New Shoes...

[SHOZ]

Originally Posted By: Quattro Pete


Quote:

I was always under the impression max pressure does not take into account the hot tire temp.

The value listed on the tire is max COLD inflation pressure that the tire was designed to safely handle. The actual (warmed up) pressure will be a few PSI higher once you start driving on the tire, and that's OK. The tire manufacturer already took that into account.


But the hot tire pressure can vary greatly, the hotter the ambient the higher the pressure.

This is why the fixation here on what the manufactures put on the door jam is so inconstant with reality. They do that more for ride comfort that performance or safety.

 

[Quattro Pete]

Originally Posted By: SHOZ
But the hot tire pressure can vary greatly, the hotter the ambient the higher the pressure.

Define "greatly", and let's stick to normal street driving and not get into race track driving.

Again, the tire manufacturer has already accounted for the increase in PSI resulting from higher temp when driving when coming up with the max cold infl. pressure listed on the sidewall, which you're not supposed to be running anyway, unless the vehicle placard tells you so.

 

[SHOZ]

Greatly in 10+ lbs. I air up the tires in the morning to the correct reading. Then drive at highway speeds and the ambient temp rises 25-30F.

And why not talk about road racing? Some say putting in a couple pounds over what the manufacture says is unsafe.

 

[Quattro Pete]

Originally Posted By: SHOZ
Greatly in 10+ lbs. I air up the tires in the morning to the correct reading. Then drive at highway speeds and the ambient temp rises 25-30F.

And that's fine if your starting point was the value on vehicle placard.

Quote:

Some say putting in a couple pounds over what the manufacture says is unsafe.

I don't see anyone saying that here, as long as we are talking about the vehicle manufacturer.

I see people advising against going 20 PSI over.

 

[Traction]

Originally Posted By: SHOZ
Originally Posted By: Quattro Pete


Quote:

I was always under the impression max pressure does not take into account the hot tire temp.

The value listed on the tire is max COLD inflation pressure that the tire was designed to safely handle. The actual (warmed up) pressure will be a few PSI higher once you start driving on the tire, and that's OK. The tire manufacturer already took that into account.


But the hot tire pressure can vary greatly, the hotter the ambient the higher the pressure.

This is why the fixation here on what the manufactures put on the door jam is so inconstant with reality. They do that more for ride comfort that performance or safety.

Again, that is why you need to check pressures on a regular basis, and adjust for current temp ranges, and even anticipate temps. In winter, if it is 65 degrees in my heated shop, and 10 degrees outside, I will add a few pounds. Same in the spring when the temps start coming up, you need to periodically bleed some pressure back off. Of course it is always changing, and OE tire pressure are not just for ride comfort. If that was the case, it would be even lower than spec. The spec pressure is to keep your tires in a safe operating range. Running Max pressure does nothing for ride, safety, or performance. I run my truck tires 5 psi under spec in town for ride comfort, but if I'm going on a road trip, or a little higher if towing, I set to spec. Like everything, you need to adjust to the conditions, which are always changing, so you can only so much, other than keep the pressure within a certain range.

 

[Nick1994]

I'd be listening to what CapriRacer says, he's a tire ENGINEER, for like 20-30+ years. He knows his stuff.

I run 20 psi front, 30 psi rear in the 1970 VW Beetle. I have 185/65-15 tires on it that are 51 psi max.

It calls for 18 & 28 psi, I like them about 2 psi higher.

 

[silveravant]

Wow. There is a lot of good information in this thread, but the most important thing to note is that trying to convince the OP of known facts is a WASTE OF TIME.

A lot of people think they know things, however many times they are wrong. Showing them facts usually only results in frustration.

 

[jadatis]

Tire pressure advice is to give the tire a deflection at wich for the speed its determined for , does not give to much heatproduction so on sertain rings it gives to high temperature at wich hardening of rubber and damage in next bendings so deflections of that rubber.

Mind that a tire rotates about 10 cycles a second at 50m/h, and every segment deflects and flexes back 10 times a second, at wich heat is produced.

Pressure advice is for about 65 to 68 degrees Fahrenheit given.
When colder ambiënt temp > lower pressure> more deflection> more heatproduction a cycle.
But also more temp difference between in and outside tire so more cooling down of tire.
Probably this heating up and cooling down goes in line , so at colder ambiënt temp the pressure is allowed lower , and vise versa.

When higher altitude so lower ambiënt pressure , you would measure a higher pressure so lesser deflection so sertainly not more heatproduction.

