What should my tire psi be?

TomCanada

Confused a bit about tire psi.  The label on the outside of our Tab 400 states 50psi but the tires are listed at a maximum of 65psi with associated payload (see photo) and that's what the dealer inflated them to (or nuCamp did) before delivery.  What should I inflate them to?  If I take out air and reduce to 50psi will that reduce my payload/total weight capacity to potentially some dangerous level?  We drove our unit home with no issues but as we get ready for our maiden voyage I would like to make sure we are riding safely.

ChrisFix

For factory tires, 50 PSI is the correct cold inflation.
The max payload at 65 PSI on the tire you picture, is above the GVWR of the camper...and I have to believe that nuCamp properly spec'd the inflation PSI for our camper's weight.

Denny16

Correct, 50psi is what then recommended pressure when tire is cold, before running it, this is also per our dealer. 

Cheers

N7SHG_Ham

I am guessing that tire did NOT come from factory?

ALL ST tires should be run at max pressure checked cold, ie before daily operation commences.

Do not run tire pressure up and down chasing the thermometer, if it goes up 10psi running on a hot day, leave, it isn't going to blow, running underinflated causes heat and that may cause a blowout. A tire isn't going to magically explode when the pressure hot exceeds the cold inflation pressure by a few PSI.

TomCanada

It's +5C here (low 40s) so I just let out the air to ~51-52psi and will check again in the morning before we head out.  Thank you all for the advice!

ps. @N7SHG_Ham it's the factory tire as it's a new unit - so not sure who hyperinflated it (perhaps the dealer)..

TomCanada

Grr internet - per this link https://www.etrailer.com/question-78836.html the 'expert' recommends that ST tires should always be inflated to their maximum.. so confusion is back lol

N7SHG_Ham

Etrailer is correct in that st tires are inflated to max on sidewall (cold). NuCamp must of changed tire supplier, I would go with the tire sidewall.

dlb

The tire experts are the tire manufacturers, not NuCamp, not the internet.  Run your tires at the air pressure listed on the side wall of the tire.  In this case 65psi.

The manufacture invested in the design of their product and it’s proper performance.  Respect their research.  They designed it that way. 

Denny16

The pressure rating on my Jeep factory tires is different than the recommended pressure on the vehicle door. I never run my tires at the pressure printed in the sidewall, never have had a blow out either. This pressure recommendation is before the vehicle is loaded. Once you have the rated load in the vehicle, or trailer, the tire pressure is going to increase. 

 The tire sidewall rating (the max pressure the tire is rated to handle) from what tire dealers have told me, is the max pressure of the tire when under a load. Manufacturers have the cold trie pressure rating based on the difference between the dry weight of the vehicle/trailer and max loaded weight. I will go with the manufacturer’s recommended tire pressure for the most part when running on a highway. 

Cheers

TomCanada

Ok so since there seem to be varying opinions, even though it's Friday after work, I decided to get pseudo-scientific and put the engineering hat back on Here's what I found..

Although I couldn't find a detailed load/psi table for my particular tire (Rainier ST 205/75R15), I found multiple other brands that have detailed load tables and they all spec the same max load (for this tire size) at 65psi.  They also line up with the simplistic spec on the Rainier website (https://www.tredittire.com/tire/rainier-st/) so I have confidence those tables can be applied here as well - it seems they're an industry standard of some sort.

These specs confirm that 65psi max load is 2150lbs, and at 50psi this drops to 1820lbs - so far so good, but is this enough?

The next step was calculating the max loaded weight of the Tab 400 - this ends up being around 3750lbs (dry weight of 2864lbs + 891lbs cargo capacity listed on the placard).  Since there will be around 400 pounds on the tongue, the most the tires will ever see on a loaded-to-the-max Tab 400 is (3750-400)/2 = 1675lbs.

Based on the above, it seems like 50psi will work just fine for us, and this may actually be desirable because it will soften the ride, resulting in less wear/tear on the Tab as well as potentially less stuff bumping around inside.

Any holes in this analysis/conclusion?

N7SHG_Ham

Less than full PSI analysis is good for tires other than ST. More than one shop in the business + as noted e-trailer all say same thing, trailer ST tires are designed to be at max cold pressure all the time regardless of load.

My pickup has e range tires and rated for 80 psi, those I run around 60 most of the time, butbi don't do the prorated air in any of my trailer tires. Theory only, but 15 years ago on a cargo trailer I did run lower, they didn't last long and I think lower pressure might of been at least partial cause. Tire store then said full psi as on the sidewalk all the time. No issues since, running my Tab tires at max which is 50 PSI and my new cargo trailer tires at 65 psi which is the max there. My cargo trailer sticker says 50, but that was the original tires, I am ignoring that sticker now.

WayneW

The fact that you’re even thinking about proper tire pressure puts you ahead of most, unfortunately. You can’t go wrong with manufacturer recommendation of 65 psi. But remember that’s max, not required, inflation. NuCamp says 50. That’s likely a compromise between max payload and reducing trailer bounce but within safety parameters. The tire would run cooler at 65psi but be a bit harsher ride. The tire would be warmer but bounce less at 50. As long as you’re within that range you’re probably good. If you’re at 35psi or 75psi (cold) you’re not. I usually run around 55 cold for our 320S BD. 

