tire width

Thanks guys.
I really don't want to trim lip at same time I need grip I am hoping for 11's. Does it make that much difference with only 1/2 inch extra tread? Btw I learned the hard way I bought a set of weld wheels with 275/60/15's off a duster and they stick outside my wheel wells about an inch and when I put my hand up the wheel well I lose even more.