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Old 08-27-2015, 10:08 AM   #1
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Tire pressure and TPMS

I'm setting up a new EEZTire TPMS which has me looking at my tire pressures again. I have Sailen tires on the front which shows Max PSI at 109.

My sticker in the cab says front axle tires should be at 95 PSI.

On the rear I have Goodyears and the tire shows Max PSI 100.

The cab sticker shows 85 for rear duels.

I haven't had my coach weighed so I'm going by the seat of my pants here. I've been running the front at 95 and the rears at 90.

When setting up the TPMS they suggest setting the upper warning at 20% over what you run and the low at 10% under what you run.

So with my Sailun if I were to set the pressure at 95+20%=114 which is fine, but if the tire is saying Max PSI is 109 should I use that as the upper alarm? The lower would be 85.5 based on the 10% rule.

With the rears set at 90 the upper limit would be 108 when the tire says 100 max psi. If I set the lower limit at 10% less then I'm running I would be setting it at 81 which seems awfully low considering the tire shows 100 psi.

Any suggestions would be helpful. I know I should have the rig weighted but I'm headed out and a scale isn't available at the moment.
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Old 08-27-2015, 10:16 AM   #2
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Quote:
Originally Posted by Vt Rv View Post
I'm setting up a new EEZTire TPMS which has me looking at my tire pressures again. I have Sailen tires on the front which shows Max PSI at 109.

My sticker in the cab says front axle tires should be at 95 PSI.

On the rear I have Goodyears and the tire shows Max PSI 100.

The cab sticker shows 85 for rear duels.

I haven't had my coach weighed so I'm going by the seat of my pants here. I've been running the front at 95 and the rears at 90.

When setting up the TPMS they suggest setting the upper warning at 20% over what you run and the low at 10% under what you run.

So with my Sailun if I were to set the pressure at 95+20%=114 which is fine, but if the tire is saying Max PSI is 109 should I use that as the upper alarm? The lower would be 85.5 based on the 10% rule.

With the rears set at 90 the upper limit would be 108 when the tire says 100 max psi. If I set the lower limit at 10% less then I'm running I would be setting it at 81 which seems awfully low considering the tire shows 100 psi.

Any suggestions would be helpful. I know I should have the rig weighted but I'm headed out and a scale isn't available at the moment.
Hi..
Just remember tire pressures are set COLD.. As they warm the pressures will rise.. So set your alarms at 15 to 20% above cold pressure and you will be fine.. The same is true for MAX pressures on sidewalls.. Cold presure..
Hope that helps.. I have the added situation of living at 9200 feet and coming down in altitude the pressures also rise.. ABut anymore I just let them be.. Truckers do this all the time..
Ron
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Old 08-28-2015, 09:35 AM   #3
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Once read a document of Semperit ( Continental) in wich pressure is allowed 1.4 times the AT-pressure of yours 100 psi. 109 psi At pressure must be a miswriting I think.

So even filled 140 psi cold at freesing point of water would not give a blowing tire when the tire warmes up to boiling point of water , then about 2 times the AT- pressure .

Once read from Capriracer or Tireman 9 that tires are tested to can stand a pressure of 2 to 3 times the At-pressure before they blow.

So dont be affraid that it will be to high.
Most Tire makers in America allow a cold pressure of 10 psi above At-pressure.
And for Truck tires ( wich in fact your tires are) even 20 psi above AT-pressure.

Also the valves are tested to can stand a higher pressure when warm.
And the maximum allowed of them is given for cold pressure when inside tire temp is outside tire temp of 18 degr C/ 65 degr F.
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Old 08-28-2015, 02:24 PM   #4
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Last year was the first time we had a TPMS on our coach ( 2005 Bounder 33R/Workhorse). It didn't work quite the way that I had imagined. To begin, as others have said, the max pressure on the tire is for maximum tire inflation cold. My factory coach cold tire inflation calls for 85PSI front and rear. The tires can go as high as 110PSI cold. I generally run 85PSI unless I am going from a hot area to a cold one and then I might inflate to 90PSI. At 85 the 120% rule would mean the alarm is set to 102PSI. That's what I did and, of course, after running for an hour the tires reached that temp and the alarm sounded. After a lot of fiddling, I found the following. The TPMS is not entirely accurate. I have a TSTsystem. Different tires will show different pressures even when the temps are the same and sometimes the cooler tire will indicate higher than the warmer tire. However, the max temp that I showed in a lot of highway driving in warm weather was around 110 degrees or so. A hand on the warm but not hot tire confirmed that the temps were within reason. The tire pressures got up to - as I recall - around 105. Every day was pretty much the same. I decided those kinds of readings were "normal" and if they didn't deviate by much all was well. I am generally more interested in a tire losing pressure than gaining, and, of course, if a tire temp starts to climb it may be a matter of concern. I think that you will find that the TPMS readings are more relative that absolute. In fact, TST says that the sensors have a variance of up to 4PSI from true pressures. My sensors read a pretty consistent 4PSI lower than my 2 tire gauges. Hope this helps.
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Old 08-28-2015, 02:30 PM   #5
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I run 92 in my front and 82 in my rear tires, weighed in fully loaded, that gives me 4lbs over the required COLD pressure requirements.

