Every NGTC car goes through a wind tunnel assessment to determine it's aerodynamic profile. The total downforce produced, and the balance of this downforce between front and rear, is standardised across all NGTC cars.
Here's a summary of one of the tests carried out, in 2013 on WSR's new NGTC BMW 125i:
https://www.tocatechnical.co.uk/wpsy...ts-17.1.13.pdf
I'm not sure if BARC (TOCA) are aware that this document is publically available, but it's indexed by Google so not exactly hard to find.