My car does the same thing when I tie down where you mentioned. How much air did you have in the tires. You could see the wrinkles forming in my rear tires. I had about 20 psi in the rear and 32 up front. If you were to tie down around the tires like Terry is asking or if ya went to the rear axle and front K-frame, what else would there be that would "give" other than the tires. It wouldn't affect the shocks or springs..