OpenIV > Ctrl+F3 > Search 'mods folder only' for 'wheels_mods.rpf' & 'wheels2_mods.rpf'
They are in 'x64i.rpf', mpheist dlcpacks & the two mplowrider dlcpacks:
If you don't find them all in the 'mods' folder, copy (copy, don't move them) those archives over to the 'mods' folder from the vanilla game folder (following the correct folder paths obvs).
Wheels are named like this 'wheel_hiend_07.ydr'
Ones ending in 'w.ydr' ('wheel_hiend_07w.ydr' etc) are the chrome versions.
You can download any wheels from the site, rename them & overwrite the vanilla ones you don't like & they will appear in place of the vanilla ones.
Just remember to add any extra textures into 'vehshare.ytd' & then use that to overwrite all the other 'vehshare.ytd's in your 'mods' folder so you don't get any texture conflicts (OpenIV > Ctrl+F3 > Search 'mods folder only' for 'vehshare.ytd' to find them all).
That's the basics anyway, any questions/issues give me a shout