BAC Forum
General Boards => Technical Support => Topic started by: Mandy Canales on April 19, 2015, 10:57:54 PM
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I was waiting for someone else to make this post and since they haven't I'm going to make a comment here regarding bead balancing and adding air pressure to your tires.
At the Pomona convention one of our coaches came in with all of us and parked in the security section. After about 3 days the driver wanted to take the coach out for a maintenance session and as he pulled out on a hard left turn his left front tire came off the rim. He had not noticed that both tires were flat. He indicated that he had checked the tire pressure a few days prior to his arrival.
Pete's Tire arrived to help solve the problem an hour later. Long story short the tires had been balanced with beads and the mechanic said the beads had plugged the valve stem causing a slow leak. The mechanic's answer to the owner was when you air up your tires that have been balanced with beads make sure the air valve is at the 12 o'clock position so that the beads have a chance to fall to the bottom of the tire.
When air is then put into the tire in that position the air will clear the passage way and the beads won't have a chance to plug the valve. A couple of hours later and some down time all were happy again. Hope this helps others.
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Both front tires were flat????? And this person was going to drive it without noticing that his front tires looked a little funny. Some people should not be allowed to drive a wheeled vehicle at any speed. I have seen a few that should not be allowed on the road or in a parking lot for that matter.
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When using beads for tire balancing, these valves are supposed to be inserted. The scorpion tail keeps the beads away from the head of the valve.
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Long story short the tires had been balanced with beads and the mechanic said the beads had plugged the valve stem causing a slow leak. The mechanic's answer to the owner was when you air up your tires that have been balanced with beads make sure the air valve is at the 12 o'clock position so that the beads have a chance to fall to the bottom of the tire.
If the metal valve stems had metal caps properly installed I can't how they could leak regardless of where the beads were. For a brief time last year I had a leaky Schrader valve on one tire, but I was still able to retain proper pressure with just the cap. This just doesn't make any sense IMO.
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Long story short the tires had been balanced with beads and the mechanic said the beads had plugged the valve stem causing a slow leak. The mechanic's answer to the owner was when you air up your tires that have been balanced with beads make sure the air valve is at the 12 o'clock position so that the beads have a chance to fall to the bottom of the tire.
If the metal valve stems had metal caps properly installed I can't how they could leak regardless of where the beads were. For a brief time last year I had a leaky Schrader valve on one tire, but I was still able to retain proper pressure with just the cap. This just doesn't make any sense IMO.
I was wondering the same thing, spray bottle dish soap and water makes it easy to find leaking schrader valves and valve stem base leaks.
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While a slow leak can be insidious, biggest problem (IMHO) is a fast leak. I had 2 instances of the valves sticking open after adjusting pressure (which can be exciting). Letting air out is an invitation for the beads to stick in the short (normal) core. If you are not aware of the need for long cores, you replace the core with another short core and set yourself up for repeated problem. Tire shop told me red capped valve caps indicate the tires contain beads.
Steve
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While a slow leak can be insidious, biggest problem (IMHO) is a fast leak. I had 2 instances of the valves sticking open after adjusting pressure (which can be exciting). Letting air out is an invitation for the beads to stick in the short (normal) core. If you are not aware of the need for long cores, you replace the core with another short core and set yourself up for repeated problem. Tire shop told me red capped valve caps indicate the tires contain beads.
Steve
I'm rarely, if ever, in a situation where I have to let air out of tires. I fill using a device like this: http://www.amazon.com/gp/product/B000YC7G8I/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 (http://www.amazon.com/gp/product/B000YC7G8I/ref=oh_aui_search_detailpage?ie=UTF8&psc=1) so I accurately know the pressure as I'm filling. Never overshoot the desired pressure, so no reason to let air out.
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Living in the desert when the summer heat hits, that cold max pressure you inflated to in the winter/spring is at a higher pressure and should be reduced.
Steve
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Steve,
I disagree with your viewpoint about reducing tire pressure as the temperature rises. The word "cold" in the tire inflation tables refers to a specific temperature (I think around 60 degrees F), and not ambient temperature. Therefore, reducing tire pressure as the temperature rises can result in underinflated tires.
Gerald
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Tire pressures increase/decrease from 1-to-2 psi for each 10F degree temperature change... according to what I am finding on the internet. Note: Most sources used 1 psi - one source used 1-to-2 psi and none used 2 psi. This tells me that when driving towards colder climes, then check the pressures more frequently along the way. When driving towards warmer climes, then check pressures less frequently. Certainly, it is better to be a bit over-inflated than alot under-inflated.
I try to check my tires if stopped for a few days because there is plenty of time and no hurry to get going. Also, while driving I monitor my tire pressures onscreen in real time with a Pressure Pro TPMS - occasionally switching to the rear camera to view the Avalanche onscreen.
