Originally Posted by Old Crows
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 10°F. 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 10°F 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.