Home | Contact Us | FAQ | Search & Site Map | Link to Us
Sign In | Join | Other 45 Sites in Network
HomeAnnouncements
Discussion Groups
By Brand
BMWChevroletDodgeFordGMHondaLexusMercedes-BenzNissanPeugeotToyotaVolkswagenOther Brands
By Topic
4x4 CarsRVsDrivingMaintenance & RepairCar AudioCollectible Cars
Country Specific
Australian ForumsUK Forums
ArticlesAuto InsuranceBuyingCars & TechnologyMaintenanceMiscellaneousSafety
DMV Resources
Related Topics
MotorcyclesBoatsMore Topics ...

Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / October 2007

Tip: Looking for answers? Try searching our database.

Tire pressure vs ride

Thread view: 
Enable EMail Alerts  Start New Thread
Thread rating: 
news - 25 Oct 2007 03:33 GMT
Here's one I'm having a hard time figuring out:

My truck is a 90 Chev 1/2 Ton 4x4 reg cab longbox.
Stock tires were a LT225/75R16, door sticker recommends 45psi.
Current tires are LT 265/75R16's (IIRC load range D)
They're Canadian Tire M&S tires.  (Thought I wanted the ground clearance
for winter - they're the largest stock size you could get on that truck,
but now I'm wishing I hadn't bothered.)

Normally I was running them around 40-45psi, and the truck drove fine,
but like a 17 year old truck.  When I was towing my race car this
summer, I bumped them up to max pressure (65 psi) because we're fully
loaded with gear, car, and trailer.

I forgot to lower the pressure after - and the truck rides SMOOTHER.
Enough smoother that my wife was wondering if I changed the shocks or
something and hadn't told her.  This is completely the opposite of what
I was expecting - I was expecting the back tires to be just about
bouncing off the pavement over bumps.

Can anybody explain how adding 20 psi to the tires would smoothen the
ride out on an old truck?

(The shocks aren't new, only had the truck 2 years, so I'd guess they're
probably 5 years old and this thing was a farm truck for the first 15
years of existence...)

Ray
Built_Well - 25 Oct 2007 22:55 GMT
news wrote:

> Here's one I'm having a hard time figuring out:
>
[quoted text clipped - 24 lines]
>
> Ray
========

That's a good question.  The recommended tire pressure in
my manual for an '06 Camry LE is 29 psi.  29 psi also
appears on the sticker in the door jam.

29 psi produces a nice, smooth ride.  When I pumped up
the stock P205/65R15 tires by 5 psi
to 34 psi, I definitely experienced a rougher ride--could
easily feel the bumps.  Didn't like it much at all.  But my
gas mileage seemed to improve from 20 mpg city driving to
24 mpg city driving, a 20 percent improvement.  20 percent
seems like a lot.  Is that even possible?  I was expecting
5 percent at most.

Anyway, I next pumped up the tires to 38 psi, 9 psi over
the recommended 29 psi.  The stock Goodyear Integrity tires    
have a maximum cold tire inflation pressure of 44 psi, according
to the sidewall, so I'm within the safety margin.  Well, I don't
know if it's just in my mind, but 38 psi feels smoother to me
than 34 psi--I don't feel the bumps as much, and I like the ride
as much as at the recommended 29 psi.
mjc13<REMOVETHIS> - 26 Oct 2007 04:47 GMT
> news wrote:
>
[quoted text clipped - 49 lines]
> than 34 psi--I don't feel the bumps as much, and I like the ride
> as much as at the recommended 29 psi.

   I generally run our cars at about 5 psi (cold) below the maximum -
the figure posted on the car is almost always too low for both fuel
economy and a good safety margin. I get similar improvements in economy.
As for ride, different vehicles seem to be affected differently. I
suspect it may have something to do with shock/strut damping rates
interacting with sidewall damping rates at various pressures, but that's
only a guess. One other thing I've noticed: the increased wear I
regularly get warned about never happens - we always take our tires off
because of extreme age, with plenty of even tread left on them...
Built_Well - 26 Oct 2007 05:01 GMT
>    I generally run our cars at about 5 psi (cold) below the maximum -
> the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 5 lines]
> regularly get warned about never happens - we always take our tires off
> because of extreme age, with plenty of even tread left on them...
========

Yeah, I guess there's suppose to be balding that
occurs with over-pumped tires (loss of tread in
the middle of the tire).  Nice to hear that's not
necessarily so.

