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Inflatable Tires VS. Run-Flats on C5’s
Tire Showdown By: Tom Benford

Thousands of Corvette owners have experienced Goodyear unique Run-Flat Technology in the Eagle GS-C EMT (Extended Mobility Tire) since 1993. Today, the Eagle F1 Run-Flat is the exclusive tire on every C5 and C6 Corvette…

The term “Run-Flat” needs a bit of explanations; however, Run-flat tires cannot actually run flat. Instead, because of special rubber compounds and reinforced (stiffened) sidewalls, they do not go flat even when all air pressure is lost. However, they do not go flat even when all air pressure is lost. However, run-flat EMT tires allow drivers to travel at lest 50 miles at highway speeds with zero air pressure. That means you'll never be stranded on the side of the road in the way of danger, especially since today's Corvettes don't have spare tires. If you get a puncture (notice I didn't say a "flat", you just keep on driving to the nearest Run-Flat Authorized Goodyear retailer fo r repair or replacement. And, yes, run-flats can be repaired, provided the puncture occurs in the tread area - a special plug/patch is used for these repairs. However, as with just about all tires, if you get a puncture in the sidewall you can kiss that tire goodbye - sidwall punctures are the death knell for the run-flats. You should also be aware that any time a tire is patched or plugged it diminishes its speed rating.

HOW RUN-FLATS WORK:
When a Good-year Run-Flat EMT tire encounters a road hazard and loses air pressure, the vehicle remains supported by durable inserts in the sidewalls of the tire that are built to maintain their shape and derivability even with no air pressure. The vehicle can continue to travel with minimal effect on handling and braking. These tires perform so well when they're flat that C5s and C6s are equipped with special air valves a sensor system to alert the driver of any loss of air pressure. Without such a system, you might drive on the tire until it was damaged beyond repair.

THE QUEST FOR A CUSHIER RIDE:
There's no question that run-flats offer some impressive advantages over conventional tires but, as is usually the case, these advantages come at a price. Starting with the price of the tires themselves, run-flats will cost you on average about a third more than the equivalent non-flat radial; this can add up to some real money for a set of four. Run-flats also require special wheels that are design ed to maintain the bead even with no air-pressure, so if you have an older Corvette and you want to go with run-flats, factor in the price of a new set of wheels. One of the first things noticed on a C5 is that the ride is a bit stiff and the presence of a considerable amount of road noise from the tires in the cabin - these, too are common side effects of run-flats. This is one of the main reasons that many late-model Corvette enthusiasts begin to search for tires with a softer ride. Like many late-model Corvettes owners who wondered if changing the tires would be worth the expense and effort, we thought a showdown between run-flats and conventional "inflatable" radials might be a good idea.


GEARING UP:
To do a valid comparison of run-flats versus inflatable, we had to start with a level playing field. The first order of business was to get tires, and Tire Rack was our source. The company provided a pair of conventional Goodyear P275/40ZR18 F1 four-ply radials for the rear and conventional P245/45ZR17 F1 four-ply radials for the front. Tire Rack also provided the exact same sizes for Goodyear GS EMT tires for the run-flat portion of the test. Our test car was a 1998 C5 convertible. To give both the run-flats and inflatable their best advantage, a set of chrome Z06 reproduction wheels was also ordered from Mid America Motorworks. Utilizing another set of wheels meant that we were also going to need a set of tire-pressure sensors;20these were also acquired from Mid America Motorworks, along with a digital tire gauge.
Mark Mastrojohn, the manager of Tire Craft in Point Pleasant, New Jersey, installed the run-flats on the new wheels and added chrome tape weighs to the interior of the rims, then inflated them to the OEM-prescribed pressure of 30psi. He also "trained" the wheel sensors (see the sidebar). We were ready to start testing.

RULES OF ENGAGEMENT: For the objective testing, both sets of tires would be run over the same course at the same speeds, and average gasoline mileage would be measured as well as cabin noise at highway speed and 0-60mph acceleration. Subjective evaluations would include the driver's assessment of handling and cornering and ride quality, also considering driver and passenger comfort.
For the objective testing, a digital tire gauge would be used to confirm correct tire pressure and the tank would be full of high-test gasoline. The test course would consist of going from Brick to Atlantic City, both in New Jersey, and back again (100 miles round trip) on the Garden State Parkway and the legal speed limit of 65mph. A Martel Electronics 322 Sound Level Meter would be used to measure interior cabin noise at 65mph and the readings would be taken along the same stretch of the Parkway with no other cars passing or adjacent to the test vehicle. A G-Tech Pro SS Performance Meter from Mid America, would be used to measure 0-60mph acceleration and the C5's ow n DIC (driver information console) would provide the gas mileage figures for the tests.
At the completion of the run-flat tests, the car would be brought back to the Tire Craft to have the run-flats unmounted and the inflatables mounted, and the entire identical test would be repeated with the new tires. Here's how the testing went.

OBJECTIVE TEST RESULTS
Run-flats "Inflatable" Radials
Cabin Sound level 77.3dB 72.0dB
0-60mph 4.15sec. 3.95sec
Acceleration
Highway Mileage 28.mpg 25.1mpg

From these figures, you can clearly see that the run-flats were a bit noisier (5.3dB louder) in the cabin and just a tad slower in the 0-60mph acceleration test (.2 seconds slower). On the plus side, they delivered better mileage (3.5mpg more).

SUBJECTIVE TEST RESULTS: The run-flats give the car a stiffer ride that can be quite harsh on some roads and, after a couple of hundred miles of continuous driving (or as a passenger, for that matter), you feel like you've gone the distance. The stiffer ride enables you to take corners a bit faster, however, so if you don't mind giving up a little comfort in favor of better handling, the run-flats are the way to go. Bear in mind, though, that they produce more road noise inside the cabin and they seem to have a little less bite for off-the-line acceleration.
The "inflatables" are definitely the way to go if you have a long trip in mind or if you just want a softer, more comfortable ride in20general. They are quieter than run-flats and the difference in the ride is nothing short of remarkable - it really is a noticeably more comfortable ride for both driver and passenger. But because they're softer, the gas mileage that the "inflatables'' deliver isn't as good as the run-flats. Both the run-flats and the "inflatables" have their pros and cons. Let's assess each:
RUN FLATS

Pros Cons

No Spare Needed Noisier
Better Mileage Harsh Ride
Better Cornering Slower 0-60 e.t.
No Blowouts/Flats More Expensive
Special Wheels Required

INFLATABLES

Pros Cons

Softer Ride Less Mileage
Quieter Can Go Flat
Faster 0-60 e.t. Slower Cornering
Less Expensive Tire Repair Kit or Road
Service Card

Whether you stick with run-flats on your C5 or decide to go with Inflatables is a choice that only you can make. Factors such as the type of driving you do, what kind of roads you travel on, how aggressively you drive and the proximity of gas stations/tire repair facilities all come into the equation. The ideal solution would be to have a set of each mounted on wheels so you could chose what tires you want to use for a short jaunt as opposed to a long trip. But how many of us live in an ideal world?

March 2005 Vol. 9 Issue 3 Edition of Corvette Enthusiast

Vetteman Jack

Interesting read. Thanks for posting.