Front
a stock width, lifted frontend can handle 215/75R15 tires, rub-free. you can go up to 235/75R15 with a little bit of rubbing. bigger tires up front give more ground clearence, traction and floatation but reduce your turning radius. i'm content with my 215's, they are the all around best performing front tire size. i know someone who squeezed 31 X 10.5's up front with a body lift.
widened front ends give you the advantage of running larger tires with little or no rubbing and no decrease in turning radius. you could go up to 33" and have an absolute shitload of ground clearence. i think my next foray into front end mods will be widening a beam.
Rear
talking irs here, 31" tires are the tallest you can go with stock trailing arms, width is a different story. i've seen 31 X 13.5 super swampers on a baja and 31 X 12.5 boggers on a baja. i go riding with these people on a regular basis, actually. these wide mudders have the advantage of making you practally invincable in the mud. but they have serious drawbacks. they are expensive, they reduce horsepower and they can total a baja in no time.
DANGER!!!!!!!
stick with the 31 X 10.5's they work well, look beefy and are reasonably priced.
30 X 9.5's are slightly smaller, though, i could not tell a difference between the two sizes, engine performance wise.
Types
the type of tires you need depend on the type of terrain you plan on using them in. of you don't plan on going off road very much at all (wimp) then just get big street tires, they will outlast knobby mud tires like you wouldn't believe.
if you play in the desert, then get some "all terrain" tires. i highly recommend B.F.Goodrich radial all terrains.
if you play in the mud, then get some mud tires, front and rear. standard mud tires are just about all the same except the super swampers and the boggers.
Used Tires
i love used tires! they are so cheap! i got a pair of 31 X 10.5 BFG all terrains for $ 75, i'm saving them for when my 30's are worn out. i also, finally, got some mud tires. a pair of 31 X 10.5 BFG mud terrains for $ 30!!!!! granted they have little tread, but i only use them in the winter during mud season. $ 30 for a pair sure beats $ 130 each. i got a pair of wide chrome wheels cheap, so i have two sets of rear tires and wheels.
if your baja is your daily driver, get two sets of rear tires and wheels! one for the street and one for the mud. it might seem expensive at first, but it will pay because your mudders will last forever.
Power
it takes horsepower turn big tires, simply because they upset the gear ratios. 4th gear is almost unusable with anything less than a 1600 dual port motor. so get a bigger motor or a bus tranny or both. your baja will be a joy to drive if you actually have power to spare and low gears. there's a reason good 4x4's have high range and low range gearing. low gears work better off road. bus trannys have lower gears than bug trannys.
