Braking Distance Simulator

These screenshots are captured from this simulator. Start here if you are using the tool for the first time.

Pick an example, then read the difference summary. It explains what changes between A and B. An example copies A to B and changes that one tyre setting; the example uses Car A’s conditions for both cars and keeps the starting speed.

Open the Today’s conditions tab, choose a town and get its report. Check the weather time and suggested road wetness, then apply it. You return to the driving mode you came from.

Weather can suggest a wetness scenario; rainfall does not measure road water depth. Temperature is rounded to the calculator’s whole-degree input. Wind remains as entered unless you choose how it meets your direction of travel. A forecast of freezing conditions does not confirm ice on a particular road.

The imported snapshot stays fixed until you refresh it. Editing it is allowed and is marked in the weather summary.

The car drives at your chosen speed for 1.5 simulated seconds before the blue line. Braking starts at that line. The approach distance is excluded from the result.

Braking distance measures the movement after the brakes are applied. It is not total stopping distance including driver reaction time.

In Compare cars, both cars brake from the same line. The blue and purple markers show their final stopping points. When you choose First car stops, the other car’s speed is measured at that same moment—not at the first car’s stopping position.

These are modelled results, not a guarantee for a particular car or road. The existing numerical integration review remains open in this simulator.

In Compare cars, choose Different conditions, or select the Grass vs gravel example. Set the surface and weather on each car’s condition card. For example, Car A can use Grass and Dry while Car B uses Gravel and Rain. More conditions opens that car’s water depth, temperature, wind and slope controls.

Both cars start at the same speed and brake at the same line. The side view shows each road separately; the other views show the two surfaces on the same distance scale. Rain and tyre spray follow each car’s weather. The drawings remain level; slope is included in the calculation and listed in the condition details.

Use Today’s conditions to apply a report to Car A, Car B or both. Switching back to Shared conditions copies Car A’s road settings to Car B. Undo restores the previous setup. Saving a comparison includes both sets of conditions.

Use the Background buttons above Play to choose Countryside, Woodland, Coastal, Town or Clear view. The trees, rocks and street furniture come from your supplied model assets. Background choice changes the illustration only. Road surface, weather and braking calculations keep their selected settings.

The replay now drives through to both stopping points without automatically pausing at the first stop. Use Pause yourself, or use First car stops to inspect that moment.

View the imported model gallery →

Choose Side, Bird’s-eye or Behind using the large camera buttons above Play. They are always visible. Auto camera starts close and zooms out as needed to keep both cars in view. More replay options contains Fixed scale, Fit whole run, playback rate and lighting. Behind uses perspective, so there is no single pixels-per-metre scale.

Use the slider to move through the run, or jump directly to brakes on and stopped. Normal and slow playback show the same results. Day/night changes the illustration’s lighting, not physical grip. First-stop controls appear only in Compare cars.

Rain is visible in every camera view. Light rain, Rain and Heavy rain draw progressively more falling streaks. Damp or a custom water depth can wet the road without implying that rain is falling. Moving cars create spray on a wet road; braking adds a red reflection. These weather effects illustrate the chosen scenario and do not alter the calculations.

All 23 controls are still available. Vehicle type and weight are now on each car’s main card. Body style lets you choose among the three approved designs. Choose No trailer, Unbraked or Braked directly on the car card, enter its weight, then choose the trailer appearance below Body style. Settings apply immediately; use Undo to reverse a change.

Preset tread depths and pressures are examples. Enter known values for your setup; a selected grade is an assumption unless you have checked the tyre’s data. The drawing follows your vehicle type. Body style changes appearance only; choosing a different vehicle type or weight changes the calculation. A trailer is drawn when a trailer setting is enabled.

Every setting, with a close-up

Open a setting below to see the actual control, its available choices and a plain-language explanation of how to use it. These pictures show example selections; they do not overwrite your setup.

Switching tabs preserves both car setups and the chosen conditions. Single car uses Car A; Compare cars restores Car B beside it. Choosing a comparison example deliberately makes B match A apart from the example’s tyre difference, while keeping the selected speed and conditions.

Open Save, load or print your setup below the result. Save downloads a setup file including the weather snapshot. Load reopens that file. Print makes a printable result. Nothing is sent to a customer automatically.

Saved weather is a snapshot with a timestamp, not a live forecast. Refresh it explicitly when you want new conditions.

The road is measured in metres. The camera turns those metres into pixels. The replay’s clock controls how quickly the car moves through those positions.

Why 80 and 160 used to look similar

The earlier view fitted each entire run inside the same screen width. A longer run made the camera zoom farther out. Each metre then occupied fewer pixels. The default was also 0.5× playback.

Auto camera is the default and widens the view only when the cars need more room. Choose Fixed scale in More replay options to keep 1 m = 16 CSS pixels in Side and Bird’s-eye at ordinary sizes. The camera pans forward when needed but does not zoom as speed changes. Fit whole run is an overview, and intentionally changes the pixel scale. The scale strip tells you which is in use. Behind is a perspective view, so a single px/m number would be misleading.

What UPBS adds to the simple formula

The engine combines surface grip with tyre, tread, pressure, temperature, wetness and vehicle factors. Road slope changes the deceleration, and calibration connects the model to measured braking tests. A useful simplified expression is:

It also includes a brake build-up allowance. Driver reaction distance is a separate quantity: reaction distance = speed in m/s × reaction time. This simulator does not include a driver-reaction phase.

The reports behind the tool

Keep the versions distinct. The published September methodology gives 848/871 (97.4%) within its stated tolerance; the older February report gives 849/871 (97.5%). These are the reports’ recorded results, not a fresh validation of this simulator. The current replay still uses the existing simulator trace, which omits the engine’s build-up allowance. The wet-calibration transition is also under review. This update changes visual scale and playback timing; it does not repair or retune those calculations.

Sources: the linked Tyre Dispatch methodology, the archived UBPS technical report, and the unchanged engine and replay source used by this simulator. These reports are available from this tool; the original report dates and validation scope are preserved.