Well I've decided to get some new rims rather than use the fin type stocks on my 79 d100..I'd like to use a 8" wide rim thinking 235 75 15 . Been looking around to find the correct spacing....found a chart that lists stock 6" with 0 offset / no backspace info ..and found info stating LRE rims were 1 1/2" backspace with -25mm offset..is this correct? really don't want wheels poking out and of needless to say non rub either. Any info would be greatly appreciated..this is pic what may go on truck.

I can tell you that your info isn't correct, at least from a math stand point. 1.5" is greater than 25mm. 25.4mm is exactly one inch.

Also, don't forget that in 1978, LRT used two different wheel sizes for the front and rear. In 1979, all four were 15x8.

I had the factory wheels for a LONG time, but now I cannot remember the specifics of them. Age takes it tolls...

But in the end, you have nothing but room in the rear fenders on Dodge trucks. I even ran 15x10 Cragar SS's with N50's and while they filled out the space well, they were hardly jammed in there!

235-75-15 is roughly 29"s tall by 9"s wide.
They will easily fit stock 15 by 5.5 or 6 inch wheels.
If you go 15" by 8" you can upgrade easily in the future.

thanks for the info those measurements didn't seem correct to me either, however I was able to find some videos on the web on how to measure backspace and offset and it has been added to list of things to do tonight. I'm not sure of the width on the fin type mopar rims on truck now but I'll sort all that out tonight and post up measurements .