Quote Originally Posted by KaiserBill View Post
You really need to change the gearbox gears as well. But no one does that
No one does that because it's not actually needed. Transmission gear spread impacts how you make use of the engine's power as you accelerate and shift through the gears. Changing tire size has no impact on this relationship at all. If the transmission is already matched well enough to the engine's torque/power curve and the general intended usage of the vehicle, and it's not a racing transmission with reconfigurable gear ratios, then any benefit of optimizing the transmission setup to your personal preferences is not going to be anywhere near worth the cost/effort for anyone without very deep pockets.

Then again, if you have a configurable racing transmission, you probably already have pretty deep pockets, and also a vehicle for which there exist after market racing transmissions.