So i am on stock 16" rims with 205 pirelli p6's but want to go up to maybe 17 or 18" rims with 215 or 225 tires. How much will this negatively affect fuel mileage on the car?
(I assume that since you are using bigger and heavier tires, the car has to use more power/fuel)
Not so much bigger and heavier tires but more so bigger and heavier rims.
To be honest with you, between my 15's and 17's I barely noticed any fuel consumption changes. Maybe 15 - 25 km less per tank with the 17's on
what kind of rims are the lightest? aluminum? which ones are heavy? (aside from actually lifting them myself to see(for u smart alecs out there lol)).
Every factor about a rim can affect its weight... number of spokes, size, etc
Aluminium is strong while not being too heavy. you should be aiming for rims that weigh no more than 19 lbs to have a weight benefit