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Old 08-26-2015, 12:35 PM   #1
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Navion tire pressure

I have a 2007 Itasca Navion 23H. What tire pressure does everyone run? It seems to be all over the board. The sticker in the cab recommends 57 front and 58 rear. The people that installed the tires said it should be 65 front and 80 rear. I admit it seems to ride a bit better but am going on a long trip and don't want to blow a tire or ??? Should you go with the RV manufacturers recommendation or the tire manufacturers? Please advise.

Thanks,
Doug
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Old 08-26-2015, 01:20 PM   #2
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First, are tires you put on the same size and load rating as the ones recommended on the coach sticker?
Second, Is the pressures recommended by the installer at or near the max tire inflation pressure stamped on the side of the tires?
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Old 08-26-2015, 02:24 PM   #3
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tire pressure

The tires are the same size that was on it when I bought it, 4 years ago (225 75R 16). 65 is the max for single axle and 80 is the max for the duals. This is what the installer inflated them to.
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Old 08-26-2015, 03:01 PM   #4
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Sigh! It's a Sprinter with 225/75R/16E tires??? Just use the inflation recommendation on the door sill. Mother Benz and Great Father Winnebego have sorted out the TPs for you..... just use the recommendation if you are near or at the Gross Vehicle Weight Rating. More pressure is NOT better.

Again, the door sill recommendation is for Max Gross Vehicle Weight.. I'm guessing about 11,030 lbs. Are you near that? Lets not hope OVER the GVWR.

That being said.... if you are under the GVWR, you may be able to tweek down the pressure a couple three lbs and still be OK.

Recall that TPs are measured and adjusted cold.... Let's say 50F. As you drive the tires warm up... you gain 1 lb for every 10F increase in temperature. So... if you are max pressure by placard for GVWR @ 57PSI COLD you will be 60PSI when the temp is 80F. Going farther..... the max inflation pressure on my Vanco FourSeasons is 80PSI cold. Using the same example... inflated 80 PSI COLD ... at 80F I'd be at 83PSI once the tire warmed up. That is OVER the max tire pressure recommendation. Not good!

So.... go weigh your RV.... nothing fancy just get your gross weight all up ... ready to go camping. Just so you know what you weigh..... set your pressures to the placard if you are at the GVWR. You might tweek down a LB or two if you are slightly less....
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Old 08-27-2015, 03:02 PM   #5
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Originally Posted by Old Crows View Post
Sigh! It's a Sprinter with 225/75R/16E tires??? Just use the inflation recommendation on the door sill. Mother Benz and Great Father Winnebego have sorted out the TPs for you..... just use the recommendation if you are near or at the Gross Vehicle Weight Rating. More pressure is NOT better.

Again, the door sill recommendation is for Max Gross Vehicle Weight.. I'm guessing about 11,030 lbs. Are you near that? Lets not hope OVER the GVWR.

That being said.... if you are under the GVWR, you may be able to tweek down the pressure a couple three lbs and still be OK.

Recall that TPs are measured and adjusted cold.... Let's say 50F. As you drive the tires warm up... you gain 1 lb for every 10F increase in temperature. So... if you are max pressure by placard for GVWR @ 57PSI COLD you will be 60PSI when the temp is 80F. Going farther..... the max inflation pressure on my Vanco FourSeasons is 80PSI cold. Using the same example... inflated 80 PSI COLD ... at 80F I'd be at 83PSI once the tire warmed up. That is OVER the max tire pressure recommendation. Not good!

So.... go weigh your RV.... nothing fancy just get your gross weight all up ... ready to go camping. Just so you know what you weigh..... set your pressures to the placard if you are at the GVWR. You might tweek down a LB or two if you are slightly less....
Almost got it. The pressure increase is 2% per 10F. The 1 psi figure works for passenger cars that use 35 psi but not RVs at 60 to 100.

"Max Pressure" can be confusing. If you read the tire sidewall it is actually telling you the cold inflation pressure needed to carry the stated Maximum load. Some tires have the word "cold" some have "max" and some just say inflation but in each case they are referring to the minimum pressure needed to carry the stated "maximum" load.

NEVER adjust your inflation when the tire is hot. Cold Inflation Pressure is set when the tire is at ambient temperature. This means not driven more than a couple miles in the previous two hours and not in direct sunlight for the previous two hours.
Yes tire pressure will increase as the tire warms up (remember that 2% per 10F) We tire engineers know this and the tires are designed accordingly. It is NOT a "bad thing" to have the tire increase above CIP when the tire warms. DO NOT bleed down the hot pressure.

I covered this in my blog (see my profile) on March 12 2015 in the post "Minimum or Maximum inflation or Load...I'm confused"

I see nothing wrong with running at the Placard inflation pressure. Hopefully you will confirm that neither axle is over the GAWR. Having a margin is good. Few people realize that one reason cars don't have the same % of tire problems as RVs do is because they have margin in the 14 to 20% not in the 0.5% to 3% range as many RVs do .

I covered this topic March 12 in my blog post "Minimum or Maximum inflation or Load...I'm confused". Link in my signature.
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Old 08-27-2015, 04:36 PM   #6
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Tireman, Thanks for the correction and explanation. Pass. tires 1psi/10F; RV 2%/10F. ( What category is a light truck LT tire in????)

I keep it simple. Just use the placard. Drop a lb or three if I'm under the GVWR. While not perfect.... simple works.

