Monday, August 10, 2009

In the Name of Science

There is no fucking way. I stare at the last 14 inches of bead that still needs to be stretched over the rim. I double check the old tire. Yup, 26 X 1 3/8. Check the new tire. It’s the same. Check the ISO size. Both 37-590. Well, nothing for it but the metal tire levers.

Well, I finally get the tire onto the rim. My hands are shaking, my veins are pumped like I just got done climbing a 5.10, I’m sweating and breathing hard, but by god, that tire is on the rim. You experienced mechanics out there already know where this is going. What are the chances this tire will seat properly? About the same as Bruyneel calling me up for next year’s Tour.

But, hope springs eternal, so I pump it up. Sidewall says 55 p.s.i, so that’s where I take it. I give it a spin. Fully 2/3 of the tire is not seated. OK, the old frame-polish-on-the-bead trick has never failed me, so I put the wheel in the truing stand, deflate it, give it a spin whilst squirting polish between bead and rim on both sides of the wheel. Back with the air. Up to 55. Nothing’s changed. Hmmmm.

Now, I know from experience that the pressure rating on most tires has a safety factor of about two, meaning it should take about twice the maximum pressure listed on the sidewall to blow it off a wheel. Of course there are exceptions, and I welcome everybody out there to tell me I’m wrong or possibly an idiot. Your comments will be appreciated.

Our compressor is rated to 100 p.s.i. I start inflating slowly, in what I figure are about 10 p.s.i. increments. I see a little creep here and there, but when I get the compressor maxed out, there is still half the tire that isn’t seated properly. Hmmmm.

As you know, any 26 X 1 3/8 tire is cheap. We get $14.99 for ours, which means we probably paid five or six bucks for it. That’s just not that much money for the sake of adding to the overall body of cycling knowledge. I get out the safety glasses and the floor pump. I assume this will end badly, so I also cut some strips from a napkin and plug my ears. You know where this is going. I’m going to pump until one of two things happens: the tire seats or I blow the fucking thing right off the rim.

One, two, three pumps. 105 p.s.i. No change. Pump, 120 p.s.i. No change. Pump. 130 p.s.i. No change, except now I’m giddy with anticipation. I weigh in the low 180s, and it’s getting hard for me to pump, especially considering I’m trying to stay as far from the wheel as possible, even with the aforementioned safety considerations. Pump, 140 p.s.i. Still no change. My hands are actually shaking from the adrenaline. At this point, I know, on some level, that that tire will never seat on that wheel. Even if I could get it to pop, when I deflated it, it would drop back into the center of the rim. But, I’ve come this far…

So this time, I deflate the tire and squirt a little Triflow around the beads. I’m feeling a little cocky at this point, so I just blow it up as far as the compressor will take it, no pauses, no hesitation. Of course, the tire doesn’t seat. On to the pump. Again, I’m much more cavalier this time and take it to 140 p.s.i. without much thought, but then I’m back into uncharted territory. Pump, pause. Pump, pause. Pump, pause. I’m shaking. I glance at the gauge. 145 p.s.i. Pump.


I can actually watch it happen, and oh how I wish I had it on high speed film. The bead gives way at the top of the wheel, opposite the valve stem. There is a puff of talc and vaporized Triflow. Somehow, the blowout at the top of the wheel blows the wheel out of the truing stand. It hits the ceiling and crashes to the ground, and it is the highlight of my day.

I inspect the damage. The bead gave way at it’s joint. There are two pieces of wire about an inch and a half long that are protruding from the bead. I can see how they would overlap if the tire were intact. The sidewall looks like it’s been shot. The gash in the tube is a foot long. I love carnage, especially if it’s for a good cause. I now know that a cheap Kenda tire will withstand upwards of 140 p.s.i. Not for long, but it withstood it. I also know that at some point in the past, the powers that be in the bike industry decided to change a sizing standard without telling me. I put the old wheel in the stand, then a new wheel. The old wheel is a good four or five millimeters larger in diameter than the old one. I call the customer and tell him he needs a new wheel, or he’ll continue having problems finding tires that seat properly. He understands, buys the new wheel and tire, and I’m happy to have intentionally blown a tire off a rim on purpose. Sometimes, this job doesn’t suck. Sometimes.

1 comment:

  1. First. Where are you ant1? Nice going, I laughed out loud while waiting for the tyre to do its thing.