BAC Forum
General Boards => Technical Support => Topic started by: KC Snellgrove on November 24, 2019, 10:34:28 PM
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GOOD DAY Fellow Beavers. It has been long time since I have traveled in cold weather. This question is for anyone with the same tire size. I am headed for Calif. over the pass if it is not snowing.
WHAT COLD TIRE PRESSURE SHOULD I HAVE?
I tried to find out. I am in desperate need, since I am leaving tomorrow.
THANK YOU FOR THE RESCUE! KC Snellgrove
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Cold pressure refers to pressure before driving.
Pressure should not be adjusted as you move into and out of a cold temp zone.
I drove truck for 30 years and never adjusted my set starting pressure.
Yes there are minor differences but none that should be adjusted to that detail
Tire pressure should be set to weight on it... whatever your normal setting for your weight , is correct
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THANK YOU SO MUCH! I appreciate your advice. :) KC Snellgrove
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KC,
The ambient temperature has a significant impact on the air pressure in your tires. The PSI recommendations for any given weight from the tire manufacturers is based on an ambient temperature of 65F. As shown in the attached chart, if the recommended PSI is 110, one needs to inflate the tire to 119 PSI if the ambient temp is 100F or 102 PSI if the ambient is 32F.
For more info refer to the tire inflation article in Common Problems (Private Members Only).
Steve
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More tire nfo (from a retired tire engineer) than anyone needs to know can be found here:
http://www.rvtiresafety.net/
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KC,
The ambient temperature has a significant impact on the air pressure in your tires. The PSI recommendations for any given weight from the tire manufacturers is based on an ambient temperature of 65F. As shown in the attached chart, if the recommended PSI is 110, one needs to inflate the tire to 119 PSI if the ambient temp is 100F or 102 PSI if the ambient is 32F.
For more info refer to the tire inflation article in Common Problems (Private Members Only).
Steve
Steve if I followed that I would exceed the rating of my rims (120) on a normal summer day here in Central Florida! I thought I knew what to do with tires and you have dropped a bomb on my tire inflation world!! I usually check and adjust tires to the weight on the inflation charts, for my weights, every few days when traveling. Now?
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Jerry,
The 120PSI rating is at 65F. Think about it. If you put 120PSI in your tires in Maine in the fall, obviously they are going to exceed 120 while you are in FL in the summer. That's the reason for the table. If you inflate per the table you won't have to adjust your PSI regardless of the ambient temp. Using your approach you would have had to air up the tires when your coach was in NC/TN and then aired them down when you returned to FL.
Steve
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Jerry,
The 120PSI rating is at 65F. Think about it. If you put 120PSI in your tires in Maine in the fall, obviously they are going to exceed 120 while you are in FL in the summer. That's the reason for the table. If you inflate per the table you won't have to adjust your PSI regardless of the ambient temp. Using your approach you would have had to air up the tires when your coach was in NC/TN and then aired them down when you returned to FL.
Steve
The RVTIRESAFETY.net article seems to indicate otherwise. Do not mean to argue, your advice is usually spot on. This is too important to me to not understand. I set tire pressure every morning before I start driving for the day. I set the pressure for the current ambient temp before driving. This seems the right thing to do. See blog below.
http://www.rvtiresafety.net/2015/08/what-temperature-for-cip-cold-inflation.html
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Jerry,
Follow the advice you are comfortable with. If I remember correctly, the chart I supplied came from Michelin via Ed Buker a number of years ago. I was in error in my original post when I stated that you could go below the stated PSI for a given weight at temps below 65F. See the 2nd & 3rd paragraphs. I should have re-read it before posting. Sorry for the confusion.
Steve
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Just my opinion , but after many million miles commercial driving you can over think this. We never adjusted our tires daily to the temp. Heck I never had a gauge or tpms ! I checked with a bud bar (club). The only time my truck saw a gauge was every 4 months ( 6 months on the trailers) at its pmi, or if I noticed something obvious.
Set the pressure ( sure adjust to the temp if it’s way off from 65 ) then leave it. Nobody stops and adjusts throughout the day as you go through a cold area.. like KC was asking , really? But then I’m a old guy with old methods :)
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Just my opinion , but after many million miles commercial driving you can over think this. We never adjusted our tires daily to the temp. Heck I never had a gauge or tpms ! I checked with a bud bar (club). The only time my truck saw a gauge was every 4 months ( 6 months on the trailers) at its pmi, or if I noticed something obvious.
Set the pressure ( sure adjust to the temp if it’s way off from 65 ) then leave it. Nobody stops and adjusts throughout the day as you go through a cold area.. like KC was asking , really? But then I’m a old guy with old methods :)
I’m not suggesting checking multiple times a day although I do with my TPMS. I’ve found when heading north in the spring from Florida my TPMS will wake me with a low pressure alarm at 0500 or so because as it drops in temp the pressure goes down. I will check via TOMS before I leave and if necessary increase the pressure. Just the opposite when heading south for the winter. I rely on the TPMS for normal checks.
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I'm in the same group as Bill, seems that tires on motor homes is probably the number one subject in these forums. No truck out on the road ever changes air pressures in any of their tires, we always aired to the max and ran them. The easiest way to blow out a tire is run it low on air, heat kills tires faster than any other cause probably other than curbing or running over something, we aired up the fronts to 120 and the drivers 100 or 110 and ran them, if a tire sounded odd when bumping it I would get out the air gauge.
I have been using a laser temp unit for years and have never seen a front tire over 135 degrees even crossing the desert, drive tires around 120 degrees and my coach is real heavy on the front end. I run 120 in the fronts and 110 in the back.
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I also run 120 in the front and 115 on the rears. I have 275x70 22.5s though. Thats why I was concerned putting 128+lbs in FL heat of 95+.
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KC, this is probably too late for your departure schedule, but our coaches as you recall are similar though likely weight-loaded differently. That said, when new at BCS the Goodyear tires were 110psi all around. That made for a little “stiffer” ride than I liked. At the next year’s FMCA rally in Redmond we ran the coach through the RVSEF weight test program.
The RVSEF ultimately recommended 95psi on the front tires and 105psi on the rears, which I’ve run in them since. Remember that those figures are based on my axle loads as we normally load our coach. Your slightly longer rig likely balances and distributes weight a bit differently.
When Les Schwab put Toyo tires on in 2015, they filled to 110psi front and 100psi rear. That was somewhat different than RVSEF’s figures that put less air in the front than the rears. My take was Les Schwab was using standard procedures for Toyos and coaches of our type. The RVSEF numbers were more based on our specific coach and loading, so I still follow their guideline.
I think 100psi all around would suffice for either of our rigs, frankly. 5-10 lb variations from that may slightly affect ride or wear and handling, but not be particularly hazardous. Leaning toward 110 would be better than 95; just don’t go below 95. 110 in the front will handle better but ride stiffer and wear in the tire middle faster, 120 even more so and I wouldn’t go there on coaches of our size and region of travel; 95 in the front will ride nicer but not steer as easily and be more susceptible to heating and edge wear. I’d expect 100 to be a good compromise.
The best thing would be to get an RVSEF analysis whenever the opportunity affords itself, because it precisely considers how you distribute load in your own coach, and the specifics of the tire model you’ve mounted. Check their website for such potential opportunities. https://www.rvsafety.com/schedule
In the meantime you shouldn’t go wrong going with the numbers your Michelin dealer initially used when he mounted them. He should’ve provided those on your receipt, or you could call him.
Joel