225/75/R15 Tires

[travelin texans]

Originally Posted by Camp CA

Attached is an example inflation/load table. It is for the tires on my fifth wheel trailer. It shows the load for single and dual tires.

There's a recommended tire inflation posted some where on your rv & if not the best inflation rates are posted on the sidewall of every tire, either of which is your best option.
If you feel the need to lower inflation on your truck for better ride, I definitely wouldn't, then that's one thing, but for trailer tires of any size, brand or weight rating I'd recommend using the manufacturers recommendation or the sidewall rates, anything less is, in my opinion, under inflated creating heat harming the tires shortening their lifespan.

[Camp CA]

travelin texans.......agree.....my fifth wheel trailer, truck dual rear and truck front tires are inflated to a cold tire pressure of 110 (max), 80 (max) and 65 (truck driver side door sticker) psig, respectively.

The benefit of the tire inflation/load table to verify the load capacity of the tires is > than the actual tire load.

[jadatis]

Originally Posted by Nankipoo

Got more info. Dry weight 9662. Gross 11,650. Calls for a ST225/75D/15D tire.

See thst the GAWR's are limited by the maxload of the tires. 2 x 2540lbs = 5080 lbs.
And pinload then mininally must be 12.8 % 1146 lbs.

All done by Forrest river to minimise the production cost, and in those days they got away with it.

Mayby the thechnical max of the axles is higher, but daubt it, also because of of the production cost.

Nowadays 10% reserve in maxload of tires is required. But I will go directly to my determined reserves.

GVWR 11650 lbs
Mimimum to law on pin 1165lbs
Leaves 10450lbs on the 4 tires= 2622lbs maxload a tire with zero reserve.!
10% reserve gives 2883lbs. Is already more then the 2830lbs maxload of E-load in sise ST225/75R15.
Then it even gets worse when I use my reserves.
That is lowering the maxload by 6 steps to give the tires a deflection an LT tire would need for 99mph.
Then 2883 lbs + 18% = 3425 lbs maxload needed to be able to use the referencepressure of tire and have maximum reserve without trembling the screws loose.
This would need the 235/80/16 in ST or LT in E-load
Lt would need that 2883lbs maxload, because its already calculated in maxload for 99mph, so same deflection. So same 235 sise in E-load.

[CWtheMan]

Originally Posted by Auto Parts Guy

What size tire are you guys running when going from a 15" wheel to a 16"? The smallest i see is about a 235/80r16 which is a couple inches taller than the 225/75r15. Is there a closer size for 16" wheel?

None that I would recommend.

Do you know there are a good number of ST tire manufacturers that now build the ST225/75R15 with load ranges "F" & "G"?

[Auto Parts Guy]

Originally Posted by CWtheMan

None that I would recommend.

Do you know there are a good number of ST tire manufacturers that now build the ST225/75R15 with load ranges "F" & "G"?

Howdy neighbor!
I did not know that. I've seen the E load range, if you could share a link or brand/model to the F and G in a good 15" trialer tire it would be greatly appreciated.


If anyone knows of a 16" tire with a height close to the 225/75R15, would be good too. Maybe the 5th wheels have more room to put a bigger tire but not my small camper.

[sourdough]

Here's a link to a good 15" LRF tire. You can get them at other places other than this site, it just happened to come up first;

https://www.prioritytire.com/carlisl...-trailer-tire/

[Auto Parts Guy]

Thank you! Thats what I'll go with unless someone has a good line on a 16" tire about that same diameter.

[Camp CA]

Suggest having your local tire dealer and having them source F or G rated tires for your trailer.

[CWtheMan]

Originally Posted by Auto Parts Guy

Howdy neighbor!
I did not know that. I've seen the E load range, if you could share a link or brand/model to the F and G in a good 15" trialer tire it would be greatly appreciated.


If anyone knows of a 16" tire with a height close to the 225/75R15, would be good too. Maybe the 5th wheels have more room to put a bigger tire but not my small camper.

Here are a three. I don't endorse any brands; this is just info.

FOOTNOTE: All ST225/75R15 tires are standardized to the same dimensions. The load range letters/service description numbers are not part of a tire's size. Any of the load ranges that have a load capacity equal to or greater than what the OE tires provided are valid replacements - without invalidating the vehicle certification label.


https://connect.carlstargroup.com/ca...75r-15-6h09881

https://www.prioritytire.com/transea...All%20Products

https://www.speedytire.com/tires/her...1b06ab41892f32

[Auto Parts Guy]

Thank you all for the recommendations.
So basically if the wheel can support the load and psi, then a 15" F or G tire would work.

To jump to a 16" wheel, the smallest tire diameter would be the 235/80 which is about 2.5" taller?

[JRTJH]

Originally Posted by Auto Parts Guy

Thank you! Thats what I'll go with unless someone has a good line on a 16" tire about that same diameter.

You won't find a 16" ST tire smaller than 235 80R16 which has a diameter of 30.79" and requires a wheel width of 6.5". As far as I know, that is the "smallest diameter 16" ST tire on the market.

That said, if you do consider 225 75R15 LRF tires, you'll also need to buy new wheels that are rated for the increased weight capacity. Most 15" 5 lug wheels are limited to 2150 pounds @80 PSI and 6 lug castings are rated 2830 pounds @80PSI. Actually, they are the same casting with different lug drilling/spacing which is the reason for the increased weight capacity. I don't know of any 15" wheels that Keystone installs that are rated for the increased weight and increased pressure required with the LRF tires. That's the only reason I still have LRE tires on my Cougar, even though I have 6000 pound axles.

[Nankipoo]

We ordered the Carlisle Radial Trail HD. In the 15. LRE. I was also thinking about getting 16's in a 235 with 16 inch wheels. Not sure if they would even fit but I'm afraid when the hitch comes in tomorrow I'm not going to be able to get the height needed for clearance on the RAM HD. I'm afraid the front is going to be high and the back will be real low. Guess I will find out if the big brown truck brings it early enough tomorrow.