To what I gathered on information the advice pressure is determined for 18degr C/65 Fahrenheit ( mayby 20 degr C/68 F) and at sealevel so ambiënt pressure of 1013 mb/ about 14.6 psi.

 

[SHOZ]

Originally Posted By: Traction
Originally Posted By: SHOZ
Originally Posted By: Quattro Pete


Quote:

I was always under the impression max pressure does not take into account the hot tire temp.

The value listed on the tire is max COLD inflation pressure that the tire was designed to safely handle. The actual (warmed up) pressure will be a few PSI higher once you start driving on the tire, and that's OK. The tire manufacturer already took that into account.
So if there is a large spread in ambient temperature during the day and I am doing highway driving I should let some air out of the tire???? [censored]. What about driving in the hot desert? 80F spread in ambient is not unheard of.

But the hot tire pressure can vary greatly, the hotter the ambient the higher the pressure.

This is why the fixation here on what the manufactures put on the door jam is so inconstant with reality. They do that more for ride comfort that performance or safety.

Again, that is why you need to check pressures on a regular basis, and adjust for current temp ranges, and even anticipate temps. In winter, if it is 65 degrees in my heated shop, and 10 degrees outside, I will add a few pounds. Same in the spring when the temps start coming up, you need to periodically bleed some pressure back off. Of course it is always changing, and OE tire pressure are not just for ride comfort. If that was the case, it would be even lower than spec. The spec pressure is to keep your tires in a safe operating range. Running Max pressure does nothing for ride, safety, or performance. I run my truck tires 5 psi under spec in town for ride comfort, but if I'm going on a road trip, or a little higher if towing, I set to spec. Like everything, you need to adjust to the conditions, which are always changing, so you can only so much, other than keep the pressure within a certain range.

 

[gaijinnv]

Originally Posted By: CapriRacer

It's obvious Matt doesn't know what is going on - and he doesn't want to know. He can remain willfully ignorant if he wants. I'm done!


My thoughts exactly. Time to move on.

 

[Traction]

Tires are part of the suspension package, like another spring. I believe that in NASCAR they use very small adjustments for handling, and tire tread temps, to tune the car. In their case I believe a 1psi change, changes the spring rate by 50 pounds. They do not use max sidewall pressure for safety, performance, or ride. It's a balancing act. Just use spec pressure, and forget all the rest.

 

[OVERKILL]

Originally Posted By: CapriRacer

It's obvious Matt doesn't know what is going on - and he doesn't want to know. He can remain willfully ignorant if he wants. I'm done!


My sentiments exactly. This is like trying to teach a brick how to dance the hokey-pokey.

 

[SirTanon]

Originally Posted By: Ifixyawata
The guy who runs the place I used to go to get used tires always inflated every tire to max pressure per sidewall. He said that lower pressure is just for ride quality and that inflating to max would get you the longest wear.

I always aired my tires down to OE spec after I got home.


Good move in stopping going to that particular tire shop. That's a crash/lawsuit waiting to happen.

 

[Hokiefyd]

I think this thread has forged new territory on BITOG. CapriRacer, perhaps one of the most knowledgeable people about tires, and who selfishly and patiently gives of his time so that others may understand, has been driven to the point of giving up.

That, Matt, is a real accomplishment. Perhaps not one to be proud of, but an accomplishment nonetheless!

 

[SirTanon]

Originally Posted By: Hokiefyd
I think this thread has forged new territory on BITOG. CapriRacer, perhaps one of the most knowledgeable people about tires, and who selfishly and patiently gives of his time so that others may understand, has been driven to the point of giving up.

That, Matt, is a real accomplishment. Perhaps not one to be proud of, but an accomplishment nonetheless!


I'm surprised BITOG has fed this troll for this long...

 

[tenderloin]

Originally Posted By: mattwithcats
What pressure did Ford recommend for the Explorer?

26 PSI...

http://abcnews.go.com/US/story?id=95667

"A lower air pressure gives tires more grip and a softer ride, but causes them to wear faster and creates more internal heat because of greater friction with the road. "


The Explorer tires were run softer to help stop roll over not provide a soft ride

26 lbs would have been ok..26 lbs ended up being less than that as most people do not check pressure that often..also Firestone tire purchased by Ford was low quality junk..BTW I have an older Honda Passport (Isuzu) that recommends 28 lbs all around

 

[Traction]

Originally Posted By: SirTanon
Originally Posted By: Hokiefyd
I think this thread has forged new territory on BITOG. CapriRacer, perhaps one of the most knowledgeable people about tires, and who selfishly and patiently gives of his time so that others may understand, has been driven to the point of giving up.

