# Splitter tunnels (front diffuser)

> What are splitter tunnels and what ramp angle should they use?

- Category: Car design › Car aero
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/splitter-tunnels-front-diffuser/ · JSON: https://xemstudio.com/api/geometry?object=splitter-tunnels-front-diffuser · Plain text: https://xemstudio.com/objects/splitter-tunnels-front-diffuser/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## 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.

## Sizes

| 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 |

## Where the files are

- High Performance Academy: [Aerodynamic performance devices for club level cars: front splitters](https://www.hpacademy.com/courses/aerodynamics-fundamentals/aerodynamic-performance-devices-for-club-level-cars-front-splitters) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/splitter-tunnels-front-diffuser/index.json · license: https://xemstudio.com/files/hardware/splitter-tunnels-front-diffuser/LICENSE.md

- splitter-tunnels-front-diffuser-splitter: [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) — Front splitter 200 × 300 mm with an up-turned lip at 11° (illustrative where noted)

## Questions

**Which ramp angle for low cars?**

HPA: use the low end (~10 deg) for low ride heights, the high end (~12 deg) for high ride heights.

## Fits with

- [Single-element rear wing (race car)](https://xemstudio.com/objects/rear-wing-single-element/)
- [Dual-element (two-element) rear wing](https://xemstudio.com/objects/rear-wing-dual-element/)
- [Swan-neck rear wing mount](https://xemstudio.com/objects/swan-neck-wing-mount/)
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- [Wing endplates / side dams](https://xemstudio.com/objects/wing-endplates/)
- [Front splitter](https://xemstudio.com/objects/front-splitter/)