From: tcora@PICA.ARMY.MIL (Tom Coradeschi <tcora>)
Newsgroups: rec.motorcycles
Subject: Re: Fixing a flat on a radial tire.
Date: 26 Aug 92 13:16:32 GMT
Organization: Electric Armts Div, US Army ARDEC, Picatinny Arsenal, NJ

megatek!randy@uunet.uu.net writes:
>In article <6703@tekig7.PEN.TEK.COM> jearls@tekig6.PEN.TEK.COM
>(Jeffrey David Earls) writes:
>|Last weekend I had a small piece of wire removed from the front tire
>|on my FJ.  The service guy gave me a concerned look when he saw that the
>|tire was a radial (Pirelli MP-7).  Evidently he's had problems before with
>|the patching plugs coming out of radials.  Obviously, this problem now
>|bothers me greatly.  
>
>  Just don't plan on testing the speed rating of the tire anymore.  I replaced
>my stock tire on my bike with 4,000 miles of tread left because I had a couple
>plugs put in it.
>
>  Remember how radials are made - the cords (nylon or steel or whetever) are
>wrapped around the tire radially - from one side straight around to the other
>side of the tire - NOT in the direction that the tire rotates.  When you
>install a plug or just have suffered something that put a hole in it (like
>a nail), one or more of those radial cords is probably completely severed.
>You rev that rear tire up to a pretty high speed, along with the heat that
>is generated, and the tire could conceivable give way at that point.

An interesting point, Randy. But all tires have structure (cords) which
run across the direction of rotation. The difference is that in radials,
the cords run at ~90deg to the direction of rotation, and in others it
is at some angle <90deg. In all cases, a hole in the tire (unless very
small) will sever one or more of those cords.

The issue, from my point of view (and this is based upon my experience
working in a tire shop ~12 years ago) is that you don't really want to
rely upon a plug to seal the tire. This is true for both automotive
and motorcycle tires. A patch, applied to the inside of the tire, is a
much more secure means of sealing the leak. We never used a plug to
seal a tire. In extreme cases, where there was a large hole in the
tire, we'd use a plug to fill the hole and a patch to seal the leak.
Let's look at some ASCIIGRAPHICS(tm):


Tire-> ==============||==================

                     ^^Plug (Note relatively small surface area for
                             adhesive to bond plug to tire.)

                ____________
Tire-> ==============  ==================

                ^^^^^^^^^^^^Patch (Note large area for bond to occur.
                                   Also note that it's damn near impossible
                                   to push patch thru hole.)

The patches used in today's tire repairs are bonded to the tire
chemically (as are plugs). In days of yore, a pseudo-vulcanizeing
system was used. The problems there was that extreme heat would cause
the bond to fail and the patch/plug to come loose, with predictable
results.

So, to recap (and just MHO, remember): patches is better than plugs.
If you've got a holed tire (a reasonably small hole) and can have it
patched, the tire should be usable for the rest of its wear life. On
the other hand, if you hole a tire 95 miles from nowhere and all
you've got is your BMW Plug Kit? Plug it! (What other choice do you
have?) Then have a patch applied to seal the plug. OTOH, if the hole
is large, you've likely damaged the structure of the tire (radial or
otherwise), as Randy said. So have it replaced. Even expensive tires
cost less than cheap hospitals:-{

Finally, this all applies to holes in the tread. Holes in the sidewall
are fatal (to the tire).

FWIW: The only time I ever holed a tire, the nail went in the tread
and came out the sidewall:-{ And the sucker only had ~1500 mi on it:-{:-{
-- 
 
                tom coradeschi    <+>    tcora@pica.army.mil