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11-11-2019, 08:33 AM
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#21
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Winnebago Owner
Join Date: Jun 2019
Location: NW WI
Posts: 241
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Quote:
Originally Posted by Wyatt
So, according to this tab on my coach, if I’m maxed out on weight at 16,000 lbs, I should be using 82 psi on all tires? The Goodyear table says lower... thoughts?
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I'm sure you've read all the posts. It's up to you to decide what you want to do...
Hopefully the charts mention nothing about ride. My 40' rides better than my newer 2500 RAM. Like most, it has air ride suspension...
__________________
2003 Ultimate Freedom 40', Diesel Pusher, Cummins 400, Spartan Chassis
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11-11-2019, 10:21 AM
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#22
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Winnebago Owner
Join Date: Mar 2010
Location: Akron, Ohio
Posts: 190
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Answers
Quote:
Originally Posted by TheArthurs
Our winnebago sticker says cold pressure should be 95 PSI
Our actual tires say cold pressure should be 110 PSI
Which should we be going with?
Also, looking at the tire picture, what does the 138/135L mean?
We have 2005 Itasca Meridian P39k
Thanks
Raymond and Geni
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I suggest that when you have a question you first check the "SEARCH" feature of this forum. If you enter Tire Inflation you will find many posts on the topic as seen HERE.
You might also check my Blog on RV Tire Safety
__________________
Retired Design & Quality Tire Eng. Have a tire blog RVTireSafety.NET Scheduled to give tire seminars at FMCA Convention in Perry, GA in March 2025
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11-11-2019, 10:27 AM
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#23
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Winnebago Owner
Join Date: Mar 2010
Location: Akron, Ohio
Posts: 190
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Quote:
Originally Posted by rk911
the problem with that is you don't know what the placard recommendation is based on....GVWR, weight of the empty coach as it rolled off the line, etc. the proper way is to inflate for the actual load being carried.
fully load your coach, get individual axle weights (at a minimum. 4-corner weights are best) and then consult the tire mfg's inflation chart. add a bit to that if it makes you feel better...5psi, 10psi, X%...whatever.
plan b, which some advocate, is simply using the max psi on the tire itself. that keeps things simple but you'll get a hard ride and possibly some handling issues.
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The placard pressure is by federal regulation based on the minimum pressure needed to support the GAWR. This assumes a perfect 50/50 side to side load split which very few RVs have. This is why "4 corner weights" when fully loaded is recommended.
lacling 4 corner weights I suggest you get on a trucl scale (CAT scale at many truck stops) and then assume one side is supporting 53% of the scale reading for that axle. Check the Load Inflation tables to learn THAT minimum inflation and for a little margine so you are not chasing inflation every morning as the ambient temperature changes add 10%.
I cover weight & inflation in dozens of posts on my blog.
__________________
Retired Design & Quality Tire Eng. Have a tire blog RVTireSafety.NET Scheduled to give tire seminars at FMCA Convention in Perry, GA in March 2025
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11-11-2019, 12:33 PM
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#24
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Proud “No Intent” Owner
Join Date: Jul 2019
Location: Belmont, CA
Posts: 1,779
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Quote:
Originally Posted by Jim_HiTek
Wow, so much info.
Here's the deal. That placard was put there when the RV was manufactured and left the plant with a certain brand and type of tire and with certain loading that they mysteriously determined.
Once they've been changed for a different brand, type, or even if a few years have past for that same tire type, that placard is worthless. Ignore it and get a weight for your axles, than use the tire manufacturers charts to set tire pressures based on that weight. If you get a four corner weight, recommended, then the highest weight on that axle determines the pressure in ALL the tires on that axle.
Keep in mind that RV manufacturers are trying to give the softest most cushy ride...without care for tire life. Whereas an RV owner might be more interested in tire life than cushioning. So even in a brand new RV, might check the weight you're running at, vs the tire manufacturers pressure charts, and again, set it at that, not what the placard says.
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Thanks for your feedback.
Ok, more info...
