I mean for the purposes of making sure the relative gear-whine pitch in each gear is correct for those gearboxes that do use different gear tooth pitches in different gear clusters. I've only heard a few of those though (where the gear whine pitch changes to something different when the gear is changed)
Most games just use a generic (set of) sample(s), GT included, but the way its pitch is scaled in the game is correct for gearboxes that have the same gear-tooth pitch in every gear, which is the vast majority of racing gearboxes I've ever heard. Those have the characteristic, constantly climbing pitch the faster you go, but the pitch carries on from where it left off when you do change gear - because it's only linked to road speed.
The linear speed (and so the rate that gear teeth mesh at, given a constant gear tooth pitch in all gears) at the effective meshing radius of the gears is the same as the road speed in all gears!
If you want "wobble" and chatter, you need a better driveline simulation; ignore those canned effects most games use.