Go to www.oponeo.co.uk look at Steel wheels and record the details and compare. ET is the offset, how far from the centreline of the wheel the mounting flange is. A larger ET will move the same width wheel inwards. Gets more complicated when larger width wheels are fitted. If moving from a 4.50 width to 5.00, the rim is half inch wider (13mm approx), so the ET needs to be 6-7mm less to keep the wheel centreline as was. Check however that there is room for wider rims without fouling suspension or bodywork. (Sorry its not a simple thing, which is why so many end up with fouling issues.)