Guys I need your help please. I’m looking for quiet off road tires for my 2006 Lexus LX470. I was debating between Cooper Discoverer STT Pro or BFG KO2’s. Or if you can recommend better ones. Also what is the biggest size I can go without modifications? Thank you.
You're at two ends of the spectrum there. The SST Pro is an M/T tire (even though Cooper likes to call it an A/S off-road tire) and the KO2s are a mid-aggressive A/T tire. So it really depends on what you want your tires to do best.
I've run the BFG KO2s (LT275/70R18 E) and Continental TerrainContacts (275/65R20 XL). The KO2s are a decent all-around tire but IMHO they don't live up to the hype and I believe there are now better options. They are also not particularly quiet for what they are. I'm actually looking to replace them because I want something more aggressive and capable off-road. They are 3-peak snow rated (3PMSF) and passable in the snow, but they are
NOT winter tires and don't do well on ice. If you go with K02s be careful because there is a version (DT) that is not snow rated.
The TerrainContacts are a "light" A/T tire biased toward highway performance. Very smooth and quiet on the freeway, so great as daily drivers that give you decent off-road performance. I drove "Fins and Things" (4/10) in Moab with them and even cleared "The Wall" as well as handled some flat muddy roads without any drama. Not quite as good off-road as the BFGs but MUCH better on roads.
Keep in mind that A/T tires aren't ever very good in the mud, and they also don't even come close to a winter tire in snow and ice, or even cold dry roads for that matter. 3PMSF be damned, the rubber compounds are just too hard in cold weather. I ride Nokian Hakkapeliitta R3 SUV tires in winter and they are FANTASTIC. Would also recommend the new Nokian LT3 if you need E rated tires.
So, what to buy? If you want an aggressive A/T tire with better than average snow performance the Falken Wildpeak AT3W is highly recommended. Falling somewhere between the Falken and Conti in aggressiveness is the Cooper AT3 XLT, which is also very durable, smooth and 3PMSF.
If you want even more off-road capability (including mud) and are willing to trade a small increase in road noise, I recommend looking at the new class of 'hybrid' (or R/T) tires which seek to combine the best of an A/T and M/T. I've got my eye on the Nitto Ridge Grappler, which everyone seems to LOVE, or the newer Yokohama X-AT. (FYI the Cooper R/T tire is the S/T MAXX, which I gather is quieter than the STT PRO, but not quite as smooth/quiet as the Nitto and Yoko I mentioned).
Hope that helps. Good luck!