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Old 01-23-2017, 12:20 PM   #15
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Go read your tire folks. Most likely it says something like - Max load of "N" @ "Y" PSI which in basic English states that the tire is rated to support the load (N) only if you have ( Y ) psi. If you have less PSI it will not support the stated MAX load ( Which by the way is the only time MAX is used). Less PSI may support your actual weight. I guess you can ALSO say it is the maximum because exceeding it could be dangerous, but it is in fact used as a minimum.

Tire charts are similar. The psi shown in the column is the minimum needed to support the shown weights. It is neither the minimum or maximum psi you can put in the tire but it is the minimum needed to support the desired weight.
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Old 01-23-2017, 12:22 PM   #16
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Thank you Mr. D.
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Old 01-23-2017, 12:29 PM   #17
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Originally Posted by Mr_D View Post
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. NHTSA defines truck tires as those rated for vehicles over 10,000#'s GVWR.

From the Michelin RV Tire Guide: From page 6 of the GoodYear RV Tire and Care Guide: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:
From our owners manual:
Once again we're saying the same thing using different words. If the largest load a tire is designed to carry requires a certain PSI, then that PSI is the highest pressure the tire is to be inflated. To increase the PSI would be going over the tire's design safety and wouldn't increase the tire's load capacity. It could result in uneven tread wear, (center of tread worn more than outside edges) and a harsh ride. In extreme maneuvers or conditions it could result in reduced traction or loss of control of the vehicle.

Inflating a tire to a lesser PSI than the tire and axle load requires is also bad. It can result in excessive sidewall flex, which would create heat and possible tire failure. It can also cause wandering and loss of steering control. Since air naturally leaves a tire over time, I'd imagine tire failure is most often a result of under inflation rather than over inflation. Having done long distance bicycle trips, I know from experience that if you don't check the pressures every day before a ride, you will most likely have tires under inflated, causing more effort required and more likely tire failure.

Only after weighing the RV can you safely determine the proper PSI for the weight the tire is actually supporting. The tire manufacturer's tables allow you to learn this number. Inflating to the PSI on the tire sidewall or the driver's side label would only be the proper number IF the RV was loaded to it's axle's capacity rating.

There, I stated my interpretation of the issue without using 'minimum' or 'maximum.'
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Old 01-23-2017, 12:36 PM   #18
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Regarding my comment that the tire wall information being useless. For 99% of the people driving RVs or passenger cars will never need to know what the maximum load of the tires are except when buying new and different brand or sized tires. They do need to know that the tires they have can support their actual and the stated GAWR. The PSI used should support either of these two weights. The fact that, given the proper PSI, the tire can support 500lbs more than they need is interesting and perhaps comforting, but for tire pressure purposes, useless.
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Old 01-23-2017, 02:42 PM   #19
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Originally Posted by colt9 View Post
I have a Class A 30ft with 225r70 x19.5 tires goodyear? Mfg tag is 6000# front axel 10,000# back axel duel- TOTAl for coach is 19,000#-I have looked all over for the correct pressure I should be running- the tire is marked 90psi Max. any help from you old salts? Thanks for any feed back I can get.
Already written here, that your info is questionable.
But will go from next
Front 2 tires on the axle and 6000 lbs axleload( assume weighed not GAWR.
Rear 4 tires on one axle is called dual load ,,and axleload 10000 lbs.

Googled your given tires and came to G-load LRF / 12ply.
this is to Goodyear list " maximum load single 3640 lbs/Dual 3420 lbs AT 95 psi ( 90 psi you give can be exeption but asume you miswrote) Upto 75m/h ( M speedrated).

In earlyer days the tiremaker allowed 10 psi extra and mayby for these in fact trucktires even 20 psi extra above that 95 psi.
Was adviced for higher speed and better handling.
Nowadays they dont allow it anymore , strange because for normal P-tires they give maxcold on sidewall and AT-pressure is lower.

So I first put your data in my made calculator ,wich uses an even saver formula ( higher pressure advice then official calc) and I ad a reserve wich to my conclusion still gives acceptable gripp and comfort ( so no bumping).