I was thinking of going back to 34 psi
from 38 (29 being recommended by the manual), but now
that I hear you're not experiencing problems, I might
just leave'm at 38 psi.
EdV - 26 Oct 2007 14:48 GMT
> >    I generally run our cars at about 5 psi (cold) below the maximum -
> > the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 17 lines]
> that I hear you're not experiencing problems, I might
> just leave'm at 38 psi.

I am using 31-32 psi. I never tried going more than that. Maybe I
should try it too. However, many recommend lowering pressure in snow
or wet roads, and its been raining in NJ for sometime now.
Mike Romain - 26 Oct 2007 17:54 GMT
>>>    I generally run our cars at about 5 psi (cold) below the maximum -
>>> the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 20 lines]
> should try it too. However, many recommend lowering pressure in snow
> or wet roads, and its been raining in NJ for sometime now.

Wow....

Unlike some I seem to be reading the right 'books' and running tires
fully loaded with air when the vehicle weight doesn't need that is not
only wrong, it is dangerous.

When I overinflate my tires by as little as 8 psi, I only end up with 3
1/2" of tread in the center of the tire touching ground.  They will then
spin really easy and slide out easy.  The U shape this causes also lets
water under the edges of the tire so it hydroplanes like mad.  Very Very
unsafe!

When I run proper pressure for the load, in my case 28-29 psi around
town and 32 loaded for highway trips, I then get a nice 7" of the
available 7.5" of tread touching the ground and no issues in the rain.
My tires will take 44 psi 'if' I put that kind of load on it to 'need'
that much air.

I 'also' 'use' my tires, I don't change them from age, so I actually
'see' the wear patterns.

Proper inflation allows my $225.00 each, tires to wear all the way down
evenly.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
clifto - 26 Oct 2007 18:23 GMT
> Proper inflation allows my $225.00 each, tires to wear all the way down
> evenly.

The more I think about this issue, the more it occurs to me that the
automotive engineer who specified the tire pressure for my make and model
of car and my tire size probably knows more about proper inflation than
the wrench down the street who says to inflate to the maximum allowable
pressure shown on the sidewall. So I look at the sticker behind the car
door and inflate accordingly.

Signature

One meter, to within 0.0125% accuracy (off by just under .005 inches):
       Three feet
       Three inches
       Three eights of an inch

EdV - 26 Oct 2007 19:14 GMT
> > Proper inflation allows my $225.00 each, tires to wear all the way down
> > evenly.
[quoted text clipped - 11 lines]
>         Three inches
>         Three eights of an inch

Very well said, I never thought of it that way. I tend to over inflate
a few psi more because I imagine tire gauges have some reading
inconsistencies and the fact that my tires still *looks* like it still
needs some air. I'm thinking over inflation would have the lesser evil
compared to a under inflated tire.
ChrisCoaster - 27 Oct 2007 00:21 GMT
> > > Proper inflation allows my $225.00 each, tires to wear all the way down
> > > evenly.
[quoted text clipped - 19 lines]
>
> - Show quoted text -
_____________________
Me too.  Only I overinflate the door pressure by 1-2lbs depending on
the season and the handling of the car I'm driving.  Just a tip on
your tires *looking* like they need more air:  Radials tend to look a
little "flatter" than equivalent sized bias plies set to the same
pressure.

-CC
dbu. - 27 Oct 2007 00:42 GMT
> > > > Proper inflation allows my $225.00 each, tires to wear all the way down
> > > > evenly.
[quoted text clipped - 27 lines]
>
> -CC

Five lbs makes quite a difference in ride.  I keep mine at five under
max too, at around 30 lbs
clifto - 27 Oct 2007 22:00 GMT
>> The more I think about this issue, the more it occurs to me that the
>> automotive engineer who specified the tire pressure for my make and model
[quoted text clipped - 8 lines]
> needs some air. I'm thinking over inflation would have the lesser evil
> compared to a under inflated tire.

Rather than compensate for an inaccurate gauge, I decided to slog around
until I got a gauge I trust. I have a friend who's almost anal about tire
pressure (yet who ignores the manufacturer's recommendations), and my
gauge reads the same as his three favorite gauges.

