Tire ratings and nitro filling

[Beercan]

Hi all, I am a new user on this site and also a relatively new RVer. I have a couple questions about my 2012 27 foot BKHS. I am wondering what the D means in the tire size, ST205/75D14. I need to purchase a new wheel and tire for a spare as I guess these travel trailers don't come with a spare. I purchased this from a person that purchased it last year. Before I buy a spare I would like to know if these tires are bias or radial and if not radial should I just replace them all with radials. If I decide to keep these original tires should I just deflate the tires and replace the nitro with air. Thanks for any information you can give me as I know there must be many very experienced RVs here. Thanks again, Beercan

[BarryD0706]

Welcome to the forum!

We don't really know which RV you have. Please update your profile to include that information.

The "D" is probably the load rating of the tire. The "ST" indicates that they are special trailer tires. That's all you need to know re radial/bias. Buy one of those.

There was a thread on here recently regarding nitrogen-filled tires. The consensus was that its a hoax. No need to deflate them however. Just add air (~80% nitrogen) as needed.

[Beercan]

Thanks BarryD0706, I found out the D stands for Bias ply tires. I just removed one from thr RV and noticed these tires are already weather checked on the inside and only a year old. That shows me the tires are no good so I will be replacing them all with radials before I travel far. As for the nitrogen, a hoax period. Thanks for the info. Beercan

[garbonz]

They are not bias ply. The D refers to the load rating of the tire which is posted on the tire and on the side of the camper near the passenger front. Max pressure is 65 lbs.

Your unit came with a spare, I think. Unless it was removed.

[Oakman]

If the tire size reads "ST205/75D14" then it is indeed a bias tire. The D stands for diagonal bias. Don't bother filling the tires with nitrogen, good old fashioned air is fine. The only advantage I have seen with nitrogen filled tires is they don't seem to lose air pressure the way air-filled tires do.

[Beercan]

Yes they are bias ply tires. Google tire tire size and ratings. The load rating on these tires is C 6 ply St205/75D14, if they were radial there would be an R after the 75 not D I just talked to the original owner and according to him this camper did not come with a spare tire. Thanks

[Garrette]

Just a suggestion, it could be bolted to the bottom of the frame.
My old TT came with nitrogen filled tires. Always ignored that an just used air. Never a problem. Now as far as brand, search the forum for tires. I bet it has been discussed.
While you are putting on tires, have the wheel bearings checked.

[melk-man]

the advantage to nitrogen is it won't increase in pressure as the tire heats rolling down the road. Nito is used in some motor racing these days. Is it needed ? not really.. just keep in mind a loaded trailer tire is gonna increase 3-5psi when it gets hot rolling down the highway.

[BarryD0706]

Originally Posted by melk-man

the advantage to nitrogen is it won't increase in pressure as the tire heats rolling down the road. Nito is used in some motor racing these days. Is it needed ? not really.. just keep in mind a loaded trailer tire is gonna increase 3-5psi when it gets hot rolling down the highway.

Yes it will. Any gas will increase in pressure when it gets hotter. A normal trailer tire will increase almost 10psi when it gets hot. That large amount is probably due to the moisture that was in the air fill. (A nitrogen fill may have less moisture so may have less of a pressure increase.)

[melk-man]

Originally Posted by BarryD0706

Yes it will. Any gas will increase in pressure when it gets hotter. A normal trailer tire will increase almost 10psi when it gets hot. That large amount is probably due to the moisture that was in the air fill. (A nitrogen fill may have less moisture so may have less of a pressure increase.)

check your tire increases next time out, highly doubt you are seeing a 10psi increase in pressures even loaded close to max tire capacity. It also (as some stated above) won't leak down as fast as tires filled with o2. (a benefit for those less than religious about checking before every trip !)

And i would respectfully disagree, nitro doesn't expand close to the rate/amount that o2 does. Even our roadrace motorcycle tires that deflect in shape a good amount, and reach surface temps of 200+F (with inner temps of 290+) only increase about 5-6psi if we have the correct compound, and 8-9 if we have way too soft a compund that is literally getting "greasy" at the end of a session.
lots of info out there on this. i should have perhaps amended my post to say ".. not as much as o2".. on of many articles out there doing a quick goodle search
Nitrogen vs Air In Tires - Why Nitrogen in Tires - Popular Mechanics

[garbonz]

Wow

[BarryD0706]

No one is filling their tires with O2. Air is ~80% nitrogen already, and about 18% O2.

There was another thread recently here a couple of weeks ago where many of us reported seeing ~10psi increase. I've seen it now on many trips. I don't need to check again.

If we assume that it's the gasses other than N that are leaking out, then after ~5 times of replacing that lost gas with air, we will be close to pure nitrogen already (but still with the moisture).

Oh, and just so you'll know, nitrogen and oxygen both follow the ideal gas equation of PV=nRT (which indicates that in a tire, pressure is directly related to temperature (in degrees Kelvin)).

[melk-man]

you are forgetting that most air compressors have moisture in them. some have lots of moisture (i try to drain mine every week at my home shop) . This is one reason tires filled with air increase in pressure. the moisture ! If you are seeing 10psi increases, you have a bunch of moisture in the air in the tires.. or are potentially under inflating them to begin with .
I have 2 trailers, both loaded are around 9000lb. One has air, i fill to about 72psi (e rated tires) and they go to about 77-78psi on a long haul. The xlr27 hs the nitro filled d rated tires, with fuel, bikes, water and even less psi to begin with, i don't see the same increase in psi. I'm not saying my example is the end all of the discussion, there is lots of info on nitro filling tires. I agree it isn't worth the time to find a nitro fill location, but to say it increases the same as a air from a big compressor that likely hasn't been drained of water in weeks is just wrong.
It is safe to say you won't be filling your tires with nitrogen ?

[OldCoot]

Putting pure nitrogen in tires is a total ripoff of rv owners. Nitrogen may expand less than regular air but so what? If tires are inflated to their max when cold with regular air, they will no doubt increase 10-15#. They are designed to withstand the pressure increase without doing damage. I have seen the pressure increase on mine from 10# to 14# while the temperature will approach 135° or a little higher. I have the alarm set for 157° and have never heard it sound. The biggest problem for tires (discounting road hazards & curbing) is running underinflated which will quickly over heat a tire and cause disintegration of the tire (blowout). Road hazards are just that, hazards, curbing & under inflation are both driver errors and can be avoided. Inferior constructed tires (off brand like mfgs put on units) should be replaced with a brand name like Maxxis, Good Year, etc. as soon as financially possible to prevent a blowout & costly damage to the unit. Bottom line, forget the nitrogen and leave it for airplanes and racing. Just my opinion.

[melk-man]

i totally agree paying a bunch of money for nitro filling is not money well spent.. novel idea, it does "work" as designed, but not a good cost:benefit trade off, especially for someone that keeps the tires inflated properly.