Run-Flat tires. Are they worth it?
03-10-2003, 10:03 AM
#4
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more info from tirerack:
Self-Sealing
Self-sealing tires are to designed fix most punctures instantly and permanently. These tires feature standard tire construction with the exception of an extra lining inside the tire under the tread area that's coated with a puncture sealant which can permanently seal most punctures from nails, bolts or screws up to 3/16 of an inch in diameter. These tires first provide a seal around the object when the tire is first punctured and then fill in the hole in the tread when the object is removed. Because these tires are designed to seal the tire immediately upon being punctured, most drivers will never even know that they just had a puncture. Also because these tires feature standard tire constructions, the traditional loss-of-air symptoms which accompany a flat tire remain to warn the driver if the tire is damaged beyond repair. Therefore, self-sealing tires do not require a low air pressure warning system. Examples - Firestone FT70c Sealix, Uniroyal Tiger Paw with NailGard, Tiger Paw Royal Seal and General Gen-Seal.
Self-Supporting
Self-supporting tires feature a stiffer internal construction which is capable of actually temporarily carrying the weight of the vehicle, even after the tire has lost all air pressure. These tires typically sandwich rubber between layers of heat resistant cord in the sidewall to help prevent the sidewalls from folding over on themselves and "pinching" their sidewalls in the event of loss of air pressure to give the tires "self-supporting" capability. They also feature specialized beads which allow the tire to firmly grip current original equipment and aftermarket wheels even in the event of air loss. Because self-supporting tires are so good at masking the traditional loss-of-air symptoms which accompany a flat tire, they require a tire pressure monitoring system to alert the driver that they have lost air pressure. Without such a system, the driver may not notice underinflation and may inadvertently cause additional tire damage by failing to inflate or repair the tire at the first opportunity. Typically, self-supporting tires maintain vehicle mobility for 50 miles at speeds up to 55 mph. The Firestone Firehawk SZ50 EP RFT developed specifically for the Chevrolet Corvette C5 as well as the BFGoodrich Comp T/A ZR SSS, Dunlop SP Sport 9000 DSST, Firestone Firehawk SH30 RF and Michelin ZP are self-supporting run flat tires.
Auxiliary Supported Run Flat Systems
Auxiliary supported systems combine unique wheels and tires and are currently under development for use on future original equipment vehicle applications. In these systems, when the tire loses pressure, it rests on a support ring attached to the wheel. The advantage to this type of system is that it will place most of the task of providing run-flat capability on the wheel (which doesn't "wear out" or need to be replaced), and minimizes the responsibility of the tire (which does wear out and requires replacement). Additionally, auxiliary supported systems promise better ride quality because their sidewall's stiffness can be equivalent to today's standard tires. Today, only a few vehicles (not imported into the United States) use Michelin's PAX System. Goodyear and Pirelli have announced that they will also develop run flat tires based on the PAX System, while Continental is currently developing an alternate design. The disadvantage to auxiliary supported systems is that their unique wheels will not accept standard tires and that their lower volume will make this type of system more expensive. It is too early to confirm which system, if either will be widely accepted by vehicle manufacturers and consumers in the future.<ul><li><a href="http://www.tirerack.com/tires/tiretech/runflat/runflat.htm">click</a></li></ul>
Self-sealing tires are to designed fix most punctures instantly and permanently. These tires feature standard tire construction with the exception of an extra lining inside the tire under the tread area that's coated with a puncture sealant which can permanently seal most punctures from nails, bolts or screws up to 3/16 of an inch in diameter. These tires first provide a seal around the object when the tire is first punctured and then fill in the hole in the tread when the object is removed. Because these tires are designed to seal the tire immediately upon being punctured, most drivers will never even know that they just had a puncture. Also because these tires feature standard tire constructions, the traditional loss-of-air symptoms which accompany a flat tire remain to warn the driver if the tire is damaged beyond repair. Therefore, self-sealing tires do not require a low air pressure warning system. Examples - Firestone FT70c Sealix, Uniroyal Tiger Paw with NailGard, Tiger Paw Royal Seal and General Gen-Seal.