Bought a cool new compressor from Costco a while back and just got around
to trying it. The compressor is great, but the gauge on it is off by a
lot; it read about 27 when I got the tire to 32PSI by my aforementioned
tested gauge.

Signature

One meter, to within 0.0125% accuracy (off by just under .005 inches):
       Three feet
       Three inches
       Three eights of an inch

Ray - 26 Oct 2007 19:20 GMT
>> Proper inflation allows my $225.00 each, tires to wear all the way down
>> evenly.
[quoted text clipped - 5 lines]
> pressure shown on the sidewall. So I look at the sticker behind the car
> door and inflate accordingly.

Except these people all have a say in the tire pressure:
Marketing.  "Dubs" for everyone!
The people who mandate that the OEM tires last through the warranty period.
The company lawyers who don't want a Ford/Firestone repeat.
The fuel economy guys.
The handling department.
The NVH department.

No, I'm not smarter than the car company, but I'm also not bound by the
same rules they are.

I like to use the cold air intake (intake lid) on my Trans Am.
Aftermarket ones are worth 10hp.  How can GM do such a lousy job?  In
this case, it's induction noise - the GM piece has a big honkin'
resonator on it and the aftermarket ones don't.  More air coming in =
more noise.  Also, the GM one probably cost them $15 or less, mine was $100.
(FWIW, I also didn't want to cut up a factory piece when installing
nitrous, and I can confirm the intake lid is worth a tenth at the strip.)

It's all a tradeoff.

Ray
z - 30 Oct 2007 21:15 GMT
On Oct 26, 2:20 pm, Ray <ray@!rollingviolation.example.com.invalid>
wrote:
> >> Proper inflation allows my $225.00 each, tires to wear all the way down
> >> evenly.
[quoted text clipped - 13 lines]
> The handling department.
> The NVH department.

Indeed; the "story" on the FordFirestoneFiasco was that lower than
optimal pressure was specified specifically to reduce tire grip, in
order to prevent getting enough side Gs to tip the beast over.
Unfortunately, when that came up against a run of tires on the low
side of the safety margin for abuse, due to management problems at the
factory, they blew.

"For example, the documents show that Ford lowered its recommended
tire
pressure on the 15-inch Firestone P235 ATX tires to improve the
Explorer's stability after engineering simulations showed it failing
J-turn emergency-avoidance maneuvers in 1989. The lower tire pressure
was considered a critical component of the Explorer's safe handling,
enough so that Ford weighed adding a warning sticker inside the
vehicle alerting occupants that a tire inflation level of 26 pounds
per square inch was "required" to help prevent "loss of control,
rollover and serious injury."
The warning labels were never added, however. A Ford spokesman said
Tuesday that the company made design and suspension modifications in
the final months before the Explorer's February 1990 launch that
obviated the need. Ford considered and rejected several major design
changes, including widening the Explorer by 2 inches to lower its
center of gravity. Instead, Ford lowered the vehicle by one-half inch
and stiffened its front suspension springs.
"The engineering team felt they had achieved their goal of becoming a
safety leader, so there was not the need for that warning label,"
said
Ford spokesman Jon Harmon. Nevertheless, Ford's decision to lower the
recommended tire pressure on its Explorer tires to 26 pounds per
square inch, from 30 pounds per square inch recommended by Firestone,
is expected to figure prominently when a fourth congressional hearing
over the Firestone tire crisis begins tomorrow in Washington.
-Role of Ford Explorer Design Is Studied In Connection With Firestone
Tire Suits
THE WALL STREET JOURNAL
September 20, 2000
johngdole@hotmail.com - 27 Oct 2007 05:31 GMT
> > Proper inflation allows my $225.00 each, tires to wear all the way down
> > evenly.
[quoted text clipped - 11 lines]
>         Three inches
>         Three eights of an inch
johngdole@hotmail.com - 27 Oct 2007 05:34 GMT
I'd use the recommended pressure. No less. No more. Yeah, Fords/
Firestones were just too bad, unfortunately.

