Tire pressure advice

[munz]

Hello wanderers
Recently added an Atc ocelot pop camper to my 2013 tundra. It weighs about a thousand lbs. I have cooper e rated a/t tires. Like the rest of you wanderers I spend a lot of time on bumpy rough rocky dirt roads. Before I got the camper I just had a shell and would run the tires around 35 psi when off road. 45 on the hwy. Any suggestions.
Thanks for your time
Munz

 

[buckland]

I ran Coopers for over 10 years on my Eagle/Colorado combo. When I am fully loaded with gear/water etc and wife and dog I come in around 1,400 pounds (more if I have the canoes). My truck is a mini-diesel so a tad heavier in the front. I have found the best running pressure to be 50 pounds front and 60 in rear cold. It goes up about 5 pounds when on the highway from the heat or if in hot area. When the camper is not on I usually set at around 45.

 

[munz]

Thank you for the reply! Curious how your mini diesel worked for you. Would you buy another one? How big is that motor? Strait four? mileage, power etc? If you don’t mind?
Thanks again
Munz

 

[Wandering Sagebrush]

Here’s a link to Toyo’s tire pressure chart. You can get a good idea of what pressures you should use for your load.

Congrats on the ATC!

 

[munz]

Thank you!
Munz

 

[Sagebrush Reconnoiterer]

Does your tires have multiple sidewall plies? That should also be taken into consideration when airing down. Though it doesn't appear that you air down that much; with the weight of your camper bobbing up and down, it could flex your sidewall just long enough to snag a sharp stone even on bladed roads and nick, cut or slash a sidewall.

A decade ago I had a set of old style E rated Cooper Discovery AT3 tires spooned onto my former Toyota Tacoma TRD 4x4 pickup. I believe they were two ply sidewalls; I know that they didn't have three plies. But a few years after, Cooper changed their design. Three plies does add increased stiffness, but for me more desirable than a trailside tire swap.

 

[Casa Escarlata Robles Too]

I have a 2002 1st gen Tundra AC cab with a ATC Bobcat. My tire size is LT 265 75 R16.I keep the tire pressure at 40# front and 45# rear.I always have to remind the service dept when the truck is in for a service not to change the pressure.Here in Ca there is a rule for the service depts to check tire pressure and set it at factory specs.It's a real PITA.
They always set it to my request though.
I find that these pressure settings work for me. The tires wear isn't too mush in the center or side. Just right.
Frank

 

[munz]

Thanks for all of the responses
Munz

 

[rubberlegs]

You'll get all kinds of suggestions. This is the method we use -- slightly complicated and potentially controversial. Our camper weight is all on the rear axle, so those are the tricky tires where guessing or chalk tests seem to be popular. I know a landing gear engineer who might verify or counter this method... remind me to ask him. It's requires you to weigh your axles before and after camper installation, which is pretty easy to do in WA and OR at truck scales, but not other states that we've noticed.

For the front tires, look at the placard tire pressure number and the tire size on the inside of the driver's door. Then use this website: Tire Pressure Calculator. For example, our OEM tires listed on the placard are 265/70R16 (SL, or 112) at 30 psi, but now we have LT235/85R16 E-rated tires. The website says to use 42 psi and the load capacity is 1934 lbs.

For the rear tires, I've never found solid engineering advice. The tires have a load rating in the Toyo tables mentioned in the second post by Wandering Sagebrush in this thread (Toyo’s tire pressure chart). I've decided to use the same factor of safety front and rear:

We weighed our front axle at 2700 lbs empty except for two (smaller) people in front seats, and 2700 lbs with the camper on. Rear was 2000 lbs empty, and let's say 3200 lbs with the camper for this example.​

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For our front tires, at 42 psi they are rated for 1934 lbs per the pressure-calculator webpage. Our front axle weight, empty truck was 2700 lbs (and about that with the camper), so our front tire factor of safety is:​

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Factor of safety = (2 tires) x (1934 lbs/tire) / 2700 lbs = 1.4 (or 140%), so the the manufacturer must have wanted a 40% safety factor. [Comfort, braking, cornering and safety are among many factors, although this is pretty approximate since my wife and I are not large.]​

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Let's assume the rear tires should have the same 40% extra capacity. I'm not sure this is a good assumption and I'm not a tire engineer. Anyway:​

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Tire capacity needed = (1.4 safety factor) * (3200 lbs) / (2 tires) = 2240 lbs/tire​

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Using the Toyo tables (this example is the second last line below), we need just above 50 psi for 2240 lbs, (just above the maximum for C-rated, but ok for D and E rated tires).​

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Alternatively, instead of using the Toyo tables, you can fool around with the pressure-calculator webpage by changing OEM pressures until your actual tires have the right load capacity. In this example, 36 psi for our OEM tires results in 52 psi for the LT tires to get 2257 lbs/tire capacity.​

​

Your mileage will vary and don't necessarily trust this, but this method worked well for our first set of KO2 E-rated tires. There was even wear across all four tires.

