205/55/16 should look fine on a w123.

205/55/15 would be VERY SMALL for a w123.

If you have 16” wheels, I would recommend 205/55/16 and 225/50/16.

If you have 15” wheels, 205/65/15 (or 195/65/15). I’ve seen some ridiculously large 15” tires stuffed into 107s, but never driven on them. I don’t recall the sizes, but I bet a 225/60/15 would not be insane. I dot know if it would rub, but you need to know your offsets.

If you have 14” wheels, 205/70/14 (or 195/70/14). You can go up to 75 profile for a chunkier look. I’ve seen 215 and even 225/65/14 too, on a 107, not w123 though.

Know your offsets before going insane with your tires.

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Past mb: '73 450sl, '81 280slc stick, '71 250, '72 250c, '70 250c, '79 280sl, '73 450sl, parted: '75 240d stick, '69 280s, '73 450slc, '72 450sl,