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03-30-2022, 09:54 PM
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#1
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Junior Member
Join Date: Feb 2022
Posts: 4
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Confused on correct PSI
Greetings! I have searched my question on other treads and it just confused me even more. I have a 2021 Cherokee Grey Wolf 26dbh and I bought a tpms for our long travels we have planned. The side walls say 65 psi cold. Is that max or should I pump up the tires to 65? I also read that it should be 80% of max. I measure my pressure today and all my tires read between 50-52 psi and that would be 80%. So needless to say I am confused and don’t know what I should set my tpms as the correct psi for warnings. Thank you for helping out a newbie
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03-30-2022, 10:10 PM
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#2
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Senior Member
Join Date: Jan 2020
Posts: 4,864
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What does the tire inflation card on the side of the trailer say? The 65 max PSI rating on the side of the tires indicates they are Load Range D. With a GVWR for the trailer of 7725 lbs and a hitch weight of 725 lbs, you are looking at a tire loading of 1750 lbs. Add 20% safety margin and you are looking at 2100 lbs per tire. Your factory tires are probably rated for a max load right around that number. Therefore, I'm willing to bet 2 gallons of gas, heck even diesel, that the card on the side of your trailer is going to say to inflate to 65 PSI. At 50-52 PSI, you are underinflated.
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03-31-2022, 07:54 AM
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#3
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Senior Member
Join Date: Jan 2016
Location: x
Posts: 12,423
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The sidewall psi is the cold max setting that the tire will carry its designed max load. Use this number as normal psi when setting your high and low alarms on the tpms. typically the temp alarm does not need to be changed from the Mfg setting. JMHO
__________________
Retired Navy
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho
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03-31-2022, 10:06 AM
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#4
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Junior Member
Join Date: Feb 2022
Posts: 4
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Thank you for the clarification. I will put 65 in and set that on my tpms.
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04-01-2022, 09:09 AM
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#5
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Senior Member
Join Date: May 2015
Posts: 1,397
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The TPMS shouldn't be the deciding factor. You should know what the trailer weighs and determine your actual tire load. The psi needed will be based on the tire mfgrs. weight table. It may be 65 psi or something less. Of course, you can always air up to the tire's max psi. of 65, but it may not be necessary. If it were me, I'd set the TPMS to go off at 10psi lower than what you set the tires at.
__________________
--2005 F350 Superduty Crewcab, 6.0, 4wd, short bed, 3.73 gears;
--2016 Montana 3711FL, 40'
--2014 Wildcat 327CK, 38' SOLD
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04-01-2022, 10:03 AM
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#6
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Senior Member
Join Date: May 2020
Location: Right in the Middle
Posts: 1,232
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TMPS doesn't have anything to do with how your tires need to be inflated.
1. Inflate your tires (cold) to the pressure indicated on the sidewall, 65psi. You want them to be this temperature before you start dragging the trailer anywhere. The 80% is a (low) rule-of thumb for a low pressure warning temp.
2a. For HIGH PRESSURE limits, you can set your TMPS limits to 20-25% Higher than cold PSI.
65 * 1.2 = 78
65 * 1.25= 81.25
So, between 78 and 81.25 lbs. (Personally, I'd round and set the HIGH PRESSURE limit to 80 lbs.)
2b. For LOW PRESSURE limits, you set your TMPS limits to 10-15% lower than cold PSI.
65 * .90 = 58.5
65 * .85 = 55.25
So, between 55.25 and 58.5 lbs. (Personally, I'd average and round down and set the LOW PRESSURE limit to 56 lbs.)
You will be amazed at how warm the tires get, and how that directly impacts tire pressure (warmer tires = warmer air in tire = expanded air = higher pressure). The TPMS is really there to provide EASE in accessing some necessary information, but not to be something that you need to worry over. If you have a critical rapid pressure loss (indicating a blowout), the TMPS will go off. Warmer tires on one side of the coach can indicate everything from "the sun is on this side" to "this tire is/these tires are out of alignment."
It's interesting to watch, but it's set up so you don't HAVE to watch it, the TPMS will tell you when you need to get out and pay close attention.
Happy towing!
__________________
2022 Rockwood Roo 235S
15kBTU AC; 12v fridge; 1kW roof-mounted solar panels; 80 amp MPPT charge controller; 3,500w pure sine wave inverter; 30a automatic transfer switch; MicroAir EasyStart, 600ah Chins LiFePo; Honda EU2200i (with Hutch Mountain propane conversion kit) gathering dust in the storage unit.
