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Old 10-10-2019, 11:38 AM   #58
jadatis
Senior Member
 
Join Date: May 2013
Location: Holland ( Europe)
Posts: 178
Calculated highest pressure without bumping
Gave for 9500 lbs total weight with 10% of that on pin, for the ST 225/75R15 D-load 73 psi , not allowed, but shows upgrade to E- load is advisable.
For the E-load AT 80 psi , advice 79 psi, so allowed.

For this I lower the loadindex by 6 steps , to give tire same deflection as LT tire would have.
Also the endurance is calculated in maxload for 65mph, though they give max 87mph ( N- speedrated)

Now this is my general system.

Now there are LT225/70R15 tires with loadindex 112S, so max speed 180kmph/112mph, but calculated in maxload for 99mph.
This is only 1 LI step lower then the Endurance of /75 LI 113 and can be explained by the /70//75 difference. SO HERE GOES MY SYSTEM GONE of 1 LI step difference/ 10kmph/ 6,3mph difference in speed for wich it is calculated.

Mayby in the smaller sises / there are exeptions to the rule, as I learned in time, so the sise has been given a maxload, different from what would be calculated with the gererally used formula.

This long story means that your tires dont need the lowering loadindex system I use. Then lower pressure could be totally safe and durable.

You would notice it then by bumping, so for instance rivets popping loose, with the LRD 73psi and LRE 79 PSI.

But as long as I dont know for certain , I stay with my advice in the beginning
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