Put wheel_gn5.dff and BBS_GT.txd in GTA3.img.
Open veh_mods.ini and find line with
1098, wheel_gn5, vehicle, 100, 2097152
and replace with:
1098, wheel_gn5, BBS_GT, 100, 2097152
You can replace any wheel by just changing name of dff file, but then you MUST change the or1 line in veh_mods.ini.
1025, wheel_or1, vehicle, 100, 2097152
1025, wheel_or1, BBS_GT, 100, 2097152
Hope you got it.