Recommended tire pressures

[JJump]

Thanks to all who replied to my first post-lots of good info. A set of gages is on my list for Santa!



Being new to this whole heavy hauling arena, I could use some advice on tire pressures. My rig is a '93 D350 LE dually extended cab with 235/85 x 16" tires and it pulls a 30' 5th wheel travel trailer. I pulled the combo (truck & trailer) onto a scale at a local truck stop. The scale was configured in 5 sections-kinda like 5 scales set up end-to-end. The total weight (13,700 lbs) was compiled from 3 of the 5 scales; both axles of the truck were on scale 1, and although I didn't take notice, from the data I presume that one trailer axle was on scale 2 & the second trailer axle was on scale 3. Scale 1 showed 8600lbs, scale 2 showed 2500 lbs, and scale 3 showed 2600 lbs. I dropped off the trailer & came back to get an empty weight for the truck, which was 6600 lbs. , all on scale 1.



These numbers surprised me. I never would have guessed that I had 2000 lbs tongue weight-the truck doesn't seem to settle that much with the load. That's also a little more than 28% of the total load, well over the 10-15% that I've heard is the general rule of thumb for tongue weight. The trailer weight was a big surprise too, seeing that both the previous owner & the NADA listing for the trailer stated its weight was 4200 lbs. Since then I've done some research, and actually, 7100 lbs for a 5th wheel this long is kinda on the low side. Makes me wonder if the truck scale was accurate?!



Back to tire pressures. While driving the rig back from AL to MO (mostly interstate, 60-65 mph) I was monitoring the tire's temperatures , and they always were just warm to the touch-maybe 85-90 deg F. I recall the tire pressure being around 40 psi. I've read that the way to determine correct tire pressure is to take a reading when cold & then take another when up to operation temp, like after a 15-20 mile jaunt at speed. The correct cold pressure is arrived at when you achieve a 10% increase from cold to operating pressure. Sounds like a good plan, but I always forget to take the hot pressure- Doh!



I would appreciate any input. Hopefully it might influence my fuel economy & extend my tire life. Thanks for your time!



Joe Jump

St Louis



P. S. Stupid Newbie Question: How do you attach your truck profile to the end of a message?

 

[Greenleaf]

Sorry, don't pull anything. My rig is strictly for quick get-a-ways and making smoke



Go to User Control Panel

Click on Edit Profile

scroll down to signature



I'll be looking for it



Scott

 

[AlK]

I have the Michelin tires on my truck and inflate them to 75 lbs which is 5lbs less than the maximum. I know the ride is a little rougher, but I do 99% of my driving on pavement. In my opinion by running the tires at max or just below, the vehicle handles better, improves mpg, tires last longer and the tires run cooler. On my last set of Michelins I had 100,000 km.

---

Al

 

[rdodd]

I run 55#in front and rear. Any more and i can,t stand the ride.

 

[JBournes]

Tire pressure

I pull a 37' fifth wheel with my ctd, and when i am pulling it i always make sure i have the max air pressure 80 in the tires, but when i am not pulling it i drop them back down to about 65. I look at it like this, you dont see the big rigs dropping there pressure down, but of course they have air ride to make up for the ruff ride. But as far as whats best for the tire, when you are loaded i would be sure to keep it atleast within 10 psi of the max. \



JEB

 

[Underdog]

If you post your questions on the towing,rv, forum you will

probably get plenty of opinions.

I didn't understand if the 40# tire pressure was empty or towing

your 5th wheel. If you were towing,you're looking for trouble.

I don't have a dually but ,I do tow a 31', 12,000+ #, 5th wheel.

I put 80# in the rear tires when towing and 55# in the front

tires. When running empty,I put 35-45 # in the rear and 45# in

the front. If you check the sidewall,it should tell the maximum

inflation pressure. I would run that pressure when towing.

Just my . 02.

 

[bgilbert]

Joe, at 40psi, I'm surprised you didnt blow a tire. You probly have load range 'E' tires from that size, and max cold pressure for them probly is 80psi. Find the correct cold tire pressure stamped on the side of your tires. When running loaded you definitely want to run at max cold pressure as JEB said. Running an underinflated tire will decrease fuel mileage, tire life, and make tires run hot and lead to failure. Same goes for your trailer tires, check what the max cold pressure is for them and run at that pressure. When I was running 235/85's LR 'E' I never pull anything and found that at about 55psi was bearable when empty and tires wore decently. I now run P265/75/16 which isn't a truck tire, max psi for it is 44psi. You can bet I run at 44psi since I'm already running a light tire. Tire pressure is very important when loaded. Bill

 

[sparks57]

I run E's, and I check the air pressure EVERY WEEK. It's very important to keep an eye on tire pressure. Checking them often will increase longevity, safety, and MPG.



Unloaded, always keep them at 65 front, 55 rear.



Loaded... no matter what the load, 80.

 

[JJump]

Wow, had no idea! That 40 psi I was talking about was when I was hauling the trailer back to St Lou from Alabama. The tires stayed relatively cool to the touch. I figured max pressure was for max load & I knew I was no where near max load. I figured over inflation was as bad as under inflation (loss of traction, wear down the middle of the tire). I think I'll do as recommended & post the question on the RV forum.



Thanks for all the replies-appreciate your time!



Joe Jump

St Louis

 

[dpuckett]

JJump-

ON tongue weight- better to be a little heavy than a little light. Too light in front causes swaying, bouncing, and a handful of other problems. Been there, done that, no fun.



TIre pressure. When loaded heavy (53 sq bales 100 mi down the road), I run them about 70-80 psi, depending on the weight on the tires. Empty, I run them at the max for the next LOWER range. IE- for load range E, i run them at 65 (max for Ld Rge D); for Ds, I run them at 50 (max for Ld Rge C). THis seems to be a good compromise of tire wear and ride quality, though on a dually, I have noticed NO difference whatsoever by changing tires, pressures, etc. If you run them empty at 80 psi all the time, you get bald tread centers, and half to 3/4 tread on the edges.

disclaimer- these comments are based on my limited personal experience, and you may not like the results of doing the above mentioned things. However, you are free to try somethign else if this doesnt work for you.



Daniel