This topic is split of from this one
http://www.keystonerv.org/forums/showthread.php?t=15172
for reasons that I was hyjacking that topic to much, and I promesed to make my own topic for how to compare tires for replacement and how to handle the tire-pressure advice.
Made ducument about it in word first and placed it as reaction here , so you have to scroll reaction #12 to find it.
under here the first split off reaction .
Because the maximum load was not clear of both old and final new tires I did some googling.
The old Maxis are STR ( think Special Trailer RADIAL)
found them on amazon with speedcode R ( up to 170km/94m/h) so made a remark to them because this does not stroke with ST wich is always max speed normal of 65m/104km/h, but allowed 75m/120km/h when 75psi used . for that 65m/h the maximum load is calculated.
of loadindex 113 wich stands for 1150kg/2535lbs.
Must be on the sidewall somewhere as loadindex or "maximum load 2535lbs AT 65 PSI ( cold)" also see if you can find a speedcode letter like that R they mention on the page of amazon.
The final new Bigfoot LT 225/75R16 LRE ( loadrange E= maxloadpressure 80 psi. found them at bigotires here
http://www.bigotires.com/Tire-Detail...FOOT-H-T/12602
with Loadindex 115 = maximum load 2680lbs/1215kg AT 80 psi( cold) with speedcode N = max speed of tire 140km/87m/h .
This difference in speed for wich the maximum load is calculated makes the difference small between the tires , tough the bigfoot is larger and has higher maxloadpressure.
You did not have troubles with the maxis and probably used 65 psi for them.I think 2 years is a short livetime so am not surprised that you did not have any troubles with them. Better would have been if you had treated the Maxis as an LT tire and then even for dual load for tandem-axle.
this gives 81 psi as advice wich is not allowed by TRA ( 10 psi extra is for LT and ST tires) so if you would have put them to 75 psi from the beginning , the tipical wear probably would not have happened and you probably made a longer livetime with them or more miles.
The bigfoot with 115 li are for 140km/87m/h calculated in their maximum load.
In Europe this is the maximum speed for "for trailer use only"tyres, and mostly have 2 loadindex higher then an C(omercial) tire ( Eur LT) with max speed of 160km/99m/h So the lower the speed the more maximum load .
And this is because at lower speed more deflection is allowed .
When I fill this in in my Traveltrailer calculator and use the dual load maximum load wich is 7.5% lower then single so mostly 2 LI lower + 2 LI lower for 160km/h it comes to a LI( loadindex) of 111 wich stands for 1090kg/2403lbs, it gives as answer 84 psi . So that is even as high as is allowed, with still acceptable comfort and gripp. Then my spreadsheet even gives warning of poor reserve of the tires and because of that maximum speed of 60m/h.
But with this speed all the reserves count of 1000lbs weightdifference R/L before discomfort or tire damage begins at high speed of 160km/99m/h.
Seems a bit high but used this for the bumping border . For lower speed damage begins later, so this weight difference gets more before damage begins.
End conclusion, this long story was needed to advice you a pressure that gives your new tires a longer life more miles . Probably even 6 years and 40000 miles or more.
Mind thoug that the valves must stand the 84 psi too. This is sertainly with metal valves but the HP TR 600 series snap in rubber valves are allowed a cold pressure of 6.3 bar/95psi cold.
Here a picture for the bigfoot with the reduction for speed and dual load used , so 4 LI lower then given on the page.
Mayby the difference between the maximum loads is courced by the other speeds that are used by the tire-specialist, mayby they have a list for that how far they can go. ST has 15% more maximum load then LT , I once calculated of 2 same sises ST and LT. Mayby they used that system to calculate more maximum load for the bigfoot for speed of 65m/h instead of 87m/h.
In Holland where I live cars with trailers behind them are allowed 90km/56m/h and it has chanched recently, before that is was the same as for Trucks 50m/h. So the 60m/H I gave as max adviced speed is enaugh, you probably dont drive faster.
Here the picture, and sorry it has gotten a too long story .
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