From what I've heard it will get a little softer once broken in. I can also tell you that one time I used contractor grade polyurethane to fill in the mounts on my 97 civic. I don't know what the durometer rating of it was but I'm sure it was stiffer than 70a. After 3 months it surely didn't get softer, and it rattled everything in the car pretty bad, but I didn't have any wheel hop...that's for sure.