Michelin on tire life and air pressure:
http://www.michelinman.com/tire-care/tire-saving-tips/
http://www.michelinman.com/tire-care/tire-basics/

> > Proper inflation allows my $225.00 each, tires to wear all the way down
> > evenly.
[quoted text clipped - 11 lines]
>         Three inches
>         Three eights of an inch
johngdole@hotmail.com - 27 Oct 2007 05:40 GMT
I'd use specified pressure. No more, no less.

Michelin tire life and air pressure:
http://www.michelinman.com/tire-care/tire-saving-tips/

> > Proper inflation allows my $225.00 each, tires to wear all the way down
> > evenly.
[quoted text clipped - 11 lines]
>         Three inches
>         Three eights of an inch
Mark A - 27 Oct 2007 06:45 GMT
> I'd use specified pressure. No more, no less.
>
> Michelin tire life and air pressure:
> http://www.michelinman.com/tire-care/tire-saving-tips/

They say that to protect themselves against lawsuits, since changing the air
pressure can have an adverse affect on rollover tendency of a vehicle,
especially SUV's and trucks. Trust me, there are many rollover accidents and
deaths each year, and some of those are with Michelin tires. If Michelin
started recommending tire pressures different from the vehicle manufacturer,
they would be sued for hundreds of millions of dollars each year as a result
of the accidents and deaths.

With regard to their rotation diagram, it is clearly wrong since you never
want to cross tire from one side to the other. It causes a horribly harsh
ride when you do that.
E Meyer - 27 Oct 2007 18:14 GMT
On 10/27/07 12:45 AM, in article WfAUi.46758$c9.4410@bignews8.bellsouth.net,

>> I'd use specified pressure. No more, no less.
>>
[quoted text clipped - 12 lines]
> want to cross tire from one side to the other. It causes a horribly harsh
> ride when you do that.

Huh?  Total BS.
mjc13<REMOVETHIS> - 28 Oct 2007 11:13 GMT
>>Proper inflation allows my $225.00 each, tires to wear all the way down
>>evenly.
[quoted text clipped - 5 lines]
> pressure shown on the sidewall. So I look at the sticker behind the car
> door and inflate accordingly.

    Has anyone at all said to inflate to the maximum? Was the tire
you're using now on the market when your car was designed? Do you think
that all makes and models of tire were tested by this hypothetical
engineer...?
Bruce L. Bergman - 28 Oct 2007 20:15 GMT
>>>Proper inflation allows my $225.00 each, tires to wear all the way down
>>>evenly.
[quoted text clipped - 10 lines]
>that all makes and models of tire were tested by this hypothetical
>engineer...?

 Well, some people do say to blindly "Inflate to the tire sidewall
maximum", but thankfully it's getting rarer as knowledge is diffused.
That maximum pressure is very rarely going to get you the optimum
ride, traction and tread life, usually it will make things much worse.

 If the car still has the exact OEM size and type tires on it, then
the car maker recommendations on the door sticker are still valid.
But people often switch to different size, speed rating or load rating
tires and sometimes rim size is also changed, and then you need to
(metaphorically) throw the car sticker out the window and go with the
tire maker's Load & Pressure Chart as the primary reference.

 The one thing that is important about the manufacturer label is any
front/rear pressure biases, usually related to weight distribution in
the vehicle - the tires at the heavier end of the car are usually kept
higher.  If you are figuring pressure for new tires place the same
ratio of bias between the axles, even if the overall pressures are
higher or lower because of the different tire type.

   --<< Bruce >>--
Retired VIP - 28 Oct 2007 22:21 GMT
>>>>Proper inflation allows my $225.00 each, tires to wear all the way down
>>>>evenly.
[quoted text clipped - 31 lines]
>
>    --<< Bruce >>--

The sticker the car manufacturer puts on the door regarding tire
pressure is only for the tires that originally came on the car.  When
those tires are replaced, you should go with the tire manufacturer's
recommendation on tire pressure.  The weight-bias tire pressures
between front and back might be different also.  You can ball-park the
pressure based on the max pressure on the sidewall or you can take the
car to a grain elevator/truck scale and weigh the front and back
axles.  Then look up the recommended tire pressure for that weight.
The tire dealer should have the pressure chart.

