Just find on of those trailer things the police depts uses to scare people into slowing down, and camp it until you can make passes un inhibited, and test it out. 20-30-40-50-60, and make a % difference estimate from that.

You know what I am talking about. The radar trailer....Your speed is (and in huge block letters) 56


87 Raider 4D56td v5MT1
31's..Basically Stock