Tallest and widest tire for this combination:

1968 Charger

Us CarTool mini tub and spring relocation kit

15x8.5" wheel with 4.990" backspacing.

Stock Dana 60.

I am just learning about the drag racing side of life, and I would like to know what the widest and tallest drag radial would be to fit.

If I have not provided enough information please let me know, and thank you Moparts members for some advice.

I know a 325 drag radial fits no problem...We ran them on a 70 Charger.

295 should fit no problem, and they are 29.5 so it won't look small like a 275. How fast you looking to go ?

315x60x15,295x65x15,325x50x15
A 10 inch wide wheel will work better also

That wheel will kinda limit you. I'm no drag radial expert but a 295-65-15 will fit without mini tubs, I don't know if I'd go any bigger on that wheel

Past research indicates 15x12 with 7.5" backspace, 30-ish max height and 16 to 16.5 max section width is about the limit.
Something slightly less than that should be a near perfect fit on a rim of that spec. Right around this dimension https://www.jegs.com/i/Hoosier/522/18195D06/10002/-1

Usually I don't post unless I've done something but ....ask anyone who has gone to events with me, they will tell you I've looked underneath alot of cars to see what was done (weirds people out) and took alot of notes over time. I'll probably head down that road eventually when I cut the quarters off the old b body.

Thank you all for the replies. I have a specific wheel I want to use and it is 8.5" wide. Maybe I should have the rears widened.

295-65 radial fits the 8.5" wheel perfect. It's what I run on my cuda.