Jack

---
avast! Antivirus: Outbound message clean.
Virus Database (VPS): 071027-0, 10/27/2007
Tested on: 10/28/2007 5:21:00 PM
avast! - copyright (c) 1988-2007 ALWIL Software.
http://www.avast.com
clifto - 29 Oct 2007 00:49 GMT
> <blnospambergman@earthlink.invalid> wrote:
>>>>
[quoted text clipped - 38 lines]
> those tires are replaced, you should go with the tire manufacturer's
> recommendation on tire pressure.

I can't find any. Tire dealer had no recommendation other than "30 pounds
each", which they recommend for all cars to all people (great, huh?).
If you can find a recommendation for TripleTreds on an '89 Grand Marquis
I'm all ears.

> The weight-bias tire pressures
> between front and back might be different also.  You can ball-park the
> pressure based on the max pressure on the sidewall or you can take the
> car to a grain elevator/truck scale and weigh the front and back
> axles.  Then look up the recommended tire pressure for that weight.
> The tire dealer should have the pressure chart.

The weight on my rear axle is definitely less than the weight on my front,
I'm pretty sure even with the trunk and passenger compartment loaded to
capacity. The manufacturer specified a bias of 4 PSI rear for all loads.

Signature

One meter, to within 0.0125% accuracy (off by just under .005 inches):
       Three feet
       Three inches
       Three eights of an inch

Retired VIP - 30 Oct 2007 01:08 GMT
>> <blnospambergman@earthlink.invalid> wrote:
>>>>>
[quoted text clipped - 43 lines]
>If you can find a recommendation for TripleTreds on an '89 Grand Marquis
>I'm all ears.

Do you know who manufactured the tires?  If so, contact the
manufacturer and ask for a chart.

>> The weight-bias tire pressures
>> between front and back might be different also.  You can ball-park the
[quoted text clipped - 6 lines]
>I'm pretty sure even with the trunk and passenger compartment loaded to
>capacity. The manufacturer specified a bias of 4 PSI rear for all loads.

I keep 40 front and 35 rear on my 2000 Grand Marquis.  That seems to
give the best tire wear but the ride is a bit rougher.  The tire
sidewall list 45 psi at max load.

Jack

---
avast! Antivirus: Outbound message clean.
Virus Database (VPS): 071029-0, 10/29/2007
Tested on: 10/29/2007 8:08:30 PM
avast! - copyright (c) 1988-2007 ALWIL Software.
http://www.avast.com
cuhulin@webtv.net - 30 Oct 2007 04:31 GMT
TP whatever (Tire Pressure) was indebially painted on our Army
vehicles.So was, Official only.One time I ''borrowed'' a Jeep to go to
down town Saigon to viisit my Vietnamese girl friend for a few
minutes.Al, in Mesquite,Texas said it was a good caper.
cuhulin
z - 30 Oct 2007 20:30 GMT
> The weight on my rear axle is definitely less than the weight on my front,
> I'm pretty sure even with the trunk and passenger compartment loaded to
> capacity. The manufacturer specified a bias of 4 PSI rear for all loads.

Might be a handling thing; more pressure in the rear = more grip in
the rear = more understeer than oversteer = safety on the road; and,
no offense, but I would guess the Grand Marquis doesn't get inherently
excellent handling from chassis design, so tire pressure tuning is
probably in order.
ChrisCoaster - 30 Oct 2007 01:03 GMT
> On Sun, 28 Oct 2007 12:15:27 -0700, Bruce L. Bergman
>
[quoted text clipped - 48 lines]
> Jack
> - Show quoted text -

Understood.  But just because one plus-sizes their tires, or, keeps
the same size tire but goes up a speed rating or two - IE from S to T
or V-rated, does not mean all common-sense goes out the window and the
new tires are automatically set to the max. pressure placard on the
tire.  I just had an alignment done and the car was riding smooth -
too smooth, in fact the tires were barely gripping the road! (sure
enough, the alignment shop had inflated them to 35psi - I checked -
they were 38-39psi hot).  So basically NOBODY in this country knows
how to set tire pressure!

I know my "new" Malibu(Saab-based) has a pretty hard suspension and
actually rode better with the original S-rated tires.  But I went
ahead and got H-rated tires of the same spec.  With the S-rated tires,
I could inflate them up to 3psi over the door sticker(30psi), improve
my rolling, and still have a smooth supple ride; with the H-rated
Yokohamas - 31psi. Anything higher and the whole damn car rattles like
Arlen Specter's jaw!

