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.
The Test Course And Methodology
A 28-mile round-trip course was used, starting at Tire Craft in Point Pleasant and proceeding to the Garden State Parkway (north Exit 91 in Brick, New Jersey), the roadway used for the actual tests. Using the same mile-marker posts for each test run, cabin noise levels were recorded at 35, 45, 55, 65 and 70 mph. These readings were recorded with the cruise control set for the various speeds, and level sections of the Parkway (no inclines) were used with no adjacent vehicles pacing or passing when the readings were taken. The course direction changed from north to south two miles past Exit 98, where the service area plaza was used to turn around for the return leg of the course. Again readings were taken at the five speed levels using identical mile markers on level stretches of highway as previously described. At the conclusion of the test pass, the Parkway was exited at Exit 91 south, and we returned to Tire Craft so the next set of tires could be mounted prior to starting the next test pass.
All of the run-flat tires were tested on the same day, and all of the non-run-flat tires were tested the following day. The weather was dry and hot, with temperatures averaging 90 degrees for both days. The recorded sound levels for both the departure and return test passes were tabulated and averaged then entered into the charts appearing here. Two people were present in the test vehicle for all tests; the driver (Liz Benford) who set the cruise control at the appropriate mile markers and speeds, and a passenger (Tom Benford) who recorded the sound level meter readings at these points. The windows were up, the air conditioning was on the lowest fan point, and the stereo was not turned on during all testing.
The following tires were the ones used for testing. All tires tested were 245/45ZR17s for the front and 275/40ZR18s for the rear:
The chart colors correspond to the tires on the following page.
The Pit Crew
Mark Mastrojohn, the manager of Tire Craft in Point Pleasant, New Jersey, coordinated the efforts of his staff to ensure that the test tires were mounted, balanced, inflated, and changed on the test vehicles consistently and uniformly. Jason Rodger performed the alignment on the test car, Ian Bonham did the majority of the mounting, dismounting, and balancing work, and Scott "Skittles" Grande did the actual wheel-swaps on the C5 for each test.
How Loud Is Loud?
To give you some idea of just how loud a decibel is, here's a comparative "decibel ruler" from the National Institute on Deafness and Other Communication Disorders website (http://www.nidcd.nih.gov/health/education/decibel/decibel.asp):
Surprisingly, there wasn't a wide margin between the quietest and the noisiest tires for both run-flats and non-run-flats; in fact, the difference was astonishingly small, as these examples illustrate:@ 35 mph -the quietest run-flat tire measured 71dB;the quietest non-run-flat measured 68db;Difference: 3dB
@ 45 mph -
the quietest run-flat tire measured 72dB;the quietest non-run-flat measured 72db;Difference: 0dB
@ 55 mph -
the quietest run-flat tire measured 76dB;the quietest non-run-flat measured 78db;Difference: 2dB
@ 65 mph -
the quietest run-flat tire measured 76dB;the quietest non-run-flat measured 74db;Difference: 2dB
@ 70 mph -
the quietest run-flat tire measured 78dB;the quietest non-run-flat measured 75db;Difference: 3dB
Putting things into a perspective that's easier to relate to, consider this: the total difference between the quietest tire tested at 35 mph (68dB-the Michelin Pilot Sport PS2 non-run-flat) and the loudest tire tested at 70 mph (a 79dB tie between the Goodyear Eagle F1 GS EMT and the Kumho Ecsta MX XRP which are both run-flats) was only 11 decibels-or roughly the sound level of normal human breathing.
Any time a testing program of this scope and purpose is performed, the cooperation of several individuals working in concert is required to achieve the desired end result. It's appropriate to take the time and space to thank these people here and now for their efforts, cooperation, and interest in making these tests accurate and meaningful: Mark Cherveny and Jim Davis at Goodyear, Ron DeSmedt at Contemporary Corvette, David Walker at Zip Products, Matt Edmonds at Tire Rack, Mike Park at Kumho, Lynne Slovick and Nicolas Goubert at Michelin, Shari McCullough on behalf of Firestone, and Kelly Wiard at Tire Rack for providing the excellent high-res images of our test tires.
The perception and importance of how quiet your C5 tires are should be balanced by other factors, not the least of which is price. Since petroleum is used to a large extent for the manufacture of tires, with the current price of oil, the price of tires is a major factor to consider. The confidence that run-flats inspire should be balanced with the economic considerations that non-run-flats sell for considerably less than their run-flat counterparts. Also take into consideration that today's tire technology is vastly superior to what it was a couple of decades ago, so the possibility/probability of a blow-out is not too much of a concern these days. Couple that with the fact that the TPMS of your C5 will alert you if tire pressure falls below 25 psi, so you'll have a decent window to pull over before doing any damage to your tire or wheel. If you carry a small hot (jumper) box with a built-in compressor or a dedicated battery-operated compressor in your C5, you should be able to inflate and maintain enough tire pressure to get you to a service area or gas station so the puncture can be sealed. Or, you can always call AAA and have the C5 flat-bedded to your local garage or home. Certainly, the noise level of run-flats vs. non-run-flats shouldn't be the deciding-or only-factor in making the replacement tire choice for your C5.
We hope these test results and the information presented here help you make an informed decision when it's time to replace your C5 tires, whether they're run-flats or non-run-flats.