With our OEM size LT265/70R16, we often dropped to 15 psi front, 20 rear on rough roads and washboard, and keep below 30 mph to avoid overheating the tires. I can't find some data I used to have on speeds and pressures.

For our latest "pizza cutter" narrow tires, 235/85R16, we use a bit higher, 18 and 23 psi. No "science" behind those numbers...

 

[munz]

Awesome thanks for your time! Been wandering around for thirty yrs with just a shell and gear. So now I have an extra 1000 lbs. goin on my first long off road trip soon. Probably won’t need to use four-wheel-drive. But lots of slow, bumpy rocky dirt roads. I think I’m overthinking it but I’m glad to know there’s other wanderers out there thinking the same things. The truck really isn’t that heavy overall. I think I’m gonna go 50 45 on the highway. Maybe 40 35 on the rough stuff. Thanks for your input again I appreciate it.
Munz

 

[buckland]

I love the Duramax 2.8 liter diesel 6 speed auto. I'd buy one again in a snap but I'd have to do so anywhere else in the world but US. They stopped making them for the US market. They sell them in EU Australia Asia and S America. I had a Tacoma with my FWC and it struggled. This diesel I hardly know I have the camper there. 369 pounds of torque. I get 28 MPG w/o the camper and a 12,200 mile trip to AK and back to NE I got 20MPG and we were loaded. I only have 70K on the engine so I will have this a long time. Small to get into tight spots and very comfortable. I have had only one diesel exhaust sensor go out ...and I broke a control arm but that's all in 8 years.

 

[munz]

That’s awesome. I had two tacomas before I recently went to a tundra. I loved both of my tacos but I felt like they wouldn’t be enough for the Atc camper I wanted. Very happy with the power and comfort of the tundra. I definitely miss the size of the tacos. I definitely like the size of the Colorado. Sounds like it’s reliable as well. Which is the most important to me. Good info for the future!
Thanks again for your time
Happy wandering
Munz

 

[rubberlegs]

I think I’m overthinking it but I’m glad to know there’s other wanderers out there thinking the same things.

I know I over-over-over-thunk it. But it's "fun" since I retired from thinking a decade ago! Now I think about how I used to think.

 

[Tom n N]

Recently switched to 16” E rated tires, so have been doing a lot of research and tweaking to get the pressure right, especially when (over) loaded for a trip. Rubberlegs posts on this and other threads on this subject have been especially helpful for me, as we both have similar size and weight rigs running the same size tires (all important variables to consider when considering tire pressure advice). I would like to add a couple other things I’ve learned:

The ‘chalk test’ is very useful when fine tuning the pressure, but I find that a white paint pen works even better than chalk.

Although recommended tire pressures are always given as cold pressure, always do your chalk test with hot tires, otherwise the contact patch changes when they heat up (I wasted a ton of time doing this test on cold tires).

Also watch tire temperature when airing up or down at the trailhead. My pressure readings at highway pressure increases 10# between hot and cold, and 5# at trail pressure. So for example, when I get back to pavement after a long day at low pressure, I need to fill my rear tires to 65# to get the equivalent of the 55# cold pressure I normally run. Can’t believe how many decades it took me to finally figure that out.

Tom

 

[rubberlegs]

Wow, we only get 4 to 5 psi increase on highways, measured by our truck’s monitoring system. Maybe it’s because we drive about 60 mph.

 

[Tom n N]

This was this week on a quick shake down trip to Death Valley. Was moderately warm going through Central Valley, then up 395 (but certainly not as hot as could be). Also, was running my BFG HD Terrains (basically same as BFG MT) that I use in the desert, so they may run hotter than what you use. My max speed is also around 60mph…no speeding ticket worries in my rig with the camper installed!

For road trips involving little or no off roading I have a set of Firestone Transforce tires of the same size. I’m thinking they run a lot cooler, so will watch them on trips this summer.

Tom