Why I built my own trailer simulator

With two horses and two Shetland ponies in the family, there is one skill you can’t avoid for long: driving with a horse trailer. Driving forward is easy. Reversing is a different story.

Steer left, the trailer goes right

The first time I tried to back a trailer into a spot, I learned the golden rule the hard way: the trailer swings the opposite way you steer. Your brain knows this, but your hands keep doing the wrong thing. Add a narrow yard, a gate post and a few spectators, and it gets uncomfortable quickly.

The obvious answer is practice. But practice with a real car and a real trailer needs space, time and somebody patient next to you, and every mistake can cost a scratch. I looked for something to learn the basics with first: how a trailer reacts, how far to steer, when to pull forward and start again. What I found was either expensive, built for professional truck drivers, or more of a toy than a teacher.

So I did what developers do: I built my own.

Trailer Sim

Trailer Sim is a small mobile game for exactly this: learning to reverse and park with a trailer, without a scratch on your car – or anyone else’s.

• A short tutorial teaches the controls and the golden rule.
• Ten parking levels take you from reversing straight back to backing a caravan through a gate into a narrow backyard.
• Guide lines show where the trailer will go with your current steering, in the early levels.
• A top view helps when the gap gets tight.
• Stuck? “Show me” lets an autopilot demonstrate the manoeuvre.
• Three tow vehicles and four trailers – including, of course, a horse trailer. A short trailer reacts fast, a long one slowly, just like in real life.

Under the hood

Since this is my personal blog, a few words for the nerds:

• The game is written in Odin with SDL3 for windowing, input and the GPU (Metal on Apple devices, Vulkan on Android) and Box3D for physics.
• The simulation runs at a fixed 120 Hz and is deterministic, so it also runs headless in tests. Cars have raycast suspension, a tyre model, an automatic gearbox and overrun brakes on the trailer.
• The autopilot behind “Show me” plans a reversing arc the trailer can actually follow and corrects like a human would. It also proves that every level can be solved.
• All low-poly models are built by script in Blender, and the sounds – engine, tyres, parking sensor – are generated procedurally, without a single audio file.

One important note

Trailer Sim is a game, not a replacement for driving lessons. It helped me understand why the trailer does what it does before I sat in the real car. The real thing still needs real practice – and the towing rules of your country.

If you want to give it a try, you’ll find everything on the Trailer Sim page.