We bought the coach new in July. It only has 3,000 miles thus far, so it still has the original tires that are on the placard in the coach. Winnebago is saying that maxed out weight, the tire pressure should be 82 all around. And as you can see from the CAT scale weigh ticket, I’m actually over by 100# GVRW. Yet each axle is slightly under.
The Goodyear chart is really what I’m trying to decipher. It looks as though, if I’m reading it correctly, and perhaps this is where I’m messed up, is 82 is too much pressure.
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11-11-2019, 03:51 PM
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#25
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Winnebago Camper
Join Date: Jul 2019
Posts: 17
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Quote:
Originally Posted by creativepart
Actually, you'll get a better ride and better handling if you get your FULLY loaded RV weighed and then use your exact tire's load rating chart to set the PSI based on your actual RV weight. The placard on the RV is generally too high by 10 psi or so.
My chart says 95 front and 100 rear but after careful weighing we are using 85 front and 93 rear. It made a huge difference in ride.
By FULLY loaded it means a worst case scenario - full water tank, full fuel tanks, all your stuff, loaded to go on a trip. Then you head to a CAT Scale and get each axle weighed. Then consult your tire charts and add about 5 psi to the number shown for your weight there.
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CreativePart is correct. Do not go by what it says on the tire. Do not go by what it says on the placard. Get all four wheels weighed. Then look up the tire manufacturer's chart for pressure required for a given weight.
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11-11-2019, 04:31 PM
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#26
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Proud “No Intent” Owner
Join Date: Jul 2019
Location: Belmont, CA
Posts: 1,779
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I posted the weight of my vehicle, front axle, rear axle and GVRW. I also posted the Goodyear chart. We don’t have any scales near us that will weigh individual tires, but since the tires on each axle must be the same pressure anyway, that part seems to be moot. So take the front axle weight of 5,420 lbs. for example. Looking at the Goodyear chart, what pressure would you use? 5,420 / 2= 2,710 lbs. We have the 245/70R 19.5 G tires. The chart doesn’t even have numbers for that. Thanks!
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11-11-2019, 06:53 PM
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#27
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Winnebago Master
Join Date: Oct 2017
Location: Elk Grove, CA
Posts: 3,702
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This is getting confusing, we have two owners asking detailed questions, the OP, TheArthurs and Wyatt. It would be helpful if both could let us know if they have a good answer yet.
__________________
Bob C
2002 Itasca Suncruiser 35U
Workhorse Chassis
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11-11-2019, 07:31 PM
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#28
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Winnebago Owner
Join Date: Jun 2019
Location: NW WI
Posts: 241
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TheArthurs got their answer, they're going with the placard which Winnebago recommends. Wyatt needs an answer....
__________________
2003 Ultimate Freedom 40', Diesel Pusher, Cummins 400, Spartan Chassis
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11-11-2019, 08:07 PM
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#29
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Winnebago Owner
Join Date: Oct 2019
Posts: 72
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Quote:
Originally Posted by NeilV
You go by neither. The pressure on the placard is an approximate while whats stamped on the tires the maximum safe inflation at the highest load the tire is capable of handling. For best ride and tire life you need to get the coach weighed when loaded exactly as it will be when you travel with it and then inflate the tires according to the tire manufacturers inflation table for that size and type of tire.
You may need to redistribute your stuff too if the load is not balanced well front to back or side to side taking care to not go over the front or rear axles load rating or the tires. After the load is balanced and the tires are inflated to match the load then its time to take the coach as loaded the way you will be traveling with it to have it aligned.
Those other numbers are the speed and load rating of the Toyo M154 tires.
"The M154 is a deep all-position tire designed for regional and urban service in the highest-scrub environments, where tread wear is the primary reason for tire removal. Users can typically expect a return on their investment in less than a year with this SmartWay-verified tire. Excellent, even wear in miles per 32nd and a deep tread up to 22/32" deliver maximum removal mileage, even in the drive position. Excellent fuel efficiency and high mileage make the M154 the leading value alternative tire for regional to urban high-scrub applications."
