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  1. #1
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    Gum Walls dried out, what to do ?

    Any thing to put on Gum Walls ?
    Tread is like new, low mileage, but sidewalls are real dried out and flaky.

    Tires are Nylon.
    Is it OK just to ride with them as is ?

    Size is 26x2.125. 40 pounds press. Thanks..

  2. #2
    Senior Member DannoXYZ's Avatar
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    No, they're toast, you need new tyres.

    The rubber in the gumwalls holds the fabric strands of the casing in place and allows them to be positioned for load-carrying. Without the rubber in place, the casing will allow the tube to squeeze through between the fibres. You'll have a blow-out when you least expect it.

  3. #3
    Senior Member OldsCOOL's Avatar
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    I have a '79 Motobecane Super Mirage with age-old (original??) tires with wasted gumwall sidewalls but the tread is not weatherchecked or worn. Still riding on them at near max pressure.

    You might want to replace them but it can be ridden if there are no bulges. The gum was just for good, trendy looks. Same material (if not mistaken) was used on brake lever hoods then and had the same short life problems.
    Having a flat tire as part of the total cycling experience is highly overrated. Knowing how to fix one quickly is not.

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  4. #4
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    Quote Originally Posted by DannoXYZ View Post
    No, they're toast, you need new tyres.

    The rubber in the gumwalls holds the fabric strands of the casing in place and allows them to be positioned for load-carrying. Without the rubber in place, the casing will allow the tube to squeeze through between the fibres. You'll have a blow-out when you least expect it.
    With respect to Danno, I disagree. Obviously neither of us atre actually seeing the ties, but I've seen many with dried flaking gum and the fabric intact and performing fine. Ad Danno points out the gum helps stabilize the plies a bit, but mostly it's just weatherseal. There's an adhesive between the two crossing plies keeping them form shifting, so you don't depend on the surface gum for that. I'd ride the tires but be attentive for any lumps or twists that might indicate the tire is failing. Also, if you see the plies separating anywhere where the tube could begin to balloon through, then the tire is surely toast.

    BTW- I ride tubulars, and UV and rain destroy the thin gum coating very early on, yet I've gone thousands of miles on tires in that condition.
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  5. #5
    7-speed doomsday prepper ThermionicScott's Avatar
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    Pics/more info would help. You could be describing tires 5 years or 50 years old.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
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  6. #6
    Senior Member Grand Bois's Avatar
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    Aren't skinwalls the same as gumwalls, but without the gum?

    I'm still riding some 30 year old tubulars with very crispy sidewalls and threads sticking out here and there. Someone suggested brushing on some latex, but I haven't gotten around to trying it.

  7. #7
    Certified Bike Brat Burton's Avatar
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    Hard to say. Usually its elevated temperatures and prolonged exposure to UV rays (extended periods outside in the sun for example) that ages tires prematurely, gumwalls just show things more prominently. The tread area hardens up, cracks and loses traction and braking power as well. Problem is - the tire carcass can also have degraded without it being as apparent.Given that those tires typically sell for less than $12, personally I'd toss 'em and just put on new ones.

  8. #8
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by FBinNY View Post
    With respect to Danno, I disagree. Obviously neither of us atre actually seeing the ties, but I've seen many with dried flaking gum and the fabric intact and performing fine. Ad Danno points out the gum helps stabilize the plies a bit, but mostly it's just weatherseal. There's an adhesive between the two crossing plies keeping them form shifting, so you don't depend on the surface gum for that. I'd ride the tires but be attentive for any lumps or twists that might indicate the tire is failing. Also, if you see the plies separating anywhere where the tube could begin to balloon through, then the tire is surely toast.
    True, we don't have enough data. I've just seen too many tyres with the gumwalls cracking off and seeing strips of black tube starting to peek out. Don't trust them at that point.

  9. #9
    Senior Member OldsCOOL's Avatar
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    Tires are fairly basic and inexpensive enough to warrant a change anytime you lack confidence in them. Switch 'em up. Gummies will look bad for a long long time before they finally give out....but I'm not doing heavy descents and centuries with my Moto that has them.
    Having a flat tire as part of the total cycling experience is highly overrated. Knowing how to fix one quickly is not.

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  10. #10
    Senior Member Ira B's Avatar
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    My commute has several very fast downhill runs which leads me to take the same view of tires as I do of food in the fridge.

    It may be ok but if you looking at it and even asking yourself, "gee, I wonder if this is still good" then toss it out and replace it.

    The best places (IMHO) to apply this thinking to a bicycle is tires, cables and brake shoes.
    Yep, THAT Ira

  11. #11
    coprolite fietsbob's Avatar
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    Inspect your tires over the web?, without being there?.. buy new tires..

  12. #12
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    Hmmmm. Lemee see. New tires VS emergency room and possible wrecked bike!

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    Quote Originally Posted by bobn View Post
    Hmmmm. Lemee see. New tires VS emergency room and possible wrecked bike!
    You folks need to stop the scare nonsense. Tires blow out all the time for any number of reasons, including new tires. A blowout is one of the real and everyday risks of riding bikes.

    BUT

    Blowouts rarely, if ever, lead to crashes, and even more rarely to injuries.

