i have a 97 Lt1 with the stock chrome rims they are 16's I think I wanted to get a rear set-up of weld drag-lites and nittos for the street but all can find size wise, in the welds are 15's is it ok to go smaller, also how wide should I go?

 

Weld makes a 16" drag lite called the XP. Almost as heavy as the stockers.
I have been running 15" welds for well over a year,no problems.
I believe with 15x8's you dont have to grind the caliper in the back,but 15x10's you need to modify the caliper.

 

so it's alright to run 15's in back and 16's up front?

 

If you're just running them @ the track, you shouldn't have a problem. I would not get the XPs no matter what. They look like crap and weigh too much.

You can run your stock wheels up front and the Welds in the back w/o a problem though.

If you're just doing the rears, you may have to do a little grinding w/ the Draglites. I would run the 275/50-15 555R Nitto on a 15x8 Draglite. They're only a little taller than your stock 245/50-16s.

 

I know with the Pro-Stars, the interference with the caliper is the fins against the knuckle of the wheel, where the center disc curves into the rim. That point of interference isn't going to change, no matter what the width of the rim. I didn't have to do any modifications other than grind the fins off with 15x10 Pro-Stars.

 

I had to grid a little off the caliper fins for my 15x8 draglites to fit. No big deal, just a few minutes with a file and they fit.