Either 18s or 20s will work just fine. It would be hard for me to pass up putting dubs on it. 40-45 series tires aren't too rubber band-ish. Been running similar size 275-40-20 on our Chargers for alot of year and alot of miles. Being daily drivers they do get a few curb miles... unfortunately. But they're not so short of sidewall that bent rims are an issue.
Either rim size in a 28" ish diameter tire won't have enough sidewall height to protect against curb rash, so no advantage to the 18s in your case.
But I do like the more subdued look of 18s. A buddy has restored a couple C10s, lowered, and has 18s on both (not steelies) and they give it a stockish look but a little cooler.
Vs 20s which are noticeable form 100yds out!
Boils down to what look you want. And our votes don't count! It's your truck.
Something worth mentioning that some of you probably know, but I never thought of until I took some wheels to get straightened by a wheel repair guy. If you see a pothole or sharp edge while driving and you're destined to hit it, DO NOT hit the brakes. Of course, in general, hitting it slower is better, but if you're on the brakes at all when you hit the pothole, the wheel will lock up momentarily when it loses contact or pressure with the road and then it will crash into the pothole not rolling, which causes the majority of bent rims.
