Tire pressure

[DrDaveMA]

TS192, at the FMCA rallies there is a company that weighs all 4 corners, in fact they will do 6 and up to 10 (toad and tag wheels). You missed the rally in Perry, GA last month, it will be there again in 2 years. If you do not want to wait that long check out the FMCA rally in Springfield, MA August 3-6. There are also the Good Sam and IRV2 rallies, so there are lots of places to get the weights done.

[69Stang]

Originally Posted by Smitty77

But IMO, this could be dangerous for some coach owners. Read the post that follows yours, with actual weights, and do the math on the 5% / 2 on the front axles. You will find that the weight is below the 'actual' weight of one of the tires. Yes, the extra 5 PSI may have covered this, and brought it to the 'minimum' PSI for the weight. But then there is not contingency PSI in the tires.

Smitty

You lost me on that bolded line. Can you clarify please?

So I guess I'm good since no one hollered at me and called me dummy

[TS192]

I think what he is saying is using that particular equation the PSI in the heavy tire or tires (setting pressure to the heaviest "axel end" for the whole axel) the minimum pressure for that load was not reached. Good point Smitty77. I may add an extra 5 psi to my tires and try them. That hopefully would cover this problem should it exist and shouldn't make much if any difference in the handling. Good stuff irv2. Cheers

[TS192]

ADDENDUM
That is for the heavy end.

[jadatis]

Originally Posted by 69Stang

I did a 4 corner the other day and came up with this:

LF 2780 RF 3080 Front axle GAWR 5,500

LR 5300 RR 5460 Rear axle GAWR 11,000

Total 16620. Freshwater and fuel tank full, black and grey empty. That's 120 lbs overweight. I'll travel with 1/4 tank freshwater (about 500 lbs less than full) and I moved some weight from RF to LF to make them more equal.

I'm going to run 80 PSI in my Cooper 225/70R 19.5 G rated tires. Fed Cert tag calls for 65 PSI in F rated tires.

Sound right?

Will fill it in my calculator in wich I even add 10% to the axle weight in part 2 .
When having 4 point weighing like you have, I use part 3 in wich i make highest weight on axle side 95% of the weight I calculate the pressure for.
Lowest weight 85% of weight to calculate the pressure for.
Will do it tomorrow , only answered now, to follow this topic, and I can find it back.

[jadatis]

Originally Posted by jadatis

Will fill it in my calculator in wich I even add 10% to the axle weight in part 2 .
When having 4 point weighing like you have, I use part 3 in wich i make highest weight on axle side 95% of the weight I calculate the pressure for.
Lowest weight 85% of weight to calculate the pressure for.
Will do it tomorrow , only answered now, to follow this topic, and I can find it back.

OK did it , yesterdays was sleeping time here in Holland.
Here the picture wich says that only 1 psi higher needed when using part 3 for 4 poit weighing and keeping it between 85% and 95% load%.
Front overloaded by 360 lbs =7% so if you can shift something to behind, it would be better for law.
And here as exeption to the rule , on both axles Right side more heavy.
9 out of ten its crossed between the axles.

If you look in part 2 wich gives 1 psi lower advice for both, still Front 575 lbs weightdifference possibel before damage begins at heavyest wheel on axle.
The real weightdifference is 300 lbs so still within the limits.
Rear same story so both ways calculated my system is save for the tires.

Lets see what system of TS192 comes down to.
He adds 5% instead of 10 % but ads 5 psi at the end ,
So I filled in in part 2 5% reserve added and gave 4 psi lower , added 5psi gives 1 psi higher wich is yust what my system gives in part 3, so by accident his system would give save answer in this case.
But then the pressure is calculated with my extra save formula , if you look those determinded loads back in a pressure/loadcapacity list of American make you would get lower pressure .

[69Stang]

Thanks jadatis! I did move some things from right to left. I also drained the freshwater down to 1/4 and took some things out of the MH. I'm guessing I lost 600 lbs. by doing that. I'd like to weigh again, but I leave tomorrow. I'm going to try and get another good 4 corner weight when I get back since I made those changes.

[jadatis]

In my calculation I first googled the tires and found them to be L speedrated for that maximum load. this is max speed of 75m/h.
Your maximum speed is probably not higher then 65m/h and for that a bit more deflection is allowed before tires overheat. For 110km/68m/h you can add 1 li step. Gives for LI F 129 and LI R 127 , F 87 psi and R 84 psi.
this must be seen as minimum real pressure measured with a device that is 101% acurate, wich is never possible

To find the highest pressure at wich comfort and gripp is still acceptable, you can assume a deflection of the tire meanth for 160km/99m/h and for that you should lower the maximum load for single load by 4 steps so would become 128-4=124 for rear and front.
That filled in gives F 101 psi and R 93 psi , so you can go as that for maximum reserve, with still acceptable gripp and comfort.
Idea is to try to keep the pressure at this value , so if device is off a little , you still are save for the tires.
And this only counts for the weights you gave, reweighing would give another answer.