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Old 10-20-2013, 01:14 PM   #1
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Tires say "110 lbs.PSI cold"

The Toyo tires on my 37' TropiCal DP say to inflate them to 110 lbs. PSI cold. This seems to really pound on highway strips or any kind of roughness. I'm wondering if I underinflate a little, say 10 to 15 lbs., will that help the ride, destroy whatever ridiculous fuel mileage I already get, wear my tires out really quickly, make my handling sloppy, or all or none of the above.
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Old 10-20-2013, 01:25 PM   #2
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Here's a link to some previous threads which explain how to adjust tire pressure.

https://www.google.com/search?q=Tire...earch=irv2.com
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Old 10-20-2013, 01:27 PM   #3
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Quote:
Originally Posted by michguy View Post
The Toyo tires on my 37' TropiCal DP say to inflate them to 110 lbs. PSI cold. This seems to really pound on highway strips or any kind of roughness. I'm wondering if I underinflate a little, say 10 to 15 lbs., will that help the ride, destroy whatever ridiculous fuel mileage I already get, wear my tires out really quickly, make my handling sloppy, or all or none of the above.
The pressure on the side of your tire is the max cold inflation the tire is designed for. Weigh your coach by axle if you can and look up the inflation table published by the tire manufacturer. There also should be a placard on the wall of the coach close to the drivers seat which tells the weight each axle is designed to carry and the inflation pressure required to carry that weight.
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Old 10-20-2013, 01:31 PM   #4
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Originally Posted by Steve Ownby View Post
The pressure on the side of your tire is the max cold inflation the tire is designed for. Weigh your coach by axle if you can and look up the inflation table published by the tire manufacturer. There also should be a placard on the wall of the coach close to the drivers seat which tells the weight each axle is designed to carry and the inflation pressure required to carry that weight.
Not so
The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From page 2 of the 06/07 Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."
From Cooper:
Quote:
Tire Service Life

Cooper recommends that all tires, including full-size spares, that are 10 or more years from their date of manufacture, be replaced with new tires.

Tire service life is not determined by chronological age. The useful life of a tire is a function of service and storage conditions. For each individual tire, this service life is determined by many elements such as temperature, storage conditions, and conditions of use (e.g., load, speed, inflation pressure, impacts and road hazard damage) to which a tire is subjected throughout its life. Since service and storage conditions vary widely, accurately predicting the service life of any specific tire based on calendar age is not possible.

Cooper Tire is not aware of scientific or technical data that establishes or identifies a specific minimum or maximum service life for passenger and light truck tires. However, Cooper recognizes a consumer benefit from a more uniform, global industry-wide approach to the tire service life issue. Accordingly, Cooper recommends that all tires, including full-size spares, that are 10 or more years from their date of manufacture, be replaced with new tires. Tires 10 or more years old should be replaced even if the tires appear to be undamaged and have not reached their tread wear limits. Most tires will need replacement before 10 years due to service conditions. This may be necessary even if the tire has not yet reached its tread wear limits.

Under no circumstances should a "maximum" service life recommendation for a tire be considered as an "expected" service life. Tires must be removed from service for several reasons, including tread worn down to minimum depth, signs of damage (cuts, cracks, bulges, impact damage, vibration, etc.) or signs of abuse (underinflation, overloading, improper repair, etc.).
From TOYO:
Quote:
Q: What are the consequences of inflating the tires to accommodate the actual loads?
A: If the inflation pressure corresponds to the actual tire load according to the tire manufacturer’s load and pressure table, the tire will be running at 100% of its rated load at that pressure. This practice may not provide sufficient safety margin. Any air pressure loss below the minimum required to carry the load can result in eventual tire failure.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
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Old 10-20-2013, 02:39 PM   #5
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Thank you Mr_D. Even though I am not the OP, your info is very helpful for me to understand the max pressure concept.
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Old 10-20-2013, 03:04 PM   #6
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Thanks for posting the documentation Mr. D! Some people seem to think the load/inflation charts are akin to a bible, and must be strictly followed.
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Old 10-20-2013, 03:25 PM   #7
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Originally Posted by Mr_D View Post
Not so The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire. From page 2 of the 06/07 Michelin RV Tire Guide: From page 6 of the GoodYear RV Tire and Care Guide:From Cooper:From TOYO:But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!! From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Very correctly stated. I misspoke in my first post. The most important thing to remember is to guard against driving under inflated for the load on the tire. Many coach owners add 10% to their inflation pressure to allow for an axle being loaded heavier on one end. Also be aware of the max inflation limit on the wheel many are 120-130 psi.
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Old 10-20-2013, 11:31 PM   #8
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Some information to draw your own conclusion:

