Tires: Tyre Loadings, inflation pressure, gawr

Question
Hi Barry,

We currently have some modified Landcrusiers  where the laden weight is 4,590kg (armored protection).

The tyres that are currently fitted have a load capacity of  1250kg per tyre (5000kg), max PSI 44.

Would you consider that this is too close to the maximum load weight of the tyre, if so what is a safety margin % that could be used as a rule of thumb.
Can it be considered that the manufacture builds in a safety % above the specified load rating.

Cheers and regards,

Mike.

Answer
Mike,

Yes, that is too close.

Here's the way to do this.  Start by looking at the original tire size and pressure.  That will equate to a loading (you'll need a load table for this#, then look at the original GAWR's and calculate what percent the GAWR is of the load capacity of the tire #according to the load table#.  Please note, the front and rear GAWR's are likely to be different.

Then figure out what the loading is going to be fully loaded - and using the same percentage figure out what size and inflation pressure gives you the same percent loading.  Again, the front and rear loadings will be different and the result should be similar to the original.

Alternatively, I think tires should not be loaded to more than 85% of their rated capacity when the vehicle is fully loaded.

If you need more help from me, I'll need to know what the original tire size and pressure were #on the placard) and the GAWR's as well as the new fully loaded loading on the tires.