Re: Speed ratings

[Art Borin <ArtBorin@frontiernet.net>]

Lin, Gary wrote:

> You both are right and wrong.  A tire's greatest enemy is speed and heat
> combined, with more of it coming from top speed in a straight line than from
> executing turns.

How am I worng.  You proved my point. I only disagreed with the statement below.

>Khan M. Klatt wrote:
>
>> Yes, the primary factor in speed ratings is if you're going to be riding
>>on any part of your sidewall when you make turns.
>

> But highway top speed generates more heat due to the quick flexing of the
> carcass as it rolls along.

This is friction, no?

>  Plus centripetal forces, the major factor, come
> into play above 88 mph (non-rated tires limit).  Tremendous stress is acting
> upon the carcass and belts trying to make everything fly apart the faster
> the speed.

What causes the failure?  Heat induced breakdown of the structure, or
centripetal force exceeding the original design yield strength?

> Tire speed ratings are determined by putting the tire on a dyno drum with a
> simulated load and then increasing the speed until the tire self destructs
> as explained above.



> If you guys are going above 110, you're
> cutting the safety margin on a H-rated pretty close.  Get at least a V.
> Even a cold H can blow at or above 130 due to the speed, esp. if the tire is
> slightly out of spec or previously damaged (hard pothole).  Plus a V will
> generally have better handling at all speeds over an H.
>
> Intro:  Resubbed after a period of too much mail.  My uncle has a '95
> GTI-VR6, but I only a BMW (but it is German;-) and like VW's and am on the
> GTI list.  Hope to contribute to anything technical.
>
> Gary Lin     Burke, VA     National Capital Ch.
> Metro Washington Council of Sports Car Clubs <CSP>
> '88 325is lachssilber   Conforti chip, Supersprint, ///M susp., Ints., R1's
>
> > Art Borin wrote:
> > Sorry, I disagree.The primary factor in tire speed ratings is the tire's
> > capacity to dissipate heat.  The faster the tire rotates, the more heat
> > (friction) is generated over a period of time.  The speed ratings are for
> > sustained speed, not a quick run like FlyinVR6 stated.  Thus, a H rated
> > tire can withstand a claimed 144 mph blast, as long as that speed is not
> > held for a long duration.
> >
> > Khan Klatt wrote:
> > Hi, and welcome. You may be right (I'm not an expert on these things) but
> > from my conversations with a friend who is a distributor for
> > Kelly/Springfield tires, I was led to believe it was the speed factor,
> > that you are indeed OK to go faster than the rating, as long as you
> > weren't making any significant turns (meaning a really straight road).
> >
> > Perhaps we are both right, and what might build the greatest heat in a
> > tire are angular friction (that caused by the gripping and turning of the
> > tire against the pavement) rather than longitudinal friction (that caused
> > by the tire moving in a straight line). If this is the case, you're still
> > more technically right, as the turns are simply a factor of heat. If this
> > isn't the case, then I've been misinformed, or it's a function of both
> > factors.