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Old 09-28-2016, 05:03 AM   #11
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Join Date: Feb 2013
Posts: 134
Originally Posted by Dog Show Gal View Post
Jadatas, I looked all over the tires and see nothing about speed codes. I only saw a max load of 2680 at 550 kpa.
Thats already half of the information, and again, the speedcode is not that important, so for tires info I have enaugh, but if you can give the sises I can google them . For most larger LT tires with E-loadrange in America , maximum load is calculated up to 140km/86m/h wich is N speedcode

As long as you did not weigh , we will have to go from GAWR's and GVWR,
These mostly can be found on the same plate as the pressure advices.
So look again at that doorsticker , mayby the GA/V WR are there too.

2680 lbs maximum load is loadindex 115, but not important, because the maximum load is what counts.
Because 2 tires on rear axle your GAWR rear can maximaly be 2x2680=5360 lbs , so carmaker would advice 80 psi for that.

Front is mostly lower GAWR so can do with lower pressure. And front GAWR is mostly not totally used , even when GVWR is totally used.
My selfdetermined rule for smaller motorhomes is that weight in use on front axle is GWVR-GAWR rear, allows a lower pressure then the car maker gives , because they calculate for GAWR. In case of frontwheel-drive this lower pressure is better for gripp ( in Europe 9 out of 10 motorhomes are of your sise and have frontwheel-drive, example the Fiat Ducato 14 frame ( nephews Citroen and Renault).
But in America this is probably different.

But then they assume the weight to be devided R/L 50/50%, and thats never the case for motorhomes, A weight division of 48/52 is more likely and 45/55 is also weighed sometimes .
The pressure must be enaugh for that tire with 52% ( or 55%) and the other tire on the axle then uses 48/52=92.3% of the loadcapacity that belongs to the calculated pressure, because standard rule is to fill all the tires on one axle to same pressure.
I once determined by reactions about weight and bumping, that below a Loadpercentage ( as I babtised the 92.3% in the example)of 85% discomfort begins by bumping and gripp gets inacaptible, but verry discussable.
45/55%=81,8% so if realy that loaddivision, a little discomfort, but savety first , because tire damage is worse.
Then try to shift some weight.

So best is to weigh per tire/wheel, if its possible.
The way to do that at a normal schale is described on the internet many times.
But in short, drive up to schale with only front axle and weigh, then drive totally on scale to get total vehicle weight, and substact front axle from that to get rear axle, or drive further, so front axle is yust off the schale to weigh the rear axle.
Then repeat the procedure driving with only one side on the schale , depends on if you have space besides the schale to drive over, then substract those values from the axleweights to get the other sideweight.
The road besides the schale must be about on the same hight , otherwise the gravity point shifts sideward to the lower wheel, to much and gives other weights.

Then 9 out of 10 times you weigh crossed weight-differences R/L.
For instance front R52%/L48% and rear R49%/L51%
there are even forms on the internet to fill in and do the calculation.

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