Diffuser fences / longitudinal separators — dimension sheet
Source: Xem Studio, https://xemstudio.com/objects/diffuser-fences-strakes/  (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
- Diffuser fences are vertical plates running fore-aft in the diffuser. Diffuser downforce depends on vortices formed at its edges near the inlet, which move inboard and upward downstream (Mahon, Zhang & Gage); fences organise that flow.
- On the Cranfield DrivAer model, separators at 5 deg and 100 mm spacing in a 10 deg diffuser trimmed front downforce by ~0.03 CL, improved balance at low ride height and cost only 3-5 drag counts (SAE 2018-01-0725).
- The file is a reference example built by Xem Studio from the numbers above (Fence spacing 100 mm per Cranfield test (35% model).). Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

parameter  value or range  source
Separator angle / spacing tested  5 deg, 100 mm spacing in 10 deg diffuser  Cranfield / SAE 2018-01-0725
Front downforce change  dCL about 0.03 lower  Cranfield / SAE 2018-01-0725
Drag penalty  3, 5, 4 counts at h/h0 0.25, 0.50, 0.75  Cranfield / SAE 2018-01-0725
Edge vortex origin  near diffuser inlet  Southampton (Mahon et al.)

Files elsewhere (not hosted by Xem Studio; license as stated by the publisher):
- Cranfield University / SAE: On the Aerodynamics of an Enclosed-Wheel Racing Car (Soares et al., SAE 2018-01-0725) — web — Publisher's page; dimensions are facts — https://dspace.lib.cranfield.ac.uk/server/api/core/bitstreams/9b476386-44d0-4c0f-a49e-c3372274d351/content
- University of Southampton: The Evolution of Edge Vortices Underneath a Diffuser Equipped Bluff Body (Mahon, Zhang & Gage) — web — Publisher's page; dimensions are facts — https://eprints.soton.ac.uk/22957/1/paper_35_2.pdf

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