Gave for the 75m speed minimum pressure advice of Front 86 psi and Rear 76 psi with still reserve for for instance R/L unbalance.
But this goes from the idea that you can measure the pressure 100% acurate. Also assumes weights to be given 100% acurate and not judged.

So I also calculated a highest advice with maximum reserve and still no bumping and still acceptable gripp.
then advice Front 99 psi and Rear 81 psi
So determine yourselfes if you dare to go higher then the 95 AT-pressure in front.
For this I lowered the loadindex single of 125 by 4 steps to 121 to get the needed pressure as if the tire was calculated in maxload for 99m/h.
thats why the rear has less psi to go down then front , because dual loadindex is 123 and for comfort the deflection counts.

Disclaimer: if real axleloads in use are different then I think you gave, the advice must be different.
Also look on sidewall for maxload/loadindex and AT-pressure.
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Old 01-24-2017, 03:45 AM   #20
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Little correction to my last post.
Wrote G-load but mistyped , mean F-load

And addition: If you dont want to fill 99 psi front, because the tiremakers dont allow it anymore, 95 psi ( if given on sidewall) they do allow and still will give a reserve, for things like pressure-loss in time, misreading of pressure scale, little misyudging of weights, etc.
but to my conclusions this 99 psi will still give acceptable gripp and comfort.
And you can always say that you filled 95 psi at colder ambiŽnt temperature, and by warming up it became 99 psi.
And my advice , if all is given right, is that highest advice of front 99 and rear 81 psi. Then if in time it drops to the lower advice , you still are save for the tires.

Like this because I could not edit the last post anymore.
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Old 01-24-2017, 12:54 PM   #21
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Originally Posted by wildtoad View Post
Go read your tire folks. Most likely it says something like - Max load of "N" @ "Y" PSI which in basic English states that the tire is rated to support the load (N) only if you have ( Y ) psi. If you have less PSI it will not support the stated MAX load ( Which by the way is the only time MAX is used). Less PSI may support your actual weight. I guess you can ALSO say it is the maximum because exceeding it could be dangerous, but it is in fact used as a minimum.

Tire charts are similar. The psi shown in the column is the minimum needed to support the shown weights. It is neither the minimum or maximum psi you can put in the tire but it is the minimum needed to support the desired weight.

" maximum because exceeding it could be dangerous,"

This statement may confuse and mislead some. The infaltions we are talking about are the cold inflation not the higher hot running inflation. Undamaged tires can handle significantly more pressure than the pressure associated iteh the Max Load.

If you look you will see that P and LT and even Truck tires all have similar but not identical wording so it can be confusing.

Yes we are talking about a "Max" also being a "Min" which is confusing.

Here is a post on Max infl

Here is one on Max = Min

I have a number of other posts on proper inflation.
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Old 01-25-2017, 12:01 PM   #22
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Sorry for long post but just too many minor errors

First off it's important to know we are only talking about Motorhome tire pressures and not Trailers. I only offer this in case someone just happens upon this thread and tries to apply this info to a trailer.
Second unless stated otherwise discussions on inflation should ALWAYS be about Cold Inflation Pressure. CIP is the pressure when tires have not been driven on or in direct sunlight for the previous 2 to 3 hours.

Too many comments to reply with quote from each. So to save space;


Post #2 is correct to learn the minimum tire pressure

Post #3 has good info on tire placard info. The pressure offered from RV company is the pressure needed to support the GAWR and assumes the load is evenly split side to side on each axle (We all know about assumptions)

Post #4 People should not be guessing on their tire inflation. Also they should not assume the inflation used on another RV is correct for their RV

Post #5 instead of "pressure adjusted for actual weight will be less" I offer pressure adjusted for actual weight may be less

Post #6 & 7 correct info

Post #8 I do not agree, as there are some assumptions on what your actual tire loading is. Following the advise in this post may end up overloading your tires.

Post #9 is offering information that is appropriate for passenger car tires not LT or Truck/Bus tires or applications

Post #10 is correct

Post #11 I have addressed the Minimum maximum confusion in my blog see links in Post#13

Post 12 GCWR is the rating for RV + any toad and may be 19,000# but if with F & R GAWR of 6,000 and 10,000 you probably do not have GVWR of 19,000. I would expect GVWR to be 16,000 and can be less.

