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Recommended 225/75R15 Size Tires for an 18K GVWR 5th Wheel Trailer


I bought a used toy hauler fifth wheel several years ago 38’, 18,000# GVWR, triaxle and let it rot in the FL sunshine. On my only highway trip I blew out a rear tire on the heaviest side. I’ve decided I need to replace all 7 tires spare due to dry rot and age RV is 11 years old, I don’t know about tires. It came to me with load Es on front and rear axles and load Ds on the center axle. They were all inflated to max pressure by the dealer. They are 225/75R15 Radial Trailer Tires. My questions are many, and I thank you in advance: 1 With 6 D-rated tires the factory tires, is that enough cushion to handle rough roads like ruined midwestern freeways? 2 Should I upgrade to all load Es for extra safety? Or am I sacrificing too much ride quality and therefore abusing my rig or its contents? 3 Is it possible that the axles or some other consideration decided the mismatched load ranges that I received? 4 Did inflating the front and rear axles to 80 lbs and the centers to 65 lbs lead to the tire failure? If I have mismatched tires should they all be inflated to max or to match each other? I need tires that can handle legal highway speeds with the trailer close to the max weight of 18,000 lbs., in all weather and road conditions including mountains and typical Michigan highway lack of maintenance. If seasons matter, I may be driving in the mountains in below freezing temperatures. Thank you very much for your assistance. You guys are the best!


Helpful Expert Reply:

Great questions!

To make it easier to read I will address your questions in the same type of format.

1) Trailer tires are built with a sidewall that is more stiff than passenger tires so any cushion is basically related to the suspension. When it comes to the load ratings on trailer tires you simply want to make sure that tires are rated for at least the weight rating of the axle they are installed on.

2) If load range D tires meet or exceed the weight rating of your axles then there is no need to upgrade to load range E tires, however, it wouldn't hurt anything and the tires wouldn't have to work as hard.

3) There is no reason why you should have had different load ranges on your different axles. Ideally you want to use the exact same tire for all of your axles. Either they didn't know any better or they didn't care.

4) This is the one thing the dealer got right. You ALWAYS want to have your tires filled to the cold psi rating on the sidewall. The tire manufacturers tested the tires to carry that load rating at the psi so if they are filled to something else you never know what the weight rating is. In all honesty if you didn't store your 5th wheel trailer correctly that is most likely what contributed the most to the tire failure. Let me know if you don't know much about storage and I can elaborate on that.

For your application I recommend going with the Karrier ST225/75R15 Radial Trailer Tire # AM10303. This has a load range E (2,830 lbs at 80 psi) which gives you a combined rating of 5,660 lbs for 2 tires. This will be more than enough for your axles.

This tire also has a speed rating of 81 mph which allows you to travel highway speeds without the fear of the tires overheating.

We do offer tire monitoring systems like the Tuson Towable Tire Pressure Monitoring System # TST-507-RV-6-C that really help you keep an eye on what is going on with your tires. I have attached a review video on this system as well as a link to an article about tires that you can check out.

helpful expert reply by:
Jon G

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