Community Forums

RVee'r · 03-16-2010, 12:54 PM

Quote:

Originally Posted by Tireman9

Bob, I'm not familear with Hawkshead but am wondering about the accuracy of their reading. Given that all tires leak from 1.5% to 3.5% inflation each month, you would have had to over-inflate your tires quite a bit to still be above the minimum inflation needed to carry the load based on actual tire loading.
TPMS are not a substitute for checking and adding the needed air each month. What they do is warn you of unexpected rapid (faster than 5% a month) air leakage.

Good point. I'll check the pressures with a gauge and report back.

Bob

AFChap · 03-16-2010, 02:59 PM

Quote:

can't see how it's true that ALL tires loose between 1.5 and 3% of their pressure every month based on the experience with my coach.

Me either ...I am pretty picky about keeping pressures accurate and rarely have to add air other than due to seasonal temp change in the Fall. I DO have to add air to my very low volume high pressure bicycle tires fairly frequently, but not the MH or toad tires ...knowing how air gets out of the bicycle tires I pay close attention to the MH tires, but I just don't see frequent need to aid air there...

JimM68 · 03-16-2010, 07:39 PM

Quote:

Originally Posted by AFChap

Me either ...I am pretty picky about keeping pressures accurate and rarely have to add air other than due to seasonal temp change in the Fall. I DO have to add air to my very low volume high pressure bicycle tires fairly frequently, but not the MH or toad tires ...knowing how air gets out of the bicycle tires I pay close attention to the MH tires, but I just don't see frequent need to aid air there...

I'm betting that 1.5 to 3% is refering to volume?
not pressure?

Wayne M · 03-16-2010, 07:43 PM

Today, I had the tires inspected by A & A Tire, in Kerrville, TX. I pulled in, was directed to the back yard, and immediately a tire man was there taking the duals off the street side. They were inspected, and no damage was evident. I asked, and they supplied, straight valve extensions. They also stated that there was a problem with "braided" extensions leaking. About 45 minutes to an hour later, I was back on the road. It cost me $10.35 for the valve extensions, and no other charges. Kerrville is not that far off of I-10, so if you are in the need for tires, or a check, give them a holler. It may not be as cheap as mine was, but the service is great.

Check the web site for A & A Tires, and the RV section. They have a 24 hour service with a 150 mile radius.

A & A Tire Service, Inc.
2934 Junction Hwy., Kerrville, Texas 78028
Office 830 367 4640
►Toll Free (TX only) 800 341 0409
►Fax 830 367 4929

Elkhartjim · 03-16-2010, 08:07 PM

Wayne, don't you know about the bat that all "truckers" carry?

Tireman9 · 03-17-2010, 12:13 PM

Quote:

Originally Posted by RickO

I installed the Doran 360 over a year ago and have been very happy with it but I still kept my thumper and occasionally give each tire a rap. I understand the logic of checking tires manually and using the TPMS only for a warning system... but practically speaking it's a real bear to do. I need to go with the dually extenders and replace the valves on my fronts to make the sensors easier to remove for manual checking.

I really can't see how it's true that ALL tires loose between 1.5 and 3% of their pressure every month based on the experience with my coach. For the past 18 months I've only had to add air to one tire. If I had lost 2%/month I would have lost nearly 40lbs of air from each tire and that just hasn't happened.

It has been demonstrated that "Thumpers" do not work. I am aware of demonstrations where experienced truck drivers were invited to "Thump" a few tires and then say how much air was in the tires. No onw was correct and some were off by 25psi.

RE Pressure & Temperature & time

The Percent loss measurement done in the tire industry is at constant temperature and constant barometric pressure measured continuously over a 6 month period. Pressure is taken with a transducer so there is no air loss. Most OE passenger tires have to demonstrate less than 2% per month so they usually run about 1.5%.
I have heard figures from others in the tire industry that 3% is not unreasonable.

If you start with 100psi you would loose maybe 2 psi the first month and less each month therafter. IF the temperature was the same. I assume you are using a calibrated digital pressure gauge. Correct?

I doubt that you will find an experienced tire engineer who is not willing to say that all tires loose some air each month.

