I am thinking of getting new tires and I want to get 235 instead of 225 this time since my rims are 40 offset, I am afraid 235 will stick out of the fender or will rub so instead of rolling the fender, will it be safe to slave off the offset a bit by a machine shop?

 

I've read of several people doing this on various car forums. I think as long as you don't go overboard you should be OK. For example, I think maybe 3 mm would be OK. I'm sure rim design would also affect this as well. If there is sufficient thickness on the side of the rim which meets the hub, it would be safer.

Make sure you measure how much brake caliper clearance you have. If the spokes on your rim is only say 3 mm from the brake caliper, you obviously would have very little room to shave.

 

I think 2-3mm is already good enough since I think our car should able to hold 235 tire on 42 offset and I currently on 40 offset.