Tire upgrade air preasure ?
I recently replaced my D rated Goodyear marathons with the newer Goodyear E rated endurance tires. The older d rated tires recommended air preasure is 65lbs as listed on the factory sticker on the si...
Forum Discussion
Your old and new tires are both ST ( Special Trailer) tires.
those are calculated in their maximum load for speed of 65m/104km/h.
Can even be that they give N speedrated on sidewall, wich is max speed 140km/87m/h. But St system calculates still for 65m/h.
This gives more deflection then when maximum load would be calculated for an LT tire wich is calculated for 160km/99m/h.
Better is to calculate the ST tires as if they where LT tires, so calculate maximum load for 160km/99m/h.
I found out the system for that , wich tiremakers also use, and rule of tumb is for every 10km/6.5m/h 1 Loadindex step different.
Higher speed > lower loadindex. Lower speed > higher loadindex
Then calculate the pressure for the axleload +10% (to cover unequall loading R/L per axle). And this would give for your old ST tires already a higher pressure then 65 psi. So doing that for the new St tire with 80 psi and higher maximum load, it could end in mayby even that 80 psi.
What do I need to calculate that needed pressure for you with my made extra save calculator.
Tire data ( can be read from sidewall) search for next.
Maximum load or Loadindex.
Loadrange or pressure behind AT , wich is the referencepressure in the official formula , I once got hold of and went running with.
for your tires this is old 65 psi and new 80 psi.
Speedcode, letter J is 100km/62m/h N = 140km/87m/h or that ST is exeption to universal system , Europa works with "for trailer use only "tyres, and those are N speedrated and maxload is also calculated for that speed. American tires dont always give a speedcode .
From vehicle,
best seperate axle-end loads weighed, second best axles weighed, but as long as you did not weigh, we will have to do with the Gross axle weight ratings ( gawr) but also give G Vehicle WR ( GVWR). For a trailer if 2 axles mostly the same GAWR .
maximum speed you use and wont go over for even a minute.
About that system of lowering maxload or highening up, I made a topic a while ago on this forum.
How to compare tires for aftermarked replacement
So end conclusion , your idea of going in the middel would be good because you are going to a stiffer tire ( to hold the higher pressure in) wich has lesser surface on the ground at the same deflection, but because calculated in both cases for 65m/h you can use higher pressure with still acceptable comfort and gripp, and you micht end up needing the full 80 psi.
those are calculated in their maximum load for speed of 65m/104km/h.
Can even be that they give N speedrated on sidewall, wich is max speed 140km/87m/h. But St system calculates still for 65m/h.
This gives more deflection then when maximum load would be calculated for an LT tire wich is calculated for 160km/99m/h.
Better is to calculate the ST tires as if they where LT tires, so calculate maximum load for 160km/99m/h.
I found out the system for that , wich tiremakers also use, and rule of tumb is for every 10km/6.5m/h 1 Loadindex step different.
Higher speed > lower loadindex. Lower speed > higher loadindex
Then calculate the pressure for the axleload +10% (to cover unequall loading R/L per axle). And this would give for your old ST tires already a higher pressure then 65 psi. So doing that for the new St tire with 80 psi and higher maximum load, it could end in mayby even that 80 psi.
What do I need to calculate that needed pressure for you with my made extra save calculator.
Tire data ( can be read from sidewall) search for next.
Maximum load or Loadindex.
Loadrange or pressure behind AT , wich is the referencepressure in the official formula , I once got hold of and went running with.
for your tires this is old 65 psi and new 80 psi.
Speedcode, letter J is 100km/62m/h N = 140km/87m/h or that ST is exeption to universal system , Europa works with "for trailer use only "tyres, and those are N speedrated and maxload is also calculated for that speed. American tires dont always give a speedcode .
From vehicle,
best seperate axle-end loads weighed, second best axles weighed, but as long as you did not weigh, we will have to do with the Gross axle weight ratings ( gawr) but also give G Vehicle WR ( GVWR). For a trailer if 2 axles mostly the same GAWR .
maximum speed you use and wont go over for even a minute.
About that system of lowering maxload or highening up, I made a topic a while ago on this forum.
How to compare tires for aftermarked replacement
So end conclusion , your idea of going in the middel would be good because you are going to a stiffer tire ( to hold the higher pressure in) wich has lesser surface on the ground at the same deflection, but because calculated in both cases for 65m/h you can use higher pressure with still acceptable comfort and gripp, and you micht end up needing the full 80 psi.
