QuestionI have a 3 axle 5th wheel trailer. I am trying to decide between LT and ST tires. The loaded weight is about 15,000 on 6 wheels. I can go with E rated tires, unless the aspect of 3 axles reduces the carrying capacity of the tires. It seem to with 2 axles. Is the reduction greater with three? The max 15" tire (225 /75D 15D) is about 2800 lbs per tire. It would seem sufficient in a LT tire? Help?
AnswerRon,
An ST225/75R15 Load Range D has a load carrying capacity of 2540# at 65 psi. That means that a 3 axle trailer could have a GVW of 15,240#.
AN LT225/75R15 Load Range D has a load carrying capacity of 2205# at 65 psi.
So it appears the better choice would be the ST tire - but my sense tells me that ST tires and LT tires are constructed very similarly, so may be there is some other reason for the difference.
In both cases, if there is no speed rating listed for the tire, then the speed is limited to 65 mph - AND, in both cases, the pressure may be increased 10 psi to allow operation between 65 and 75 mph, plus both a 10 psi increase and a 10% in load carrying capacity for speeds between 75 and 85 mph.
Again my sense tells me that ST tires normally don't have speed ratings and LT tires normally do - and I'll bet that is exactly why the load carrying capacity of the LT is lower. Not to mention that carrying passengers probably has a lot to do with the more conservative loading.
But I don't see the LT listed as having Load Range E's, while the ST's do - and I would recommend you go there and use the higher pressure, especially if you are having performance problems.
