Just found this Felgen-Katalog - BMW-Treff - der Treffpunkt fr alle BMW-Fans und -Fahrer with all the Bmw specs,including weights...dont know how reliable it is ,but its a reference

They have style 87s front 9.5 x20 at 26 Lbs and the rear 10.5 at 31 Lbs
Site displays in kgs,to convert to Lbs,just * by 2.204