All current WRC car generation were homologated by FIA in December 2016, so that homologation was valid since January 1st, 2017. The homologation of the Variant kit WRC 2017 is known as 400/01 for all cars, and it is valid till the end of the year 2024.
Once the cars were homologated, the Appendix J of the Article 255 sets which parts of the car require homologation and which are free of homologation. Regarding the main parts of the aero package, the parts requiring homologation when modified versus the original part included in 400/01 are:
1. Body openings, which are only allowed for the cooling of:
‐ engine, transmission
‐ power steering
‐ electric/electronic equipment
‐ cockpit/ driver
‐ air conditioning system
‐ power assisted gearshift system
‐ shock absorber
2. Roof panel and roof vents (VO)
3. Engine bonnet
4. Boot lid
5. Fenders, air inlet/outlet and louvres (VO)
6. Door and door sills
7. Front bumper and lower (removable) part, although air ducts and mountings are excluded
8. Rear bumper, openings and louvres (VO), although wheel visibility and mountings are excluded
9. Rear diffuser and rear protection
10. Rear wing, Trailing edge / Angle bracket (gurney flap), secondary profile and wing position
11. Front and rear wheel arches and housings
VO means variant option, affecting to parts that have to be homologated but do not require the use of a joker, such as louvers in fender openings, or fans in radiators.
On the contrary, those parts impacting on car aerodynamics whose homologation is not required and can be freely replaced are:
1. Rear mirrors
2. Underbody protections
3. Front bumper air ducts and mountings
4. Rear bumper wheel visibility and mountings
There are different types of homologations (see full definitions in Appendix 2021 J Article A251 Classification & Definitions):
ER – Erratum: replaces and cancels an incorrect piece of information previously
supplied by the constructor on a form.
ERJ – Erratum joker: counted for each article modified.
VO – variant option (supplied on specific request).
VK – variant kit (supplied on specific request).
VF – variant supply: two suppliers providing the same part for the manufacturer and the client does not have the possibility of choice.
VP – production variant (supplied on request and available from dealers).
ET – evolution type: modifications made on a permanent basis to the basic
model (complete cessation of the production of the car in its original
Use of variants: the competitor may use any variant or any article of a variant as he
wishes, only on condition that all the technical data of the vehicle, so designed, conforms to that described on the homologation form applicable to the car, or expressly allowed by Appendix J.
Each homologation is identified by the combination of two numbers: 4XX / YY
4XX meaning the total number of homologation, starting from 400
YY is the number of homologations of the type (ER, VO,…)