In the past several months of writing the C5/C6 Solutions column here in Corvette Fever, I've received a surprising number of letters and emails from various readers looking for quieter replacement tires than the stock Goodyear Eagle F1 GS EMTs for their C5s. Honestly, I never thought the Eagle EMTs were all that noisy myself, but then again my C5 convertible has several modifications (including a low-restriction 3-inch-diameter exhaust system) that make it a bit louder than a pure stock C5 would be-but that's the way I like it. This interest in finding quieter rubber intrigued me, however, especially since I didn't have a good answer for these readers. So I set out to find out which tire(s) were actually the quietest ones you could put on your C5.
At first we were going to restrict our investigation to run-flat tires only, but then we decided to include non-run-flat tires as well. This decision was made for several reasons. First, only three other manufacturers in addition to Goodyear made their run-flat tires available for testing; second, a considerable number of C5 owners have abandoned the security of run-flats, opting instead for less-expensive (and less-stiff) non-run-flat tires; and third, we felt that expanding the testing to include non-run-flats would give a broader spectrum of how the most popular C5 tire brands (and models) fared on a level playing field.
To keep the testing 100 percent objective, only the in-cabin noise levels were measured-no subjective information (e.g., ride quality, cornering, braking, acceleration, and so on) was collected or reported for these tests. The resulting test numbers are the measurements recorded on a Martel Electronics Model C-322 Sound Level/Data Recorder decibelometer. The Martel meter was mounted with foam insulation on the flexible stalk that usually holds the GPS unit in the test vehicle. Only the raw data as recorded is being shown here.
The Test Vehicle
A '98 C5 convertible was the test vehicle. The car has SLP ZL7 modifications made to it, including tuned headers and a double-D, low-restriction, after-cat exhaust system. The normal, in-cabin sound level when idling is 63dB (decibels), which is our baseline figure. Prior to starting the tests, the car received a full alignment at Tire Craft in Point Pleasant, New Jersey, where all of the tire mounting, inflation, balancing, installation, TPMS training and demounting were performed. Two identical sets of black powder-coated Z06 Motorsports wheels were provided by Zip Products for use in these tests; the front wheels were 17x9.5 inches and the rears were 18x10.5; the TPMS (tire pressure monitoring system) sensors were provided by Contemporary Corvettes of Bristol, Pennsylvania; and all tires were inflated to 32 psi prior to the commencement of each test pass. A natural harmonic resonance from the exhaust system occurs between 53-57mph as a result of the SLP modifications to the test C5; hence the cabin noise levels are resultantly louder during this speed band for all tires tested.