Roadie Elite Vehicle Safety Harness - Size 4 For dogs from 25 to 35 lbs with a rib cage circumference of 23.5" to 25.5" To get the RIB CAGE CIRCUMFERENCE measure your dog around the LARGEST part of his/her rib cage just behind the front legs while your dog is standing. Make this measurement SNUG, and be sure you can fit one finger under the measuring tape not two. In an auto accident a 60 pound dog in a car traveling 30 mph will hit an object ten inches in front of her/him at 1,200 pounds per square inch. Roadie's patented design stands up to extreme forces during sudden stops, sharp turns, and the unexpected. In fact, the Roadie has been tested and was shown to exceed S.A.E. tensile strength standards for human seat belts. And unlike other harnesses, Roadies includes no collar to choke and no metal or plastic parts to break. The Roadie comes in 8 sizes to best fit your dog.