Not to steer the conversation off topic, but I don't understand why most folks in the Tacoma world (I'm coming from Jeeps) talk offset vice backspace. Telling someone you have a wheel with -6 offset and not saying what rim width you have is no help. For example, -6 offset on a 9.5" wide wheel is only about 5" backspace, which may not be enough backspace to clear the stock UCA with some larger tires like the OP is asking about. -6 on a 8.5" wheel however would be closer to 4.5" backspace and provide plenty of clearance. I'm running a 9" wide wheel with -12 offset, which also comes out to 4.5" backspace, same as a 8.5" wheel with -6 offset. My point being offset is relative to wheel width. Does no good to know one value without the other. Also, backspace is ultimately more important when talking about clearing larger tires in my opinion. I can see why offset and rim width would matter in some applications where you were trying to keep the tires inside a fender well, but I don't think that's the case with 99% of Tacoma owners asking about negative offset and larger tires.
To try and answer OP's question, I'm running 9" wide wheel with -12 offset (~4.5" BS), and 285/70R17 (~33") tires. I'm also on stock suspension waiting on lift to arrive. Clears the UCA fine, but had to do quite a bit of trimming (CMC, viper cut, additional inner liner trimming). Even with 2-3" lift, you'll likely rub with 33" tires offroad unless you limit articulation in some way. Add chains into the mix and it'll be even more challenging. Hopefully others will weigh in with first-hand experience, but I think you'll find that running 32" tires may be as big as you can go while still clearing chains unless mainly sticking to flat roads.