Michelin RV Tire Guide
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Old 10-21-2013, 02:44 AM   #9
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A Goodyear engineer told to never inflate LESS than 80% of the max on the sidewall. This was when our fleet trucks were replacing with newer tires with greater max pressures than a previous brand or load rating.
The sidewalls as you know are different from brand to brand. The label on the door is not for all conditions or loads.
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Old 10-21-2013, 05:06 AM   #10
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The pressure written on sidewall or belonging to the loadrating is , as esplained already, not the maximum pressure of the tire. Also saw this pressure needed for the maximum load called the maxloadpressure, and in a formula sheet I got hold of from ETRTO it is called the reference-pressure , will shorten it further to Pr.
But what is that maximum pressure then?
I once concluded of information of semperit ( from continental) wich writes that standing still the tire is allowed to bare 2 times the given maximum load at 1.4 times the Pr ( cold).
Standing still there will be no heatening up by driving, so only by by higher outside temperature in time.
So I think the tire-maker supports a absolute pressure of 1.5 times the Pr.
Or the other way around, they determine the maximum pressure they can stand in for and take 2/3th of that for the Pr.

10 psi higher then Pr is adviced for LT and ST tires in several articles.
LT for more then maximum load at verry low speeds and better handling.
ST for higher speed then 65m/h.

To use the pressure loadcapacity-lists of the tire makers in America is somewhat dangerous.
Best is to use my made lists wich takes care the deflection of the tire stays the same over the whole range of pressure/loadcapacity, wich is the goal of all the calculations, so also of those that are used to make those pressure/loadcapacity lists.
Can be found on my public map of skydrive that belongs to my hotmail adress with same username as here. https://skydrive.live.com/?cid=a526e...E092E6DC%21904
take the USA map and first search for the Pr and open the pdf begining with the Pr. You can pick for per tire/per axle single or axle dual so you dont have to devide by 2 or 4 first.
Then search in that list the maximum load of your tires or loadindex, and in that row search for the axle or highest tire-load on the axle, +10% to get the needed pressure.
Because my calculation takes care of that same deflection , it is allowed to go verry low in the pressure.

But also you can use my motorhome-tire-pressure-calculator to be found in this map
https://skydrive.live.com/?cid=a526e...E092E6DC%21793

then all the reserves are done automatically, and you will get some extra information about loaddivision overloading and possible weightdifference on the axles. If only GAWR's give they are used , when real ( assumed) axle loads are given those are used.
If advice goes over the Pr but less then 10 psi , the pressure kinds are made red to warn but still ok. If more then 10 psi the advice pressures also are made red to , to warn you are going over the border the tire-maker supports.
Then take your own conclusion about why it needs to be that high.

First download the needed spreadsheet and then open it in Excell or Open office CALC on your computer. For that CLICK RICHT on the needed document, and choose download from the dropdownbox.
dont leftclick or use open in EXCEL or WEB-APP, first is to complicated and asks you to log in with your hotmail adress, second tries to open it in an excell like program in the cloud and then gives messase that it cant handle some things I used in the spreadsheet.

So topicstarter use my spreadsheet or the lists and se how low you can go savely.
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Old 04-12-2016, 12:03 PM   #11
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Good hints. Another thing I was told your post alludes to is speed and pressure as we occasionally had farm or construction equipment. Never ran tires bulging from low pressure.

Tim Chitwood once told me they pulled off their jumps and Driving on two wheels by using regular tires but they put pressure at 60-80 lbs. Since they were not running on the highway nor very fast, the sidewall was nice and stiff for their jumps and spins.
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Old 04-12-2016, 07:17 PM   #12
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Quote:
Originally Posted by miwok View Post
The sidewalls as you know are different from brand to brand. The label on the door is not for all conditions or loads.
The placard posted near the driver's seat shows the minimum pressure required to carry the maximum weight that the axles are rated for.
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Old 04-12-2016, 08:48 PM   #13
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Originally Posted by Alan_Hepburn View Post
The placard posted near the driver's seat shows the minimum pressure required to carry the maximum weight that the axles are rated for.
One note of caution: the tires shown on the placard may not be the same as those on the coach.
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Old 04-12-2016, 09:03 PM   #14
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Toyo Tires: https://toyotires2-1524598101.netdna...ntenance_0.pdf

Replacement tires are properly inflated when they provide the load capacity the Original Equipment tires provided when serviced to the vehicle manufacturer's recommendations.
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