Self-Supporting
Self-supporting tires feature a stiffer internal construction which is capable of actually temporarily carrying the weight of the vehicle, even after the tire has lost all air pressure. These tires typically sandwich rubber between layers of heat resistant cord in the sidewall to help prevent the sidewalls from folding over on themselves and "pinching" their sidewalls in the event of loss of air pressure to give the tires "self-supporting" capability. They also feature specialized beads which allow the tire to firmly grip current original equipment and aftermarket wheels even in the event of air loss. Because self-supporting tires are so good at masking the traditional loss-of-air symptoms which accompany a flat tire, they require a tire pressure monitoring system to alert the driver that they have lost air pressure. Without such a system, the driver may not notice underinflation and may inadvertently cause additional tire damage by failing to inflate or repair the tire at the first opportunity. Typically, self-supporting tires maintain vehicle mobility for 50 miles at speeds up to 55 mph. The Firestone Firehawk SZ50 EP RFT developed specifically for the Chevrolet Corvette C5 as well as the BFGoodrich Comp T/A ZR SSS, Dunlop SP Sport 9000 DSST, Firestone Firehawk SH30 RF and Michelin ZP are self-supporting run flat tires.
Auxiliary Supported Run Flat Systems
Auxiliary supported systems combine unique wheels and tires and are currently under development for use on future original equipment vehicle applications. In these systems, when the tire loses pressure, it rests on a support ring attached to the wheel. The advantage to this type of system is that it will place most of the task of providing run-flat capability on the wheel (which doesn't "wear out" or need to be replaced), and minimizes the responsibility of the tire (which does wear out and requires replacement). Additionally, auxiliary supported systems promise better ride quality because their sidewall's stiffness can be equivalent to today's standard tires. Today, only a few vehicles (not imported into the United States) use Michelin's PAX System. Goodyear and Pirelli have announced that they will also develop run flat tires based on the PAX System, while Continental is currently developing an alternate design. The disadvantage to auxiliary supported systems is that their unique wheels will not accept standard tires and that their lower volume will make this type of system more expensive. It is too early to confirm which system, if either will be widely accepted by vehicle manufacturers and consumers in the future.<ul><li><a href="http://www.tirerack.com/tires/tiretech/runflat/runflat.htm">click</a></li></ul>
03-10-2003, 10:13 AM
#5
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Short answer: Probably not worth it on the A4. Long Answer (inside)
Currently, runflat tires consist of a compromise between performance/comfort and convenience/safety.
Runflat tires typically have a very stiff sidewall with little flex. This hampers both performance and comfort, as it translates into a stiffer, noisier ride, and handling suffers a bit.
OTOH, if you do get a flat tire, it is convenient not having to replace the wheel/tire, and if the puncture occurs at moderate/high speed, the runflat tire will probably help the car continuing safely in the current direction.
In some ways, think of it as an added form of insurance. But, like insurance, you end up paying for it in terms of additional cost for the tires and tire monitoring system, as well as in a performance/comfort hit.
On a Corvette where you don't want to carry a spare tire, it is worth it if you're willing to accept the performance/comfort hit.
On an A4 which is already pretty heavy, carrying a spare is not much to ask. So, runflats probably aren't worth it, unless you refuse to change a flat yourself, and don't want to have to wait for roadside service.
Runflat tires typically have a very stiff sidewall with little flex. This hampers both performance and comfort, as it translates into a stiffer, noisier ride, and handling suffers a bit.
OTOH, if you do get a flat tire, it is convenient not having to replace the wheel/tire, and if the puncture occurs at moderate/high speed, the runflat tire will probably help the car continuing safely in the current direction.
In some ways, think of it as an added form of insurance. But, like insurance, you end up paying for it in terms of additional cost for the tires and tire monitoring system, as well as in a performance/comfort hit.
On a Corvette where you don't want to carry a spare tire, it is worth it if you're willing to accept the performance/comfort hit.
On an A4 which is already pretty heavy, carrying a spare is not much to ask. So, runflats probably aren't worth it, unless you refuse to change a flat yourself, and don't want to have to wait for roadside service.
03-10-2003, 11:08 AM
#6
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Unsafe without monitoring system
If you get run-flats, you'll need to also get a tire pressing monitoring system. The reason is that these tires work so well when punctured that you might not notice the problem. Since the sidewalls will only support the car for so many miles before failing, you can drive on the car until the sidewall of the punctured tire finally fails without any warning. This is why all cars sold with run-flats as original equipment have such a system (e.g. MINI).
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