When they heat up they can go as high as 102 in the fronts and 92 (about 10% or more) in the rears depending on how hot it is out and driving speed.

My little coach is only 32' and weighed in around 17,500 fully loaded, gasser.

Hope this helps...
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Old 08-31-2015, 02:38 PM   #6
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Thank you for the replies.

I received and installed the EEZTire TPMS. I set the pressures on cold tires at 95 front and 90 rear. I set the upper limit at 20% and the lower at 10%.

Quickly about the EEZTire set up. What a nice surprise to find that the instillation was very simple after having watched a set up video on line. I bet I had it unpacked, programmed and installed in 30 minutes.

Anyway, headed out on a 6 1/2 hour trip to northern Maine. The system was working great and showing me pressure and temp. As the day warmed and I was on the highway for a couple hours one of the inside rears set off the upper pressure alarm. All four were within a few PSI but only one hit the 20% mark. I slowed down and the tire would drop one psi. The temps were in the high 90's to 101.

I silenced the alarm and didn't worry too much about it. Once at the campground I bumped up the pressure of the rears to 95 PSI colc, adjusted the upper alarm limit and on the way back the same thing happened. Again I didn't worry too much about it, but I am wondering if this is an indication that I should be changing out the tires.

I hd changed out the two front tires last summer with Sailun's and have been happy with them. The pressure in them didn't rise more them 10PSI and they ran consistently much cooler then the backs. I was thinking the rear duel's would run at a higher temp the the front anyway.

The rear tires are Goodyears and are pushing 10 years old. I know everyone says to change them with age but I've been pushing it. Even the tire dealer told me they looked good and when I changed the fronts he looked at the inside of the tires and said he wouldn't have replaced them.
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Old 09-01-2015, 10:41 AM   #7
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The main thing is to set the pressures at whatever the load chart says for the load the tire is carrying. Do not be concerned about what the pressure does after the tire is warmed up from travel and the sun. My front tires are set at 115 psi which is 5 psi above what is required. I set them on a 60* morning one year ago. The TST monitor will show as high as 138 psi on a 100* day on black asphalt. According to Michelin, that is normal and not to be concerned. I have not had to add or release air in a year. The cold pressures in the morning of travel are between 110 and 117 psi which is affected by temperature and altitude. I pretty much ignore the tire temperature while rolling as the sensors are moderated by the ambient air temp. After being parked and in the shade, the true temperature will show up.
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Old 09-01-2015, 10:50 AM   #8
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Quote:
Originally Posted by Vt Rv View Post
Thank you for the replies.

I received and installed the EEZTire TPMS. I set the pressures on cold tires at 95 front and 90 rear. I set the upper limit at 20% and the lower at 10%.

Quickly about the EEZTire set up. What a nice surprise to find that the instillation was very simple after having watched a set up video on line. I bet I had it unpacked, programmed and installed in 30 minutes.

Anyway, headed out on a 6 1/2 hour trip to northern Maine. The system was working great and showing me pressure and temp. As the day warmed and I was on the highway for a couple hours one of the inside rears set off the upper pressure alarm. All four were within a few PSI but only one hit the 20% mark. I slowed down and the tire would drop one psi. The temps were in the high 90's to 101.

I silenced the alarm and didn't worry too much about it. Once at the campground I bumped up the pressure of the rears to 95 PSI colc, adjusted the upper alarm limit and on the way back the same thing happened. Again I didn't worry too much about it, but I am wondering if this is an indication that I should be changing out the tires.

I hd changed out the two front tires last summer with Sailun's and have been happy with them. The pressure in them didn't rise more them 10PSI and they ran consistently much cooler then the backs. I was thinking the rear duel's would run at a higher temp the the front anyway.

The rear tires are Goodyears and are pushing 10 years old. I know everyone says to change them with age but I've been pushing it. Even the tire dealer told me they looked good and when I changed the fronts he looked at the inside of the tires and said he wouldn't have replaced them.
Mine were 10 years old too and they looked GREAT, however; when I did put new ones on, I had no idea how much the old ones were 'squirming' on the road until the new ones were on. Of course ride, noise etc are always wonderful with new tires, but I was amazed at how much straighter the coach ran down the highway. Sounds silly, but the new tires looked a lot bigger than the old ones too when they were new. My fronts I just had replaced and they look bigger than the 7 year old Gladiators that were on there too. Even though its the same size tire, the new ones look bigger.



I know, sounds like I'm having my stroke in installments....
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