im lost when it comes to tire sizes so im looking for some input i just got some 18x10.5 wheels for the rear and i was wondering what would be the best tire size for fit, ride quality/handeling i was looking at some 285/40 also im lowering the car as well about 1.5" in the back would there be any issues?

 

a 40 series tire would be just fine since the rim is 18" diameter, but since it is 10.5" wide, I'd go with a 295

I am running a 295/30/20 on my 20x10's out back.

 

my buddy is running a 305 and it looks beast!
i would suggest a 305/40/18

 

I agree, since you have a 10.5" wide rim, a 305 would work/look great also.

 

What's the offset?

 

offset is +50mm

 

Here's my 275/40/18's on 18x9.5 w/50mm offset. Note that I'm not lowered:

 

those look mean as hell are the front the same size? i could just imagin what a 305/40 would look like, im thinking 295/40 or 35 for me

 

Yes, I'm running the 275's on all 4. If I had to do it again though, I think I'd put 255's up front. The 275's are havoc on truck rutted roads. The front end wants to track every edge and shifts side to side.

 

Take a look at the available 285/40 and 305/40's and make your decision there. 255/45 best up front. Keep in mind 305 will change your final drive ratio.