Yes the tires will wear a little faster but the stock goodyears don't get that great of mileage anyway.30psi you would be fine for driving on the road(3psi is not that much),I've driven 50+ miles at 12psi through the mountains with no problems before.As for sand with the OEM tires I would go down to 18psi,don't go lower the OEM tires can't support the KJ under that for to long(big risk of blowing a bead).The OEM tires are passenger car tires so getting a set of good LT(lite truck) tires will increase on-road traction and offroad capibility even by just getting A/T tires.