Does every suspension lowering need to be registered?

If the kit is homologated exactly for your model and the manufacturer's declared lowering range is reflected in the registration documents, a separate registration may not be needed. For a larger deviation or unmarked parts, registration is required.

Why does lowering the suspension affect other things on the car too?

Changing the car's ride height shifts axle geometry (toe, camber), may require headlight re-aiming, and affects the ground clearance needed to clear bumps — which is why a geometry check and headlight adjustment are recommended after lowering.

Lowering the suspension — sport springs and dampers

Sport springs, dampers, or a height-adjustable suspension are among the most common modifications — and also among those with the biggest knock-on effects on a car's other systems.

What you need

The parts used should be homologated (ECE/EU) exactly for your model, or a technical assessment from an accredited testing body must exist. If the resulting ride height or geometry deviates from the range approved in the registration documents, registering the change at the local transport department (ORP) is required.

What to watch out for

Axle geometry — lowering shifts toe and camber angles; a geometry alignment is recommended after installation, otherwise uneven tire wear is likely.
Headlight aim — changing the car's height also affects headlight aim; after a significant lowering, it's worth re-aiming the lights so they don't dazzle oncoming drivers.
Ground clearance and wheel arches — too low a suspension can lead to insufficient ground clearance or tire contact with the body at full steering lock or full compression — both grounds for failing inspection.
Combining with wider wheels — if you're also changing wheels at the same time, check the offset and sufficient clearance from the wheel arches together with the lowered suspension.

Recommendation

Before installation, discuss the specific kit with a technician or directly with STK K-technik — it can save you a second registration appointment if it turns out additional geometry work or adjustment is needed.