A cautionary tale --

While walking home from the train station yesterday, I met a gentleman who had just replaced a blown-out front innertube. He had a modern bike with (presumably) hook beaded rims, so I don't know what went wrong in his case.

However ...

This morning I suffered the same fate during the last 4 miles of a 25-mile ride. I was using an old Weinmann smooth-sided 27" rim and a Vittoria Zaffiro tire, inflated to 80 lbs when cold at 6:45 a.m. By 8:30, the ambient temperature had increased by 15 degrees F, and this, coupled with the heat generated by rolling and braking, probably pushed the pressure above a safe level.

I was going slowly at the time and brought the bike to safe stop, but this has scared me into giving up on smooth-sided rims and backing off to 70PSI until bead hook-sided replacements arrive.

I don't think 15 Degrees change would have a very significant effect - probably just about 3% .
I googled a pretty good article that cites this along with some other interesting inflation info to consider, below.

Tire Pressure Article
By staff reporter Vikki Leonard

July 2009

Keep up with your bike’s maintenance and tire pressure for the summer by following these 3 tips:

1. PUMP IT UP
Proper tire pressure lets your bike roll quickly, ride smoothly and fend off flats. Narrow tires need more air pressure than wide ones: Road tires typically require 80 to 130 psi, mountain tires 30 to 50 psi and hybrid tires 50 to 70 psi. To find your ideal pressure, start in the middle of these ranges, then factor in your body weight. The more you weigh, the higher you pressure needs to be. For example, if a 165-pound rider uses 100 psi on his road bike, a 200-pound rider should run closer to 120 psi, and a 130-pound rider could get away with 80 psi. Never go above or below the manufacturer’s recommended pressures.

2. STOP RESISTING
Traditional wisdom says that higher tire pressure equals lower rolling resistance, because on a smooth surface hard tires flex less and create a smaller contact patch. But no road is perfectly smooth. Properly inflated tires conform to bumps and absorb shocks. Over inflated tires transmit impacts to riders, which sacrifices speed and comfort. On new pavement, your tires might feel great at 100 psi, but on a rough road, they might roll faster at 90 psi. In wet conditions, you may want to run 10 psi less than usual for improved traction. And if you’re a mountain biker who rides to the trailhead, keep in mind that while your bike rolls smoothly on the road with 50 psi, it might feel better on the single track at 38 psi.

3. KEEP IT IN THERE
The pent-up air in your tubes wants desperately to join its friends in the atmosphere. If you ride over sharp objects, immediately sweep your tire with a gloved hand to remove debris. For ultimate protection, use tire liners or puncture-proof inner tubes. To avoid pinch flats when you ride over bumps, maintain proper air pressure and unweight your wheels by sharply pushing your bike downward before the bumps then pulling it upward as you roll over them. For each 10-degree-Fahrenheit drop in the temperature, your tire pressure drops by about 2 percent. So if the temperature dips from 90 degrees Fahrenheit to 60 degrees Fahrenheit, your road tires would drop from, say, 100 psi to 94 psi. Those six pounds are noticeable and worth adjusting for. Get in the habit of checking your pressure before each ride.


Thanks to Bicycling Magazine for these great tips !


PS - I want to caution anyone running old, non-hooked rims - this article and others refer to pressures that are ostensibly "normal" for todays wheels and tires but would have been ridiculously high back in the day. You need to consider that.