Gear ratio with drag radials

[ctrlraven]

With a 3.55 rear and 255/50-16 drag radials my effective gear ratio should be 3.90 right? My friend with a gt mustang has the 3.27 oem gears and is going to be doing the same drag radial/wheel setup as me, what would be his effective gear ratio?

[Grifter]

you, 3.91

him, 3.23

its about the same size tire for him..

[ctrlraven]

Thank you sir.