Arcade kart suspension and springs

The suspension dictates heavily how the Kart feels. You generally want very hard suspension for a classic Kart Racing experience. Though, you can tweak it however you like.

The suspension settings are in the details panel or the class defaults of BP_KartPawn, under Kart Base Settings > Suspension.

The wheels are not physics objects: each spring is a line trace (a raycast suspension) from one of the Suspension Locations below.

Springs, ride height and jumping

Suspension Locations dictate where the suspensions should be cast from. You can also move these locations by their gizmos in the viewport.

Spring Length is the length of the line cast, ergo the spring.

Target Suspension Height sets the desired height, that the spring tries to reach. The spring can push, as well as pull the Kart.

When not in air, it is directly responsible for keeping the Kart planted on the ground.

When jumping, the Kart cannot come off the ground because of this, so when jumping, the spring is briefly deactivated.

The Suspension Reactivation Speed then says how fast the spring is reactivated, except when the Kart reaches below the Suspension Reactivation Height, then the springs will get reactivated earlier.

Spring force and clamping

Spring Force is the force multiplier of the spring, and Spring Dampening dampens the spring, so that it won’t bounce up and down endlessly.

Clamp Spring Force is optional, but recommended depending on what your use case is. I was noticing when developing this Kart Pawn, that a high spring force is desirable, because it can react very quickly to the changes in terrain and jumping just works way better with a harder spring, especially when driving on hills.

However, when driving over small bumps, the spring would sometimes launch the Kart too high into the air, because the spring force would be too high. So the solution: Keep the high spring force and thus reactivity, but clamp the maximum force possible.

Suspension settings

Setting	Default	What it does
Suspension Locations	4 entries	Points the springs are cast from, relative to the Kart. Move them with their gizmos in the viewport.
Spring Length	40	Length of each spring’s line cast, in cm.
Target Suspension Height	35	Height the springs push or pull the Kart to.
Suspension Reactivation Speed	4	How fast the springs switch back on after a jump. 4 means after a quarter of a second.
Suspension Reactivation Height	35	If a spring gets closer to the ground than this during a jump, the springs switch back on early.
Spring Force	100000	Force multiplier of the springs. Higher means a harder, quicker suspension.
Spring Dampening	4000	Calms the springs so the Kart does not bounce up and down.
Clamp Spring Force	Off	Limits the spring forces to the two values below.
Max Allowed Upward Spring Force	1350000	Strongest push a spring can give. Only visible when Clamp Spring Force is ticked.
Max Allowed Downward Spring Force	1350000	Strongest pull a spring can give. Only visible when Clamp Spring Force is ticked.

Related settings

These live in other categories, but they decide what happens when the springs lose the ground.

Setting	Default	Where	What it does
Jump Height	425	Kart Base Settings > Drifting > Stage 0: Pre-Drift	How strongly the Kart is launched upwards when it jumps or hops into a drift.
Gravity	3200	Kart Base Settings > Custom Gravity	The Kart’s own gravity, used instead of the world’s. It only applies when enough wheels are off the ground (or the slope is steeper than Max Ground Slope). On the ground, the springs keep the Kart down.
Wheels In Air Needed For Gravity	2	Kart Base Settings > In Air	How many springs must lose the ground before Gravity applies.
Wheels Needed For Air	3	Kart Base Settings > In Air	How many springs must lose the ground before the Kart counts as in air.

New suspension settings in 1.1

Version 1.1 adds two settings to the same category and more freedom for the spring layout. Coming in 1.1

Setting	Default	What it does
Suspension Ignores Other Karts	On	The spring casts and the ground check look through other Karts, so a Kart never climbs onto another Kart’s body. Other Karts are handled by the kart collision settings instead. Turn it off to let other Karts count as ground.
Trace Channel	Visibility	Collision channel used for the spring casts and the ground check. Use a custom trace channel if, for example, translucent objects that block Visibility should not hold the Kart up, or if you want dedicated kart-ground collision.

• Suspension Locations can have more or fewer than four entries. Add one with the plus button, or remove one from its down chevron menu. Then check that Wheels Needed For Air and Wheels In Air Needed For Gravity still fit your number of springs. Coming in 1.1

Next steps

• Adjust speed, acceleration and turning.
• Set up drag per ground type in Surfaces and walls. Coming in 1.1