Anyone have 20" 305 50tys on a 2003 or newer GMC excab 4x4?
I'm trying to figure out what kind of offset I need so the do not stick out of the wheel well.

 

I'm not real sure the exact offset but I think most rims are made to fit flush with a properly sized tire (275-295). With a 305 tire, it might stick out just a small whisker. If I had a choice between a tire sticking out or being tucked in, I would choose the one sticking out ever so slightly...

 

My rims are 5 5/8 backspace and they stick out just a wisker with 275/55 r20's.

 

305's are a good tire choice if your truck has the factory fender flares. If not go with 285/50/20. That is the size tire I have and it fits the wheel perfect and doesnt stick out. Its just right. I have Centerline Stingray III's, Im not sure what offset they are, I think it's 5".

 

I have a 285/50/20 tire and I think it is the perfect size all around tire. I especially like the looks of it from the back.

 

I've been running 305/50's for 3 summers now. Without flares they wud stick out a bit tho. GM recommends 285's when they sell u their 20" rims as that tucks and doesn't have any rub. 305's look awesome handle great around hairpins and off ramps, but man are they heavy! I did sway bars last yr and together with those tires I can take corners with near anything. Thats said I'm gonna embark on a police style wheel setup once the motor is ready to lighten the truck up a bit. R/

 

I order to determine the correct offset/backspacing, we need to know the width of the wheels.

 

I agree that the 285/50 20's are the way to go, that's what I have on my Gibbs wheels and they seem just right IMO. There's a guy at SilveradoSS.com that is or was running 305/50 20's on his SS, I think his screen name is Autoguy. You might be able to catch some pics of what you're looking for with a little searching over there.

 

I'm runnin 285-50s on 20x9 with a 5.5 backset they are almost flush maybe stick out a tad.