Somebody explain this..

Discussion in 'The Gutter' started by Little Android Man, Jul 26, 2004.

  1. Little Android Man

    Little Android Man Free Cup!

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    this isnt really important so i put it in the offtpoic..

    so on my mod ive got a dx32 and a monty tire, and at 13psi, it rolls, folds and slips everywhere, and ive pinched twice. so today i got my tryall rim and i figured id go out and finish off the dx32..i ran about 3psi, or at least just enough to keep the sidewall off the ground, and i slammed the crap out of the rim, i tried doing the biggest stuff i could and landing as hard as i could, just to mess up the rim, and not ONCE did the tire fold, roll, slip (except on the rim) or pinch.

    what the hell is up? it did the same when i did that huge gap that started the flatspots in my rim..8psi, and i nailed the rim so hard that the bead touched the nipples, and it didnt pinch. i wa nt to know if runing this low of pressure is at all beneficial? i mean besides the innevitable flatspots and dents in the rim, but how come the tire is so shitty with more psi in it?
     
  2. MegamoMidwest

    MegamoMidwest chicago crew

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    if the bead touched the nipples then the tire would have to be unseated off of the rim.


    the PSI makes the bead of the tire pull away from the rim (this is how tubeless tires work sort of). Alex rims tend to be pretty difficult to mount tires on, and monty tires are hard to get on anything, so the low psi and the tight bead would equal stationary tire.

    Even with that logic, at 8 psi the tire should unseat and slip around so I really dont know whats up. and god knows how the hell you didnt pinch that shit.

    I wanna try 8 PSI on my old wheel because I just got a new king hub laced to a D521 and its gonna be swiggidy sweet.

    sorry for rambling. I wanna go riding right now! its dark though and my riding partner is out of town.

    poop

    -Paul
     

  3. Andreas

    Andreas All About Trials

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    i think i have only pinched my rear wheel like, 1 or 2 times in the year and a half i've been riding. why? arrow racing rim seats the tube real low. i can rim out all day long, yet i will never pinch. how do i know? well, see the thing is: i DO rim out all day long, yet never pinch ;)

    so yeah, it definately has to do with what kind of rim set up you have as well. something like a dx 32 in theory (my theory anyways) will pinch more (because the tube is more exposed) as opposed to an Arrow Racing rim in which the tube sits real close to the rim, and because of the V shape not much of the tube is exposed. this means that when you rim out, your tube won't be as affected.

    I hope that made sense
     
  4. Little Android Man

    Little Android Man Free Cup!

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    andreas, ya that makes sense..i dont get whats wrong still though.

    and Paul, im saying the sidewalls were folded over so much on some places (of the rim that is) that they actually touched the inside, but the tire still sat inside, i mean if ixed it and all but, hwo come it never pinched? ive pinched at 13psi+, with DH TUBES even, and now im running this litle condom thing inside my rim and i cant get it to pinch at all. im not saying thats bad..but how come it cant always be like that?

    when i still cared about the wheel ive got now, i used to keep the pressure up to try to avoid rimming out, i like to make my parts last? but then when i did, it seemed like every third time id pinch it. even if it was like a slow slow leak or something, it still sucked. so now ive got virtually no air in my tire, like just enough to put the tube onto the sidewalls of the tire, and it will not pinch for anything. i like it, its fun, but im only doing it to finish off this rim, and even still it just wont die...hopefully my tryall will work this well
     
  5. Andreas

    Andreas All About Trials

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    i know why.

    think about a tube being heavily inflated. you can't even push your finger into it and compress it, right (talking like 100 PSI here). Now think about a tube that's say....20 PSI, a common ground for trials riders i suppose. Think about how easy it is to squeeze the tube flat with your fingers. Now also keep in mind the amount of resistance your tube is making. It's making a considerable amount of resistance, but you are still able to compress it. Now lets take a tube at 3 PSI. You compress the tube with no problems (more likely because the tube is practically flat even without force on it). now think about the resistance the tube is giving back - none (basically).

    With 100PSI in your tube, the object will puncture the tube before it compesses your tyre. No questions asked- if you rim out- your tube will pinch.

    with 20 PSI in your tube, when you rim out on an object, the tube will pinch more because the air in your tyre has enough resistance that the object (whatever your tyre is on) will PUNCTURE teh tube before the tube has a chance to COMPRESS fully.

    Now lets take a 3 PSI pressure tube. It has no resistance basically, so when an object hits that, it will just slam into your rim. The tube won't be slowing it down any.

    I hope that made sense. Either i'm onto something or i really don't know what i'm talking about. i hope it's the first one.

    in either case, running low pressure all the time is bad, seeing as your tyres will flop everywhere ;)
     
  6. Little Android Man

    Little Android Man Free Cup!

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    hah thats the thing though, they never once really folded over so iwas siting on the rim alone, im guessing because of the whole resistance thing like what you said, but it was cool. im gonna ride all day tomorow like that haha...i wana smash this rim.
     
  7. Andreas

    Andreas All About Trials

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    just take it off a 5 footer and don't drop your front end ;) or maybe have fun gapping to a curb from a few feet up, with a gap!
     
  8. Little Android Man

    Little Android Man Free Cup!

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    haha yea today i was doing these like 6 foot pedal gap things to a curb, like just far away enough for me to slam the corner and jump off the bike, but id make sure to smash the fuck out of it..which is why i was wierded out by it not pinching. haha my correction hops werelike 2 feet high and the made the ground quiverrrr..i tried doing like lines of pedal hops where i djust jump up and slam the bike down and go for a long distance then up something and back down..nothing wanted to kill my tube, but my rim is certainly cooked. tomorow im planning on hitting my new rail gap haha...oy i really need to go to bed