Specifically I'm worried about the front rubbing when I take turns or hit bumps with portly passengers... Anyone have any issues with 255s being too large in the front?

My vehicle is stock with no mods: 2015 Lexus IS 250 AWD where the tires are: 225/40/18 and 255/35/18.

The new wheels are 19 x 8.5 with an offset of +40 and the new tires are 255/30/19 all around but want to know what issues I may have before mounting them.

 

You may have some rubbing issues running a 255 up front. I've heard people have issues with a 245 as well, but with a lowered suspension.

 

You’re right Eric, the 255s in front appear to have some rubbing when making turns at speed. The rubbing seems to only be on the inner wheel well lining, not the fenders. So I guess my options are:
1. Get smaller tires
2. Modify or get a more concave inner wheel well lining

Option 2 would be much cheaper but haven’t heard of anyone doing this... thoughts?

 

If it was me I would use a wheel spacer.
And yes you can remold the plastic liners with a heatgun and a damp cloth

 

My 2014 IS350 AWD F runs on 255/45/50 (rear) and 225/50/18's front. The fronts rub slightly when turning to tightly or when hitting a bump. If you run this size on a tire size comparison chart, you should be able to tell about whether your proposed size will make the cut. As Lexyaaaas stated, a heat gun can be used to reshape the lining. Here is a good "how to":