The Z71 is built for offroad use.
There are a number of ways to distinguish between Chevrolet and General Motors Z71 and Z85 models. The first is to check inside the glove compartment to locate the identification tag. That is an easy method of distinguishing between the two vehicle models. You can also examine the suspension, wheel diameters, engine and fender flares and look for evidence of torsion bars as well. Torsion bars are only present in unmodified Z71 vehicles.
1. Look inside the glove compartment for a small identification tag which may have Z71 or Z85 printed on it.
2. Measure the shock absorber spring coil height. According to GMC, Z71 Chevy cars have 1.81 inch shock absorbers. The Z85 shocks will measure less than 1.81 inches. You may also consult the owner’s manual. Look for the “Specifications” page. There you should find a section entitled “suspension,” which will detail the specific sizes of the shocks and springs. This can be done independent of a physical examination.
3. Look for jounce bumpers under the car, in the same location as the wheel suspension. The Z71 has off-road jounce bumpers, which are elasticated cushioning components that stiffen the suspension. Jounce bumpers have an unusual design and include a mounting plate and one or two tubular extensions which stick out from the mounting plate, so they are easy to spot. They look like stacked donuts.
4. Measure the wheel diameters and tire sizes. The Z71 has larger wheels with a greater diameter and thicker tires. The Z85 has 265/70-17 tires whereas the Z71 can take larger 285/70-17 tires.
5. Lift the hood and look inside the engine compartment for a flat, metal plate designed to keep out rocks and debris as the vehicle moves across rugged terrain. The protective plate will be located underneath the engine, between it and the undercarriage. You may also get onto your knees and look under the vehicle for the skid plate. It is a flat, metal plate which lies directly below the undercarriage and is affixed to it with metal bolts at either corner. If either protective plate is present, the vehicle is a Z71. Z85 cars do not have such protective plates because they are not four-wheel drive, off-road-style vehicles.
6. Measure the fender flare widths using your measuring tape. Start from the inside edge and measure to the outside edge of the curved flare. Fender flares are usually black plastic curved arches which add additional coverage to the existing wheel arch over each of the tires. The Z71 has wider fender flares than the Z85, adding up to 2.25 inches of extra tire coverage. Standard Z85 flares measure 17 inches, so the Z71 would have at least 19.25 inch flares from edge to edge. Fender flares are also known as wheel arch extensions, as explained by Jungle Fender Flares.
7. Slide under the car and look for torsion bars beneath the engine. They are large, heavy pieces of metal stretching the width of the chassis. They serve as supports for the whole undercarriage, so are very easy to spot because they stand out. Only the off-road Z71 has these extra supporting structures..