Yes it will affect the height of the sidewall. You should remain within 3% of the rolling radius.currently have 255/30/19 on the back of my 63
Tyres are knackered, it seems from this thread that 265/30/19 are an option but surely this will affect ride height fractionally and monitoring systems ?
265 is the width
30 is the tyre profile
19 is the diameter
255/30/R19 are the same as 265/30/R19 only wider.