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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > What's run-flat tires?



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      03-11-2011, 11:41 AM   #1
xhf
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What's run-flat tires?

what's fun-flat tires?i am wondering what are they?what are some advantages of run flat tires?are they better than normal tires?
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      03-11-2011, 11:43 AM   #2
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Basically they fill up when you have a flat and they are not so well with handling but many cars come standard with it now because there too cheap to put in a spare
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      03-11-2011, 11:43 AM   #3
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      03-11-2011, 11:55 AM   #4
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Typical misinformation as common on this board.

Run flat tires have stiffer sidewalls that are able to support the weight of the car without being properly inflated. You can generally drive for about 50 miles or so when deflated.

In practical terms this means that you can safely drive to a tire shop if you happen to run over a nail and don't have to worry about changing your tire on the side of the road, in the rain and at night.

That said, the stiffer sidewall gives a harsher ride and the tires are not always immune to catastrophic failure following a run-in with a major pothole.
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      03-11-2011, 11:55 AM   #5
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The side walls of the run-flat tires are stiff enough to carry the load of the car without any air in them up to a surtain speed and range.
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      03-11-2011, 12:10 PM   #6
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Quote:
Originally Posted by ceb View Post
Typical misinformation as common on this board.

Run flat tires have stiffer sidewalls that are able to support the weight of the car without being properly inflated. You can generally drive for about 50 miles or so when deflated.

In practical terms this means that you can safely drive to a tire shop if you happen to run over a nail and don't have to worry about changing your tire on the side of the road, in the rain and at night.
That said, there is a chance that the side wall will break down during this 50 mile trip, and you would end up having to replace the tire rather than patch it up as you would do for a conventional tire. So if you want to save your RFT after a flat, stop the car as soon as your TPMS warning goes off and have it towed to a tire shop.

IMHO it was invented for lazyass people who can't spend 10 mins changing a flat. Whenever I get a BMW survey asking "What would you like BMW to change about their cars?" I always convey my displeasure about RFT tires.
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      03-11-2011, 02:07 PM   #7
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Quote:
Originally Posted by mad_max View Post
That said, there is a chance that the side wall will break down during this 50 mile trip, and you would end up having to replace the tire rather than patch it up as you would do for a conventional tire. So if you want to save your RFT after a flat, stop the car as soon as your TPMS warning goes off and have it towed to a tire shop.
Correct. The tire will be toast if you drive it without air.

This is the reason that some shops will refuse to repair RFTs - because you cannot tell if the sidewall has been damaged.
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      03-11-2011, 02:14 PM   #8
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Quote:
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IMHO it was invented for lazyass people who can't spend 10 mins changing a flat. Whenever I get a BMW survey asking "What would you like BMW to change about their cars?" I always convey my displeasure about RFT tires.
I can't imagine RFT's were designed or even used 100% for the reason of being lazy. Some cars just don't have the room for a full size spare. The donut spares are worthless so the next best thing is to run a tire that can get you to the nearest repair facility.

A full size spare in even a 5 series trunk would take up the majority of it.
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      03-11-2011, 02:21 PM   #9
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Basically they fill up when you have a flat and they are not so well with handling but many cars come standard with it now because there too cheap to put in a spare
Really? Seriously? I read this like 10 times just to make sure. You're joking, right? Please say yes. If not, please tell me what they fill up with exactly?
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      03-11-2011, 02:25 PM   #10
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Originally Posted by emmgrilli View Post
Really? Seriously? I read this like 10 times just to make sure. You're joking, right? Please say yes. If not, please tell me what they fill up with exactly?
The sidewalls are stiff because they contain canisters of air that release when the TPMS sensors detect a flat...duh.
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      03-11-2011, 02:27 PM   #11
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The sidewalls are stiff because they contain canisters of air that release when the TPMS sensors detect a flat...duh.
Ohhhh right! They should fill up with helium so the car can float to the nearest tire shop.
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      03-11-2011, 03:48 PM   #12
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Quote:
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The side walls of the run-flat tires are stiff enough to carry the load of the car without any air in them up to a surtain speed and range.
well put

I would add they also may no longer be used once you drive that 50 miles to the tire shop and a new tire will be required further they do put a lot of pressure on your soft alloy rims (that may be running on a 2.5 degree camber, therefore may contribute to cracking your wheel rim ~ further expense for a new wheel).

Then of course good luck finding that replacement tire best look for a hotel / motel while waiting for the replacement tire to arrive.

Hope he packed an overnight bag

bottom line ... ditch them RFT, a lot of people do ...
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      03-13-2011, 01:24 PM   #13
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Quote:
Originally Posted by ihsanshaik View Post
Basically they fill up when you have a flat and they are not so well with handling but many cars come standard with it now because there too cheap to put in a spare
OMG - - - - - -
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      03-13-2011, 02:01 PM   #14
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Runflats were originally designed as an answer to the product liability lawsuits from people driving with their tires underinflated. Then (IMHO) the manufacturers recognized the profit potential in them, and between those two incentives, here we are.

The end result, you pay more, you get less.
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