That, Matt, is a real accomplishment. Perhaps not one to be proud of, but an accomplishment nonetheless!


I'm surprised BITOG has fed this troll for this long...

True, but it is amazing how many other people out there don't understand anything, "Beyond Round and Black" which was a BFG publication from 30 years ago.

 

[Astro14]

Originally Posted By: SHOZ
Greatly in 10+ lbs. I air up the tires in the morning to the correct reading. Then drive at highway speeds and the ambient temp rises 25-30F.

And why not talk about road racing? Some say putting in a couple pounds over what the manufacture says is unsafe.


You're confused about the word "ambient"...as well as the word "cold" as it applies to tires.

Ambient means the outside air temp. Checking the tires cold means that they are at ambient temperature.

So, it's 70F outside, you check the tires when they've been sitting for at least 3 hours, and aren't baking in the sum (which can raise the temperature quite a bit). That way, they're at ambient.

They will heat as you drive, and the pressure will go up (PV=nRT,..). There are so many variable in the degree to which they heat; starting pressure, speed, load, cornering, and yes, ambient temperature, which determines dissipation rate...that it's an inconsistent measurement for determining which pressure to run.

So, manufacturers specify a "cold" reading. That's what you should check, set, and adjust for load, or anticipated speed. My S600 specifies a cold pressure for "normal" driving and a different pressure for high speed driving as well as an adjustment for full load.

As ambient temperature changes, the pressure in the tire will change (PV=nRT again) and once you've converted temperature from Kelvins to Fahrenheit and pressure form Pascals to PSI, it turns out that a 10 degree (F) change in ambient, will change the pressure by about 1 PSI.

So, knowing that, you can set cold pressure in anticipation of weather changes. For example, today in Virginia Beach, it was 70 degrees. Next week will be in the 30s, so today, when I checked the pressure, I set it 4 PSI over the usual cold pressure that I run. That way, the tires will be at normal pressure when the temperature returns to seasonal normal.

 

[Virtus_Probi]

Originally Posted By: SirTanon
Originally Posted By: Ifixyawata
The guy who runs the place I used to go to get used tires always inflated every tire to max pressure per sidewall. He said that lower pressure is just for ride quality and that inflating to max would get you the longest wear.

I always aired my tires down to OE spec after I got home.


Good move in stopping going to that particular tire shop. That's a crash/lawsuit waiting to happen.


Even a tire shop that I like a lot and still use always used to massively overinflate my tires. I suspect that they felt that most people never checked their tire pressure and that maybe people wouldn't be horribly underinflated next time they came back to the shop that way. I did notice that the last couple of times I went there, they actually were leaving me with reasonable pressures.

As much as I like that place, they have screwed things up here and again. One time I bought new tires from them, I drove away thinking I had purchased the [censored] tires in existence. They called me later in the day and asked me to PLEASE look at my tires carefully...I asked why, and they confessed that they found ONE of the tires I had ordered in their warehouse. Sure enough, I looked at the car and had three of the tires I wanted, plus another of the same brand but different model...and SIZE. Probably a result of their working model, when they are not busy you will have 4 guys working on your car at once to get you out of there fast. They literally run over as you are driving up and sometimes are jacking the car up before I get out.
They apologized to me a million times, but that was an AWD car and I was concerned about it being damaged. Tried a chain store down the road from them next time, waited an hour in a line only to see that the customer who was leaving when I got there kept coming back over and over saying there was something wrong. Finally cut my losses and went back to the old place, they got me out in half an hour.

 

[mattwithcats]

Update,

Got the Saturn on the highway today.

Ride was a little bouncy, but no control problems, and MPG were 40.
A little more breaking in, and I should be back to 44...

As I drive for fuel economy, (snicker) I am adding (laugh), 2 PSI (ROFL), to 39, and then seeing how she handles.

If I was driving the family around, I would take two PSI out, and see if the bounce bouncing goes away...

Difference between 205/60 and OEM 185/65 tires in driving, the 185 are a little squirrely, and a very slight tendency to wander side to side...

205's just want to go straight, a minor effort is needed to turn the wheel. Car handles like it's on rails, ripped a 25 MPH exit off the highway, onto another highway, without slowing...

Good tire, good price, better treadwear (and price) than the Generals RT43's, my only complaint is these are directional.

Another consideration was the Ironman IMove, 420 A A, I believe. Price was the same, I took the 20% more tread, and sacrificed side to side rotation...

My apologies to CapriRacer, It was not my meaning or intent to upset you...