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04-01-2022, 02:24 PM
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#7
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Senior Member
Join Date: Mar 2017
Location: Yorktown VA
Posts: 113
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Quote:
Originally Posted by Rhumblefish
TMPS doesn't have anything to do with how your tires need to be inflated.
1. Inflate your tires (cold) to the pressure indicated on the sidewall, 65psi. You want them to be this temperature before you start dragging the trailer anywhere. The 80% is a (low) rule-of thumb for a low pressure warning temp.
2a. For HIGH PRESSURE limits, you can set your TMPS limits to 20-25% Higher than cold PSI.
65 * 1.2 = 78
65 * 1.25= 81.25
So, between 78 and 81.25 lbs. (Personally, I'd round and set the HIGH PRESSURE limit to 80 lbs.)
2b. For LOW PRESSURE limits, you set your TMPS limits to 10-15% lower than cold PSI.
65 * .90 = 58.5
65 * .85 = 55.25
So, between 55.25 and 58.5 lbs. (Personally, I'd average and round down and set the LOW PRESSURE limit to 56 lbs.)
You will be amazed at how warm the tires get, and how that directly impacts tire pressure (warmer tires = warmer air in tire = expanded air = higher pressure). The TPMS is really there to provide EASE in accessing some necessary information, but not to be something that you need to worry over. If you have a critical rapid pressure loss (indicating a blowout), the TMPS will go off. Warmer tires on one side of the coach can indicate everything from "the sun is on this side" to "this tire is/these tires are out of alignment."
It's interesting to watch, but it's set up so you don't HAVE to watch it, the TPMS will tell you when you need to get out and pay close attention.
Happy towing!
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Excellent summary on tpms and tire pressure. Thanks.
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04-01-2022, 02:27 PM
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#8
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Senior Member
Join Date: Jun 2016
Posts: 5,055
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Quote:
Originally Posted by Dbrock22
Greetings! I have searched my question on other treads and it just confused me even more. I have a 2021 Cherokee Grey Wolf 26dbh and I bought a tpms for our long travels we have planned. The side walls say 65 psi cold. Is that max or should I pump up the tires to 65? I also read that it should be 80% of max. I measure my pressure today and all my tires read between 50-52 psi and that would be 80%. So needless to say I am confused and don’t know what I should set my tpms as the correct psi for warnings. Thank you for helping out a newbie
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I follow Roger Marble, the tire engineer who has a blog on RV tire questions.
His info and answers to questions I have asked him has resulted in the following info that I follow:
1. The numbers posted on the tire sidewall indicate the MINIMUM cold inflation pressure needed to carry the maximum load the tire was designed to carry. CIP numbers in tire load tables is also the minimum CIP for the specified load. Going marginally over that CIP is acceptable. For a tire indicating 65 you are OK with 66 or 67 PSI. Also, the tire is designed to have higher PSI when running. Do not reduce PSI once running, even on a hot day.
2. Roger recommends running tires at the max CIP on tow-able trailers due to his work on inter-ply shear issues even if trailer weight does not call for the max. Check his blog for more info.
3. On other vehicles CIP should be set by the actual weight the tire is carrying.
4. Even on tow-ables, you should get the actual weights for the rig. Ideally get weights at each wheel position. If you can only get weights per axles, use the axle weight/2 + 10%. Vehicles almost never have equal side to side weights. Adding 10% to the 1/2 the axle weight gives margin for this issue. Good to know your trailer isn't over-loaded.
5. Tires age out. There are manufacturers recommending replacement, or at a minimum, a professional wheel off inspections at 5 years. It is almost guaranteed that on a RV trailer, the tire should be replaced way before tread wear calls for a replacement.
6. Running under-inflated tires for the load is pretty much guaranteed to cause premature tire failure.
Safe travels.
__________________
Al
I am starting to think, that I will never be old enough--------to know better.
Tolerance will reach such a level that intelligent people will be banned from thinking so as not to offend the imbeciles. Fyodor Mikhailovich Dostoevsky, Russian Novelist
S.E. Mich. Flagstaff 26FKWS / 2022 F-150 3.5 EcoBoost SCrew Propride
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04-01-2022, 02:38 PM
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#9
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Senior Member
Join Date: Jan 2020
Posts: 4,864
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If the trailer came with Load Range D tires from the factory, and you replace them with Load Range E tires - I just don't see the need to run the Load Range E tires at the full 80 psi. Tire manufactures have inflation pressure v. weight charts for a resason.
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04-01-2022, 02:59 PM
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#10
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Senior Member
Join Date: Feb 2022
Posts: 516
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Quote:
Originally Posted by NavyLCDR
If the trailer came with Load Range D tires from the factory, and you replace them with Load Range E tires - I just don't see the need to run the Load Range E tires at the full 80 psi. Tire manufactures have inflation pressure v. weight charts for a resason.
