
Subject 
Author 
Date Posted 
Forum


RE: Tire pressure
Filled it in, in my made extra safe motorhome calculator. Gave front 100 psi and rear 99 psi, so 100 psi all around .
Then maximum reserve, with still acceptable comfort and gripp.
In my calculator, I use an extra safe formula, wich leads to higher pressure then the officially used european formula, wich on its turn leads to higher pressure then the officially used formula in America.
But first I add 10% to the given loads.
I assume you weighed fully loaded per axle , and devided by 2 front, and 4 rear.

jadatis

12/28/19 01:37pm 
Class A Motorhomes


RE: Question about tire pressure
https://i.imgur.com/XZTGUMU.jpg
https://i.imgur.com/16eSae2.jpg
I went to the CAT scale today with all my gear, full tank of diesel, full cassette reservoir (3 gallons), and full fresh water tank (40 gallons). Looks like I'm under my GAWR for the axles, but very slightly over GVWR.
With this new information, I recalculated.
Apeared to be singleload behind.
Not lowered, for offroad, as I did in first calc, it gave F52psi , R 73 psi.
When lowered with my pigheaded system, F 67 psi , R 95 psi( wich is not allowed anymore, so 80 psi) .
Then in the end 65/ 80 psi has not been a bad guess.
But can you give me , if your tires have those profileblocks, that cover part of sidewall or not.

jadatis

09/12/19 03:06am 
Truck Campers


RE: Question about tire pressure
If you yust give me , GAWR's , always on a sticker somewhere, and if single or dual load behind. Then I will calculate for that, and you are pretty safe.
And yes, if dual front often max and rear liwer, and if single behind, often rear max and front lower.
And if you have those agressive profileblocks, can you comfirm that
GVWR , and max speed you use would be nice, but not that important.

jadatis

09/01/19 12:43am 
Truck Campers


RE: Question about tire pressure
@ gritdog
Topicstarter MG1912 gave these weights in his opening post, wich I Quoted.
Though I also daubt these weights, for those if axleweights this pressure is safe, so no overheating.

jadatis

08/29/19 11:08am 
Truck Campers


RE: Question about tire pressure
My 2007 Ford F350 6.0 supercab long bed SRW has Nitto Terra Grappler G2 A/T LT295/70R18 E 129/126Q tires front and rear. The truck came with 275/70R18 LRE tires, which were replaced by the previous owner. I wrote to Nitto to ask them about recommended tire pressures for my truck camper application (~3,000 on front axle and ~7,000 on the rear axle). I received what seemed to me like a lawyerly response:
"Based on the information provided, the calculated pressure for your Terra Grappler G2 tires is 65 PSI cold pressure on the front tires and 68 PSI cold pressure on the rear tires. At these inflation pressures, your tires are supporting the same amount of weight as your OEM tires did per the vehicle manufacturer's specifications. For any increase in pressure due to towing, we would recommend referring to your vehicle owner's manual for any instructions."
I was surprised because I would have thought they'd recommend closer to 80 PSI for the rear tires. Is their response cautious due to liability concerns? The reference to OEM tires and the vehicle owner's manual makes me suspect this. Or do the recommended pressures sound right?
My advice with these given weights is F 39 PSI and R 52 psi, but disclamer is that your given weihts are right. And that is the most tricky part in it all . So also this is a lawyery advice.
Added 10% to axlelloads, and lowered the maxload a tire by 20%/ 8 LIsteps, because offroadkind, with probably large profileblocks that cover part op sidewal.
Assumed rear Dualload axle so 4 tires behind.
This is for highway use up to 99mph, if the car can do that speed.So maximum reserve with still acceptable comfort and gripp.
For in SandMud and ontrack it can be much lower.
Edit: assumed axlelweights to be F 3000 R 7000, or where they axleends weights? Then 82F and 103 rear.

jadatis

08/29/19 04:44am 
Truck Campers


RE: Tow Vehicle Tire Pressure
35 psi is a tipical advice for standard load Ptires. It is the reference pressure, wich is the pressure for wich the maximum load is calculated for referencespeed of 160kmph/99mph. Carmakers advice it nowadays often and dont calculate it anymore, I think for reasons of responcibility.
I once got hold of the European formula to calculate pressure, and went running with it, and now call myself pigheaded Dutch tirepressure specialist. Moast american towing vehicles have large tires with a maximum load that can carry almost the whole gross axle weight rating, so if calxulated , pressure for the Ptire would give about 26 psi. And after the Ford Firestone affaire, carmakers have become scared to advice this.
But this means that you dont need to highen up this 35 psi, it already has such reserve, that you can drive a bit overloaded and faster then 99mph.

