QuestionI have a travel trailer that has a gross wt. of 8500 lbs. The trailer has a tandem axle with tension suspension. I have heard that passenger car tires are more durable than "trailer service only" tires. If I replace the "trailer service only tires" with passenger tires that have a weight rating of 2225 lbs. would that be safe? Thank you.
AnswerEric,
No. In fact passenger car tires are less durable.
One of the problems with ST (Special Trailer) tires is that:
1) The trailer manufacturers buy on the open market, and have no direct connection to their tire supplier.
2) They, at best, choose tires that are barely adequate load and speed wise - and, at worse, provide tires that are grossly short of what is required for nearly trouble free usage.
Because of those 2 above:
3) ST tire manufacturers tend to exit the business regularly - meaning the niche would be occupied by manufacturers new to the market and don't understand the issues involved with these tires (or don't care!)
So here's what I think your should do.
Go weigh the trailer. Weigh it hitched to the tow vehicle with just about everything you can possibly think you'd ever put in it 9and the Tow vehicle. If possible, weigh it tire by tire, by if not possible, at least axle by axle.
In theory, the load on each tire ought to be less than 2125#. (BTW, you did the math wrong!)
Then some more math:
In theory, the tow vehicle ought to be handling some of the load - I've heard between 10 and 15%. This is commonly called the tongue weight. Let's use the lower value - 10%
That means the tires ought to have a minimum load carrying capacity of 1913#.
I think that there ought to be a 15% reserve load capacity - and that means the tires ought to have a minimum load carrying capacity of 2199# - let's call it 2200# - and, of course, more would be better.
The type of tire:
ST or LT type tires are designed for this type of application. But passenger car tires are not. If you want to use a passenger car tire, then you have to derate the tire by 10% - or a passenger car tire should have a minimum load carrying capacity of 2420#. That's a preety larger tire.
So let's do a comparison.
An ST205/75R15 has a load carrying capacity of 2150# at 65 psi - the load is a little short, but this will do for the comparison.
A P265/75R15 has a load carrying capacity of 2469# at 35 psi - a little more load than needed.
That's 6 sizes different!
In the process of selecting a tire for your trailer, you need to consider then rim width and the space in the fender wells.
Lot's to consider. Good Luck
