i have new front tires and half worn rear tires (275/40/19). I find the car scary at highway speed in heavy rain. Car is new to me so not much to compare to. Are 275 prone to hydroplane?

I had the same issue in my car with the staggered setup and actually did hydroplane. The car ended up hitting the side of the curb at about 35 on a side street (speed limit 40) and curbed the wheel up pretty bad and bent the strut control arm so bad the car was undrivable. Had it towed to my family’s business and replaced the arm for about $100~ dollars from an online vendor (can’t remeber specifics as it was over a year ago.) After I replaced that stuff I took it to my local tire shop and they found that the insides of the tires were super worn and needed replacement (1/32 tread.) The outsides looked fine, but the cords were showing on front and rear edges. I replaced all tires with Pirelli P-Zero Nero tires and don’t like them at all (lots of road noise and little grip, but great in snow and rain.) I also had the car aligned and tires rotated at MB dealer for $300. (Side Note: is it true that MB is the only place you can have the car aligned properly? That’s what they told me and the car drove so much different after. They did something to the Airmatic properties and the ride height increased prolly half an inch or so. ) Anyways back to topic. Make sure your car is properly aligned and tires aren’t wearing on insides. I had just bought my car 4 months prior to this happening and only put about 4K miles on the car when they looked trashed. The tires looked fine when I bought the car (were only a year old Michelin PSS.)