jadatis

07/17/19 04:03pm 
Travel Trailers


RE: Tire PressureTruck and TT
Only for trailer I calculated.
55 psi is maximum pressure , for 6750lbs , at wich no bumping and maximum reserve and livetime.Assumed Tandemaxle.
Assumed tires of TT to be STtires , wich are calculated in maxload for 65mph.
To get the highest pressure without bumping , I gave the tire a deflection as if the maxload was calculated for 99mph, and assumed 10% on pin, and of axleweight left , I added 11% . Deliberately did not calculate for your given estimated real weight of 6390 lbs , because estimating is always dangerous. But if so could even do with lower.
The TV also not calculated because weights estimated even more dangerous.

jadatis

06/30/19 10:51am 
Travel Trailers


RE: Front tire pressure?
Your cupping is not from low pressure, though that can make it worse.
Alignment, bad shockbrakers( already mentioned) and someting loose are the real cources. Even going to wider tires and not compensating that in the alignment, has influence. Even the weightdivision here can havevits influence. Higher pressure then gives less cupping , but your fillings come out if your teeth.

jadatis

06/18/19 07:48am 
Truck Campers


RE: Front tire pressure?
Answer to above
What you give is lineair calculation, and is not bad .
Official European calc is
( A/B) ^ 1.25 x 80 = psi.
The ^1.25is to the power, like square is ^2, and root is ^0.5.
But you dont add 10% first . Wich is for R/L unbalance, but also for pressureloss in time or misreading or inacuracy of pressure device.
Then it would give lineair 3190/3420 x 80 = 74,61 psi , so lineair calc comes to about the same as my extra safe calc is 75 psi.
Must have missed something , where did you get the 3472 maxload from?

jadatis

06/18/19 07:14am 
Truck Campers


RE: Front tire pressure?
Filled in in my made motorhomecalculator, it comes to F 41 psi , R 75 psi.
Googled your sise tire to be loadindex 123 for single load is maxload 3420 lbs, E load AT 80 psi.
Front that low??!! Yes , search the GAWR's, and you probably discover that rear is already overloaded, and front still have a comfortable reserve.
The vehiclemaker calculates for GAWR's ,and for that it probably needs 60 psi.
Are these the original sises and loadrange ( E load / LRE AT 80 PSI) . If the weights are right, and tirespecifications I found too, especially the low front gives better comfort and gripp, but you yust gotten used to the kidneybelt:B
My calculator adds 10 % to the given loads( so yoy weighed ? !), and then calculates the pressure with a formula that gives higher pressure then the official European, wich America uses too but only for Ptires since 2006.
So my calculation is certainly not to low.
Determining the real weights is the most tricky part, in this all, but you weighed fully loaded, so also all the persons? , wich gives you already bonuspoints.

jadatis

06/18/19 05:43am 
Truck Campers


RE: Max tire pressure and temp setting
If you have sensors screwed on the outside on the valves, the temperature reading cant be trusted, they give something between outside and insidetire temp.
So the pressure then is the only reliable.
But that once you descent from the mountains, and use the brakes to often, the temp in tire can rise to boiling point of water ( 212degrF/100degrC), and with that the pressure rises about 40%.
You can not set your TMPS system that high, so then dont be alarmed if the allarm goes off, you the know its a fals alarm, and better concentrate on the driving.
Normal use when driving about 50mph at outside temp of 65 degrF, the inside tire rises to about 110120 degr F, and with that the pressure rises about 10 to 11% .
Hottest inside tire temp that is probably still save or tires , so no overheating of rubber , is ( estimated by me) 140 degr F, and it would rise the pressure about a good 15% , but when hotter outside mayby 150degr and more , so when you set it to 15 to 20% upper alarm , I think you are OK.
Then when it goes off, and you suspect other factors ( like that descending from mountains or hot outside temp or sun shining on tire)you yourselfes know its a fals alarm and dont be annoyed by the beeps and ignore them.
But when only driving that alarm, you probably have a problem.
Low alarm can often go off in winter in the morning, because cold temperature outside then same as inside tire , from 65 degr filled goes down about 8% when freesing so 32 degr F outside so inside tire.
So low alarm can do with 10% , or less if you also then realise its from cold outside temp, and ignore it.
When its colder outside the tire can have lower pressure without overheating the rubber when on higher speed, wich is the goal of advice pressure.
Temp differences are larger then, so better cooling down of rubber of tire, wich allows the more heatproduction the more deflection of tire then gives.

jadatis

04/10/19 05:09am 
Travel Trailers


RE: Tire pressure / dually / TC
RAM 3500 dually that will soon have a TC on it.
It's a question of what should the rear tire pressure be and I'm wondering what you run your dually at. The camper should be around 45k pounds. I'm planning to install Crossfire Equalization and need a number...psi.
RAM said 65 psi
Tire manufacture,Nexen Roadian,said 80 psi
Both said 80 psi for the front.
Who's correct?
I can calculate it for you, but need weighed axleloads , or better axleendloads.
The estimation you do is verry dangerous.
Also need 3 things of tires.
1. Maximum load or loadindex for dual, but give it all so also single.
2. Loadrange or better pressure behind AT .
3. Max speed of tire or speedcode.
As long as you dont have weighed loads fully loaded as you go on trip, we will have to use the GAWR's, also give GVWR.
And what configuration, drive axle duall we know, but alao TAG axle?

