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07-09-2023, 04:56 PM
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#43
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Senior Member
National RV Owners Club Holiday Rambler Owners Club
Join Date: Nov 2015
Location: Monrovia, IN
Posts: 579
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I have yet to find a facility or scale that will do 4 corner weighing. The best I can find with CAT scales in truck stops is a per axle weight. Where y'all finding these places? Inquiring minds want to know.
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1998 National Seabreeze 1330 Limited Chevrolet P37 chassis 7.4 Vortec 2014 Jeep JKU Sport Toad
Me, Beautiful DW, sometimes kids & grandkids
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07-09-2023, 05:03 PM
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#44
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Senior Member
Newmar Owners Club Freightliner Owners Club
Join Date: Jun 2022
Posts: 219
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I use local truck scales provide by ODOT. Drive in one way and measure one side, then the other when they are closed and truck traffic is light.
Some have just enough room between the pad and the building to drive the correct way both times. Helps to have an assistant w WT.
It's good to have readings from multiple scales that tally. Even though it reads zero when unloaded, one can never be 100% is correct with a load. Not sure how often ODOT checks.
__________________
2021 KSDP 3412 / XCR -< 2020 Kia Soul LX [AF1]
Ian, Marylou & Jackie {woof!}
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07-10-2023, 09:33 AM
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#45
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Senior Member
Join Date: Dec 2013
Location: Lake Havasu City, AZ & Plover, WI
Posts: 6,403
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Quote:
Originally Posted by m.elliott63
I have yet to find a facility or scale that will do 4 corner weighing. The best I can find with CAT scales in truck stops is a per axle weight. Where y'all finding these places? Inquiring minds want to know.
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Try your State highway Patrol. The WI State Patrol (Vehicle Inspection Division) came to my home, blocked the road so I could be in the middle of the crowned street when I drove onto their individual scales. No charge and they were happy to help set the tag suspension pressures and verify what each position was carrying for correct tire pressure.
__________________
2006 Monaco Executive 44 Denali
2013 43 QGP Allegro Bus ( SOLD )
2013 Avalanche
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07-10-2023, 09:33 AM
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#46
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Junior Member
Join Date: Feb 2020
Posts: 25
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If you really want to be OCD, you would stop every 100 miles and adjust for the weight, outside air temperature, and barometric pressure changes.
Tires have issues if they are over or under-inflated. But there is a fairly wide margin in the middle where they can operate safely and you wouldn't be able to see any wear difference.
And if you are going to operate like this I would have at least two sets of gauges that are calibrated monthly.
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07-10-2023, 09:50 AM
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#47
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Senior Member
Newmar Owners Club Freightliner Owners Club
Join Date: Jun 2022
Posts: 219
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Quote:
Originally Posted by MAXEPR
If you really want to be OCD, you would stop every 100 miles and adjust for the weight, outside air temperature, and barometric pressure changes.
Tires have issues if they are over or under-inflated. But there is a fairly wide margin in the middle where they can operate safely and you wouldn't be able to see any wear difference.
And if you are going to operate like this I would have at least two sets of gauges that are calibrated monthly.
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That's not necessary. 30°F results in a ≈3PSI rise in pressure. Pressure rises far more from road surface and carcass flex, underinflated carcass flex being a tire killer.
The import of this thread is not driving on rock hard tires inflated FORTY pounds over axle load.
Big motor homes may run closer to tire max PSI than small ones, but duals and tag axles still run lower than fronts.
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2021 KSDP 3412 / XCR -< 2020 Kia Soul LX [AF1]
Ian, Marylou & Jackie {woof!}
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07-10-2023, 09:58 AM
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#48
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Senior Member
Ford Super Duty Owner
Join Date: Feb 2017
Location: Manhattan (Little Apple) Kansas
Posts: 2,966
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Quote:
Originally Posted by MAXEPR
If you really want to be OCD, you would stop every 100 miles and adjust for the weight, outside air temperature, and barometric pressure changes.
Tires have issues if they are over or under-inflated. But there is a fairly wide margin in the middle where they can operate safely and you wouldn't be able to see any wear difference.
And if you are going to operate like this I would have at least two sets of gauges that are calibrated monthly.
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No one is saying to stop and adjust pressure every 100 miles. What they are saying is to adjust tire pressure to match the weight of the coach. If your tire loading tables say to set COLD pressure to 100 PSI but your placard says 125 PSI and your tires have max COLD pressure of 125PSI. You traveling in Texas with 100-degree weather and your tire pressure climbs 30 PSI at loading tables of 100 now your PSI is at 130 but if you are at the placard you are at 155 PSI and tires are rock hard and not only affect ride quality but also tire wear.
My previous coach placard said 125 PSI and the load tables was between 85 and 90 PSI and I run mine at 100PSI and stop the center of the tire wearing faster than the outside edges improved ride quality.
