FAB54, we've now settled on which tires have been giving you problems, namely 165/80R13 car tires. First of all, if you did in fact still have B78/13 on your trailer before the original problems with Sears in Canada, they were way too old to still run safely. Trailer tires should be replaced every 4 years, at most 5 years regardless of how good they look or how much tread they still have on them. Tires contain natural oils that work to the surface as they are rolling and help keep them pliable. Tires that sit a lot age faster because these oils don't have an opportunity to work to the surface and they also have constant UV exposure if they are not covered up. Trailer tires aren't unique--car tires age just as fast if they sit around as much. Tires should be treated every 4 weeks or so with a protectant like 303 that does not contain petroleum distillates. Typical tire dressing should not be used as all it does is make the tire look wet and black and the petroleum distillates in them draw the natural preserving oils to the surface and actually age the tire faster.
Here's a quote from a fairly recent thread on tire failure and a link to the whole thread:
Originally Posted by henryj
Thanks for sharing your experience Don--glad the only pain was in your wallet, but sure not a nice way to start a holiday. Others' experiences like this add to our collective knowledge that makes it worthwhile belonging to a group like this.
When a tt tire looks like shredded spaghetti it's hard to tell what the original cause of failure was. It could have been a simple puncture and miles of driving that totally shredded the tire. The tandem axles completely mask this gradual failure, or a blowout too, unless we hear it go. I have no idea how far one has to drive to shred a tire, but they have no strength without air in them. Any manufacturers' tt tire will appear to have had a catastrophic failure after a couple of miles at 65 mph.
While the tandem axles hide a tire failure from us they have another equally serious effect. In a gradual or sudden failure the full weight of that side is picked up by the partner tire. Tt tires don't have any reserve singly, but they are adequate in pairs. My axle weight is just under 5000 lb. with 1000 lb. on the tongue. So each ST205 is carrying 1250 lb., well under its rated load of 1820. If one of my tires fails, the other is immediately carrying 2500 lb. and is seriously overloaded. If my trailer is at it's 7000 lb. maximum with 1000 lb. tw, the surviving tire is dangerously overloaded at 3000 lb. This is LT245 territory and that's at 80 psi. Imagine the sidewall flex and heat buildup in our ST205 at only 50 psi.
So we now have one shredded tire and one that looks perfectly normal and we buy one new one. A couple of trips later the stressed out partner tire fails, we don't notice right away and similarly toast the brand new tire we just bought. I'd hate to do it too, but believe the only solution is to always replace both tires... and if they're 4 yr old Missions I'd bite the bullet and replace all 4.
Although Mission tires do make me uneasy, there's one other thing to keep in mind. Sunline used Mission tires, most of us with newer trailers have them, many are 4 yr old now, and so when they fail we're going to hear about it. If you check around the Internet there are also folks plenty unhappy with Goodyear and Carlisle--apparently both made in China now too. I installed a TPMS for added security, but have never checked the tires as often and as closely as I should except when greasing bearings.
The point here is, if you have had a rash of tire failures, you need to replace all 4 at the same time. One reason this forum is so helpful for all of us--and I've learned an amazing amount since joining--is that we all need to be informed consumers and know what is needed rather than relying on sometimes poorly trained sales people with no RV experience. In other words, if people have been selling you 165/80R13 car tires one or two at a time, they simply didn't know any better.
I would avoid the big box stores when buying tires, and that includes Sears, which I believe is no longer even in the tire business in Canada. Any mechanic with whom you have a good relationship can get you any tire you want through his wholesale connections and probably has enough experience to advise you too. I think national tire chains are good too as they are most likely franchise owners with some years of experience. I don't mind if the kid flipping my burger has fuzz on his face, but I won't buy a tire from him
If you know exactly what you want and have a place to get tires mounted, tirerack.com is also a good supplier. I've never bought from them as shipping to Canada is a huge cost, but my brother in IL has not bought tires anywhere else for years and I know some here on SOC also use tirerack.
Finally as to which tire to get. You're on you're own when it comes to brand--read the whole thread linked above--but I would get ST185/80R13C as listed here:
This gives you the extra capacity Steve was talking about too and it's a minimal extra cost. Double check the width of your rims, but they are almost certainly the 4.5" specified.