Where to find factory original tire size

[bhayden]

We have a 1978 Argosy 24. It's hard to what previous owners have done regarding replacing tires. Where can I find what size tire was fitted at the factory?

[bhayden]

... in my owners manual of course According to it the 24, 27 and 30 foot tandem axle Argosys in 1978 used 7.00x15 Load Range C tires and the recommended inflation pressure was 40psi. Sounds about right for my 24 foot trailer traveling light but a tad on the low side for a 30 footer running near max GVWR.

FYI, for the single axle Six Metre Minuet the factory spec'd tires were 7.75x15 Load Range C at 35 psi.

I'm not exactly sure how to covert the old sizes into modern day aspect ratio. The choice is a 205/75R15 with an 8" section width and 27.1" dia or a 225/75R15 with a section width of 8.8" and 28.3" dia. If the aspect ratio of the original equipment tire was 1:1 diameter would be 29". If it was the more "modern" 78 aspect ration that brings the diameter down to more like 26". From what I could dig up on the web tires ending in .00 had an average aspect ration of ~92 so that would be 27.88" dia.

I'm leaning toward the 225/75R15 for a little more ground clearance (important for where I'll be driving). It should also allow me to run a lower pressure and keep a good safety margin on the load range.

[overlander63]

Hi. A quick forum search on "tire sizes" will net you many hours' reading material, but the short answer is: 7.00x15C was OEM tire size for your coach.
If you want to go radial ST225 75R15 is the closest metric equivalent. You can go with the D rated tires, but you should keep the lower inflation pressure, which should be 50PSI.

[AndyPenny]

On a '76 Argosy 24ft., would 10-ply ("E" Rated) 225/75-15s be overkill? If so, what is the downside?

[Inland RV Center, In]

Originally Posted by AndyPenny

On a '76 Argosy 24ft., would 10-ply ("E" Rated) 225/75-15s be overkill? If so, what is the downside?

To use 10 ply tires, at any pressure, would be the same as using solid tires.

You should never exceed 8 ply tires, and even at that, keep the air pressure down to 45 to 50 psi.

Additionally, if your wheels have been in use for a long time using 6 ply tires, then if you want to change to 8 ply tires, you must replace the wheels, if they are steel. If not, the wheels will split.

When you "overkill" the tires, load eqaulizing hitch rating, and the tow vehicle suspension, you immediatel you will start to punish the trailer shell and frame, followed by other strange damages, such as to the furniture and appliances.

Airstream and Argosy trailers were designed to have a soft ride. If that ride becomes harsh, which also includes over rated or bad axles, then many damages to the trailer will take place.

Andy

[OregonArgy]

Originally Posted by bhayden

FYI, for the single axle Six Metre Minuet the factory spec'd tires were 7.75x15 Load Range C at 35 psi.

I'm not exactly sure how to covert the old sizes into modern day aspect ratio. The choice is a 205/75R15 with an 8" section width and 27.1" dia or a 225/75R15 with a section width of 8.8" and 28.3" dia. If the aspect ratio of the original equipment tire was 1:1 diameter would be 29". If it was the more "modern" 78 aspect ration that brings the diameter down to more like 26". From what I could dig up on the web tires ending in .00 had an average aspect ration of ~92 so that would be 27.88" dia.

This kind of stuff just makes my eyes bleed. It is funny how I can figure out so many things on this "vintage" trailer from plumbing to appliances to rotten floors, but the simple rubber round things it runs on is a mystery to me. It's funny that we can't just go buy tires.

I'm replacing tires on my 6-metre Minuet this week. Should I just let them go for it and put on tires that match those numbers you wrote about above? They were going to repack the bearings. Is this okay? Will the trailer brakes pose a problem for them?

I'm using a very reputable tire company here in the northwest, Les Schwab. He seemed to know exactly what my trailer needed when I read him the numbers from my tire's sidewall. Is there anything I should be concerned about?

[overlander63]

Originally Posted by OregonArgy

This kind of stuff just makes my eyes bleed. It is funny how I can figure out so many things on this "vintage" trailer from plumbing to appliances to rotten floors, but the simple rubber round things it runs on is a mystery to me. It's funny that we can't just go buy tires.

I'm replacing tires on my 6-metre Minuet this week. Should I just let them go for it and put on tires that match those numbers you wrote about above? They were going to repack the bearings. Is this okay? Will the trailer brakes pose a problem for them?

I'm using a very reputable tire company here in the northwest, Les Schwab. He seemed to know exactly what my trailer needed when I read him the numbers from my tire's sidewall. Is there anything I should be concerned about?

Without going into (again) the pros and cons, just get a set of ST225 75R15 tires, brand of your choice, and load rating that comes closest to what is in your owner's manual. Obviously, cheaper is not always better, but that should be your decision.

[OregonArgy]

Thanks, 63. Did you have any thoughts about repacking bearings or if the trailer brakes will get in the way. I'm guessing that every trailer my sizr or bigger has brakes. They wouldn't be surprised by that.

So ST225 75R15 (Load rating C) is where it's at. Thanks, again.

[overlander63]

Originally Posted by OregonArgy

Thanks, 63. Did you have any thoughts about repacking bearings or if the trailer brakes will get in the way. I'm guessing that every trailer my sizr or bigger has brakes. They wouldn't be surprised by that.

So ST225 75R15 (Load rating C) is where it's at. Thanks, again.

Your trailer came with brakes on all wheels (except the spare--duh). Many Argosy trailers had 10" brakes instead of the 12" brakes that were standard on Airstreams. It would be a very good idea to repack the bearings, and you can check the brakes while you're there (the brakes will be exposed when you remove the hub to repack). Springs and magnets seem to be the most common things to be non-operable when you check them.

[bhayden]

Originally Posted by OregonArgy

I'm using a very reputable tire company here in the northwest, Les Schwab. He seemed to know exactly what my trailer needed when I read him the numbers from my tire's sidewall. Is there anything I should be concerned about?

We've used Les Schwab for just about all our tire needs for many years. The Toyo brand that they carry are great (used to be sold under the Les Schwab "house brand"). Overall we've had good service from all the Les Schwab locations but it does differ WIDELY from one store to the next. A couple of the local stores were basicly clueless when it came to trailer tires. They don't stock them and all they could do was cross reference a size in the catalog. The store out in Monroe on the other hand was fantastic. That's partly I guess because they're in a more rural area and deal with farm machinery, horse trailers and the like on a daily basis. I think it's also because that store has a commercial side that does heavy trucks and trailers. It's also been there for years. It seems the newer stores don't have the level of expertise that the more establish locations do. I believe Les Schwab is a franchise and each store is individually owned.