Community Forums

Sky_Boss · 01-04-2013, 09:05 PM

Quote:

Originally Posted by Tomp4801

Per any tire manufacturer's tire inflation chart, the tire should also be inflated based on the axle weight, which obviously varies from coach to coach. So there is no single "right" inflation for everyone.

Actually...don't you hate that lead in? Tire pressure is based on wheel weight and whether that "wheel" is single or dual.

I figure you probably meant that but just in case...

Tomp4801 · 01-04-2013, 09:35 PM

Quote:

Originally Posted by Sky_Boss

Actually...don't you hate that lead in? Tire pressure is based on wheel weight and whether that "wheel" is single or dual.

I figure you probably meant that but just in case...

But of course! Just wanted to point out that there is no "one size fits all" answer.

Arch Hoagland · 01-04-2013, 11:20 PM

Quote:

Originally Posted by PlayItForwrd

This conversation is exactly why I wish the tire or motorhome mfr's... just ONE of them-- would publish what they consider acceptable air pressure for a "running" tire. Or at the least, some kind of "adjustment" figure for very low ambient temps. Because-- does anyone know what the amount of temperature rise a typical tire develops at different ambient temps? I'm guessing here, but I'm thinking my 22.5's on my 12 ton motorhome probably get to around 140° on a 90° day, a 50° rise. But it's like 5° outside right now, and I'm pretty sure after a few miles they're going to be MUCH warmer than 55°, but how much? If I put in 100 psi at 5°, will the temperature rise actually result in too much pressure after driving awhile?

I know how much the temp goes up on each tire because every time I stop I use an IR gun on them, along with the brakes and rear end.

All I'm looking for with temp is to see that they are all about the same temp. A tire that is quite a bit hotter than the rest of them tells me it's low on air or I've got a dragging brake problem.

I check the pressure in the morning with no sun on them.

distaff · 01-05-2013, 09:24 AM

Koop - I actually said I put 10 in, that meant that at -22 F I was still 5 down, what I didn't say is that I always run a little hard, so I was still above the chassis rating. I drove for 30 minutes and checked them again and I was up the other 5 PSI. Three days later in Nevada I was up 15 PSI on a 60 F morning and had to back them all off.

You are right when you say you mustn't rely on tire internal friction to get an under inflated tire up to rated pressure, but you also need to remember that "cold inflation" means 60 F. I have read that a change of 10 F equals one PSI, but that is true of auto tires, I found that -22 to +60 on RV tires it was actually more like 15 psi difference.

Low temperatures play havoc with TPMS up in the north, so you have to learn to ignore them a few weeks of the year and do it manually.

palehorse89 · 01-05-2013, 09:38 AM

Here is some good reading on this subject:

Tire Tech Information - Air Pressure, Temperature Fluctuations

sgtjoe · 01-05-2013, 06:50 PM

Quote:

Originally Posted by palehorse89

Here is some good reading on this subject:

Tire Tech Information - Air Pressure, Temperature Fluctuations

Now that is some great info. I'll try to post what my psi is when I reach Vegas. Currently I have filled mine to 100psi at 28 degrees. Let you all know in a few days.

Gary RVRoamer · 01-06-2013, 08:51 AM

Tire pressure gains or loses about 2% for every 10 degrees F., so for a 100 psi tire to drop to 86 implies a 70 degree temperature change. Some of your difference may be a leak rather than temp change.

Don't over think this - just air up to recommended pressure when the tire is "cold", i.e. has not been driven for at least several hours. "Cold" means the tire is cold rather than hot from driving-generated heat and has nothing to do with ambient temperature. However, if you move to an area where the ambient temp is warmer or colder than your last stop, re-adjust the "cold" tire pressure as needed. And of course, monitor the psi periodically anyway, to detect slow leaks, which are common.

palehorse89 · 01-06-2013, 09:03 AM

Gary, you hit this right on the head, don't over think this! Is a leak possable? Checking tire pressure when is really cold outside is not a good practice, take a average outdoor temp of 50-60 deg and use that and check pressure. If it was 10deg. outside I don't think it is a good time to check tire pressure unless it is looking flat. I f you have not had a problem when it was parked and ran last and it looked ok I would get in it and drive, when the outside temps. warm up and tire is cool, check it then. Truck drivers are not always checking thier tire pressures as they move across the country daily and the climate changes, they would never get anywhere. Again, due to the nature of owning a rv one tends to over think various subjects.

sgtjoe · 01-06-2013, 10:05 AM

Thanks for all the comments/suggestions. We've decided to postpone our travels South until the Temps here warm enough to not only maintain a decent tire pressure but to also be able to remove the thick ice and snow off the roof safely.

Also, as I was airing up the back tires I noticed the DOT tire dates, DUH ME, I had completely spaced replacing the rears. Date 2805, I'd say pushing 8 years is not too smart.

BTW, my outside dual that was reading 100psi yesterday is now showing 89psi on my TPMS this morning at 9 degrees. It could be a leak. New tires will fix that.

Another BTW, these are XRV's and there is not one hint of a crack anywhere, not bad for 8 year old tires, huh.

distaff · 01-06-2013, 11:04 AM

Joe - good catch on the tire age. I agree that down 11 PSI overnight is a leak. Having said that, I have had a situation where I thought I had a slow leak when one tire lost about 10 PSI in the week (sitting) following testing them all. I aired it up and it never lost a pound of pressure again - and I'm talking about 6 months including driving a few thousand miles.

I suspect that the valve may not have seated properly after testing it, but when I put air in it and tested it again it seated tight.

As for Don's comment about the complexity of getting the pressure right for each wheel, you just have to weigh each side of each axle (for me that is 6 weights) when loaded, and work out the correct pressure, and make a note of it. In my case this called for different pressure on all three axles, but I prefer to run hard, so I use this as my base line and inflate the rear 6 tires to 100 psi (only need 90 on the tags and 95 on the drives) and 120 on the steer tires.

I should get an IR gun, I do a hand test on each tire when I stop, but the hands get dirty. And I never drive more than 20 miles without testing the pressure in each tire. It is tedious but it beats a problem at roadside.

Arch Hoagland · 01-06-2013, 03:43 PM

distaff said:
And I never drive more than 20 miles without testing the pressure in each tire. It is tedious but it beats a problem at roadside.

Huh? Every 20 miles?

sdennislee · 01-06-2013, 04:21 PM

Quote:

Originally Posted by Arch Hoagland

distaff said:
And I never drive more than 20 miles without testing the pressure in each tire. It is tedious but it beats a problem at roadside.

Huh? Every 20 miles?

I assumed he meant, that after adjusting air pressure he would only run 20 miles before stopping to check.

ralphie · 01-06-2013, 05:02 PM

After reading tire pressure posts for years now, and reading everything from tire mfgrs., you are supposed to air your tires in the AM without regard to ambient temperatures and according to the respective tire mfgr's chart. No need to adjust PSI after that except to replace lost air or adjust to changed loading, and every tire I've ever had has lost some air over extended periods.