Baseline (Widescreen) Solution & Issues
Setup only lists 4:3 resolutions.
The selected resolution is stored as a two-digit value in Data_Gen\Config.bin. A -WideScreen switch is listed in MotoRacer3.exe but has no apparent effect.
How to use the hack:
Get into a race
Click File > Open Process, and choose "MotoRacer3"
Open the cheat table
Change the resolution values to what you want
Go back into the game
Don't change the resolution while in the menu as that can make it unusable. Fix available from the PC Gaming Wiki Community Files (search there).
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
Widescreen solution should work. (Untested)
4k UHD Specific Solution & Issues