__________________
2020 Newmar Baystar 3005 Gas V10 - 2024 Maverick Hybrid
1280 Watts Solar - Victron MultiPlus-II Inverter 600 Amp Lithium Battery
2008 Aspect 1993 Airstream Classic
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07-10-2023, 12:26 PM
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#49
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Senior Member
Join Date: Dec 2013
Location: Lake Havasu City, AZ & Plover, WI
Posts: 6,403
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Quote:
Originally Posted by CWSWine
No one is saying to stop and adjust pressure every 100 miles. What they are saying is to adjust tire pressure to match the weight of the coach. If your tire loading tables say to set COLD pressure to 100 PSI but your placard says 125 PSI and your tires have max COLD pressure of 125PSI. You traveling in Texas with 100-degree weather and your tire pressure climbs 30 PSI at loading tables of 100 now your PSI is at 130 but if you are at the placard you are at 155 PSI and tires are rock hard and not only affect ride quality but also tire wear.
My previous coach placard said 125 PSI and the load tables was between 85 and 90 PSI and I run mine at 100PSI and stop the center of the tire wearing faster than the outside edges improved ride quality.
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The pressure increase would not be the same starting cold @125 compared to 100 psi. Much less flex and heating when starting @ 125 cold. I agree that the ride and tire wear would suffer @125 cold, but the pressure increase would also be much less.
__________________
2006 Monaco Executive 44 Denali
2013 43 QGP Allegro Bus ( SOLD )
2013 Avalanche
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07-10-2023, 04:26 PM
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#50
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Senior Member
Newmar Owners Club Freightliner Owners Club
Join Date: Jun 2022
Posts: 219
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Quote:
Originally Posted by Crasher
The pressure increase would not be the same starting cold @125 compared to 100 psi. Much less flex and heating when starting @ 125 cold. I agree that the ride and tire wear would suffer @125 cold, but the pressure increase would also be much less.
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Pressure is proportional to temperature change. P2 = P1 x dT. T is in °Kelvin. 68°F Room temperature is 273°K so going from room temperature [20°C] to 104°F [40°C] is a factor of 1.16 - REGARDLESS of the starting pressure. 50PSI becomes 58PSI, 100PSI becomes 116PSI static. Enough to make an adjustment? Probably, assuming 104°F is the cold temperature.
Pavement temperatures in full sunlight range from 30°F to 50°F hotter than ambient in the heat of the day, i.e. about 2PM to 4PM.
I've never seen a sidewall / temperature increase test or chart, but I think it's reasonable to assume its a small percentage relative to road friction and contact heat transfer.
In 2016, K. M. Jeong of Kumho did FEA analysis on radial truck tires and concluded the bead broke before the sidewall fibre gave way. Hydrostatic pressures over 250PSI.
Prediction_of_Burst_Pressure_of_a_Radial_Truck_Tir e_Using_Finite_Element_Analysis
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2021 KSDP 3412 / XCR -< 2020 Kia Soul LX [AF1]
Ian, Marylou & Jackie {woof!}
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07-10-2023, 05:29 PM
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#51
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Member
Join Date: Jan 2021
Posts: 39
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I've done "tire tuning" all my life & on all my rv's. I've only weighed 1 axle at a time but the best handling I ever get is trial & error making sure to always stay above the placard #'s. Turns out with my current rig at 11,500 gvw and in camping trim the front tire placard #'s are spot on. The rear not-so-much. At the placard of 65psi for the rear I had all sorts of wander/side to side movement. Bumped up to the sidewall max of 80psi & it handles like a different rig.
FWIW I use 60F on my TPMS as my baseline "cold" tire psi.
We deal with -20 to +95 temps so I can get very close with my tire psi reading when 60F shows on my TPMS.
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07-10-2023, 06:45 PM
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#52
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Senior Member
Join Date: Sep 2019
Location: Colorado Springs, CO
Posts: 1,331
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Some of you seem to make this more complicated than it should be.
I use the axle weight ratings for my coach.
9000 front
15500 rear
Since those ratings are the MAXIMUM the coach should weigh, that's what I use. Since I'm probably not right at the maximum, the tires may be slightly overinflated, but not by much. Maybe if I had a big DP with such huge CCC that the coach weight could vary by a few thousand pounds, weighing could be more important.
I have TOYO. Going by their inflation chart for my tires i should have
90 PSI front
85 PSI rear
That's what I have them inflated to. I see no need to put in more than necessary as a "safety" factor.
Tiffin's placard says 100 PSI in all tires. That made for a very harsh ride.
I look at my TPMS in the morning before driving. Depending on outside temp sometimes a colder temp will put the PSI slightly below. I don't mess with adding 1-3 PSI. I look at what the PSI rises to during driving and it goes up to the same pressure regardless of not adding more when it's really cold. The difference between driving in cooler weather vs hot weather results in a slight difference in the increase, but it's only 2-3 PSI difference.
Even though the tires start out at similar PSI, the inner dually's always increase faster and slightly more overall.
