Splitter tunnels (front diffuser) — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/splitter-tunnels-front-diffuser/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)
Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
Catalog version: 2026-10-20

Sizes: see table below
- Splitter tunnels are small diffusers cut into the splitter that expand the air from the splitter floor up into the wheel well, deepening the low pressure under the splitter. HPA says this can roughly double front downforce compared with a flat splitter.
- HPA recommends a 10-12 deg ramp (low end for low ride heights) with a ~100 mm kickline radius, starting at about a third of splitter length on short overhangs or half on long ones.
- The file is a reference example built by Xem Studio from the numbers above (11 deg = middle of HPA's 10-12 deg ramp; tunnel width illustrative.). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

parameter  value or range  source
Tunnel ramp angle  about 10-12 deg  HPA splitter
Kickline bend radius  about 100 mm  HPA splitter
Kickline start  ~1/3 of splitter length (short), ~1/2 (long)  HPA splitter
Outboard tunnel wall  ~50 mm outboard of inside tyre shoulder  HPA splitter
Front downforce gain vs flat splitter  roughly double  HPA splitter

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- High Performance Academy: Aerodynamic performance devices for club level cars: front splitters — web — Publisher's page; dimensions are facts — https://www.hpacademy.com/courses/aerodynamics-fundamentals/aerodynamic-performance-devices-for-club-level-cars-front-splitters

Free files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/splitter-tunnels-front-diffuser/index.json
API: https://xemstudio.com/api/geometry?object=splitter-tunnels-front-diffuser