Endurance Tires

[Jack2k]

New Imagine XLS owner here -
I'm reluctant to post this because I realize there has been much discussion before - I just can't find much on this forum.
My 22MLE has a GVW of 6995. I'm gonna try and add a couple of snippets from the Goodyear website that show you should not be @ 65 psi unless your load is 2040 (7000 max divided by 4 = 1750/tire) so using their figures, I should be running the tires @ about 50 psi.
What is the rationale for running your endurance tires @ 65 psi?
Be easy on me 😉
Thanks!

[TedS]

I choose to run at max load pressure even though I am not at max load. My reasoning is to have the load margin rather than trying to adjust to my actual load which may vary. I am not seeing excessive center tire wear at max load pressure. Tire temperatures remain low.

[howson]

Jack2k,
The snippet you posted from Goodyear's website sums it up quite nicely. The only caveat I'd add, or perhaps better stated as a clarification, is if an owner is going to vary from the placard recommendation then it is vital to know the weight on each tire. The assumption that the weights will all be the same is, in my experience, going to be proven false in the majority of cases given how GD lays out their floorplans.

When I had my 315RLTS weighed, the front street side tire was the heaviest (snip below from the 2019 weigh).



Since 2700 lbs was the highest weight, the norm is for all four tires (on my heavy trailer!) to get aired up to that weight measurement.

I've since made significant changes to my trailer, including the tires, but basing the pressure used on the heaviest tire weight is (I think) still valid.

My fellow moderator, Cate&Rob, came up with an alternative way (other than using a WeighSafe facility) to measure individual tires if you're interested. His method is post 7 in a thread about the Sherline scale that can be found here: https://gdrvowners.com/towing-and-hi...g-helpful-info

Howard

[Scott'n'Wendy]

The tire is at it's strongest at max psi. So that's what I run. With my trailer, that would be 80psi cold. I could run them a bit lower but that would increase heat and increase the chance of failure....so I don't.
Some say the trailer has a better ride with lower pressure. Beats me how they know. Accelerometer on the counter maybe...lol

[Cate&Rob]

In addition to uneven static weight distribution, there is dynamic load. Consider the increased load on the tires when the trailer lurches to that side. Best to run the tires at rated pressure . . . which is what is required by the tire pressure label on the left front of your RV.

Rob

[Jack2k]

Thanks for your input. On my previous (much lighter) trailer I ran the tires about 10# under max rating and wondered what you, with your heavier rigs, did.
I appreciate your responses. TedS , howson , Scott'n'Wendy , & Cate&Rob

[Madonnell]

For those who advocate for max tire pressure regardless of weight on tire, realize there is a real handling, braking and safety tradeoff. (if anything, use the pressure on the label on the trailer, which has accounted for all of this assuming a fully loaded trailer and original size tires. But this is how you get there...)

The contact patch for a tire is the area of the tire which makes contact with the ground. A larger contact patch provides more grip for braking and stiction when maneuvering or on wet/slick surfaces (while also increasing rolling resistance and heat). For a given tire and weight on the tire, the air pressure in the tire determines the size of the patch. In an ideal 'balloon' tire, the size of the patch would literally be weightOnTire/poundsPerSqInch (an 80 psi tire carrying 2000 lbs would have a 2000/80 = 25 square inch contact patch) . It's quite a bit more complicated for real tires due to rubber & sidewall stiffness and tread patterns, which is why manufacturers publish the weight-pressure tables referenced in earlier posts.

So, too low tire pressure results in a larger than needed patch size, increased sidewall flexing, higher rolling friction, increased tire temperature, and potentially early tire failure. Bad.

But significantly high pressure ain't great either, resulting in too small a patch size, and reduced grip and braking and handling performance. Also Bad. Not as catastrophically bad on a daily basis, but very catastrophically bad on that one day in the rain or during an emergency stop. A softer tire also results in a softer ride, with less jostling and bouncing of the stuff in your trailer while you are driving across the potholes from h*ll at 79.9 mph.

Luckily, the tire manufacturers have thought of all this, and using all sorts of models, simulations, and testing (or perhaps just a really fancy ouija board), have come up with the correct nominal pressure for their tires to trade off these considerations. That's what these tables represent.

It's also worth noting that there has got to be huge latitude in the acceptable pressures. Driving dynamics mean that the load on a tire is way higher or lower at any given time compared to these static measurements. And heating during a day of driving means a tire which you set at 80 psi in the morning is going to be at 95 or 110 in the afternoon (which means the tire has to handle acceptably across this full range of pressures). Here again, the tire manufacturers are not dummies, and their weight-pressure tables take all of this into account to come up with the best nominal cold fill static pressure for their tires. (They are probably even aware that tire guages are often off a few pounds and that the side in the sun will be warmer)

So, what do you do? I personally follow the trailer tire manufacturers recommendation for tire pressure, based on the appropriate table for my tires and weight. (if you use LT tires on your trailer, a lot of the assumptions are wrong - not sure the right answer then). I use actual measured weight on tire (max across all the tires), or my best estimate of it. Or if I only know or can estimate the total weight on all 4 tires, I divide by 4 the round up a bit to account for probably uneven loading.

