We coast as much as possible and shift into lower gears. We can't smell it until we stop. We got out and sniffed around each tire and felt them. The culprit is the trailer. I have an infrared gun. I never thought to take it with us. I will take the tires off and have a look. We will have to readjust my trailer brake controller and have another go this weekend. We keep our cargo pretty minimal. There isn't much cargo in the car. 2 adults and a teenager travels in the car. We ocassionally throw some last minute groceries in the back on our way out. We thought about adding some leaf spring helpers to stiffen the back end though.