{
 "version": "2026-10-20",
 "license": "Dimension sheets: CC BY 4.0. Standard and published-size files: CC BY 4.0. Xem Studio's own designs (files_license = Xem Studio Design License): free to use and sell things from, not to redistribute as files — https://xemstudio.com/license/. Other publishers' files: their own license, linked beside them.",
 "slug": "splitter-tunnels-front-diffuser",
 "name": "Splitter tunnels (front diffuser)",
 "kind": "standard",
 "category": "Car design",
 "group": "Car aero",
 "year": null,
 "question": "What are splitter tunnels and what ramp angle should they use?",
 "tags": [
  "vehicle design",
  "car aero",
  "rc design",
  "aerodynamics"
 ],
 "aliases": [
  "splitter tunnels",
  "front diffuser",
  "splitter diffuser",
  "splitter ramp angle",
  "kickline",
  "front underbody diffuser",
  "splitter tunnel design",
  "wheel well diffuser",
  "splitter venturi",
  "front tunnels"
 ],
 "overall_mm": {
  "length": null,
  "width": null,
  "height": null
 },
 "official_cad": false,
 "xem_status": "free-files",
 "les": false,
 "free_files": 1,
 "url": "https://xemstudio.com/objects/splitter-tunnels-front-diffuser/",
 "sheet_txt": "https://xemstudio.com/objects/splitter-tunnels-front-diffuser/sheet.txt",
 "sheet": {
  "basis": "Design rules and figures from the cited sources; example geometry by Xem Studio",
  "overall_mm": {
   "length": null,
   "width": null,
   "height": null
  },
  "notes": [
   "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."
  ],
  "table": {
   "columns": [
    "parameter",
    "value or range",
    "source"
   ],
   "rows": [
    [
     "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"
    ]
   ]
  }
 },
 "sheet_text": "Splitter tunnels (front diffuser) — dimension sheet\nSource: Xem Studio, https://xemstudio.com/objects/splitter-tunnels-front-diffuser/  (sheet CC BY 4.0; files Xem Studio Design License, https://xemstudio.com/license/)\nBasis: Design rules and figures from the cited sources; example geometry by Xem Studio\nCatalog version: 2026-10-20\n\nSizes: see table below\n- 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.\n- 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.\n- 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.\n\nparameter  value or range  source\nTunnel ramp angle  about 10-12 deg  HPA splitter\nKickline bend radius  about 100 mm  HPA splitter\nKickline start  ~1/3 of splitter length (short), ~1/2 (long)  HPA splitter\nOutboard tunnel wall  ~50 mm outboard of inside tyre shoulder  HPA splitter\nFront downforce gain vs flat splitter  roughly double  HPA splitter\n\nFiles elsewhere (not hosted by Xem Studio; license as stated by the publisher):\n- 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\n\nFree files (Xem Studio Design License, Xem Studio; STEP + STL, 1 parts): https://xemstudio.com/files/hardware/splitter-tunnels-front-diffuser/index.json\nAPI: https://xemstudio.com/api/geometry?object=splitter-tunnels-front-diffuser\n",
 "sources": [
  {
   "publisher": "High Performance Academy",
   "title": "Aerodynamic performance devices for club level cars: front splitters",
   "url": "https://www.hpacademy.com/courses/aerodynamics-fundamentals/aerodynamic-performance-devices-for-club-level-cars-front-splitters",
   "formats": [
    "web"
   ],
   "license": "Publisher's page; dimensions are facts",
   "license_verified": true,
   "hosted": false
  }
 ],
 "xem": {
  "status": "free-files",
  "sheet_free": true,
  "mesh_price_usd": null,
  "step_price_usd": null,
  "tolerance_mm": null
 },
 "related": [
  "rear-wing-single-element",
  "rear-wing-dual-element",
  "swan-neck-wing-mount",
  "gurney-flap-wickerbill",
  "wing-endplates",
  "front-splitter"
 ],
 "fits": [],
 "dimensions": "exact (nominal, no printing tolerance)",
 "dimension_rule": "All geometry on Xem Studio is exact (nominal, true size) with no printing tolerance. Where a part meets another part, the object lists its mating features (feature, exact size, what it mates with, fit class: press, slide, run, socket, clamp or designed). Apply your process's allowance to those features only; 'designed' gaps are part of the design and stay as drawn.",
 "mating": [],
 "faq": [
  {
   "q": "Which ramp angle for low cars?",
   "a": "HPA: use the low end (~10 deg) for low ride heights, the high end (~12 deg) for high ride heights."
  }
 ],
 "files_license": {
  "name": "Xem Studio Design License",
  "holder": "Xem Studio",
  "url": "https://xemstudio.com/license/",
  "note": "Xem Studio's own design: free to use, print, modify and sell things made from it; not to be republished or redistributed as files."
 },
 "offers": [
  {
   "file": "splitter-tunnels-front-diffuser-splitter",
   "formats": [
    "step",
    "stl"
   ],
   "price_usd": 0,
   "license": "Xem Studio Design License",
   "step": "https://xemstudio.com/files/hardware/splitter-tunnels-front-diffuser/splitter-tunnels-front-diffuser-splitter.step",
   "stl": "https://xemstudio.com/files/hardware/splitter-tunnels-front-diffuser/splitter-tunnels-front-diffuser-splitter.stl",
   "note": "Front splitter 200 × 300 mm with an up-turned lip at 11° (illustrative where noted)"
  }
 ],
 "markdown": "https://xemstudio.com/objects/splitter-tunnels-front-diffuser/index.md"
}