the track because the game is cheating to make it fun.
The Secret Sauce: How Games Fake What They Can’t Calculate
Here’s the truth: No game can simulate a real car perfectly. The complexity is too high. So, developers use tricks to make the illusion convincing.
Trick 1: Weight Transfer Simplification
In reality, when you brake, weight transfers to the front tires. When you accelerate, weight transfers to the rear. This changes how much grip each tire has.
In games, this is often pre-baked. Instead of simulating the suspension compression in real-time, the game uses a lookup table or a simplified formula that estimates weight transfer based on acceleration/deceleration values.
Trick 2: Tire Warm-up and Degradation
Real tires need to warm up to reach optimal grip. In sim games like Assetto Corsa, tires have a thermal model. The game calculates the temperature of each tire based on slip, load, and surface temperature.
But in many arcade games, tires are just “on” or “off.” You can slide out forever without your tires wearing down.
Trick 3: The “Snap-Back” Drift
In Mario Kart, when you drift, the game forces a rotation. It’s not a real drift; it’s a rotation boost. The game says, “You’re turning left, so I’ll spin you left and give you a speed boost.” This is purely game design, not physics. But it feels good because it’s responsive and rewarding.
What Players Get Wrong About Car Speed
This is the most important part. Even experienced gamers misunderstand how speed is represented in games.
Misconception 1: “I’m Going 200 MPH, So Why Does It Feel Slow?”
In sims, speed is relative. If you’re in a go-kart, 200 MPH is impossible. If you’re in a Formula 1 car, 200 MPH is everyday driving. The game doesn’t “feel” slow because the physics are accurate—your brain just isn’t calibrated to the visual scale.
Example: In Forza Horizon 5, if you’re in a Bugatti Chiron and driving at 200 MPH, the world outside the window moves slowly because the car is large, and the FOV is narrow. In Mario Kart, the world moves fast because the camera is close, and the tracks are designed to feel chaotic.
Misconception 2: “Drifting Is Just Turning While Going Fast”
No. Drifting is a controlled loss of traction. In real life, you drift by breaking the rear tires’ grip while maintaining throttle. In games, drifting is often a mechanic that rewards you for holding the drift button.
In Mario Kart, drifting is a boost mechanic. You hold the drift button, charge up a mini-turbo, and release it for a speed burst. The “drift” is just a visual animation. In Forza, drifting is a skill that allows you to carry more speed through a corner by managing tire slip.
Misconception 3: “More Horsepower = Faster in Every Situation”
Not true. In games with realistic physics, weight matters more than horsepower. A light car with 300 HP will beat a heavy car with 500 HP on a technical track. This is because acceleration is \(F/m\). If mass (\(m\)) increases, acceleration decreases, even if force (\(F\)) increases.
Example: In Gran Turismo, a light sports car like the Mazda MX-5 can outperform a heavy supercar like the Lamborghini Aventador on twisty tracks because the MX-5 can change direction faster.
The Code Behind the Magic
Let’s look at a simple example of how a game might calculate acceleration. This is pseudocode, but it shows the logic.
# Simple car physics model
class Car:
def __init__(self, mass, max_force, drag_coefficient):
self.mass = mass # in kg
self.max_force = max_force # engine max force in Newtons
self.drag_coefficient = drag_coefficient
self.velocity = 0 # in m/s
self.position = 0 # in meters
def update(self, delta_time, throttle, brake):
# Calculate engine force
engine_force = throttle * self.max_force
# Calculate drag force (simplified)
drag_force = self.drag_coefficient * (self.velocity ** 2)
# Calculate net force
net_force = engine_force - drag_force
# Apply brake force
if brake > 0:
net_force -= brake * 10000 # Arbitrary brake force multiplier
# Calculate acceleration (F = ma)
acceleration = net_force / self.mass
# Update velocity
self.velocity += acceleration * delta_time
# Update position
self.position += self.velocity * delta_time
return self.velocity, self.position
This is a very simplified model. Real games have:
- 4 independent wheels with individual slip calculations
- Suspension dynamics
- Gear ratios and engine RPM
- Tire temperature models
- Aerodynamic downforce
But this code shows the core principle: Force generates acceleration, which changes velocity, which changes position.
Why Some Games Feel “Floaty”
If you’ve ever played a game and thought, “This car feels like it’s on ice,” you’ve encountered poor physics tuning. Here’s why that happens:
- Low Friction Coefficients: The game designer set the tire grip too low.
- High Mass: The car is too heavy, so it accelerates slowly.
- No Weight Transfer: The car doesn’t “squat” under acceleration or “dive” under braking, making it feel disconnected.
- Camera FOV Too Wide: A wide FOV makes speed feel slower because objects move less across the screen.
Example: Mario Kart uses a low friction coefficient and no weight transfer to make drifting easy and fun. Forza uses high friction and complex weight transfer to make driving feel demanding and realistic.
The Future: AI and Procedural Physics
As games become more advanced, developers are using machine learning to tune physics. Instead of manually tweaking tire coefficients, AI can analyze real-world telemetry data and adjust the game’s physics to match.
We’re also seeing procedural physics, where the game calculates tire grip based on the surface in real-time. If you drive on wet grass, the game calculates the reduced friction based on the water depth and grass density. This is still in its infancy, but it’s the future of realistic racing games.
Conclusion: It’s All About the Illusion
At the end of the day, video game physics is a compromise between realism and fun.
- Sim racers prioritize realism because they want to feel like they’re driving a real car.
- Arcade racers prioritize fun because they want players to feel fast and exciting.
Neither is “wrong.” They’re just different approaches to the same goal: making the player believe they’re in control of a vehicle.
So next time you’re playing a racing game, remember: the speed you feel is a calculation, the drift you execute is a simplified model, and the G-forces you imagine are a visual trick. But that doesn’t make it any less immersive. In fact, it makes it more impressive that developers can fool your brain into feeling something that isn’t there.
And if you still think Mario Kart’s physics are “unrealistic”—well, you’re right. But that’s why we love it.