I also watch the temperature readings on the TPMS and they stay consistent with road surface temps.
Weights change depending on whether the gas tank is full, freshwater tank, propane tank, on-board supplies, etc. I'm not going to weigh the coach to account for all this.
Just finished a 2 month trip and the tires have the same PSI at home as when we left. Never messed with them at all. We live at 6000 feet and our travels took us as low as sea level and as high as 10500 feet. TPMS indicated there was never anything to be concerned about.
I just don't see what's to be gained by going through all the bother.
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Don & Vicki
2017 Tiffin Allegro Open Road 36LA, F53 chassis, V10
2020 Ford Escape Hybrid SE Sport AWD, RVibrake3, Blue Ox
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07-11-2023, 12:17 AM
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#53
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Senior Member
Commercial Member
Join Date: Mar 2010
Location: Akron, Ohio
Posts: 2,909
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Quote:
Originally Posted by Holland2017
Weighed my coach, set tire pressures according to tire mfg recommendations.Then drive in 85-95 degree temperatures and a those tire pressures change so now what am I surpose to do? Just asking for friend.
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The tables are referring to the cold pressure. We know the pressure will increase when you drive the vehicle.
You may find some self appointed "experts" on various RV forums telling you to do all sorts of "tuning" of pressure but unless you are setting up a race car that is not the correct process.
The Tire tables are almost 100% universal around the world (except for small variations due to calculations done in metric and conversion to SI or vis-a-versa.
Tire companies do not consult the RV company on what to put on the Certification Label and it is the vehicle mfg responsibility by federal regulation to put the minimum inflation on the label that would be sufficient to support the GAWR.
Since the RV company wants to use the lowest cost tire for the trailer you will find that most of the time the inflation on the label specifies the inflation to just meet the GAWR which is the highest inflation for that load range tire.
No one is suggesting adjusting inflation daily. Before TPMS it was suggested to check inflation in the morning of each travel day. The general suggestion to follow the label inflation is reasonable given that most RV trailers are running at max capacity.
I have dozens of posts on Inflation on my blog. RV Tire Safety net I have so many because for some reason very few people Google how to set tire pressure and filter the posts to follow only those tire engineers that own RVs and are familiar with RV special application and needs.
I am only aware of two actual tire design engineers on-line on RV forums.
__________________
Retired Design & Quality Tire Eng. 50+ years experience. Recognized in the industry and in court as an expert in failed tire inspection as I have performed thousands of failed tire "autopsies".
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07-11-2023, 06:16 AM
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#54
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Senior Member
Join Date: Oct 2012
Posts: 880
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@ post #50.
I wonder why street temperature goes down again above 95 degrF air temperature in your given tabel. And why 3 times 95 degr F airtemperature given.
Oh I see already, given. Per hour of the day.
But it looks like both tabels are the same.
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07-11-2023, 07:09 AM
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#55
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Senior Member
Join Date: Mar 2019
Posts: 6,903
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Quote:
Originally Posted by IEales
That's not necessary. 30°F results in a ≈3PSI rise in pressure.
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The formula is a 2% change in pressure for each 10 degrees F change in temperature, up or down. 100 PSI tires would see a 6 PSI change, not 3.
Ray
__________________
2020 Forest River Georgetown GT5 34H5
2020 Equinox Premier AWD 2.0L/9-speed
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07-11-2023, 07:21 AM
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#56
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Senior Member
Join Date: Oct 2012
Posts: 880
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Depends on the cold filled pressure, so is for for instance 30 psi filled 3% /10 degr F, as rule of tumb.
I made a list for cold filled pressure at 70 degr F.
Then behind that the degrF change per 1 psi.
Is easyer to calculate with on the road, and you only have to remember for your cold filled pressure at 70 degr F. But if you use it for 60 degr F cold filled, it wont give dramatic differences.
100psi gives 4.5 degr F / psi.
30 degr F/ 4.5 degr F = 6,7 psi
And that is dry gascompound, no water in it.
So for 100 psi, 2% is a good rule of tumb.
Here it is,
70degrF./degrF/psi
20 psi/ 15,5F/psi
21 psi/ 15F/psi
22 psi/ 14,5F/psi
23 psi/ 14 F/psi
24 psi/ 13,5F/psi
25 psi/ 13,5F/psi
26 psi/ 13 F/psi
27 psi/ 12,5 F/psi
28 psi/ 12,5 F/psi
29 psi/ 12 F/psi
30 psi/ 12 F/psi
31 psi/ 11,5 F/psi
32 psi/ 11,5 F/psi
33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/psi
97 psi/ 4,5 F/psi
109 psi/ 4,5 F/psi
110 psi/ 4 F/psi
126 psi/ 4 F/psi
127 psi/ 3,5 F/psi
148 psi/ 3,5 F/psi
149 psi/ 3 F/psi
177 psi/ 3 F/psi
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