Reply
 
Thread Tools Search this Thread Display Modes
 
Old 05-20-2015, 08:33 PM   #1
2 Rivet Member
 
1992 25' Excella
Grants Pass , Oregon
Join Date: Apr 2012
Posts: 82
Images: 3
Tire Pressure vs. Carrying Capacity

Tire pressure question: Is tire pressure and tire carrying capacity directly proportional all the way through the range of possible air pressures? In other words, is the following hypothetical analysis correct?

For the sake of simplicity with the math, Iíve used round numbers:

Letís assume that a particular tire will safely carry 4000 lbs. at 100 psi.

Does this mean that the same tire will safely carry 3000 lbs at 75 psi, or 2000 lbs at 50 psi, or 1000 lbs at 25 psi???

Is this how it really works?


Thank you.
__________________

__________________
Doug C is offline   Reply With Quote
Old 05-20-2015, 08:40 PM   #2
Full Time Adventurer
 
BoldAdventure's Avatar
 
2007 27' International CCD FB
Nomadic , USA
Join Date: Jul 2013
Posts: 2,743
No.
__________________

__________________
Family of 4 living, working & exploring the USA in our Airstream.
OUR BLOG | FACEBOOK | INSTAGRAM
BoldAdventure is offline   Reply With Quote
Old 05-20-2015, 08:55 PM   #3
Rivet Master
 
1973 25' Tradewind
Beautiful , Oregon
Join Date: Sep 2009
Posts: 548
No is a good answer to an interesting question but could someone chime in with a little more info. I have had the same question myself.

Many Thanks

Tony
__________________
Tony S is offline   Reply With Quote
Old 05-20-2015, 09:03 PM   #4
Rivet Master
 
HowieE's Avatar
 
1991 34' Excella
Princeton , New Jersey
Join Date: Aug 2003
Posts: 6,811
Images: 12
You will find the answer here. The chart is good for any manufacture.

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
__________________
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles

HowieE is offline   Reply With Quote
Old 05-21-2015, 08:06 AM   #5
2 Rivet Member
 
Berkel-Enschot , Noord-Brabant
Join Date: Apr 2014
Posts: 30
I also thought it was that easy when I asked an European tyre-manufacturer it.
What you use is the logical math and is not even that bad to use.
The Tyre-maker answered me also back with NO its more complicated.
But then I mailed back if they use some kind of formula for it, and they sent back a copy of formula to calculate pressure for a sertain load, and the extra's for higher speed and camber angle ( alighnment wheels like this /-\ on the axle).
Went running with that and learned myself excell to make spreadsheets for it.
The formula al over the world has a power in it , Europe uses 0.8 to calculate loadcapacity for a sertain pressure ( so the other way around then the formula I got) and this formula is more often used to make pressure loadcapacity lists.

When I declared this formula holy , I made some spreadsheets and bothered also American fora with it, and came to a document of american IR J.C.Daws who introduced another formula wich is lineair but with still a loadcapacity at zero pressure. I babtised that the construction load. He compares it with the different calculations in Europe and America ( USA uses different powers as 0.5( root) 0.65 , 0.7 but stepped over for the P- tires and XL/reinforced/Extraload to the EUR calculation with power 0.8 as late as 2006.

To begin with I will give a picture of several calculations for , then you see the logical calculation you do , is not that bad, but also give an "on the road methode wich is also simple to use, and comes pretty close to the ever to be constructed ideal formula.

Also my determined formula and see how small the differences are between that and logical and on the road methode.



Also I will give link to the public map on my One-drive that belongs to my hotmail.com adress with same username as in this forum .
3/4th about tire-pressure so sniff around.

https://onedrive.live.com/?cid=A526E...e092e6dc%21128

Sertainly other questions will pup up after you read this all.
then in this topic ask this Dutch pigheaded self-declared tire-pressure-specialist.
__________________
jadatis is offline   Reply With Quote
Old 05-21-2015, 09:01 AM   #6
Rivet Master
 
Arcticfox's Avatar

 
2013 28' Flying Cloud
Central , Saskatchewan
Join Date: Mar 2014
Posts: 1,026
interesting..... thanks
__________________
Trying to use my camera to create memories - not photographs!
Arcticfox is offline   Reply With Quote
Old 05-21-2015, 09:33 AM   #7
Rivet Master
 
HowieE's Avatar
 
1991 34' Excella
Princeton , New Jersey
Join Date: Aug 2003
Posts: 6,811
Images: 12
That formula may hold for P tires but P tires are not recommended for trailer use.
__________________
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles

HowieE is offline   Reply With Quote
Old 05-21-2015, 01:42 PM   #8
Rivet Master
 
tjdonahoe's Avatar
 
2013 31' Classic
billings , Montana
Join Date: Feb 2010
Posts: 1,843
My 1973 23' avion came with car tires and it was all it ever seen, never any problems, it's weight was around 6000 lbs.
__________________
tjdonahoe is offline   Reply With Quote
Old 05-21-2015, 01:51 PM   #9
Rivet Master
 
SteveH's Avatar
 
2005 39' Land Yacht 390 XL 396
Common Sense , Texas
Join Date: Sep 2007
Posts: 5,311
Just my opinion, but I would try to avoid using "P" metric radials on a travel trailer. I would, however, use an "XL" rated SUV tire before I would use an "ST" tire. They're usually rated for more weight than a "C" weight rated tire.
__________________
Regards,
Steve
SteveH is offline   Reply With Quote
Old 05-21-2015, 03:18 PM   #10
2 Rivet Member
 
Berkel-Enschot , Noord-Brabant
Join Date: Apr 2014
Posts: 30
Nothing wrong with P-tires for a TT as long as the maximum load is enaugh.
an ST ( special trailer) tire is calculated in its maximum load for lower speed ( 65m/h) so more deflection allowed.