Now, maybe some more education if you have time..... much ink has been spilled over getting individual wheel weights and finessing the pressures for unequal weight distribution among the different wheels. I suppose..... in the perfect world.... that's the right thing to do. In the real world, that's a pretty tall order for the average/below average RVer. Most folks have no idea what their RV actually weighs anyway. Most folks have trouble just keeping air in their tires; weights below GVWR, and speeds in the sane range. So, I'm an advocate of 'simple.'

So, I'm thinking that given the average RV.... there's always going to be some asymmetrical weight distribution. Weight distribution changes daily if you are using it due to fuel use, water use, waste tank levels, food use.... a dozen things. So what you set up today very precisely is going to be wacko a couple miles or days down the road. And, that RV weight may change over time as mods and upgrades are made over the life of the vehicle.

While no one builds a perfectly balanced RV, it's likely almost all made today are pretty close to having equal weight distribution side to side. And if they don't its no big deal for the average guy... unless it is orders of magnitude out of whack. Seems like for the average guy, setting up air pressures for asymmetrical loads is probably looking a little OCD. And they are more likely to default to checking that the assure that the beer cooler is full and working.

I'd rather see someone be consistently in the ball park on placard settings for every trip rather than fussing around with tailored pressures.

So what's your experience? Is asymmetry really worth worrying about or just extra details ?

Second question..... is there any data to support the idea that tailoring TPs to asymmetrical loads improves tire wear, longevity, safety?
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Old 08-28-2015, 02:15 PM   #7
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Originally Posted by Old Crows View Post
Tireman, Thanks for the correction and explanation. Pass. tires 1psi/10F; RV 2%/10F. ( What category is a light truck LT tire in????)

I keep it simple. Just use the placard. Drop a lb or three if I'm under the GVWR. While not perfect.... simple works.

Now, maybe some more education if you have time..... much ink has been spilled over getting individual wheel weights and finessing the pressures for unequal weight distribution among the different wheels. I suppose..... in the perfect world.... that's the right thing to do. In the real world, that's a pretty tall order for the average/below average RVer. Most folks have no idea what their RV actually weighs anyway. Most folks have trouble just keeping air in their tires; weights below GVWR, and speeds in the sane range. So, I'm an advocate of 'simple.'

So, I'm thinking that given the average RV.... there's always going to be some asymmetrical weight distribution. Weight distribution changes daily if you are using it due to fuel use, water use, waste tank levels, food use.... a dozen things. So what you set up today very precisely is going to be wacko a couple miles or days down the road. And, that RV weight may change over time as mods and upgrades are made over the life of the vehicle.

While no one builds a perfectly balanced RV, it's likely almost all made today are pretty close to having equal weight distribution side to side. And if they don't its no big deal for the average guy... unless it is orders of magnitude out of whack. Seems like for the average guy, setting up air pressures for asymmetrical loads is probably looking a little OCD. And they are more likely to default to checking that the assure that the beer cooler is full and working.

I'd rather see someone be consistently in the ball park on placard settings for every trip rather than fussing around with tailored pressures.

So what's your experience? Is asymmetry really worth worrying about or just extra details ?

Second question..... is there any data to support the idea that tailoring TPs to asymmetrical loads improves tire wear, longevity, safety?
I did the math in detail in my Blog post of Mar 3 2014. The formula gives 1.89% change for each change in temperature of 10F. This based on a "perfect" gas. Realistically the tire as a container is not "perfect" and the gas isn't absolutely 100% of a specific element.
The results in a "Rule of Thumb" of 2% for 10F which works for all types of tires.

RE weight imbalance. The objective is to ensure tires are not under-inflated which can damage the tire. Over-inflation by a few psi is not a problem and isn't going to damage a tire as quickly as under-rinflation.

Now there is a small % of RVs that have side to side loading on an axle of 50/50 but as with any distribution there are some that may be off as much as 40/60 or worse. Most seem to fall near the 48/52 to 45/55 range which is why I suggest that without knowing your actual side to side loading it is better (more conservative) to assume you are out of balance than to assume you are in balance.
If you take the axle load number that is easy to get at any CAT scale at a truck stop and assume one side has 53 to 55% of the load then you have a reasonable chance of being correct. So use the % you are comfortable with when calculating the probable load on the heavier end when consulting the Load inflation tables for your motorhome.

Yes things vary but if you apply the suggested margins when doing the calculations and ensure the tires always have more than the minimum inflation needed to carry the load you have probably eliminated 70 to 90 % of the tire failures that occur.

The reality is that the majority of RV owners have one or more tires or axles in overload. This fact is based on over 30,000 data points, This why at a minimum every RV owner should get their unit on a scale at least once.

If you review the posts on my blog about weight and inflation you will see detailed examples of how to do the calculations.

Now if someone chooses to guess on their actual weight then decides not to bother to inflate the tires to either the numbers in the published tables or even the numbers on the sticker on the RV and then uses a pressure gauge that has never been checked against a new digital gauge and only checks the air once a year because they don't think a TPMS is worth the money, I see no reason to feel sorry for them when they have a tire failure.

You know the saying that you can lead a horse to water but can't make them drink. I feel its the same with tires. I can provide the information, calculations and warnings in my blog but if people choose to ignore the fact based information and go with the "old wives tales" then all I would ask is that they don't come onto a forum and complain about tire failures.
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