Dry Rot on Tires
02-27-16, 04:07 PM
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Dry Rot on Tires
Sheldon Brown's website:
I had one so-called "dry rot" tire come apart on me inconveniently, I have another one that is running strong after many miles. I think there is a tendency among many to replace tires often when they don't need it.
Dry Rot
"Dry rot" is a fungus that infects cellulose-based materials: wood, paper, cotton and the like.
Sometimes people speak of bicycle tires as if they suffer from dry rot, but this is not generally correct. (The exception would be for cotton-cord tires, but those pretty much disappeared by the mid 1960s, at least as far as clinchers are concerned.)
What people commonly call "dry rot" is a deterioration of the rubber, usually on the sidewalls. This is particularly common with gumwall tires that have been exposed to ozone damage. (A common cause of this is storing a bicycle near a household furnace. The brush-type motors on such furnaces often create sparks, which in turn create ozone.)
This type of damage is ugly, but not structurally significant, as long as the cords (fabric) of the tire are intact.
Generally, if a tire isn't lumpy/misshapen when inflated, and has not had the tread area worn too thin, there is no reason to replace it, no matter how ugly the sidewalls get.
Sheldon Brown's Bicycle Glossary Dr - z
"Dry rot" is a fungus that infects cellulose-based materials: wood, paper, cotton and the like.
Sometimes people speak of bicycle tires as if they suffer from dry rot, but this is not generally correct. (The exception would be for cotton-cord tires, but those pretty much disappeared by the mid 1960s, at least as far as clinchers are concerned.)
What people commonly call "dry rot" is a deterioration of the rubber, usually on the sidewalls. This is particularly common with gumwall tires that have been exposed to ozone damage. (A common cause of this is storing a bicycle near a household furnace. The brush-type motors on such furnaces often create sparks, which in turn create ozone.)
This type of damage is ugly, but not structurally significant, as long as the cords (fabric) of the tire are intact.
Generally, if a tire isn't lumpy/misshapen when inflated, and has not had the tread area worn too thin, there is no reason to replace it, no matter how ugly the sidewalls get.
Sheldon Brown's Bicycle Glossary Dr - z
02-27-16, 11:14 PM
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I've had good luck riding old gumwall tires that had cracked sidewall rubber, but lighter tires have thinner sidewall rubber and much thinner casing plies, so the outer ply of an old lightweight tire becomes weakened from exposure and thus extremely vulnerable to "outer-ply failure", which results in a bulged, mis-shapen tire casing.
Older tires also have a tendency for the bond between overlapping plies under the tread to de-laminate, with resulting same bulged and mis-shapen tire casing and torn tread.
Also, with older tires, the tread cap may tend to dissociate and part company with the casing, not to mention that the tread will wear at a greatly accelerated rate.
I run older tires at minimal pressures (do to my 140lb weight) and feel relatively safe doing so, but I also have a lot of experience in inspecting such tires for their suitability for an expected service interval.
Near-maximum pressures should not be applied to aged tires imo.
Older tires also have a tendency for the bond between overlapping plies under the tread to de-laminate, with resulting same bulged and mis-shapen tire casing and torn tread.
Also, with older tires, the tread cap may tend to dissociate and part company with the casing, not to mention that the tread will wear at a greatly accelerated rate.
I run older tires at minimal pressures (do to my 140lb weight) and feel relatively safe doing so, but I also have a lot of experience in inspecting such tires for their suitability for an expected service interval.
Near-maximum pressures should not be applied to aged tires imo.
02-27-16, 11:32 PM
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I'll replace whatever doesn't instill confidence.
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02-27-16, 11:33 PM
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I read that before too, at Sheldon's site, and it surprised me, that they're supposed to be safe. I think it would just bother me too much, in the back of my mind, and tires aren't that expensive. But it's nice to know, they "probably" won't disintegrate, for unplanned bike purchases, like yard sales. 
02-28-16, 07:30 AM
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If that "inconvenient" event happens to a front wheel as you are flying around a corner or changing lanes in traffic you will likely have a different perspective in the future.
