Safe Tire Pressure

[dznf0g]

I posted this over on a TPMS thread. Maybe this will explain why I am so adimate about this subject....or not

"Guys, I'm not trying to be arnry, nor am I trying to say that TPMS temps are no good. I am saying that I have found noplace where I can find a correlation between the reading and what actual temps are where it matters, at the shoulders and across the tread ON THE INSIDE, where the bonding of tire components are.

Measuring the sidewall (where???) may very well match the air temp in the valve stem, but how do those temps correlate to the temp at the shoulder...and what is your baseline for accepting your readings elsewhere as normal? And what IS normal at the shoulder? The only readings I can find concern NASCAR and on Hoosier tire site refering to racing tires and conditions. Not a good comparison.

See the graphic below: The temps of the middle of the sidewwall don't change much, but they claim that 14* can make a difference at the shoulder??????? These are questions.....I don't have the answer, but we need a baseline for normal, regardless of how or where we measure."

[purman]

Originally Posted by dznf0g

I agree Jason, I believe (what I am trying to figure out) is that there is a proper pressure rise, for each tire size/brand/type, where that rise will be 4 PSI, (again, under my climate, geography, and speed).

My THEORY, and only a theory at this point, is that the automakers do EXTENSIVE validation testing on tires and the behavior we can note with TPMS vs. load. vs speed, etc., we should be able to translate over to the AS where we are deviating form OEM tires and be able to answer these nagging proper pressure questions. (How's that for a run on sentance?)

I think that (especially those of you with lighter rigs) can find that 4 psi mark, and reduce pressure till you see a rise greater than that, then back up to the pressure where you just see 4 psi (or your number for your climate, speed.....that you normally see on your properly inflated TV). At least you will be running the temps that an OEM automaker has deemed good to go. That's a lot more than we have to go on with our AS questions.

I just haven't found it yet on my rig...and I am not sure why, based on the info above.

One problem is if you change climate you have to change tire pressure. I live at 7000 ft and can change climate in 20 min and again in 1 hour or less depending which way I drive. . I don't want to have to change my psi while traveling so I am finding that happy medium. This is my first trip with the new tires and I may lower the psi back down to 60 psi on the way home and see if there is a difference in ride or psi gain and temp. I will let you know.

[dznf0g]

Originally Posted by purman

One problem is if you change climate you have to change tire pressure. I live at 7000 ft and can change climate in 20 min and again in 1 hour or less depending which way I drive. . I don't want to have to change my psi while traveling so I am finding that happy medium. This is my first trip with the new tires and I may lower the psi back down to 60 psi on the way home and see if there is a difference in ride or psi gain and temp. I will let you know.

Agreed. your baseline pressure will always need to be adjusted due to weather and other environmental conditions. When and how much to compensate is each of our choices.

[dznf0g]

Well, I found something. Have no idea as to the credibility of this read. Capriracer....care to share your knowledge as to these temps and how we may interpret them using infrared on the outside of the tire shoulder and using TPMS (both the pressure rise method and stem air temp method)?

Why Temperature?

(is there an error in #2 sub section 3? Shouldn't those be Ferenheit figures, not Celcius?)

[mefly2]

Originally Posted by A W Warn

I read the things you posted from the Silverado Owner's Manual. I have been driving 1500 Chevy trucks for the last 30 years or more. I have about 1,000 miles on my first 2500. (always drove Fords before) What I noticed early on about the tires on the Chevys, especially on the 4 wheel drives, was the tires always were worn more on the outer edges before the end of the tread life at the center of the tire. Balance or alignment was not the problem. After many sets worn this way over the years, on the advice of a friend, I started adding about 5 PSI above what was on the door placard. (still below the max psi on the sidewall) Once I started doing this I always got even wear and an extra 5 or 10,000 miles on the tires. The ride was better too. I'm a believer in this, and will continue to do so.

My experience is in agreement with AWW - if the tires are uniformly worn on both outer edges of a single tire (front or rear), more pressure is needed for even wear. If, however, (as is most visible on 4wd lugged front tires) there is wear only on the outside or inside edge of a single tire, it is most likely an alignment problem. In several other threads, issues have arisen about uneven tire wear on the TT. Isn't out of alignment another source of heat / rise in tire pressure? I have been told that misalignment of TT axles is mostly over looked.

[dznf0g]

Originally Posted by mefly2

My experience is in agreement with AWW - if the tires are uniformly worn on both outer edges of a single tire (front or rear), more pressure is needed for even wear. If, however, (as is most visible on 4wd lugged front tires) there is wear only on the outside or inside edge of a single tire, it is most likely an alignment problem. In several other threads, issues have arisen about uneven tire wear on the TT. Is out of alignment another source of heat / rise in tire pressure?

Certainly, scrubbing will raise temperature.

http://www.infraredimagingservices.com/left-tire

This is a great reason to carry a infrared thermometer and measure across the tread face; right center and left.

[CapriRacer]

Originally Posted by dznf0g

......I am, however, confused by this statement. I had always understood, and TireRack states (for whatever that is worth) that the correlation is 1psi = 10 degrees, irrespective of the starting pressure.....

That only applies to passenger car tires.

Yes, yes, I know. Tire Rack doesn't say that - but they should!

Again, up to a 10% rise in pressure is OK regardless of the starting pressure. (and I checked with some other extreme tire pressures - like 300 psi for aircraft - and it works there as well.

[richinny]

dznf0g

since you've got such an interest in tire pressure i was wondering if you've tried filling the tires with nitrogen? your customary detailed reporting would give it a lot of credibility.

