The car seemed fine until I got up to highway speeds. At speed, it shook horribly. I stopped and checked the tire pressures. Left Front 45, Right Front 45, Right Rear 45, Left Rear 23. I would guess the left rear tire is badly out of balance or the wheel is damaged. When checking tire pressure, I also noticed all four tires had cracked rubber on the sidewalls. I drove the rest of my trip concerned about a tire blow-out. Thankfully, I made it back without incident.