02-28-16, 08:09 AM
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Any tire over about 15 years old needs to be replaced IMHO. I had too many bad experiences with old tires back when I was a poor kid. Now that I'm a financially secure adult I buy new ones when needed.
02-28-16, 10:05 AM
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I wouldn't want to take off on a long ride with a questionable tire, ditto for commuting to work generally speaking as well.
I think part of this includes a personal visual inspection of the tire as well. I think I can get a good idea if the fabric and structure largely look intact.
Part of the deal with dry rot is, it can destroy the tire to remove it so it might keep going on as long as it is on the wheel.
I think part of this includes a personal visual inspection of the tire as well. I think I can get a good idea if the fabric and structure largely look intact.
Part of the deal with dry rot is, it can destroy the tire to remove it so it might keep going on as long as it is on the wheel.
02-28-16, 11:09 AM
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Let me repeat that older tires are not suitable for use at the upper limits of their pressure rating in my experience, but are relatively safe at lower pressures if such pressure is suitable for the rider's weight and conditions. I have too many bikes to buy new tires for. I thus have had to select from discarded tires, which I have a lot of experience doing by now. Luckily I am light enough to run the lower pressures that have proven suitable for use with older tires, up to 15 years old in some cases. The really old tires suffer tread wear at an alarming rate and are generally too fragile to trust fully. And any used tire could have suffered trauma or chemical exposure, etc., so be careful.
02-28-16, 11:16 AM
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Very true. Risk level equals likelihood times consequence and in a corner at speed or traffic the consequence can be ugly so I like to keep the likelihood as low as reasonable. My two crashes like this were a beer bottle slash and a piece of plastic catching the sidewall from a cat carrier that exploded near by when it hit the pavement. I ride a lot of bikes and ozone/UV damage was present on that tire, but as you say it could have happened with any tire, I will never know.
02-28-16, 01:20 PM
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What's interesting about C&V foldable clinchers with Kevlar casings is the latex rubber coating over the sidewalls eventually succumb to age/dry rot, but the Kevlar stays good, so what happens is the latex rubber eventually turn into dust, falling off the sidewalls, but the tires look OK at a glance, as every strand of casing remains in place till they eventually let go from the bead, as there is no more rubber at the sidewalls to keep everything together under pressure. I was so lucky my two decades old Specialized Turbo VS which I foolishly insisted on still using, did not let go on the road, but did overnight, in my garage after a day ride. Did not even notice that all the sidewall latex coating was all gone till after the blowout in my garage....
02-28-16, 02:53 PM
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What's interesting about C&V foldable clinchers with Kevlar casings is the latex rubber coating over the sidewalls eventually succumb to age/dry rot, but the Kevlar stays good, so what happens is the latex rubber eventually turn into dust, falling off the sidewalls, but the tires look OK at a glance, as every strand of casing remains in place till they eventually let go from the bead, as there is no more rubber at the sidewalls to keep everything together under pressure. I was so lucky my two decades old Specialized Turbo VS which I foolishly insisted on still using, did not let go on the road, but did overnight, in my garage after a day ride. Did not even notice that all the sidewall latex coating was all gone till after the blowout in my garage....
Do you think it's the rubber that restrains the pressure in the tube?
When your tire burst, were there broken cords in the casing, or did they just move apart and let the tube out which then burst?
The same environments attacking your rubber are also at work on your cords, including the Kevlar.
02-28-16, 02:58 PM
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Luckily I was able to turn 'round and get back to the car without the sidewall failing completely. I scrapped both tires as soon as I got home.
DD
02-28-16, 04:04 PM
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Definitely hip to the ozone damage.
When I was in highschool, the police recovered a bike that had been stolen from me. It has been ditched in a field and laid on its side for about 8 months. The sidewalls that faced the sun were faded and cracked. The rear blew out on the first ride after I regained possession.
When I was in highschool, the police recovered a bike that had been stolen from me. It has been ditched in a field and laid on its side for about 8 months. The sidewalls that faced the sun were faded and cracked. The rear blew out on the first ride after I regained possession.