-CC
ChrisCoaster - 01 Nov 2007 00:41 GMT
> On Sun, 28 Oct 2007 12:15:27 -0700, Bruce L. Bergman
>
[quoted text clipped - 47 lines]
>
> Jack
_____________________

*Posted two days ago but disappeared into cyberspace* <sigh> here we
go again...

Just because one plus-sizes their tires or goes up a speed rating(IE
from S to H or V rated) doesn't mean to throw common sense out the
window and fill the tires to their maximum pressure as listed on the
tire.

My 2005 Malibu(Saab based) came with S rated tires.  The door placard
said 30psi.  I could go as high as 33 and still be comfortable with
them and get better gas mileage.  I recently upgraded to the same size
tire, a Yokohama, but H-rated.  Now I can go up only a pound or two
over the door placard pressure.  The Malibu has a hard suspension
already, and going significantly above GM's recommendations is like
riding the Coney Island Cyclone.  Fun, but not as fun.  31psi is where
they'll stay.

-CC
Daniel Who Wants to Know - 29 Oct 2007 05:46 GMT
>>>>Proper inflation allows my $225.00 each, tires to wear all the way down
>>>>evenly.
[quoted text clipped - 32 lines]
>
>    --<< Bruce >>--

I know of one vehicle for sure where the factory recommended pressures
aren't the best to choose even for the OE tires and that car is the '01-'03
Prius.  The factory recommends 35 front 33 rear but many owners have noticed
underinflation wear patterns such as edges wearing faster than the center at
the factory pressures and have used higher pressures instead such as 40/38
or 42/40.  Some have even foolishly exceeded the sidewall max cold ratings
but I have not yet heard of anyone showing overinflation patterns such as
center wearing faster.  A side bonus to this seems to be increased fuel
mileage
ChrisCoaster - 29 Oct 2007 18:00 GMT
On Oct 28, 3:15 pm, Bruce L. Bergman
<blnospamberg...@earthlink.invalid> wrote:
> On Sun, 28 Oct 2007 10:13:27 GMT, "mjc13<REMOVETHIS>"

>   The one thing that is important about the manufacturer label is any
> front/rear pressure biases, usually related to weight distribution in
[quoted text clipped - 6 lines]
>
> - Show quoted text -
__________________
Not if you owned a 1996 Ford Contour GL as I once did, size
P205-60R15.
Front: 31psi Rear: 34.

Try ta figger that one out!

-CC
z - 30 Oct 2007 20:20 GMT
> > Proper inflation allows my $225.00 each, tires to wear all the way down
> > evenly.
[quoted text clipped - 11 lines]
>         Three inches
>         Three eights of an inch

Back in the days when dinosaurs which came from Detroit ruled the
Earth, it was pretty much a given that the recommended pressure was
way low for reasons of ride comfort, and "serious" drivers would pump
another five or so pounds in. The advent of compacts and Japanese cars
has made this wisdom unreliable, but by the same token, you still
can't rely on the recommended pressure to be the best performance
(excluding comfort) wise. A little trial and error may be in order.

Elsewhere, I saw a rule of thumb **for an approximate starting place**
for trial and error:
Pressure in PSI=
Total weight of car/100 + 2 lbs extra on the heavier end of the car +
2 lbs if car has stock suspension

(Notice that trial **and error** should take care that the error part
isn't too bad.)

That said, my experience is that with pressures at recommended or a
few lbs higher, I've never seen excess wear on the centers, indicative
of overinflation.
Ray - 26 Oct 2007 19:13 GMT
> Wow....
>
[quoted text clipped - 23 lines]
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's - Gone to the rust pile...

That's the thing on my truck - I feel my tires are WAY overinflated, but
the ride and traction say otherwise.  unfortunately, it's going to snow
here soon, so I'll see how the grip compares vs normal pressures.

I've been meaning to do that in the winter anyway - run my tires at 5
pound increments from 20 to 50 and see if I can determine any difference
in handling or traction.  I know on my Trans Am, I can feel the
difference between 30 and 35.  The tradeoff is 35 gives a sharper turnin
 but there's more traction at 30 - the back tires spin easier at 35.

