want clear idea about the offset ??

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hi there
just want to know some info about the offset.
I have my stock wheels with 55+ offset (( 15 inch wheels and tire size is 195/60 )), whould it be the same if I use a 17 inch wheels with 40+ offset and a 15mm spacer (( If I'm not wrong it will be 55+ which is the same offset as my stock wheels ))
will be any rubbing if I use 235/40 with total 55+ offset