Speed Rating is L so 75 MPH max and load rating is stated for single and dual use so 138 = 5205 lbs each in single application and 135 = 4805 lbs each in dual applications.
See: https://www.toyotires.com/commercial...-position-tire
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Wow!! Great info here. Thanks so much for taking the time to explain 😃
__________________
'05 Itasca Meridian P39K
Looking forward to our next Chapter!!
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11-11-2019, 08:30 PM
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#30
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Proud “No Intent” Owner
Join Date: Jul 2019
Location: Belmont, CA
Posts: 1,779
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Yep. I’m still in the dark on this one.
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11-11-2019, 09:26 PM
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#31
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Winnebago Owner
Join Date: Mar 2010
Location: Akron, Ohio
Posts: 190
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Quote:
Originally Posted by Wyatt
Thanks for your feedback.
Ok, more info...
We bought the coach new in July. It only has 3,000 miles thus far, so it still has the original tires that are on the placard in the coach. Winnebago is saying that maxed out weight, the tire pressure should be 82 all around. And as you can see from the CAT scale weigh ticket, I’m actually over by 100# GVRW. Yet each axle is slightly under.
The Goodyear chart is really what I’m trying to decipher. It looks as though, if I’m reading it correctly, and perhaps this is where I’m messed up, is 82 is too much pressure.
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Two issues. 1. You do need to lose at least 100# to meet GVWR
2. F scale 5400 x 53% = 2873 Min inflation 80 psi +10% = 88
R scale 10680 x53% = 5660 /2 = 2830 Min infl 80 =10% = 88
You should never go below the lowest inflation on a load inflation chart.
__________________
Retired Design & Quality Tire Eng. Have a tire blog RVTireSafety.NET Scheduled to give tire seminars at FMCA Convention in Perry, GA in March 2025
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11-11-2019, 10:36 PM
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#32
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Proud “No Intent” Owner
Join Date: Jul 2019
Location: Belmont, CA
Posts: 1,779
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Thank you Tireman. I really appreciate your input. We came home with 1/3rd full water, 1/3rd full septic grey water and 1/4 black. By my calculations, dumping those would have put us well under max GVRW. I Should probably lose some weight myself, which would also help.
One last question, your calculations included a 53% factor, Why is that factored in? And, are you using the Winnebago sticker or the Goodyear chart to come to your assessment. Thanks, as always.
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11-11-2019, 10:37 PM
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#33
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Proud “No Intent” Owner
Join Date: Jul 2019
Location: Belmont, CA
Posts: 1,779
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And one more thing, what the 10% increase beyond your results? Just trying to learn here...
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11-12-2019, 03:17 PM
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#34
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Winnebago Owner
Join Date: Mar 2010
Location: Akron, Ohio
Posts: 190
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Quote:
Originally Posted by Wyatt
And one more thing, what the 10% increase beyond your results? Just trying to learn here...
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The 53% is just a rule of thumb for an estimate on what the heavy end of an axle migh be supporting. Some will have more some less. I have found a number of owners reply that once they get actual 4 corner weights they discover the heavy end is between 52 and 54 % pf the axle.
10% is my official "Expert Opinion" (yes I am a court accepted "Expert" for tires) to give you a reasonable Reserve Load. It also will cover you for changes in ambient of almost 50F so you are not chasing a 1 or 2 psi change in inflation. A tire will run longer with a +10% inflation and you will do less work. If you were to run -10% I would expert shorter tire life and possible a failure in the long term.
__________________
Retired Design & Quality Tire Eng. Have a tire blog RVTireSafety.NET Scheduled to give tire seminars at FMCA Convention in Perry, GA in March 2025
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11-12-2019, 03:33 PM
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#35
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Proud “No Intent” Owner
Join Date: Jul 2019
Location: Belmont, CA
Posts: 1,779
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Quote:
Originally Posted by Tireman9
The 53% is just a rule of thumb for an estimate on what the heavy end of an axle migh be supporting. Some will have more some less. I have found a number of owners reply that once they get actual 4 corner weights they discover the heavy end is between 52 and 54 % pf the axle.