I tow a Reflection 303RLS. My total weight on the axles (measured at a Cat scale) has been about 10800 with minimal water in the tank, or 2700 lbs per tire. I round that up to ~3200 lbs to account for uneven distribution and sometimes carrying more water. Looking at the tables for my ST235/80R16 Hercules H901 tires, this gives me ~75 psi. So I run them between 75 & 80 cold - as long as they are in that range in the morning, I'm comfortable with it. (as of last week I have 6000+ lb axles and springs on it. If my weight creeps up, such as if I start carrying full water tanks regularly, I might adjust up a bit - these tires are rated for 105 psi max cold, so I have some headroom).

My 2c.

[TedS]

The problem I find with that reasoning is that all the adjectives are relative. Better, worse handling. Shorter, greater stopping distance. More, less contact patch. More, less flex. By selecting max inflation and dealing with the resultant handling, sufficient load capacity, acceptable tire flex, tire heating, etc., takes away adjusting, rounding up; all guessing. RVing should be closer to tow and go rather than adding such a worrisome exercise. FWIW

[Madonnell]

that's what the tables are for. Eliminate all that guesswork, and trust the experts to do their job. I only have 3 technical degrees and a lifetime of DIY - I'd be foolish to think I know more about this than the guys who spend their lives doing it

[Scott'n'Wendy]

And heating during a day of driving means a tire which you set at 80 psi in the morning is going to be at 95 or 110 in the afternoon

I have no problem with people using the tables and guessing their tire loading on any given morning, or trip. but....I set mine to 80psi cold in the morning in Ontario at -8*C and have never exceeded 90psi through the day. I didn't bleed out any pressure until I was in Las Cruces NM...it was 21*C. Needed to bleed off 3psi. I was driving at 75mph. I don't think any tire would gain 30%+ pressure?

[Crespro]

The eTrailer folks have some experience with trailer tires. I follow their advice and keep our "G" rated tires close to 110 PSI. I understand this is well over the 80 PSI required for about 3,000# to 3,300# per tire. As Mark correctly notes, they run about 125 PSI when warm.

After three decades of RVing, I am always concerned about tires. It is the weak link for fifth wheels in terms of safety. I plan to change mine at about three to four years.

Best,

Charles

+++++++++++++++++++++

Tire Pressure Recommendation for Taskmaster Tire # TTWSF20515C
Question:
I have Task Master tires, ST 205/75D15 on a trailer. Whats the suggested tire pressure? Thanks!

asked by: Bob V

Expert Reply:
The Taskmaster tire you have is the part # TTWSF20515C which has a PSI rating of 50 and a max load of 1,820 lbs.

With trailer tires you have to always run the max pressure rating listed to ensure you get the full weight capacity. So for your tires you need to keep 50 psi in them.

[TucsonJim]

I run mine at max pressure because I don't want to fiddle with getting the tires weighed each time I change the load on my trailer. And I usually have a different load out each time I hit the road.

But having them at the max pressure was a real blessing for me one time. I had all four tires at 80 psi. While driving on city streets in Tucson, our TPMS alerted to a pressure loss in one of the tires. I knew there was a Discount Tire shop about 2 miles away. By the time I got there, the punctured tire was down to 20 PSI. If I'd started out lower, it would have been below 20 PSI and probably broken the seal around the bead and ran flat.

Jim

[Country Campers]

If going by the Cat scale weight on a 303 and dividing by 4 this can make a bad situation. The 303 is known to have 1000# heavier side on the street/drivers side of the RV from the factory. This will of course change when loaded, increase for sure with the pantry.

At our first National Rally we had our complete rig weighed by the tire. Attached is a pic of all that information. In the top right you will see the weight for each tire. Middle left you will see the tire inflation chart where they explained what pressure I could run my tires according to the tire weights. There is no way I will run my tires at 30 or 40 psi according to the chart and what their recommendations are. I choose to run at 75 psi cold and will continue, tire and sticker states 80 psi. The sticker and info on the tire sidewall is there for a reason, and the tire people know better than I do.



Brian

[TucsonJim]

Country Campers - (Going off topic for just a minute).

The "heavy beverage" note caught my eye.

Jim

[howson]

I think my case is an exception to "always run the sidewall stated pressure". The ST235/80R16 Sailun S637s on my 315RLTS have a max pressure rating of 110 psi ("G" rating). According to the Sailun chart, that's for a load of 4080 lbs per tire. (!)

That's why I have ran them at 80 psi ("E" rating, or 3420 lbs per tire per the Sailun chart) since I have a good idea of the max load (as noted in a previous post) as the trailer was loaded down at the beginning of a trip. Based on wear data, I'm going to run at 90 psi in the future. See https://gdrvowners.com/forum/operati...nd-conclusions

More on the initial Sailun install here: https://gdrvowners.com/forum/operati...talled-315rlts

Howard