Simulation

Switch to Drive in the toolbar — next to Plan and 3D — and Circuit Builder sends a car around the line you’ve drawn, working out a speed and a steering angle at every point along it. Watch the lap play out in the 3D viewer, or scrub to any point on the course with the lap slider. Anywhere the car doesn’t have enough room is flagged right there in the panel, so you find out before you build the thing, not after.

Tuning the line

The line’s shape is adjustable, and every control solves it live as you move it — what you see while dragging is the real line, not a rough preview.

• Apex position sets where the clip sits inside a corner; past halfway through the turn counts as a late apex.
• Clip tightness is how close to the edge of the lane the line aims, wherever the car has room to spare.
• Line smoothing controls how much distance the line takes to move across the circuit — higher spreads a transition over a longer stretch instead of chasing every wiggle in the corridor.
• Manji wavelength is how far the car travels per flick, in car lengths, when it’s weaving down a straight.

Three more controls shape how the car carries angle rather than where the line goes: manji angle (how much steering angle it holds mid-weave), transition speed (a ceiling on how fast it can swap sides), and speed variation (how much it slows for tight corners — turned all the way up it’s physically accurate, but reads as lurching).

Running more than one car

A run can hold up to six cars, added to the lineup one at a time. One car is Solo, two is Tandem, and three or more is a Train. The lead sets the line, and every car behind it follows at the Follow gap you set, measured in car lengths. Circuit Builder checks that gap for you — it flags when the lead and chase car’s footprints would actually make contact, so you find out from the panel instead of watching the run to see it happen.

Picking a car model

The car gallery lets you pick a real make and model for every car in the lineup, but it’s cosmetic. The clearance math behind every tight-spot check and every contact check still runs on your circuit’s RC scale, not on which model you chose. Changing the body style changes what you see on screen; it never changes whether a layout actually clears.