10% is my official "Expert Opinion" (yes I am a court accepted "Expert" for tires) to give you a reasonable Reserve Load. It also will cover you for changes in ambient of almost 50F so you are not chasing a 1 or 2 psi change in inflation. A tire will run longer with a +10% inflation and you will do less work. If you were to run -10% I would expert shorter tire life and possible a failure in the long term.
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Really good info. Thank you so much for taking the time to indulge my questions in detail. Now I can obsess about something else...
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11-13-2019, 06:06 AM
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#36
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Winnebago Owner
Join Date: Jun 2014
Location: Gulf Coast, Alabama
Posts: 92
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Quote:
Originally Posted by Tireman9
10% is my official "Expert Opinion" (yes I am a court accepted "Expert" for tires) to give you a reasonable Reserve Load. It also will cover you for changes in ambient of almost 50F so you are not chasing a 1 or 2 psi change in inflation. A tire will run longer with a +10% inflation and you will do less work. If you were to run -10% I would expert shorter tire life and possible a failure in the long term.
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All tires see an increase in pressure as the day warms up, and as they are driven on the road.
If suggested pressure is 80, but operating pressures becomes 90, is it more prudent to set cold pressure less than 80(75?) and therefore see operating numbers closer to the suggested amount during use?
On a related subject, most of us rarely check tire pressures on our cars/trucks, and have likely been surprised when we check them and see a 50% loss of pressure in a tire, even though it looks to be inflated properly.
That said, is discussion about +/- 10% more theoretical than practical?
__________________
Rick and Sandy
2003 American Eagle, 52K miles
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11-13-2019, 08:34 AM
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#37
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Winnebago Owner
Join Date: Jun 2019
Location: NW WI
Posts: 241
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Quote:
Originally Posted by bamaboy473
If suggested pressure is 80, but operating pressures becomes 90, is it more prudent to set cold pressure less than 80(75?) and therefore see operating numbers closer to the suggested amount during use?
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No. Because the recommended pressure is when the tire is cold. They already factored in when the tire heats up as it goes down the road.
__________________
2003 Ultimate Freedom 40', Diesel Pusher, Cummins 400, Spartan Chassis
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11-13-2019, 02:30 PM
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#38
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Winnebago Owner
Join Date: Mar 2010
Location: Akron, Ohio
Posts: 190
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Quote:
Originally Posted by bamaboy473
All tires see an increase in pressure as the day warms up, and as they are driven on the road.
If suggested pressure is 80, but operating pressures becomes 90, is it more prudent to set cold pressure less than 80(75?) and therefore see operating numbers closer to the suggested amount during use?
On a related subject, most of us rarely check tire pressures on our cars/trucks, and have likely been surprised when we check them and see a 50% loss of pressure in a tire, even though it looks to be inflated properly.
That said, is discussion about +/- 10% more theoretical than practical?
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No we only talk about "Cold Pressure"
Your RV owner's manual probably says to check your tires at the start of every travel day. This is because the mfg knows that there is a much smaller margin on RV application ( less than 10% and possible less than 5%) while our regular cars have a 25% to 40% load capacity margin.
My +10 is used when trying to learn what your cold pressure should be. It is there to help cover the daily +/- in cold pressure due to ambient temperature changes and to cover the probable 2 to 5% error in your tire gauge.
__________________
Retired Design & Quality Tire Eng. Have a tire blog RVTireSafety.NET Scheduled to give tire seminars at FMCA Convention in Perry, GA in March 2025
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11-13-2019, 03:50 PM
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#39
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Winnebago Master
Join Date: Nov 2011
Location: Full time RV'er
Posts: 1,230
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Wait a sec here Tireman9. Are you saying that tires specifically made for RVs have less of a safety factor (margin) than tires for a typical passenger vehicle?
What about big truck tires (which is what I use instead of RV tires)?
Asking for clarification...
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