Let's see if my calculations are correct
Point of beginning. BMW's measures " 7,5x18 ET49 " and " 8,5x18 ET52 ".
My car is a BMW e81 130i pack M.
1 º FRONT RIM (to increase ahead to 8x18, we would have 1/4 of 1 inch (25,4 mm) more as every side), be read:
6,35 mm + (RIM 7,5) + 6,35 mm = RIM 8,0
Therefore and in order that it was not rubbing within we extract the ET in 6,35 mm.
Total ET 42,65 (aprox. ET43).
2 º BACK RIM (to reduce behind to 8x18, we would have 1/4 inch less as every side), be read:
-6,35 mm + (RIM 8,5)-6,35 mm = RIM 8,0
Therefore and to compensate we extract ET, in two parts. The first one to compare the front exit (6,35) and the second thing to compensate the loss of width in the back wheel (6,35 x 2 = 12,7).
Total 19,05 mm towards out. Total ET52 - 19,05 = 32.95 (aprox. ET33).
8x18 ET43
8x18 ET33
And in the differential of checking it would stay ...:
8x18 ET43 re-turned made-to-measure original it would be ... 7,5x18 ET 36,65 (aprox. ET37)---12,35 (49 - 36,65) millimeters towards out with regard to the measure OEM.
8x18 ET33 re-turned made-to-measure original it would be ... 8,5x18 ET 39,35 (aprox. ET39)---12,65 (52 - 39,35) millimeters towards out with regard to the measure OEM.
I want to install these wheels:
A e81 could look at this:
These wheels are habitual in WRC, specially in production category:
