RXGS

iTrader: (2)

I was just wondering would a 18x8 rim with a 225/45/18 tire and a 50 offset fit my car that has 20/60/16 tires with 16's I'm not sure of the offset but it is a 2001 Lexus Es300

zig@tr

The offset is high you could benefit from a 5-10mm spacer to push the wheel out further. The 225/45R18 is taller than OEM by .4" ,225/40R18 would be better with the extra width in the tire.

RXGS

iTrader: (2)

Would a spacer be necessary for it to fit?

zig@tr

Probably. The front wheels will be really close to the inside suspension components and when turning full lock to lock they might rub the inside fenders. The wheels are just tucked under the vehicle more than they should be, but you can always do a test fit and if it doesn't work you always have the option to add the spacer. The taller tire you are using also compounds the problem and will probably make the spacer required in order to get these on there with zero issues.