How to choose the right Rims

i have been using this set of 18inch rims with falken tires for almost a year now, came along when i bought this car, after a wheel and about 30k km of travelling, the tires started to emit this very loud sound when i pick up, the sound goes away at a higher speed of 80km/hr and above, i noticed too the Fuel consumption of the car went up as well as a result.

initially i thought there was something wrong with my brakes but after checknig with a few mechanics, they all said my rims were too big and advised me to switch to a smaller set of rims. with bigger rims means bigger fuel consumption too of about 8km per litre or less.

after some inspect on the tires i realized the front set of wheels is balding internally, what i did first thinking my tires were faulty i switch the back wheels to the front, the sound got louder this time and i was concerned, finally i decided to bring the car to M and Q at Tampines behind Safra for an inspection along with my usual servicing, Mr Chia was friendly and honest in my dealings with him, basically he told me it was the tires that were the culprit, just switch to smaller set of rims, he recommended 15 or 16 which is the recommended stock size for a e36 318ia.

anyway to cut the long story short, i learnt too that my car was previously lowered, and as a result with the larger rims, the weight is caving internally on the car, resulting in a negative camber, thus the inner thread of the front wheels are wearing out fast than the ones at the back.

so i decided to change my rims quickly, a friend recommended a tire shop along Ubi Avenue called LS at blk 53, they had a set of almost brand new BBS rims and they do trade in which was just what i need.

BBS is a german brand, they manufacture forged alloy rims which are stronger and much lighter than my steel rims, after trade in i had to top up about $300, the original price was $800 for the set of BBS rims, they charged me $175 for a piece of Firenza 225/40 tires, 225 is the wdith of the tire, not sure what the 40 meant, all in i paid about $1000 for the BBS rims and the new tires.

it's been 3 days since and the car feels much lighter than before, pick up has improved tremendously. however i think the 17inch is probably still too big for my ride, whenever i do a u-turn u can hear the tires rubbing against the inner side of the car.

my wife was more concern that the BMW logo was gone from the rims. i will assess the situation and hopefully the camber situation is alirhgt, worse case scenario is to switch to 16inch instead.