Rainline: one wet circuit, three laps, and your own ghost to beat

01  What Rainline is

Rainline is a time trial rather than a race. No field to beat, no traffic, no opponent — just you, a stopwatch, and three laps of one street circuit called Harbour Nine: nine corners through a wet harbour district after dark. A lap takes about 45 seconds once you know the road, which is short enough that the right response to a bad one is to press R and go again.

It runs in a browser tab: no install and no account, on a desktop or a phone. The page opens onto the circuit already in motion, and the first key you press drops the camera in behind the car — that keypress is already your first steering input.

02  One circuit, on purpose

Most games in this genre offer a list of tracks. Rainline offers one, because Harbour Nine was authored corner by corner rather than generated and then accepted. The nine corners are individually shaped and named, T1 to T9, and they do not repeat a character: the fourth tightens after inviting you to unwind early, and the seventh is a hairpin whose apex sits late enough that almost everyone runs wide out of it the first time.

The rules are enforced by measurement rather than by walls. Twelve checkpoints are spaced evenly around the lap, every one must be crossed in order for a lap to count, and a lap that misses one is announced rather than quietly credited. Run wide and the surface punishes you: grip on the verge falls to roughly 60% of what the road gives, and the verge drags. Past nine metres beyond the road edge the car is put back on the line with two seconds added to the run — small enough that a mistake does not end a session, large enough that the barrier is not a shortcut.

03  The car is built to slide, and there is no physics engine in it

Rainline does not use a rigid-body simulation. The car is a kinematic model — position, velocity, heading — stepped a fixed 60 times a second, with the road handled as a distance-to-a-line test rather than as collision against a 3D mesh. That is why it loads instantly instead of downloading a physics engine first.

What replaces the physics is a single grip curve, and it is the most important thing in the game. Tyre grip rises to a peak at about eight degrees of slip, then falls to a plateau where a sliding tyre still does around 70% of its job. That number is what makes the car drift rather than spin: past the limit you lose speed and precision but keep control, and the slide still answers to the wheel. The rear tyres are given slightly less grip than the front, which is what makes the tail step out first and the car rotate into a corner at all.

Two controls follow. The handbrake is not a brake — it barely slows the car; it takes grip off the rear axle and rotates the nose, which is how you point the car at the exit of a slow corner. And because a slide you cannot catch is not a feature, counter-steering is helped: when your wheels point where the car is actually travelling rather than where it is facing, it straightens up faster. Past roughly 34 degrees of slide the car starts pulling its own nose back toward the direction of travel — an outright arcade concession, because an honest model turns a deep slide into a ride you are no longer driving.

04  Your ghost, and the number that makes you restart

Your fastest run comes back as a translucent car running beside you. It is not a recording of where the car went; it is a recording of what you did — the inputs, frame by frame — replayed through a second copy of the same simulation. Because the simulation is deterministic and every run starts from the same rolling state, the ghost drives your lap exactly as you drove it, and the file is a few kilobytes rather than a video. When somebody has set a time today, their lap runs alongside yours, with your gap to it read out at the last checkpoint you both crossed.

The ghost is what you spend your time on, but the number that makes people press restart is at the end of the run, and it is arithmetic rather than a replay. The lap is cut into twelve sectors and the results screen adds up your best time in each of them. That ideal lap is not a simulation of something nobody drove — it is a lap your own three attempts already contain between them, which turns "I was nearly there" into "there is a third of a second on the table and I know which corner it is in". The two-second off-track penalty feeds into it honestly: a mistake inflates one sector, so a sector you drove cleanly on another lap wins and the ideal quietly excludes it. When the ideal and your best lap are the same number, the screen says PERFECT.

05  What the wet night look costs, and how it is paid for

The rain and the neon are not a filter over the top. The road is a genuine planar reflection — the lit signs, the barriers and the headlights are re-rendered into a half-resolution buffer and reflected in the wet surface, which is what makes a flat road read as water — and over that sit bloom, rippling road normals and rain. It is much the most expensive thing in the frame, which is why Rainline has quality tiers rather than one fixed setting.

The tier starts from a guess about your device and is then decided by measurement: the game watches its own frame times for the first few seconds, steps down if they are bad, and tells you it did. It only ever steps down, never up, and you can override it by hand. On a phone it runs at a reduced tier, and it is not the same game — Rainline is built for a keyboard.

06  Times, names, and what we do not claim

Your times and your ghost are stored in your own browser, on your own device. Nothing follows you to another machine and clearing your browsing data clears them — the same reason there is no account to sign up for.

The daily board is the one thing that goes over the network: today’s ten fastest runs, read once when the page loads and written only when you set a personal best. None of it is on the path to playing — if the request fails, the game runs with your own ghost and the page says the board is unavailable rather than showing stale or invented rows.

• Your name on the board is generated from our own word lists: five options and a reroll button. There is no text field anywhere in Rainline, and nothing you type is ever published.
• The share link is the result card — your time, your best lap and a top-down trace of the line you actually drove, packed into the URL itself.

07  Questions people ask

Is Rainline free, and do I need an account?

Free, and no account. Nothing is installed and there is nothing to sign up for — the game runs in the browser tab and is supported by advertising. There is no paywall on any part of it, the daily board included.

How long is a lap, and how long does a full run take?

A lap of Harbour Nine is roughly 45 seconds once you know the circuit, and a run is three laps, so a little over two minutes. The results screen shows your three lap times and your ideal lap before you decide whether to go again.

Does Rainline work on a phone or an old laptop?

It runs, but it is honest about the trade. On a phone you get a reduced quality tier — no road reflections and half the rain — plus two-thumb steering on automatic throttle. On a weak laptop the game measures its own frame times, drops a tier to keep the frame rate up and tells you it did; you can override it by hand. A keyboard and a desktop are the intended way to play.

Can I play it offline?

No. The page loads over the network each time and there is no offline mode, so you need a connection to start a session. Once the page is up the driving itself is local — the only request the game makes is for the daily board, and a failed one does not stop you playing.

Is the leaderboard verified? Can people cheat their way onto it?

The board is for fun — times are reported by your browser and we do not verify them. We do not run a referee service and would rather say so plainly than imply one. Nothing about your own session depends on it: the ghost you race is your own, and the ideal lap is computed from your driving alone.

Why is there only one track?

Because Harbour Nine is authored corner by corner rather than generated — nine individually shaped corners, one spline driving the road surface, the checkpoints, the off-track test and the reset point. One circuit built properly was the choice over five built thinly, and the ghost chase is what turns it into something to keep playing rather than a single lap to look at.

08  More from the shelf

• Driftline — Drift the Neon Mile. Beat the AI.
• Isobath — Drop a pin. Find out how wrong you were.
• Dewkeep — Keep a creature. Grow a little world.
• Tilewright — Draw seven tiles. Outword the AI.

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