Tire Test Question

[pineranch]

OK, they are 614's! Start of trip a month ago, outside temp 85 and at sea level. Set pressure to 95 psi and this pressure remained constant all month.
Been sitting for 2 weeks at 3500 feet and average temp 45-55. Pressure is 90 psi on all four tires.
A. Air back up to 95 psi.
B. Leave it alone.
Thanks,
Mike

[stiles watson]

You adjust the pressure to the desired level for the temperature where ever you are. The pressure is taken when the tire is cold.

[pineranch]

OK Stiles, I know there is an answer there someplace, how about a hint, A or B.
Mike

[8.1al]

If you are going on the road, set the pressure to 95 before you leave, if you are not going anywhere leave them alone

[LonnieB]

quote:By 8.1al

If you are going on the road, set the pressure to 95 before you leave, if you are not going anywhere leave them alone

I agree.

[pineranch]

Thanks, heading out Monday. Just find it strange they all 4 dropped exactly 5 psi.
Mike

[stiles watson]

That they all dropped together is a good thing. It means it is because of the ambient temperature, not because you have a leak. Occasionally, you will have one side slightly higher than the other because that side is getting the sun and therefore a bit warmer.

[swanny]

ok Guy's this is so easy, so here we go. Just click here www.physicsforums.com/showthread.php?t=320368








Enjoy

[HOOK]

I think if I understand correctly that you first checked pressure in a warmer climate. If so, with all 4 showing the exact same 5# loss, my decision would be this; If I were going to same colder climate with high altitude, I would increase to first pressure, but if Iwere going to a warmer climate, lower altitude, I would drive far enough to raise temp. of tires and if possible to low enough altitude for atmospheric pressure to rise some, and then recheck. 5# is not a great amount, yet I would only go as short a distance as nec.

[Hooker]

quote:Originally posted by stiles watson

You adjust the pressure to the desired level for the temperature where ever you are. The pressure is taken when the tire is cold.

Agree. Some of you guys are making this way too complicated. Get up in the morning, check the TP (tires are cold, you haven't gone any where yet), set TP to what it should be. Leave it alone for that day's travel.

[Ozz]

quote:Originally posted by pineranch

Thanks, heading out Monday. Just find it strange they all 4 dropped exactly 5 psi.
Mike

Where to now?

[pineranch]

A week in Idaho, Couer de' Alene, Lewiston, Kamiah then on to see if the aliens are back in Devils Tower.
Mike

[awaywego]

I was in Jackson Hole and 87 degrees. I set the pressure to 80 on my previous Montana and headed to Arco Idaho. Crossing the Desert where it was 115 degrees and I blew 2 tires. After that I always set them at 75 so they could heat and increase a little.
Really depends on the outside temp.
I now have the G614's and keep them at 95-100.

[Phil P]

Hello OZZ

If you 18 wheeler weighed about 450 tons at the beginning of the trip and only about 250 tones at the end of the trip, your tire rotation speed hovered around 200 Mph, operated in a temperature of about –50, had blowout safety plugs to control rapid deflation when hot and you don’t want a oxygen / nitrogen gas mix blowing on the hot brakes then you would inflate your tires with nitrogen and avoid a large portion of the pressure change from temperature. LOL

By the way the description above is the Boeing 747-8.

Also how is your tire wear at 95 Psi.

Phil P

[01RAMer]

Here's what I've been told: Add 1% of pressure for each 5 degree cooler at destination temperature. Reverse this for warmer destination temperatures. Generally, except in the desert by the sounds of it, higher pressures are better then lower pressure. Also been told that good tires commonly will lose 1% to 5% of pressure per day.

[Hooker]

quote:Originally posted by 01RAMer

Also been told that good tires commonly will lose 1% to 5% of pressure per day.

I'm not so sure I agree with this...if you lose 5% a day...in three weeks your tires are flat.

[8.1al]

I would be mighty unhappy if my tires lost 1% a day

[Parts Ed]

Now if I lost 1% a day for three weeks, I'd be happy!!

[Waynem]

I disagree with most of what has been posted - not all mind you, just most. So not to single anyone one out, please take this in good humor. But here are the facts.

For every 1000 feet of altitude, tires will see a .48 psi change of pressure. So rising or descending 10,000 feet would result in a 4.8 psi difference. So if you started with 85 pounds you would finish with 89.8 pounds going up. Going down you would finish with 80.2 psi. (don't forget possible temperature changes - see below)

For temperature changes there will be a 2 percent increase or decrease, as appropriate. Considering these factors, consider what pressure you want to run at that will leave you a margin where you don't have to adjust tire pressure for hot/cold/hot or cold/hot/cold weather, and altitude if your pressure is within the rate chart and not running maximum or minimum. You HAVE TO WEIGH you rig to determine the correct pressure for your weight. It is best to weight each tire individually, but then pressure to the highest rating for the entire axle. That is, each tire on the same axle will have the same pressure.

Example: at 85 psi, changing temperature -30 degrees would be 6 percent loss of air
or about 5.1 pounds. At 90 psi, a 30 degree drop in temperature will be 5.4 pounds and will still leave you at 85 psi, still possibly within range of tire loads.

Now consider DW gains some weight (I didn't say that). And let us say that your present weight at 85 psi allows you to add an addition 170 pounds of weight (lay off the donuts). Whereas, at 90 pounds you may (depending on tire chart) be able to add 690 pounds of weigh eating as many donuts as you (DW) want.

You have to be the judge of where your comfort weight is and put in the PSI right for you and within tire manufacturers specifications.

Personally, I'd run your tires at your weights that would allow you to have a margin of error. Do not concern yourself with temperatures related to road heat. The tires are manufactured with that in mind.

So, depending on the weight of your rig, and the weight on each axle, the tire manufacture's chart will give you the information you need to not have to change the air every time you (your tires) get cold, hot, high, or low. Just check them in the morning to see if they are within the manufacturer's specifications. If you go up in altitude, you will be coming down in altitude at some point and you will still be within spec's if you follow the charts.

If you wish, give me the exact number on your tire as to size and load range, and the weight of your axles and I'll do a little math. I don't have a Monty anymore, but tire pressures apply to all vehicles. My tires are 255/80R22.5 and cost between $400-500. I want to make darn sure I get a full life out of them.

Good luck.

p.s., I'm not a tireman - I just look at the chart. I hope my figures are correct. The above is/are my humble opinion, based on Michelin's guidlines.

[exav8tr]

Yeah, What Wayne said!!! (substitute apple turnovers for the donuts).... Forecasting 113 degrees here tomorrow, wonder what they will do in that heat.........I think I will go check them at different times tomorrow.........