Ray
z - 30 Oct 2007 20:23 GMT
> >>>    I generally run our cars at about 5 psi (cold) below the maximum -
> >>> the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 48 lines]
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's - Gone to the rust pile

Interesting; normal recommendation is more inflation to prevent
hydroplaning; might be a difference in tread pattern. I assume your
tread pattern is pretty "aggressive" and therefore probably doesn't
need help channeling the water out, compared to the close-treaded
allseason car tires?
Mike Romain - 31 Oct 2007 00:22 GMT
>>>>>    I generally run our cars at about 5 psi (cold) below the maximum -
>>>>> the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 50 lines]
> need help channeling the water out, compared to the close-treaded
> allseason car tires?

I can see too low also allowing water to get under the center of the
tread and causing trouble.

I do have large tread lugs which channel water although some folks cuss
these tires in the wet.  They behave for me.  Most seem to be running
them too hard though.  They seem think larger tire means larger pressure.

We use a 'chalk' test to see.  That is running some chalk marks across
the tread and drive a short bit straight, then seeing how much chalk is
left.  On my style of tire, the best footprint for traction and handling
leaves about 1/4" on each edge not touching.

Running either too low or too hard is pretty bad on large tires in
particular and in certain conditions can cause big trouble.

I even remember the Volvo 240 GLT I used to own also didn't like hard
tires either, they would hydroplane bad.  They were 60 series, so 'wide'
tires.

Mike
z - 31 Oct 2007 15:45 GMT
> We use a 'chalk' test to see.  That is running some chalk marks across
> the tread and drive a short bit straight, then seeing how much chalk is
> left.  On my style of tire, the best footprint for traction and handling
> leaves about 1/4" on each edge not touching.

Oh yeah, good idea; I'd forgotten about that. A while back I got
enamored of trying to take the tire temps across the tread like the
pros do and wasted a lot of time and effort trying to get usable
readings with the crappy equipment I can afford on no budget; should
have remembered the simple old techniques.
mjc13<REMOVETHIS> - 28 Oct 2007 11:11 GMT
>>>   I generally run our cars at about 5 psi (cold) below the maximum -
>>>the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 21 lines]
> should try it too. However, many recommend lowering pressure in snow
> or wet roads, and its been raining in NJ for sometime now.

    I sometimes drop the pressure in Winter, to maybe 34, but I think
the tire itself matters more than the pressure.
mjc13<REMOVETHIS> - 28 Oct 2007 11:10 GMT
>>    I generally run our cars at about 5 psi (cold) below the maximum -
>> the figure posted on the car is almost always too low for both fuel
[quoted text clipped - 18 lines]
> that I hear you're not experiencing problems, I might
> just leave'm at 38 psi.

   35 is fine if you aren't sure your readings are accurate. 38 is
probably best of you can get it.
John S. - 26 Oct 2007 15:03 GMT
> Here's one I'm having a hard time figuring out:
>
[quoted text clipped - 24 lines]
>
> Ray

I had a similar experience with a Ford F250 with a heavy duty
suspension.  If the tires were run at 40 psi the ride was kinda
jiggly.  Run at 65 psi the ride was stiff but smooth if that makes any
sense.  The only reason I can give is that at low pressure those big
tires flex a lot more than the shocks move.  By upping the pressure
the rate of flex or movement of tire and shock was brought closer
together.  Whether that is true or not is at least open to question.
Seems to make sense to me though.

The downside of running those big tires at high pressure when the
truck was empty was that the centers wore a bit faster than the
outside.
Ray - 26 Oct 2007 19:07 GMT
>> Here's one I'm having a hard time figuring out:
>>
[quoted text clipped - 37 lines]
> truck was empty was that the centers wore a bit faster than the
> outside.

that was kind of my guess too.  I'm going to see what happens when
winter comes as far as traction goes - I'm worried that there won't be
any grip because the tires will be overinflated, but it can't be any
worse than the grip I had with the old tires (none) in the snow.

Ray

Rate this thread:






 
Sign In
Join
My Latest Posts
My Monitored Threads
My Blog
My Photo Gallery
My Profile
My Homepage

Start New Thread
Enable EMail Alerts
Rate this Thread



©2008 Advenet LLC   Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.