The speed rating is the maximum the tire is rated to be safely driven at,
and there is a separate temperature rating rating the tire's ability to
handle the buildup of heat and how well it dissipates heat.  There is a
rating of A, B and C.  Of course, everything is woven together.

Some of the ratings for tires are the speed rating, temperature rating and
traction rating.  Speed rating is generally what speed this tire is rated to
safely travel at, and generally doesn't relate to the top speed or speed of
the car.

Traction rating is on a scale of AA, A, B and C and is based on the tire's
ability to stop on a wet, straight line surface such as asphalt or concrete.

Temperature I described above.  The higher the speed rating, normally the
softer the rubber, lower aspect ratio (the 2nd number - example, 235/40-18).
That's 235mm for the width, 40 is the sidewall (40% of 235) and 18 is the
wheel diameter in inches.  40 is a low profile tire so when cornering there
is less flex.  Less flex can mean better handling.  Of course, a low profile
tire like this is normally on a sportier car so the speed rating is often
higher.  A higher speed rating often affords a softer rubber for better
handling but you sacrifice tire longevity.  You may also find more high
performance tires not rated as all season, so it's almost useless in the
snow/ice.  Rubber compound and the tread pattern/sipes will make a
difference for traction, cornering, stopping in the wet, rolling resistance,
etc.  The high performance tires with the high speed ratings are normally a
softer rubber with a shorter tread life.

Now - about the V and H rating on the Michelin.  It doesn't matter if it's V
and H on a Michelin, Bridgestone, Goodyear, Firestone, Kuhmo, Cooper, BF
Goodrich, Dunlop, etc.  The UTQG governs the rates for all brands.  Is there
a difference between V and H?  Yes.  The V is a higher performance tire, and
therefore put on the higher trim level car such as an Accord EX V6 whereas
and Accord I4 would have the H rated tire.

Why some places may refuse to "downgrade" a tire?  Liability and safety.  If
you downgrade, you may be sacrificing what the car was designed for so your
handling (such as emergency handling) may go down.  Let's say there's a
Porche that can top out around 140mph, but Dad decided to save $$ and change
the tires/wheels to a downgraded "S" rated tire.  Little Johnny decides to
take the car out for a joy ride (like he's done in the past) in his dad's
Porche at 120mph and wipes out.  Yes he's driving illegally but it's also
riding on below spec tires.  Who gets the blame - the driver, the owner who
authorized this, or the shop who downgraded the tires?  Did the shop advise
the owner this may affect the handling and driving characteristics?

A great resource for tire specs, definitions, and reviews is
www.tirerack.com.  Of course you can do a google search too for the
different speed, traction, temperature and wear ratings.

There's much more information out there.  Major differences in tires, even
within the same brand.

-Dave

no correlation that i know of.  it's the construction of the tire and
the ability of the rubber to dissipate accumulated heat that give it the
speed rating.  neither assure handling or traction.

I often wonder about the differences (if any) when a tire model comes
in different speed ratings.  The rating refers only to the tire's
resistance to coming apart at high speed.  This attribute doesn't
guaranty that the tire handles well.  Of course, high performance
tires tend to come with higher speed ratings than Costco all season
radials.  But is there any inherent correlation between speed rating
and handling, especially when you can get nominally the same tire in
different ratings?

the energy is not a performance tire - it's a high mileage low rolling
resistance tire.  you're not going to gain anything paying to replicate
their "speed" rating.

It's time for some new shoes for my '03 Accord V-6.  I know people on
this usenet group are not all that fond of the OEM Michellin Energy
MVX4 91V tires, but I have been happy with them.  Good snow and wet
pavement performance, quiet and good mileage.  That's good enough for
me.  I buy my tires at Costco, so straying away from the mainstream in
tires is not an option for me.

I see that the Energy tire has been replaced with the Primacy.  It's
supposed to be a blend between the old Energy and another higher-end
Michellin tire.  There is a $30 per tire difference between the V and
the H ratings in the Primacy.  Is there any real reason to spend the
extra $120 to get the V rating again?  I do spend some time on the
road, so 80 mph is not uncommon.  I don't know why Honda uses the V
rating in the first place, unless it is just a marketing tool.

Dick