Quote:
Originally Posted by markcee
Tire size was provided in my next post (#54), prior to your reply.
I do not believe it's relevant whether or not my weight is CAT scaled or not (it was, but rounded), as my scenario is simply asking for a 'what if', my trailer weighs this much loaded and I have no idea what each axle/tire weighs. Doesn't matter if I tell you 8317 pounds or 9212....the formula to use, based on tire inflation charts, should be the same....that's what I'm trying to determine from your input.
As for tongue the weight....I am not sure what you are asking as far as 'is it part of my GVWR?'. I know what GVWR is and I know what tongue weight is and as CAT scaled I was just over 1200 lbs, based on 3 passes (with WDH active, with WDH bars off, and truck only) and my loaded trailer weight was in that 8500 lb ball park.
Excuse my snippiness, but I believe this is confusing, as the majority of experienced users simply tell you to load up, inflate to tire sidewall max PSI and don't exceed what is on the trailer placard....I'm just looking for a simplification for answering this when all that is known is the loaded weight of the trailer.
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If all you know is the trailer load on the tires (Truck scale reading) there are some things you want to consider.
If you assume incorrectly that all 4 tires carry the same load you could end up overloading one or more tires and not know it.
If you get the individual axles weighed than you can try assuming that one end is supporting 52% of the axle load from the truck scale. This may not be correct but it may prevent some overloading.
Once you plug the tire load figure into the Load/Inflation tables you can learn the MINIMUM cold inflation you should ever run.
Because of the unique Interply Shear forces trailers impart on the tires it would be to your advantage to ensure at least a +15% Reserve load with 20% being better. Do the simple math and learn how much air to put in your tires to get 115% or 120% of the measured load capacity. That inflation may be under the tire sidewall or sticker inflation number which is good. If you need more inflation than the tire sidewall or sticker number you need to run the tire sidewall number AND off load some stuff to lower your weight.
There is no simple formula to plug in the GVWR to give the needed inflation as there is more than simple static loading involved (Interply Shear)
The sticker identified the minimum inflation needed to support the GAWR assuming the weight is split side to side 50/50 which is unrealistic but that is what is done.
Actual scale weights of the load on each tire are the best way to learn how much air is needed as a minimum to support the measured load.
Since we know that over half of ALL RV's have a tire or axle in overload it is clear that most owners are not following the warning about overloading and under-inflation.
The primary reason for this is cost cutting as RVs do not come from the MFG with a 50% reserve load.. Also if there is space in the RV people fill the space with little thought on how much the stuff weighs.
8317 /4 = 2080 assume an out of balance between axle of 2% means one axle may be carrying 4323# and assuming one end of the heavier axle has 53% of that axle load then we are looking at 2292#
Your ST 225/75R15 LR-D need a minimum of 60 psi to support that load with no meaningful Reserve. If we want a 15% Reserve then 115% of 2292 = 2636# which suggests 75 psi in LR-D tires.
That's how you figure out what you need.