    If you cannot manage a blowout on a bike you shouldn't be riding in the first place, because blowouts can and do happen anytime.

    I'm not saying you'd want to ride torn up, dried out waiting to blow tires on a high speed alpine descent, but you should be able to make a value judgment balancing the condition of your tires and the type of riding you're planning on.

    Also, getting back to the OPs original question, there is very little direct correlation between the condition of the gum on the outside of the tire, and the structural integrity of the wall. A weak wall will manifest id a distorted or lumpy tire. If the tire inflates uniformly round, it's sound to ride on.
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  14. #14
    Senior Member BCRider's Avatar
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    The cracking of the gumwalls isn't that big a deal. However the access it provides for water and air to reach the cotton belt threads and allow them to rot very much is a big deal. If you can see the threads through the cracks then it's simply time to sigh and replace them. If there's no big bulges or noticable degrading of the threads that you can see in the cracks you don't need to replace them today but it would be wise to get some over the next couple of weeks.

    Frankly brushing on anything to fill the cracks and try to extend their life seems like folly to me. Once the dust and crud of daily life is in the threads it will continue to rot and cut away at the thread fibers. So once the threading is exposed to the elements of the daily ride for even a short while the doomsday clock begins ticking down...
    Model airplanes are cool too!.....

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    FBinNY nailed it.

    I've ridden lots of miles on tires with dry-rotted sidewalls... as long as they're not showing bulges, and I'm just doing my usual commute-around riding. To be safest you should get new tires, but it's probably not that urgent.
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    it's 'leaving the scene of an accident' because no state government has passed a law against 'leaving the scene of an on-purpose'.

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    Remember, He stated " The sidewalls are real dried out and flaky". No mention it's just the gumwall. This shows he is concerned about safety. If he wasn't concerned about the condition of the tires, why ask the question?
    I agree with Ira B. If in doubt throw it out. Tires are cheap enough.
    FBinNy--Do you have the stats to back up your statements or are they your opinions?

  17. #17
    7-speed doomsday prepper ThermionicScott's Avatar
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    Quote Originally Posted by BCRider View Post
    The cracking of the gumwalls isn't that big a deal. However the access it provides for water and air to reach the cotton belt threads and allow them to rot very much is a big deal. If you can see the threads through the cracks then it's simply time to sigh and replace them. If there's no big bulges or noticable degrading of the threads that you can see in the cracks you don't need to replace them today but it would be wise to get some over the next couple of weeks.
    If the OP's tires have cotton (rather than nylon) threads, he DEFINITELY needs to replace them, as they would date to the 1960s or earlier. Agree on everything else.
    Quote Originally Posted by chandltp View Post
    There's no such thing as too far.. just lack of time
    RUSA #7498

  18. #18
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    We can't tell you if it's OK because we don't know what OK is for you. If you mean will they fail suddenly or are they dangerous right now - If there's no bulging anywhere on the tire and the bead line thin raised ridge of rubber near the rim on both sidewalls) is the same distance everywhere then the tire is most likely perfectly safe right now. If the above situation changes then you should replace them tires.

    OR

    If it's worth $30+ bucks (plus labor if you choose) to not have to worry about it, then replace them.

    One other consideration is that the tread rubber, though it generally holds up better, may not be in great shape either, potentially affecting braking and handling.
    Last edited by cny-bikeman; 07-11-12 at 08:16 PM.

  19. #19
    Ride, Wrench, Swap, Race dddd's Avatar
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    I am tending to agree with several of you. But have not seen the tires.

    First, to clarify, a GUMwall tire is one that has thick rubber over the casing fabric, and not a matter really of what color it is. Thicker rubber protects longer, even after showing cracks, while "skin-side" sidewalls usually has a thin rubber layer that simply "evaporates" over time, for lack of a better term.

    At such point that the casing fabric shows thru and displays an irridescent whitish look (typically on a skin-side tire's sidewall), that is the outer ply in the weather-weakened "imminent failure" mode, which may be followed by an outer-ply failure (S-bend in tread center, and bulging) or a total failure (where the tube escapes confinement and blows out).
    The point at which this happens is unpredictable, but much more likely when inflated up nearer to the tire's rated pressure.
    Thus, a light rider can more-safely ride older tires because of the lower inflation pressure requirement.

    Another problem with aged tires is that the outer-ply overlap (under the center of the tread) tends to simply de-laminate due to a loss af adhesion between the overlapping outer ply layers. Some sort of "drying out" or chemical breakdown of the "rubber" that holds that lap joint together.

    I weigh 155 and ride on older tires at fairly modest pressures, but will discard tires that show aged outer ply fabric.
    The gumwalls are more forgiving generally because the fabric plies are also thicker and so the entirety of the stressed fabric isn't so close to being exposed to sunlight and smog (ozone). The thicker rubber, though cracked, also does much to ward off the sort of abrasion damage that can readily chafe away on old skinwall tire's outer ply and lead to failure.
    I've had several such age-related tire failures, and now am generally able to avoid the problem by inspecting the lighter tires more carefully for sidewall aging and by staying well below max pressure.
    Last edited by dddd; 07-11-12 at 06:46 PM.

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