Will give link to topic I started on RV forum, about maximum load in relation to maximum speed of tire.
http://www.rv.net/forum/index.cfm/fu...d/27477930.cfm

A stiffer tire needs more pressure for the same load then a less stif tire.
Compare LT C-load to P-tire of same sises if you can find it.

HowieE writes that the formula would only hold for P-tires, bus do you mean the official one or the logical one.
For P-tire and XL// the offical one with Eur 0.8 power comes close to the to natures law ideal one, but the higher the AT-pressure , so LT tires E-load for instance the logical formula is better then official EUR one.
__________________
jadatis is offline   Reply With Quote
Old 05-22-2015, 04:59 AM   #11
4 Rivet Member
 
2000 30' Excella
2014 30' Classic
Princeton , Iowa
Join Date: Mar 2012
Posts: 302
As an old truck driver, a man who has driven over 3 million miles and is now a retired camper man you have the right approach. More weight more air up to the tire rating. Too much air you wear out the center of the tire, too little air you wear out the edges of you tire. More air it rolls easier so less fuel. Too much air you give up ride. I have car tires on my pickup and run 35 with out trailer (number on the door) and 40 pulling an 30 ft. airstream. I have regular tailer tires on trailer and run 60. This has been working good. Tires wearing well and good ride.
__________________
larryglarson is offline   Reply With Quote
Old 05-22-2015, 05:26 AM   #12
Rivet Master
 
r carl's Avatar
 
Vintage Kin Owner
Lin , Ne
Join Date: Dec 2009
Posts: 2,056
Quote:
Originally Posted by SteveH View Post
Just my opinion, but I would try to avoid using "P" metric radials on a travel trailer. I would, however, use an "XL" rated SUV tire before I would use an "ST" tire. They're usually rated for more weight than a "C" weight rated tire.
P metric tires do have a flimsy sidewall don't they, I like LT tires.
__________________
The higher your expectations the fewer your options.
r carl is offline   Reply With Quote
Old 05-22-2015, 06:22 AM   #13
CapriRacer
 
CapriRacer's Avatar
 
I'm in the , US
Join Date: Sep 2012
Posts: 624
Quote:
Originally Posted by Doug C View Post
Tire pressure question: Is tire pressure and tire carrying capacity directly proportional all the way through the range of possible air pressures? In other words, is the following hypothetical analysis correct?

For the sake of simplicity with the math, Iíve used round numbers:

Letís assume that a particular tire will safely carry 4000 lbs. at 100 psi.

Does this mean that the same tire will safely carry 3000 lbs at 75 psi, or 2000 lbs at 50 psi, or 1000 lbs at 25 psi???

Is this how it really works?


Thank you.
No.

Long Version: Barry's Tire Tech

Short Version: The load curve is a curve. (I think I just made a funny.) While it is close to linear, it is indeed a curve.

And in the region we use, inflation pressure is not linearly proportional to the load carrying capacity. Put another way, a 10% reduction in inflation pressure does not result in a 10% reduction in load carrying capacity - it is less.

That's why you need the load tables.

BTW, this applies to ALL tires - passenger car, truck, trailer, aircraft, lawn and garden, bicycle, motorcycle, etc.
__________________
CapriRacer is offline   Reply With Quote
Old 05-22-2015, 11:58 AM   #14
1 Rivet Member
 
2012 25' FB Flying Cloud
Portland , Oregon
Join Date: May 2014
Posts: 10
Tire pressure vs carrying capacity

PSI is really dictated by the load the vehicle will have to carry. There should be no issues with having the psi lower than the maximum rating as long as it is sufficient to carry the load of the vehicle, and you would want to consider the full load with water, luggage etc.. when factoring total weight of loaded vehicle and appropriate PSI required for the load.

Load and PSI works as you assumed. Attached is an industry standard for trailer tire loads and comparable PSI.

Any reputable and knowledgeable tire dealer (like Les Schwab) can explain how it works and what tires are right for your load and trailer/driving conditions.

Monitor tire wear and adjust pressure accordingly. Over inflated tire on an Airstream rides rougher and may shake out the rivets (per my dealer). So I called Airstream (Ohio) and they have no real justification on what tires are installed, other than that is how we have always done it.

Goodyear inflation .pdf
__________________

__________________
Hophead is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cargo Carrying Capacity (CCC) of 23' Safari SE LS OrangeKid 2007 Safari SE 45 04-05-2010 09:26 PM
Cargo Carrying Capacity for 2009 Bambi pattimarty 2005 and newer - Bambi all models 22 03-11-2010 01:10 PM
Tire Pressure Gauges- Pressure Varies! Ray Eklund Tires 14 07-06-2008 09:34 AM
Canadian Tire's $129 Tire Pressure Monitoring System SilverCottage Tires 9 10-30-2007 08:55 PM
Carrying Canoe on top of 1971 Safari Larry71 1969 - 1973 Safari 30 08-02-2005 10:48 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 06:48 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.