[DeTomaso] 265/50-15 tires

Garth Rodericks garth_rodericks at yahoo.com
Thu Jul 26 14:31:47 EDT 2012


Jack,

Just curious, what's the point of your message?  What are you trying to tell us?  I don't understand.

There is a HUGE difference between an 'S' rating and an 'H' rating. The following are a few excerpts from an interesting thread with info from a tire engineer for a major tire manufacturer:

All tire manufacturers utilize an "over-design / under-utilize" methodology.  It's been found that barely meeting the conditions - load 
capability, speed capability, etc. - results in a certain rate of 
failure in the real world.  And while we can talk about under inflation, 
road hazards, etc., the reality is that over-specifying a tire results 
in reduced failure rates.

Pretty much every tire will pass an S rating.  (Please note that I'm 
limiting the discussion to regular passenger car tires.  Winter tires 
and light truck tires are a different story - similar, but 
different.)  And T ratings are not much of a stretch.

So an S rating would - on the surface - seem to be adequate for use in the US where there are speed limits everywhere.

But,
 in order to pass an H speed rating, a tire more or less has to have a 
cap ply.  This change has a profound effect on failure rates, way beyond
 what the increase in speed rating suggests.  The failures rates are so 
low for tires with cap plies that court room "experts" claim that tire 
manufacturers are negligent for not using cap plies even in their S 
rated products.  (My response to that is that these "experts" must also 
be saying that tires ought to have a minimum of an H speed rating - and 
if that is true, the "experts" ought to be lobbying NHTSA to specify H 
rated tires for any tire sold in the US.)

But the point I want to
 make is that the step between T and H is enormous from a tire 
durability point of view.  And I don't recommend anyone use anything 
less than an H rated tire.  Considering that the risk of a tire failure 
includes fatality, the cost / benefit seems to be there.


A cap ply is an additional layer of a fabric and rubber composite that is applied over the belts and oriented in more or less the circumferential direction.  What it does is restrict the growth of the tire in the 
circumferential direction - like centrifugal forces.  But I also think 
it adds bulk and reduces the standing wave, which may actually be more 
important in the context of tire failure.
Source: http://www.eng-tips.com/viewthread.cfm?qid=159900

Additional info:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CGcQFjAB&url=http%3A%2F%2Fwww.nhtsa.gov%2FDOT%2FNHTSA%2FVehicle%2520Safety%2FTest%2520Procedures%2FAssociated%2520Files%2FTP-139-02.pdf&ei=5IkRULfdCcfhrAfQjYGAAw&usg=AFQjCNEYEuipPu_2ACn67-1IsQDHUhGMHw&sig2=2c9ZNOZl-06muDXE-nk4vQ



--- Original Message ---
"S" speed rating = 112 mph max sustained (30 min. test)
"H" speed rating = 130 mph max sustained (30 min test) That may mean that's all the mfgr decided to ask they be tested to, or.... FWIW- J DeRyke


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