[dznf0g]

Originally Posted by CapriRacer

That only applies to passenger car tires.

Yes, yes, I know. Tire Rack doesn't say that - but they should!

Again, up to a 10% rise in pressure is OK regardless of the starting pressure. (and I checked with some other extreme tire pressures - like 300 psi for aircraft - and it works there as well.

OK! finally! So when I find that point where 10% is met, I have arrived?

For example:

65psi with 7 - 9 rise is a little low
70psi with 7 - 9 rise ....maybe...

If I try and see

75psi with, say 7 - 8 psi rise is perfect.

FYI, I did find a site (upthread) that says 1 psi/10 degrees for passenger tires

and

2 psi/10 degrees for "truck and RV tires"
But it was a class 7/8/9 truck tire site. What do they consider LTs? Passenger or "truck" ?

[dznf0g]

Capri, Could you provide any insight on the questions in post #101?

[CapriRacer]

Originally Posted by dznf0g

OK! finally! So when I find that point where 10% is met, I have arrived?....

No, no, no. The 10% should be considered a maximum before action is taken - not a target. In street tires, cooler is always better.

Oh, and those other posts that folks have been requesting comment on - I'd like to think about those a bit. I'll comment later.

[dznf0g]

Originally Posted by CapriRacer

No, no, no. The 10% should be considered a maximum before action is taken - not a target. In street tires, cooler is always better.

Oh, and those other posts that folks have been requesting comment on - I'd like to think about those a bit. I'll comment later.

So what is the target on LTs, if they are different than P metrics?

And.... why is it common and normal to see a p metric with a 4 psi rise and a cold pressure of 35psi per the placard with no load in the bed running solo?

Sumptins' sqwuee, again.

What am I missing?

[dznf0g]

Originally Posted by richinny

dznf0g

since you've got such an interest in tire pressure i was wondering if you've tried filling the tires with nitrogen? your customary detailed reporting would give it a lot of credibility.

Didn't mean to ignore you, I posted and it didn't take??????

richinny, I can't even figure out air.....and you want nitrogen???????
It'll be an interesting experiment, if we can ever get a logical answer to air.

[richinny]

lol, from what i read you should get less variance in the pressure due to temperature. i'm hoping it would make things easier on you :-)

[Ag&Au]

[QUOTE=richinny;1217186]lol, from what i read you should get less variance in the pressure due to temperature. i'm hoping it would make things easier on you :-)[/QUOTE

I am not an expert, and I'm too lazy to do the math. However, if this is true, it seems to me it would be a very slight difference. I am certain this slight difference would vary depending on the humidity of the air you inflated the tire with. This has a lot to do with the fact that air is 78.09% nitrogen. If you Google nitrogen in tires, you will find a lot of results, the vast majority dedicated to debunking the benefits. I have no stock in either a air or nitrogen company so I don't care. However I do have a degree in Atmospheric Sciences (Meteorology) so I know a little about how gases work. Some would tell you that I also have a lot of experience in the production of hot air.

Ken

[dznf0g]

[QUOTE=w7ts;1217203]

Originally Posted by richinny

lol, from what i read you should get less variance in the pressure due to temperature. i'm hoping it would make things easier on you :-)[/QUOTE

I am not an expert, and I'm too lazy to do the math. However, if this is true, it seems to me it would be a very slight difference. I am certain this slight difference would vary depending on the humidity of the air you inflated the tire with. This has a lot to do with the fact that air is 78.09% nitrogen. If you Google nitrogen in tires, you will find a lot of results, the vast majority dedicated to debunking the benefits. I have no stock in either a air or nitrogen company so I don't care. However I do have a degree in Atmospheric Sciences (Meteorology) so I know a little about how gases work. Some would tell you that I also have a lot of experience in the production of hot air.

Ken

From what I have read, and know, I tend to agree with you. It is a moneymaker though. They got my 92 year old father with these claims and about $50 of this money. Like he's ever going to drive over 50 mph....and somehow air worked for him for some 75 years!

[purman]

Originally Posted by w7ts

However I do have a degree in Atmospheric Sciences (Meteorology) so I know a little about how gases work. Some would tell you that I also have a lot of experience in the production of hot air.

Ken

I produce a lot of hot air too, and my wife complains about it all the time

[Ag&Au]

Originally Posted by purman

I produce a lot of hot air too, and my wife complains about it all the time

I think we are talking about opposite ends of the body.

[CapriRacer]

Originally Posted by dznf0g

Well, I found something. Have no idea as to the credibility of this read. Capriracer....care to share your knowledge as to these temps and how we may interpret them using infrared on the outside of the tire shoulder and using TPMS (both the pressure rise method and stem air temp method)?

Why Temperature?

(is there an error in #2 sub section 3? Shouldn't those be Ferenheit figures, not Celcius?)

Yes, I think there is an error there.

I also think this web site - which is all about trying to sell a TPMS - exaggerates things. I think that tire explosions due to elevated temperatures (auto igniiton) are incredibly rare. I'm not buying their premise.

I think having a tool like this might be helpful in correlating surface temperatures with internal temperatures (and pressures).

[CapriRacer]

Originally Posted by dznf0g

So what is the target on LTs, if they are different than P metrics?....

There is no "target". There is only a trigger level where action should be taken.

- and no, it isn't different between the 2 types of tires (or any tire, for that matter).

Originally Posted by dznf0g

........And.... why is it common and normal to see a p metric with a 4 psi rise and a cold pressure of 35psi per the placard with no load in the bed running solo?....

I don't think it is. If folks are getting this type of thing, the engineer in me would want to investigate further to make sure this is what it is claimed to be.