i have a 90 bronco II and it has 30 9.50 15s right now and will soon have some 31 10.50 15s and all i have done is replaced my worn out stock shocks with the same size but new so its all stock size, i work at les schwab and they or any tire place for that matter can tell you the biggest possible tire you can fit on it.
-kohl
Stock tires on the Bronco are 31x10.5 R15 with stock rims.
a 33-12.50 will fit stock
33x12.5
you can fit a 33 in tire
Bone stock with 15" steel wheels you can put 33" tires but they'll rub when the wheel is turned all the way. 31" tires won't rub. a 2" body lift is cheap and easy and will allow 35" tires. Offset wheels will allow a 33x 12.50 r15 tire under a stock Bronco and not rub
you can fit a 33"x12.5" tire
The biggest stock tire I have seen is a 245/70/16
You could possibly get up to about a 35 but the safest bet is 33.
Max tire size with stock suspension is 31"
For stock truck a 31 inch tire is the biggest possible and even this tire will rub
235 75R 15
31 x 10.50