Max Tire Pressure?

"Pop`" > wrote in message
news:rDp5i.12842$xV.7601@trnddc05...
> C. E. White wrote:
>> "Ray" > wrote in message
>> ...
>>> C. E. White wrote:
>>>> is likely too high. Years ago, manufacturer's usually recommended
>>>> different pressures for different conditions (speed, load). In
>>>> recent years, this has been replaced by a one pressure fits all
>>>> situations recommendation. It is my belief that this pressure is
>>>> probably higher than necessary for most conditions since they
>>>> have
>>>> to allow for maximum load and speed and the manufacturer's need
>>>> to
>>>> achieve the highest possible mileage ratings for CAFE.
>>>>
>>>> From http://www.michelinman.com/care/tip1.html :
>>>>
>>> <snip>
>>>> "For continuous high speed driving, tire pressures should be
>>>> increased by 3 to 5psi above the normal cold inflation
>>>> recommended.
>>>> However, for passenger tires, never exceed the maximum inflation
>>>> pressure molded on the sidewall. The inflation pressure for light
>>>> truck tires may exceed that molded on the tire by 10psi. Any
>>>> recommended front to rear pressure differential should be
>>>> maintained."
>>>
>>> fwiw, my 2001 Trans Am's sticker has a 30psi rating for normal
>>> driving, and a 38psi rating for sustained speeds above 100mph. I
>>> love that sticker.
>>
>> Wow, I am surprised GM doesn't get sued over that one. I mean if
>> the
>> sticker says you can go 100, you probably should....
>>
>> Do you remember when manufacturers were installing tires with an 85
>> mph maximum speed rating? I thought that was insane, even though
>> the
>> National Speed Limit was 55. Now things have gone in the opposite
>> direction - cars come with tires rated for 135 mph, even if they
>> have
>> governors limiting them to 105. And tire stores force you to buy
>> the
>> higher rated tires even if you never plan to go over 80....
>>
>> Ed
>
> Some tires are now rated for 75 mph. You're thinking about specials
> or European tires.

Nobody is selling cars with tires rated for only 75 mph today in the
US. I can't say what is happening in the rest of the world. My Ford
Fusion came with P225/50VR17 - 93V tires - they are rated for 149 mph.
If I go to Sam's or Costco to buy replacement tires they will insist
that I buy tires of the same speed rating. There is no way that Fusion
is going to do 149 mph unless I drop it off a clift.

Ed

Neat trick, the chalk thing. Elegant, simple, revealing.

Good thread. I'm deflating my tires as I type.

Altho I did read someplace that underinflation leads to more punctures than
high-er inflation.
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"Mike Romain" > wrote in message
ng.com...
> Proctologically Violated©® wrote:
>> Awl--
>>
>> I noticed that the recommended tire pressure for a vehicle is usually
>> well below the max. printed on the tire.
>> For example, on my new Honda Fit, the door says 32 psi, but iirc, the
>> tire says 40 or 45 psi.
>>
>> What goes into this recommendation by the car mfr?
>> (Recall the Firestone tire debacle, which I heard was largely caused by
>> Ford recommending unrealistically low pressures, for a cushier ride.)
>>
>> It seems to me that filling the tire to the *tire mfr's* printed max
>> should be OK, giving me 1. better mpg's 2. perhaps a bumpier ride, and
>> 3. perhaps less traction/longer braking distance than the car mfr's
>> recommended psi.
>>
>> Since I drive pretty much slow as **** anyway (or with the "flow of
>> traffic"), mpg's are my main priority, as long as I'm not positively
>> risking my life.
>> I've noticed no uneven wear on previous cars, by filling to the max.
>
>
> We run mostly oversized tires on our off road Jeeps so we need a way to
> find the compromise for best traction and best handling vs gas mileage and
> safety.
>
> We use the chalk method of running a few lines across the tread and
> driving straight, then stopping to see how much is left. The best for
> grab is usually no chalk except about 3/8" at each edge. This is lower
> than the mfg vehicle spec which gives about 1" on each edge.
>
> When my 33x9.5" tires to use one specific case are at 26 psi I have all
> 7.5" of tread touching but a soft sidewall. Good for slow speed only.
>
> At the vehicle's spec of about 30 psi, I have about 3/4" of chalk on each
> side. At the max of 45 psi for the tire maker, I only have 3 1/2"- 4" of
> tread touching the ground! This leaves a gap that just screams for a
> little water to get lift off!
>
> I run at 28-29 psi and get good wear with decent handling and decent
> enough mileage which is a compromise. If loaded I run at 32 psi though.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> Canadian Off Road Trips Photos: Non members can still view!
> Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
> (More Off Road album links at bottom of the view page)

C. E. White wrote:
>
> Wow, I am surprised GM doesn't get sued over that one. I mean if the
> sticker says you can go 100, you probably should....
>

The actual sticker says:

"See owner's manual for tire pressure needed at 160 KM/H (100MPH) or
higher speeds, where legal, and for additional tire information."

The owner's manual (which I don't have handy) lists the 38 psi as the
pressure required for driving above 100.

Considering in stock form, this car can push 160mph, I see why the
sticker exists. I don't know what percentage of F-Body
(Camaro/Firebird) owners race their cars, but it's pretty high.

Ray

Pop` wrote:
>>
>> Do you remember when manufacturers were installing tires with an 85
>> mph maximum speed rating? I thought that was insane, even though the
>> National Speed Limit was 55. Now things have gone in the opposite
>> direction - cars come with tires rated for 135 mph, even if they have
>> governors limiting them to 105. And tire stores force you to buy the
>> higher rated tires even if you never plan to go over 80....
>>
>> Ed
>
> Some tires are now rated for 75 mph. You're thinking about specials or
> European tires.
>
>

What Ed's referring to is a lot of tire places won't sell you anything
but a stock size, stock speed rating tire.

If your car came with an H speed rated tire, it would be ok to buy a V
rated tire, but not ok to step down to an S rated one, even if you're
not planning to exceed the speed limit of an S rating.

It's mostly a CYA thing for the tire place and the manufacturer. Even
though the highest legal speed limit in Canada is 110km/h, my Trans Am
came with tires rated to 149mph+.

Ray

Proctologically Violated©® wrote:
> Neat trick, the chalk thing. Elegant, simple, revealing.
>
> Good thread. I'm deflating my tires as I type.
>
> Altho I did read someplace that underinflation leads to more punctures than
> high-er inflation.

If you ask 10 people their recommended tire pressures, you'll probably
get 11 answers.

When in doubt, with stock tires on a stock car, stock pressures are
usually good enough.

Once you start changing sizes, widths, compounds, tire types (radial vs
bias ply, street tire vs race tire), racing, offroading, lifting,
lowering, trailering... then you need to worry.

Ray