pwa wrote:Now I was thinking that heat induced blowouts happened because the inner tube got too hot and the material failed. Is that not the case?
Brandt certainly didn’t think so.
Such a failure would hiss down relatively slowly (seconds) and not make the “loud bang” you heard. A loud, explosive noise is evidence the tube burst outside the tyre.
If you look at the geometry of a deep rim well compared to a circular tube up in the tyre at very low pressure, you can see that if only the unconstrained bottom quadrant or so of the tube stretched into the rim corners we’d have failures with butyl tubes merely from inflation to high pressure unless the tube, as it is being inflated, slid to take in material beyond the quadrant. It must do this even without talc, because I never powder my tubes and they don’t burst on inflation from excessive stretch into the rim well. With latex tubes I can see some minimal evidence of stretching into the corners of the bead-rim interface but that has never been a problem either. Latex tubes, having low hysteresis, are impressively slippery even without any form of lubrication.
Even if occasionally problematic stretching occurs on inflation, no additional stretching occurs with temperature rise from braking, since the tube is constrained by tyre and rim.
Studies and energy calculations show that rims usually only get a little over 100°C with hard braking (carbon rims get hotter at the surface because they conduct heat badly – another reason not to use them). That isn’t hot enough to give an inner tube trouble by itself even if the tube weren’t insulated by tyre and rim tape and only briefly exposed to the rim at that temperature anyway, besides having its own heat capacity, all of which combine to make it unlikely the tube reaches even 100 degrees.