Suggest you check "Ideal Gas law" PV=NRT which is reasonable for tires. Air is about 80% Nitrogen so works for tires inflated with Air or that have been inflated to the 96% Nitrogen.
Volume does not change significantly and N does not change for the air in the tire over time. R= 8.314472 J·K−1·mol−1
So if you want to do the math go ahead but I prefer to use a rule of thumb for pressure vs temp is 1 psi per 10°F change. Hot = increase. I have heard others claim as much as 2 psi per 10°F. I think it depends on how dry the air is.

Tireman9 · 03-17-2010, 12:18 PM

Quote:

Originally Posted by Wayne M

Today, I had the tires inspected by A & A Tire, in Kerrville, TX. I pulled in, was directed to the back yard, and immediately a tire man was there taking the duals off the street side. They were inspected, and no damage was evident..........

Glad you had them inspected.
They did dismount each tire and used X-ray or Sherograph inspection to be sure there was no damage internal to the srtucture of the tires...Right?

Mike Canter · 03-17-2010, 12:20 PM

I agree that tires will always loose air. The problem is that we RVers do not have a contant environment to measure in. Our temperature and barometric pressure is always changing. Same goes for oil in a motor. Some guys say their motor does not use oil. It has to use oil or the cylinder walls and valve guides are going to wear out. The problem again is the measurement environment of having the same amount of oil drain back from the motor into the pan and having the motor level and the temperature of the oil.

Mike Canter · 03-17-2010, 12:22 PM

What would worry me about that tire being flat was the fact that the bead was broken loose and the tire was away from the rim. To me that indicates that tire was driven with no air in it. If you let the air out of a stationary tire it normally will not pull away from the rim.

Wayne M · 03-17-2010, 02:06 PM

The tire was apparently driven for 20 miles or less without air.

No, there was no electronic inspection.

You can stop scaring me now - I'm going to live with the decision, and I hope it is a right one. Don't follow me to closely behind.

RickO · 03-17-2010, 04:40 PM

Thanks for the insights Tireman9. I'll only add that:

1) no, I don't use a calibrated, digital tire gauge.
2) yes, I'll agree that "thumpers don't 'work'". My only reason for mentioning it was that I can detect a tire which is flat or very low.
3) I certainly wouldn't argue with a "reputable tire engineer" if they told me that all tires lose "some" air every month. My experience just doesn't support that they all lose 1.5 to 2%/month.
4) when faced with a choice between math and rule of thumb... I'll take math.

Mike Canter · 03-17-2010, 05:00 PM

Wayne, sorry didn't mean to scare you but it is better to be warned. When my rear tire went I first had a severe vibration from the back. Didn't know what it was and actually asked by wife to walk back and see what she thought. Big mistake because then it came apart. Looking back I think I would have had time to pull over from when the vibration first started and the belt came off. I was lucky that it was the inner tire so it did not do body damage. It took me some time to pull the belt out from the suspension.
You will be OK.

Big Dan · 03-17-2010, 05:06 PM

Thanks for the reminder. I can't afford a tire pressure monitor, so it does me a lot of good when I read a post such as yours. Gives me a little nudge in the right direction, if you will.

I'm glad it was something (relatively) simple and inexpensive for you.

RVee'r · 03-17-2010, 06:41 PM

Quote:

Originally Posted by Tireman9

Bob, I'm not familear with Hawkshead but am wondering about the accuracy of their reading. Given that all tires leak from 1.5% to 3.5% inflation each month, you would have had to over-inflate your tires quite a bit to still be above the minimum inflation needed to carry the load based on actual tire loading.
TPMS are not a substitute for checking and adding the needed air each month. What they do is warn you of unexpected rapid (faster than 5% a month) air leakage.

Well, I checked today and as a matter of fact all six tires were 1-2 pounds less than when I jotted down the original pressure reading from installation. So, that alone means I'll check them before heading out on a trip. The HawksHead readings were consistent with my gauge, meaning, the readings were also lower than originally.

Were talking 16" tires with 60 lbs. of air so it wasn't anything drastic or critical, but it is, however, somewhat significant. Thx Tireman