#14 & #15 are correct

#17 almost but "To increase the PSI would be going over the tire's design safety" is misleading as sometimes tires with higher Load Range are used on smaller, lighter vehicles. In my particular case my Class-C came with LR-E (80 psi) but based on actual measured load needed less than LR-D (65) to support the load.
ALSO "Inflating a tire to a lesser PSI than the tire and axle load requires is also bad." is making some assumptions that actual tire load and axle rating are somehow connected. Both are important and neither should be exceeded

#18 "99% of the people driving RVs or passenger cars will never need to know what the maximum load of the tires are" Not correct. Data from actual RV weights on tens of thousands of measurements by RVSEF shows that over half of the RVs on the road have one or more tire in overload. IMO this is because people are not able to look at an RV and know how much it weighs. They do not realize how heavy most of the "stuff" they put into the RV is.

#19 and #20 show the importance of ensuring the numbers posted reflect reality and what the writer intended. We all make typo errors and need to correct them whenever possible.
Also US Tire & Rim Association industry standard Load & Inflation tables are in 5 psi increments. (yes there are some in kPa but for our purposes lets avoid unit conversions that introduce possible errors) So if we use the PSI tables we find the inflations in 5 psi increments so I do not know where 99, 81, 86, 76 psi come from unless someone is using kPa and trying to convert. Side note 75 mph is Speed Symbol "L". M Speed is 81.


General comment on speed in RV application. I have seen statements in the big three tire company specifications books showing 75 mph Max speed in RV application no matter what the individual tire Service Description says. This limit is placed on the operating conditions expected in RV application. Some of you know of the 10% de-rating of P type tires when placed in LT or trailer service. This is another example of an operating condition dictating an adjustment in the tire upper limits.

Hope I have cleared up some of the confusion in this thread.
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Old 01-25-2017, 12:10 PM   #23
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Old 01-25-2017, 12:16 PM   #24
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Tireman9, Thank you for your careful review of the previous posts. I suggest you write up a proper article about RV tires, their inflation and inspection, etc. Then post it on the forum in a place where we can all refer to it and cite it in future posts. There's a lot of bad information and questionable, even dangerous advice from some posters.
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Old 01-26-2017, 10:52 AM   #25
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Tireman9, Thank you for your careful review of the previous posts. I suggest you write up a proper article about RV tires, their inflation and inspection, etc. Then post it on the forum in a place where we can all refer to it and cite it in future posts. There's a lot of bad information and questionable, even dangerous advice from some posters.


Bob, You might check out my blog as mentioned in my signature. I have over 250 posts on Tires, wheels, valves and TPMS. Most with a view on the RV owner.
There is a partial "index" on the left and 10 most popular posts on right along with one of my RV tire videos on the home page.

I try and monitor 5 to 8 RV forums but I do have a life and the wife complains that I spend too many hours each day posting on tires.
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Old 01-26-2017, 10:22 PM   #26
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Should have a sticker near the driver's seat that looks something like this:



What motorhome do you have?

Edit -
Found that you posted about having a Trail Lite 281. What year? On a W16 chassis? P32?

A 2000 or so P32 would have a 15,000 GVWR, 6,000/10,000 front/rear, 19,000 GCWR. That it?
I 100% agree. You will never find a tire manufacturer that recommends running less air pressure than the vehicle mfgrs tire placard. In fact, Michelin, Goodyear, and others state on their website to never run less pressure than listed on the tire placard.
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Old 01-26-2017, 10:49 PM   #27
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I 100% agree. You will never find a tire manufacturer that recommends running less air pressure than the vehicle mfgrs tire placard. In fact, Michelin, Goodyear, and others state on their website to never run less pressure than listed on the tire placard.
Here we go again. Tireman9?

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Old 01-27-2017, 12:18 PM   #28
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Here we go again. Tireman9?

Ya'know, all you gotta do is prove me wrong and I'll never post about tires again.
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