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Tire pressures increase/decrease from 1-to-2 psi for each 10F degree temperature change... according to what I am finding on the internet. Note: Most sources used 1 psi - one source used 1-to-2 psi and none used 2 psi. This tells me that when driving towards colder climes, then check the pressures more frequently along the way. When driving towards warmer climes, then check pressures less frequently. Certainly, it is better to be a bit over-inflated than alot under-inflated.
I try to check my tires if stopped for a few days because there is plenty of time and no hurry to get going. Also, while driving I monitor my tire pressures onscreen in real time with a Pressure Pro TPMS - occasionally switching to the rear camera to view the Avalanche onscreen.
If you remember back to high school chemistry, gas pressures increase with increasing temperature. The relevant calculation is (P1)(T1) = (P2)(T2) where temperatures are expressed in Kelvins (degrees Celsius plus 273).
So if you wanted to know what the pressure of a tire would be when it is 10 degrees (Fahrenheit) hotter your equation would be:
P2 = (P1) (T2/T1)
Since 68 degrees F = 20 C and a change of 1 C =~ 2F then if your tires are pressurized at 100 psi at 68 degrees then at 78 F they will be roughly 5 degrees C hotter. Therefore,
P2 = (100 psi) (273 + 25)/(273 + 20) = (100) (1.017) = 101.7 psi
So the correct answer is that pressures will increase or decrease 1.7 percent for every 10 degree change in temperature which for our tires translates roughly into 1.7 psi
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Guys,
I'm confused. While I agree (now) with Gerald in general, I still don't know what the "cold" temperature is. The data I find on inflation at the mfgr's web sites don't specify a "cold" temperature other than ambient. Goodyear (see attached) seems to confuse it even more (for me at least) by stating "always inflate tires to the cold maximum no matter what the ambient temperature is." Then they state "We caution operators not to bleed air pressure down on cold tires when at high ambient temperatures." (See pg 40 of linked doc).
http://r.search.yahoo.com/_ylt=A86.J3Vy0zdViR0AU_onnIlQ;_ylu=X3oDMTEzNnZmNmszBHNlYwNzcgRwb3MDNwRjb2xvA2dxMQR2dGlkA1lIUzAwMV8x/RV=2/RE=1429750771/RO=10/RU=http%3a%2f%2fwww.goodyeartrucktires.com%2fpdf%2fresources%2fservice-manual%2fRetread_S5_V.pdf/RK=0/RS=9CrSMIv5AwC1RrPwL5mrKBd4ktQ-.
Huh? Do I set pressure at 60-70F or 90-100F. If at 95, do I de-rate PSI to allow for the higher ambient. If so, to what temperature? I know I'm missing something basic but having one of those days....
Thx! Steve
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Cold temperature is defined as the temp before you start driving, regardless of the ambient. Think about it, from my previous calculations there is only a 1.7 psi difference per 10F change. so if you pressurized your tires to the maximum when it was 40 degrees outside you'd only have a 6 psi difference even at 100 degrees. In reality you're unlikely to be fooling with your tires when it's 40F outside so the real differences are going to be even smaller.
The tires are designed to be pressured up to maximum sidewall rating (or an appropriate pressure for the load) and then driven. That will raise their temps and pressures quite a bit. My TPMS typically will show ~10-12 degree increase in pressure after a couple of hours of driving. There's nothing wrong with the pressure, when hot, exceeding the max sidewall temps.
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Joel,
I purchase 4 tires, have them mounted in Phoenix in July, and aired up to max psi of 120 with a 115F ambient. In Oct I drive to MN and lose a steer tire to road hazard. I have the new one mounted and aired to 120psi in a 30F ambient per Goodyear and your guidance. It would seem that the net will be about a 14psi delta between the AZ and MN tires. Wouldn't I want to have the MN tire aired up to match the AZ tire PSI (which should be about 105.5 psi)?
Steve
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First of all, it would seem highly unlikely that you would need to have your steer and drive tires be at the same pressure, let alone the maximum sidewall pressure. Don't you know your wheel weights and don't you inflate your tires to match those weights?
Anyway, that being said, I would always want the tires on the same axle to have the same pressure so if you replaced only a single steer tire I would most definitely want the other to have the same pressure. Reading your comments, I presume you don't have a TPMS system on your MH. I wouldn't be without one; I know my tire pressures to the nearest one psi.
Joel
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Joel,
The numbers I used were for example only. As to weights, I know what each corner weighs and air up accordingly. Regardless, the point I was trying to make is that one cannot fill to the same cold psi regardless of ambient temperature. You need to take temperature into account.
Steve
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I have a 2000 Marquis, and my tire pressures are 120 PSI for 295/80/22.5 Michelins all of the way around by weight specs. I have a TPS system and I try to maintain my tire pressure based on an ambient temperature of 60 degrees F. So I check my tires early in the morning if possible to get the cool temperature. However, when I leave my house in the Phoenix area in a week or so for the summer, it will probably be in the 90s and my tires will probably have 125 PSI in them when I drive out the driveway.
Gerald