I did check that. However, I cannot say how is this applied:
1. If that gear ratio is fixed at the beginning of the season but can be adjusted differently by different teams using the same car. For example actual F1 rules.
or
2. The gear ratio is specific to the car and all teams using the same car have the same gear ratios.
If the right approach is 1 the gear ratio should be open.
On the other hand if the correct approach is 2the gear ratio should be closed and match real values.
In sector 3 they seemed to use approach number 2 and tuned those values either with real data or data deduced from onboard cameras.
https://forum.sector3studios.com/index.php?threads/gtr3-class-update-march-2016.4598/
For the radical GT3, the gearbox is the following.
https://shop.quaife.co.uk/81g-quaife-rpe-7-speed-sequential-ultra-compact-transaxle-gearbox
It has the following options for straight cut gear teeth which are the ones being mounted in Radical GT3.
Gear Ratios Straight cut (Spur)
1st 2nd 3rd 4th 5th 6th 7th
2.438 1.889 1.500 1.238 1.043 0.897 0.774
2.438 1.889 1.500 1.286 1.115 0.958 0.833
Final Drive Ratios
3.056 3.130 4.067