jadatis

03/29/19 10:46am 
Truck Campers


RE: Max tire pressure
Once read from Tireman9 or Capriracer , that tires have teststandards, so they have to stand a pressure of 2 to 3 times the pressure behind AT.
So your 80 psi can rise to 160 to 240 psi before they blow.
I would not try this at home, if tire is already damaged by using to low pressure once, so overheating has happened long enaugh, it will blow sooner.
But gives an idea that only for the tires, you dont have to be affaid of putting for instance 120 psi in it ,if its undamaged.
In old PDF I have from Semperit ( Continental Group) they prescribe 140% of that pressure behind AT( official referencepressure, but will call it ATpressure furtheron). Then the tire is allowed 2 times the maximum load when speed zero so standing still.
Continental group in Europe gives on many tires 2 pressures.
1. The pressure behind AT but without AT in front of it right behind the servicedescriptions ( example 255/70R16 121/119R 65psi)
2 on the other side behind the maxload information "maximum inflation pressure of 10 psi higher then 1 (so then 75 psi).
, and this is also cold pressure .
Also old documents of Goodyear gave for ST tires a 10psi higher pressure for 75mph.
Nowadays, if not given on tiresidewall, you may not fill cold pressure higher then ATpressure.
In earlyer days it was allowed.
Cold pressure is when inside tire airtemp is outside/ambiënt temp, that simple.
But sun can heat up the tire inside even when standing still.
Also exaust pipe yust in front of rearwheel can make that tire hotter .
Cold pressure advice and also ATpressure is meanth for 18or20degrC/65or68degrF.
So you can always argue when filled fi 90 psi on AT80psi tire, that you filled it at freesing point( 0degrC/32degrF), and the pressure has rissen to that 90 psi now its 65 degr F.
Suppose you fill at freesing point of 32 degr F your tires with 1,4 times the ATpressure , and in use the temp in tire goes to boiling point of water so 212 degr F, Then the pressure in tire will rise to a small 2x ATpressure , so still within the teststandards of 2 to 3 times AT. Boiling point of water it can incidentially get in the tire, when descending the mountains and using the brakes to often.
Then heat of brakes is transported trough the rimms to the tire inside.
I suspect tiremakers to sometimes fi put a Dload designed tire( AT 65 psi) in the market as Eload ( AT 80 psi) , because especially american market asks for it.
But then the 2 to 3 times higher then AT wont go anymore.
Mayby thats the reason why they standard dont allow higher then ATpressure anymore.
For P tires , only maximum cold pressure is given on sidewall, of 44 to 51 psi , and for XL sometimes even 60psi.
The ATpressure of a standardload Ptire is USA system 35 psi always, and EUR system 36 psi with exeptions to lower.
XL/reinforced/EXtraload USA 41psi always, EUR 42psi with exeptions to higher and lower.
So for P tires its normal standard to allow higher cold pressure then AT.

jadatis

03/19/19 06:11am 
Tech Issues


RE: Motor home tire pressure
Hello Everyone,
I have a 2001 Monaco Night 36’ DP. My question is about tire pressure. The tires are Goodyear G 661 HAS load range H 255/70 R 22.5 The tires say max. pressure 120#
I am not sure what the correct pressure should be. I have not weighed the RV but I have a Cat Scale ticket from the previous owner. He weighted it ready to travel. Full fuel gear and water.
The ticket shows a total of 27,140# but 3120# of that is his toad. The front weight was 8640#. The rear was 15,380#. If I understand this right that means each front tire has 4320# on each. The rears (duallys) have 3845# on each of the four tires.
The sticker in the coach says to inflate front and rears to 80#. I have looked for an inflation chart on the internet for these tires and have not found an exact match. I have found very similar Goodyears that say the rears should be at 80# and the front at 85#.
When I checked the tires, they are at 90#. I would like to lower the pressure a little to help with handling. The RV has the steering box that is not adjustable and has some play in the wheel and wonders a bit at high way speed 6065 mph.
Any insight on correct pressure or where I can find a chart is appreciated.
Thanks as always,
Lurker
Have put weigts of former user in my made extra safe calculator.
Gave Front 103 psi so make it 105, and rear 99psi so make it 100.
Ofcource new weighing, as suggested, is better, wich you then can use for years, the little variation will be covered by the reserves I put in.
Calculator spreadsheet first adds 10% to weighed axleloads, and then calculates with a safer formula then those are used for the official lists, so higher pressure outcome.

jadatis

02/15/19 09:20am 
Class A Motorhomes

