Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site tekchips.UUCP
Path: utzoo!linus!decvax!tektronix!tekcrl!tekchips!eirik
From: eirik@tekchips.UUCP (Eirik Fuller)
Newsgroups: net.bicycle
Subject: Re: Tire Pressure, etc.....
Message-ID: <214@tekchips.UUCP>
Date: Thu, 19-Sep-85 12:26:31 EDT
Article-I.D.: tekchips.214
Posted: Thu Sep 19 12:26:31 1985
Date-Received: Sat, 21-Sep-85 11:59:50 EDT
References: <5490003@acf4.UUCP> <4200023@uiucdcsp>
Reply-To: eirik@tekchips.UUCP (Eirik Fuller)
Organization: Tektronix, Beaverton OR
Lines: 40
Summary: 



I have my doubts that Turbos would fail to meet their pressure
rating; in my experience, Specialized tires are very 
conservatively rated; I have also read of Turbo S's holding 240 psi,
nough to crumple some rims. I regularly ride my 27 by 1 
Touring II's (rating: 95 psi) at 120 psi, with no problems.

The single most likely reason for blowing a tire off of the rim
is a pinched tube. I have seen brand new bicycles with pinched tubes.
One in particular worked fine until I inflated the front tire to its
rated pressure (which, apparently, had not been done in the shop that
sold it); the result was a deafening boom. It never had the same problem
again, once the tire was properly mounted.

I suspect that your Turbo was pinching the tube slightly, so that it
took a bit of shifting around for the tube to work its way into such a 
position that it could lift the bead. I have seen such a delayed reaction
many a time, especially with high temperatures to help out.

To help in avoiding pinched tubes, it is a good idea, when mounting a
tire, to get the tube entirely inside of both the tire and the rim before
working the second bead over the rim (this also makes it easier to mount
the second bead). This situation is easy to detect because the inside 
of the tire will be touching the rim all the way around the wheel on the
side left to be mounted.

I don't know about what pressure is optimal for rolling resistance
(though I would expect it to vary greatly with the properties of the road
surface), but I do know that rim damage is much less likely with fully
inflated tires when hitting curbs and such; a rim is only likely to dent
when the tire bottoms out, which is less likely at high pressures. I would
rather repair a blowout then take a flat spot out of a rim (though I have
done both often; both require removing at least one bead of the tire, but
the latter requires a tool which I don't generally carry on the road).

The flat tires I do get (which never result from pinched tubes) 
probably aren't much influenced by tire pressure. My last puncture was
on a 26 by 1.5 tire at 50 psi. A determined piece of schrapnel will
work its way into anything.