I want to buy all new BF Goodrich ATs for my 01 XJ Sport I bought last week. What's the biggest size I can fit on it with no lift? What size can I fit with a 3 inch lift? I also plan on putting on flat fender flares no matter if I lift it or not, if that changes what size tire can fit with little to no rub.

With no trim and no lift 30's are probably the biggest you can fit. With minor trim and a 3" lift you should be able to get 32's or 33's in with proper back spacing. With minor trim and flat fenders probably 31's with proper back spacing, still might rub on LCA at full lock.

no lift
https://www.cherokeeforum.com/f2/max...e-95-a-117016/
https://www.cherokeeforum.com/f2/big...-sport-115035/
https://www.cherokeeforum.com/f2/tir...please-116270/

Generaly people say 30-9.5's, or 235/75/15's

3" lift
https://www.cherokeeforum.com/f67/32...ch-rub-125172/
https://www.cherokeeforum.com/f2/3-l...re-size-46142/

Generaly people say 31's.

I haven't seen the flat flares installed so I will let somone who has comment on how much room hey give you... But you will always have somone saying 33-35's as they cut a lot and bump stoped almost all up travel.. it comes down to how much your willing to cut.

^^This is correct!^^
30x9.50 15 is the largest with out any modification such as cutting or lifting.

BTW, The search button will get you far.