Confusion about 255/45/ZR18 tires on a BoatMate Trailer

[crispywake]

I've got a 2010 21' Malibu Ride with a BoatMate dual axle trailer.  The tires on the trailer are pretty old and seeing some dry rot, so I was looking to replace them.  I called my local tire shop (large chain) and asked for replacement tires, giving them the size of the current tires and they were very confused, saying there are no trailer tires that size.  The current tires are 255/45 ZR18 103Y Extra Load NEXEN N3000 tires, and the wheels to my knowledge have never been replaced.  Is this a proper setup for this trailer?  Can I replace the tires with any 255/45/18 XL tire?  I used to tow every weekend on this setup for years and never had any issues, but now the boat is kept on the water and the trailer is only used about once a year (if even) so looking to replace as cheaply as possible but making sure I have a safe setup.  Boat dry weight is 3,500 lbs.  Thanks in advance.

 

[Nick55]

Yeah, those are SUV tires.  Seems that’s what are put on 18” rims when you get them.  If they started questioning you about the fitment, you can ask for tires that fit a 2013 Toyota Tacoma X-runner, and unless you aren’t handy, you can drop the wheels off instead of taking the trailer in (I had to do that on my last boat trailer….). I checked around, there are lots of XL load rated tires available in that size, usually around $200 each.  You may be able to price check/shop around too if it’s a big name tire store. I did that at Discount Tire for both my trailers and my truck tires.  

[Cole2001]

I would see if you could fit 255/55/18. That is what all of the newer trailers come with. Gets you a little extra payload and sidewall. 

[crispywake]

Thanks for the feedback.  My main concern was just making sure this was safe and I didn't somehow end up with some whacky unsafe setup.  It seems like this is somewhat common practice to use car/truck tires and not specifically trailer tires.  I was looking at getting these -- https://www.discounttire.com/buy-tires/falken-ziex-ze960-a-s/p/44992.  They're the cheapest 255/45/18 XL tires I could find at $162, but will see if I can fit 255/55/18s too. 

The load index is 103, which is 1,929 lbs per tire, multiply by 4 tires = 7,716 lbs.  Dry weight of boat is 3,500 lbs, so if my understanding of this and my maths are correct I should be able to stack 2 of my boats on top of each other and have weight to spare.  I feel comfortable with that (not stacking 2 boats and towing... but the safety factor on the weight ).  So unless I'm missing something about using car/truck tires (people on the internet of course have drastically varying opinions on this after searching), and seeing this appears to be common even directly from manufacturers (?), I'll roll with it.    

@Nick55 Did you have to take the wheels in because Discount Tire refused to fit these tires directly on your trailer?  They did seem really confused and skeptical and said they would have to look at the trailer and check out the situation.

 

[Nick55]

They were very skeptical.  And honestly, I didn’t really want to leave my boat and trailer at the shop for anyone to hook up to while it was there.  So that made the whole decision process easier for me.  
 

I will also add, don’t shop on price alone, look at treadwear ratings (not the warranty) but the AA, A,B ratings too for treadwear, temp, etc. 

[crispywake]

7 minutes ago, Nick55 said:

They were very skeptical.  And honestly, I didn’t really want to leave my boat and trailer at the shop for anyone to hook up to while it was there.  So that made the whole decision process easier for me.  
 

I will also add, don’t shop on price alone, look at treadwear ratings (not the warranty) but the AA, A,B ratings too for treadwear, temp, etc. 

Makes sense, I'm a little less worried because the boat isn't on the trailer and it sounded like they'd just do the work while I waited.  Honestly I will probably only tow on this trailer maybe 1 or 2 more times before I'm ready for an upgrade, so as long as it's safe to pass along to someone else, I'm not too worried about the longevity of the tires.  Right now I think they're too dry rotted to tow on or pass along to someone else without feeling sketchy about it.