For a standard Suzuki with standard wheels, vented disks are not nescessary, I agree. But for larger wheels and engine and combined with the slightly larger caliper piston, yes they play a part. also for my Jimny they are less prone to warping, though my current vented discs (cheap) has a slight shake.
I use calipers and hangers from the nineties long Vitara, 93 to 98.
Since I have ABS I use Jimny diesel discs as the center hole is larger 107.8mm for ABS. standard SJ and Jimny without ABS has 107mm.
For no ABS cars the Vitara Discs will fit. Jimny diesel calipers and hangers is next on my list to try.
To get the larger 1.6 engine approved here in Norway the extra brakes is a must now. (as it should be in my opinion) Rear discs do not get approved here yet and the kits are a bit like chopped wood those I have seen. Easier to get original parts approved here as there is lesser need for documentation.
By the way it seems the SJ rear brakes are wider than on my newer Jimny. haven't tried to fit them or taken any measurements but might try some day.