ScottG

My (admittedly limited) understanding is that trailer (ST) tires are a different species than automobile tires. In most cases, trailer tires are intended be run at or near their maximum to provide adequate resistance to sidewall flex (or some such thing).

That said, most of the ST tires I've seen have a 50psi max rating. What to do when the max rating is 65psi is beyond me...  :-) 

ChrisFix

@TomCanada
@ScottG
I found the same size Rainier on Amazon, but with a 6PR instead of the 8PR of Tom's pictured tire...and it has a max inflation pressure of 50 PSI...just to add to the confusion.
https://www.amazon.com/Rainier-ST-ST205-Radial-Trailer/dp/B016DQST4S

I wonder if Covid supply issues have nuCamp using a different version of this tire with the higher Max Inflation pressure and load rating? If so, which pressure is correct for the T@B still remains open, but I think I'm now in the "inflate to the sidewall max pressure" camp.
My 400 Boondock has the knobby Rainiers, with a max pressure of 50 PSI on the sidewalls...and a 6 PR rating.

mona

I’ve been running Goodyear Endurance on my 320 for the past three years. Excellent tires, and still look new. On the sidewall it states, For max load inflate to 65psi. Since the max load for the tire is much higher than the weight of what the T@B puts on the tires, I experience the bounce bounce over 50psi. So 50 it is for me. Since yours is a 400, I would run at 65psi. If bouncy, let some air out. 

Jeannie

Dalehelman

Our tires are rated at 50psi max load. I found at 50psi the tires were wearing in the middle of the tread. At 35psi the wear was on the outside edges. At 45psi the wear is even across tread. So 45psi is what I have been at for the last four years. 320 T@b with Goodyear Marathons 

Denny16

That is a very good way to determine the ideal tire pressure for your setup.
cheers

Bayliss

Not to pile on here, because it is somewhat redundant, here is what I previously copied from Goodyear's website:

“Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire.  Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles.  Using the inflation pressure engraved on the sidewall will provide optimum load-carrying capacity and minimize heat buildup.”   (I underlined "trailer tires" for emphasis.)

I set my Boondock tires at 50 PSI cold, but I agree that somewhere between 45-50 PSI (depending on the trailer load) is an appropriate range.

DougWW

Okay, I'll weigh in here... the functional tire pressure should be less than the maximum rated tire pressure on the tire. Sure the manufacturer will allow for heating of the tire, hot summer days and the like, but maximum pressure is still maximum pressure and should be related to carrying maximum loads.
There is more to the sidewall stability than just pressure. The tread of the tire needs to sit flat on a surface, and if the tire is too hard for the load it is carrying, the centre will bow out and wear out very quickly.
If I ever ran my 3/4ton truck at maximum pressure on the side wall the tires wouldn't last 20,000km. At the same time when the truck is fully loaded then I up the pressures to compensate, and lower them back to door post normal when I'm done.
There is no reason to overthink this. If your T@B is "loaded normally" like the factory expects, go with their recommendation. If you've added a whole load of recreation gear to it, then up the pressure 5 or 10 lbs. it's all good.

Homebodyatheart

@Dalehelman I had my bearings repacked recently and at 50psi I have middle wear. The tech suggested 38psi which I think is too low, and my gut said 45. You’ve confirmed 45psi for my 320S. Thanks Dale!

Dalehelman

@Homebodyatheart
your welcome 

TomCanada

For the record - I had also emailed nuCamp and they responded back with this short video: 

https://nucamprv.freshdesk.com/support/solutions/articles/44001816818-tire-pressure

In a nutshell, Creed recommends max sidewall pressure, but also says we can back off 3-4psi to soften the ride but he wouldn't recommend going below that..

OlyCampers

Recent experience learnt me that tire pressure does matter. Failed to check tire pressure before we left recently. Arrived at our first overnight destination. Gave the hubs a touch -- not quite hot but definitely very warm! Checked the cold tire pressure next morning. 40 psi! Had a bicycle pump handy, got my morning workout pumping up the tires to 50. Checked the hubs again at my next fuel stop. Cool as a cucumber! I'm now a firm believer in staying on top of tire pressure. 

ChrisFix

I purchased this tire pressure monitor a couple of months ago - and it might be the best accessory I've purchased for the T@B.
It takes the worry of "I wonder how the tires are doing back there?" off the table. Both pressure and temperature are clearly displayed, with alarms for slow and rapid deflation. And while the kit comes with an easy to wire RF extender, it is not needed at all for our small trailers - making this kit just a matter of screwing on the valve stem monitors.
https://www.amazon.com/gp/product/B0797LQ44K/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Dalehelman

@ChrisFix
If it eliminates stress and worry it’s a good thing.

Denny16

Nice find.
cheers

Travelin3D

After de-winterizing, my tires were a bit low so I topped them off at 50psi. Just yesterday I had the trailer in to Miller’s in PA to have the brakes adjusted, bearings repacked, etc. Preston rotated the tires and also recommended 45psi as the optimal pressure, so that’s where they’re set. Great dealership and service.

dsfdogs

@ChrisFix I've been using that TireMinder for a couple years, without the RF extender, and love it. As Dale said, it eliminates stress and worry (and wonder) of what's going on back there!