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Reading between the lines, I think he is stating generically about tires that come installed. Though not exactly spelled out this way, I read it to state, inflate "oem" tires for max trailer weight, even if not running max. So if you upgrade, you wouldn't inflate to max tire pressure, just to max trailer capacity regardless of occasion. Not sure I necessarily agree, it's just the way I "interpreted" it.
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04-01-2022, 03:04 PM
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#11
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Senior Member
Join Date: Jan 2020
Posts: 4,864
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Quote:
Originally Posted by NewToTheForce
Reading between the lines, I think he is stating generically about tires that come installed. Though not exactly spelled out this way, I read it to state, inflate "oem" tires for max trailer weight, even if not running max. So if you upgrade, you wouldn't inflate to max tire pressure, just to max trailer capacity regardless of occasion. Not sure I necessarily agree, it's just the way I "interpreted" it.
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Every trailer that I have ever seen has listed the maximum inflation pressure for the load range of tires installed as the recommended inflation pressure on the placard on the side of the trailer. I meant to mostly respond to this:
"2. Roger recommends running tires at the max CIP on tow-able trailers due to his work on inter-ply shear issues even if trailer weight does not call for the max. Check his blog for more info"
Which begs to question, why do tire manufacturers have inflation pressure v. weight charts? Does Roger know more than the manufacturer who made the tire?
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04-01-2022, 03:04 PM
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#12
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Paul & Dianne
Join Date: Oct 2018
Location: NH
Posts: 199
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Quote:
Originally Posted by NavyLCDR
If the trailer came with Load Range D tires from the factory, and you replace them with Load Range E tires - I just don't see the need to run the Load Range E tires at the full 80 psi. Tire manufactures have inflation pressure v. weight charts for a resason.
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This. When we replaced the Castle Rocks with GY Endurance, I started with the GY's at their 80 max psi. They heated up and went up to 92-93 psi... on an 80-deg day, so not super hot... and the 5er was skipping like a rock on a pond behind us at 60-65 on a good road. Checked the GY tire tables, and we could run at 70 for the load we're carrying... although that is right at the load. I generally run with cold at 75 now and things are fine. That extra few psi can make a big difference; you may not need, or want, every last psi.
__________________
2019 Rockwood 8299BS
2019 F350 Lariat 6.7 CC SRW
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04-01-2022, 03:48 PM
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#13
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Senior Member
Join Date: Apr 2015
Location: Ontario, California
Posts: 2,146
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Quote:
Originally Posted by phillyg
The TPMS shouldn't be the deciding factor. You should know what the trailer weighs and determine your actual tire load. The psi needed will be based on the tire mfgrs. weight table. It may be 65 psi or something less. Of course, you can always air up to the tire's max psi. of 65, but it may not be necessary. If it were me, I'd set the TPMS to go off at 10psi lower than what you set the tires at.
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I like setting them at Max unless it's an exceptionally cold morning and you know the day is going to be really hot.
I love my TPMS and won't leave home without them. I set them about 8 to 10% below my cold inflation pressure
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04-01-2022, 03:50 PM
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#14
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Senior Member
Join Date: Apr 2015
Location: Ontario, California
Posts: 2,146
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Quote:
Originally Posted by ThruHiker
This. When we replaced the Castle Rocks with GY Endurance, I started with the GY's at their 80 max psi. They heated up and went up to 92-93 psi... on an 80-deg day, so not super hot... and the 5er was skipping like a rock on a pond behind us at 60-65 on a good road. Checked the GY tire tables, and we could run at 70 for the load we're carrying... although that is right at the load. I generally run with cold at 75 now and things are fine. That extra few psi can make a big difference; you may not need, or want, every last psi.
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Yep that is often what I've done to establish the pressures I will set my motorhome at. It doesn't call for pressure at the maximum limit of my tires and I do verify the weight tables.
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04-02-2022, 01:00 AM
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#15
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Senior Member
Join Date: Jun 2016
Posts: 5,055
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Quote:
Originally Posted by NavyLCDR
Every trailer that I have ever seen has listed the maximum inflation pressure for the load range of tires installed as the recommended inflation pressure on the placard on the side of the trailer. I meant to mostly respond to this:
"2. Roger recommends running tires at the max CIP on tow-able trailers due to his work on inter-ply shear issues even if trailer weight does not call for the max. Check his blog for more info"
Which begs to question, why do tire manufacturers have inflation pressure v. weight charts? Does Roger know more than the manufacturer who made the tire?
