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Thread: Clincher tyre tubes and pressures

  1. #21
    Join Date
    Sep 2005
    Location
    Sarasota, Florida
    Posts
    3,807

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    I never thought of motocross tubes, Steve. As I stated years ago, I've had a lot of trouble with modern tubes, and mostly on my bicycle. I now run a quality tube from a local bicycle dealer and have had fewer blow-outs. I'll look into the Malcolm Smith tubes.
    Eric Smith
    AMCA #886

  2. #22
    Join Date
    Aug 2013
    Posts
    720

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    Eric, thank you for your reply. i cannot remember where i got the motocross 4 mm tube idea, it was from somewhere, i am thinking this thread or the link on page 1 of this thread "OcchioLungo wordpress." Know that there are no 20" MX tubes available, so i fit a 19 inch tube, rather than a 21" tube, so that there is no bunching of the tube one could expect with a 21 inch tube. i will suggest the heavy 4mm thick tube will give a bit more sidewall inflexibility.....? thoughts anyone?

    before i write further, i feel it necessary to state i am discussing solo riding the Coker 3.85x20 diamond tread clincher tire on a new Al McRoberts rim (and i weigh 180 pounds). (the Rider's Handbook refers to this tire as a 3.85x27 and the tire is also known as a 3.85x20) clearly blowouts are a worrisome concern for us folks who are willing to risk a "like original" accident due to a clincher blowout.......

    and - i am not trying to over-think this topic, i am simply trying to understand what physical forces are in play on the clincher tire in it's under and over-inflated states. clearly my questions/musings may be the same to some as trying to figure out how many angels fit on a pin-head..... i just want to make sure i have done my due diligence by checking tire psi every time before i go out on a ride and what folks feel appropriate psi for solo riding should be. Considering the number of conditions that can contribute to blowout, i cannot help but wonder if clincher's are not getting an unnecessarily bad rap despite their inferior design.

    the reason i am giving this thread a little CPR is because my local buddy is getting ever-closer to the day he'll have his 29JD on the road and he and i have had some back and forth convo's about clincher tire psi, i.e., follow Rider's Handbook settings, follow what other people are saying their experience is, over-inflate vs. under-inflate, so forth, so on. he has been told by a rider of recognition that 20 psi is all that is needed in a 3.85x28 (20 inch rim) and of course the Rider's Handbook says inflate front = 15 psi and rear 20 psi. (i have been running 40 psi in my tubes without incident thus far.) another reason for keeping this thread on life-support is there may be new experiences people can share since we last discussed the topic in 2012-2013.....

    thoroughly reading the OcchioLungo article, it seems the consensus of the information in the article and folks with hundreds if not thousands of miles is a range between 40-45 psi.

    again, what i have noticed absent in these discussions is:

    1. the condition of the rim in which blowouts occurred ?
    2. what psi guys were running that had these blowouts ?
    3. what type of tubes were fitted in these cases of blow outs ?
    4. what is the condition of the bead in which blowouts occurred?

    Clearly, any one of these factors are critical and could cause a blowout, and any combination of these factors one could assume would even further increase the risk for blowout.

    can ANYONE think of a good reason why the factory would publish 15/20 psi for the 3.85x20 tire ?? and why we are saying inflate to 40-45 psi ??

    it seems reading this thread, there are at least four conditions that can contribute to a clincher blowout....
    1. the tire rolls of the rim due to under-inflation....correct ??
    2. the bead gets "cut" and simply pops off rim from under-inflation....correct ?? and..... WHAT DOES CUT MEAN ?? the bead actually is severed from the body of the tire...?? Would this "cut" be caused by a sharp bead edge of an old original rim...? or by any rim due to under-inflation....???
    3. over-inflation, the bead literally blows off the bead....??
    4. the valve stem severs due to under-inflation because the tire actually "walks" on the rim and as a result the stem shears at the point where the stem comes through the hoe in the rim...???

    it seems obvious, in the case of under-inflation, the tire could literally roll off the bead, especially in corners. and i guess if the tire is under-inflated, as the tire is walking, especially if the bead is sharp, then the bead will get "cut" ?? in the cases where the tire blew off the bead of a parked motorcycle, what was the psi? What was the rim condition? Was the tire in hot sun and psi increased?
    Last edited by Steve Swan; 07-01-2018 at 01:23 PM.

  3. #23
    Join Date
    Jan 2007
    Location
    Milwaukee
    Posts
    37

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    I have read this thread and learned a lot from all your posts. I am currently working on a 26 BA/AA that actually starts and runs after sitting for 40-50 years. I starter another thread asking for help with clinchers but didn't get much response, so I thought i'd post here.
    Now that the engine runs and all is there for it to ride, I decided that it needs to be able to roll....
    I just started the project of removing the well worn and partially rotted rear tire. After reading the posts on tubes and pressures I was interested to see what was lurking inside the tire.
    What I found (see attached picture) was a Firestone tube from? that had be patched at least 9 times with patches of various colors and dimensions. I was also surprised that the tube was designated for the tire size 3.85x18. Whoever had this bike used the tube and tire for all it was worth.
    I have ordered replacement Cokers and welcome any advice on mounting them.

    Ed
    Attached Images Attached Images

  4. #24
    Join Date
    Aug 2013
    Posts
    720

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    Quote Originally Posted by eddiepanhead View Post
    I have read this thread and learned a lot from all your posts. I am currently working on a 26 BA/AA that actually starts and runs after sitting for 40-50 years. I starter another thread asking for help with clinchers but didn't get much response, so I thought i'd post here.
    Now that the engine runs and all is there for it to ride, I decided that it needs to be able to roll....
    I just started the project of removing the well worn and partially rotted rear tire. After reading the posts on tubes and pressures I was interested to see what was lurking inside the tire.
    What I found (see attached picture) was a Firestone tube from? that had be patched at least 9 times with patches of various colors and dimensions. I was also surprised that the tube was designated for the tire size 3.85x18. Whoever had this bike used the tube and tire for all it was worth.
    I have ordered replacement Cokers and welcome any advice on mounting them.

    Ed
    why not just use that tube....?

    don't over think mounting the tires like i did. get tires as warm as possible, lying in hot sun good. Put them on by hand, dry. despite what others say, cut a tiny relief in edge of both bead sides for valve stem to protrude through. tape the valve stem to avoid scratching paint. put one side of tire on. put the tube inside tire. inflate the tube to push the bead across the hole in rim for valve stem, you might have to do this several times so valve stem can be put through hole. put on second bead, they sort of roll on sort of inside out, installing clinchers not the same as installing drop centers. the hotter the tire is the better your chances of mounting with hands only. if you don't seem able to get the last few inches of bead over rim, then tape any tool you deem appropriate for the job at hand.

    if you don't care for my method, there's a number of threads on the forum to study or you can google videos off internet. one fellow mounts the tire using a plastic bag. apparently i'm too inept to do it same as he did it, all i manged to do was get in the bag and not the tire. ha.

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