The aluminum wheels are corroding which is causing the tires to loose air pretty regularly.
I replaced the original tires (hankook) at approximately 25,000 miles due to minimal tread left on them, cupping and they provided a harsh ride. the new tires and original wheels were balanced during installation. the whole borrego shakes when driving between 10 and 35 mph. i took it back to the new tire installer and had them all rebalanced. it still shook but less than before. i have had them rebalanced two additional times at two different tire sales and service retailers since the first two balancings on the new tires. i have had the wheels and tires rebalanced four times in the 7,000 miles the new tires have been installed. the shaking has never been resolved. i suspect the lug holes in the wheels are no longer round. *tr