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I should have been more verbose on what I posted. My understanding is that Roger's recommendation of max CIP is for multi-axle trailers. Stress is induced because the tires do not track the same when turning. That is what causes the shear forces. There are videos on the web showing how one tire scrubs in and the other scrubs out. This would be very pronounced during tight turns, like what we often have to use when backing into campground sites. For this reason, I always try to do a couple of straight forward/back moves of the trailer when parking, if at all possible, especially if on pavement to relieve the stress.
On single axle trailers, using the trailer weight and tables would be the proper solution.
FWIW, I have upgraded to LR E tires from the OEM LR D. I have elected to run the new tires at 80 PSI and haven't noticed any differences from the old tires. Trailer doesn't seem to be "bouncing" any more than before and no change to trailer contents after a drive.
__________________
Al
I am starting to think, that I will never be old enough--------to know better.
Tolerance will reach such a level that intelligent people will be banned from thinking so as not to offend the imbeciles. Fyodor Mikhailovich Dostoevsky, Russian Novelist
S.E. Mich. Flagstaff 26FKWS / 2022 F-150 3.5 EcoBoost SCrew Propride
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04-02-2022, 08:33 AM
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#16
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Junior Member
Join Date: Nov 2015
Posts: 14
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We replaced our tires with Load G. Inflate to 110 cold at max. We were told it is ok by two different tire stores. After a cracked rim, another tire store told us the cheap aluminum rim cold not handle that much pressure and we needed to run at 80 psi. Any comments as to the confusion with max psi and reduced psi?
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04-02-2022, 09:37 AM
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#17
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Senior Member
Join Date: Jan 2020
Posts: 4,864
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Quote:
Originally Posted by dweaver2
We replaced our tires with Load G. Inflate to 110 cold at max. We were told it is ok by two different tire stores. After a cracked rim, another tire store told us the cheap aluminum rim cold not handle that much pressure and we needed to run at 80 psi. Any comments as to the confusion with max psi and reduced psi?
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What was the rating stamped on the rims?
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04-02-2022, 10:16 AM
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#18
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Senior Member
Join Date: May 2015
Posts: 1,397
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Quote:
Originally Posted by dweaver2
We replaced our tires with Load G. Inflate to 110 cold at max. We were told it is ok by two different tire stores. After a cracked rim, another tire store told us the cheap aluminum rim cold not handle that much pressure and we needed to run at 80 psi. Any comments as to the confusion with max psi and reduced psi?
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There shouldn't be any confusion yet I see it all the time. One should never put in more than the max psi printed on the tire and the same goes for wheels. Using less than max psi should be a function of knowing the load and using the tire mfgrs. inflation chart.
The wheels that came on my FW were clearly embossed max 110psi. So, I upgraded to G-rated tires and at my weight, I need to use 100psi. I recently discovered a cracked rim, but I don't know if it's a consequence of a cheaply made wheel, or using higher psi.
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04-03-2022, 05:13 AM
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#19
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Senior Member
Join Date: Jun 2015
Location: Albuquerque
Posts: 1,228
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I upgraded my single axle utility trailer from Load Range C to D. I tried inflating the tires to 65 psi listed on the sidewall. The trailer bounced so much that the eggs in my ice chest broke.
__________________
2009 Roo 21ss + 2007 Superduty 6.0
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04-03-2022, 08:23 AM
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#20
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Senior Member
Join Date: Apr 2021
Posts: 2,302
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Tire Pressure Woes
We replaced the original factory tires on our trailer with new tires and choose to upgrade from load range C to load range D. This DID NOT change the maximum load rating of the trailer as that is defined by the axle design. So regardless of the tire rating, the axle load specifications will be the limiting factor.
Now reading many of the earlier posts, it is suggested to consult the tire chart for inflation values based on load. Well, that may be good, but darn if I load the trailer, have it weighed, and adjust the tire pressure every time we use it. Case and point, we do weekend trips and the trailer is lightly loaded as we camp at full-service campgrounds. Then we do longer trips where we have to carry everything for 8 or 10 days including a tank full of water.
Taking the position the load range D tires have maximum cold inflation of 65 PSI, I see nothing wrong or unsafe inflating the cold tires to 65 lbs regardless of the load. That gives the maximum load capacity of the tires. The load rating of the axles remains the same. What else is there to be concerned about?
Also, I seem to recall where dual axle trailers do not double the weight rating of one axle weight rating. For example, if one axle is rated at 3500 lbs, the two axles would not be 7000 lbs but would be 80% of the sum of the two axles or 5600 lbs. Can anyone lend credence to this? Or is this some internet smoke and mirrors?
73
Bob, K4TAX
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