What is the biggest tire that will fit on a 1991 Mazda B2600i?

I don't know what the biggest you can run is. I think they made them with different ride heights. but I can tell you my 10.50 31 15's are the biggest that will fit with out modifying my suspension.

to get any bigger i would need to relocate the from axle backward and add a body lift.

in fact they rub a little on the finder flairs when there new.

I recommend BFG All-Terrain T/A KO , 31 x 10.50R15, Radial. thats what have run for years.for the money and how long they last you can't go wrong.

btw your speedo's gonna read 19 mph under your real speed.