Tire Pressure 101 for Duallies

[prestinb]

I am looking for some help concerning load and inflation charts. After studying them and figuring out how they are calculated, I am still missing a couple things that I was hoping someone could fill me in on. So here goes...



Stock Tire - 235/80/17 E Rated = 3169lbs @ 80 psi Single

2892lbs @ 80 psi Dual



My truck is a 2008 3500 DRW Reg Cab 4x4.



Scale Weight = 7580lbs 4548lbs Front Axle / 3032lbs Rear Axle



Calculating Load Per Axle:



Front Axle = 2 x 3169 = 6338 4548 / 6338 * 80 = 57. 4 psi

Rear Axle = 2 x 2892 = 5784 3032 / 5784 * 80 = 41. 9 psi



This works out to be almost perfect for the light load settings of 65 Front / 40 Rear. (A extended, crew, or mega might be spot on. )



Here is my question...



Why is the weight of the rear axle only divided by 2 instead of 4 since there are 4 tires sharing the load?



Any insight would be greatly appreciated. Thanks!



prestinb

 

[HBarlow]

What is the source of the load and inflation charts you inquired about and are apparently quoting?

I'm thinking that the inflation pressure specified by Dodge for the three Dodge Ram drw trucks I've owned/own have all been something like 65 psi front and similar for rear. Maybe I haven't looked in a long time and what I think I remember as Dodge specs is not correct.

In any case, what I prefer and have always used is 70 psi inflation on front tires and 60 or 65 psi on rears. This inflation pressure has always served me well whether running empty of loaded to (occasionally beyond) GCWRs specified by Dodge.

I have always experienced normal wear patterns and good service life and never experienced a tire failure whether on OEM Goodyear or Ameritrac tires or the Michelins I always buy as replacements.

 

[Flexiheep]

Not that I own a dually, but it could be a safety factor thing. You don't always get good distribution of the weight between a pair of dual, severe road crown, curbs, even cornering could load one tire in the pair more than the other.

 

[THoltz]

The Michelin tire manual that came with my truck says for truck fully loaded to run 65 psi in front and 50 psi rear. I run 65 front & 55 rear. I still run the Michelin LT235 85R 16 E rated M&S tire which was the original tire.

 

[Blu-meanie]

I'm with Harvey: 70 lbs front - 65 lbs rear. If you run empty a lot, then go by the door tag which is around 40 lbs rear. It's a pita to inflate-deflate the duals. I used to drop the rears after towing, but now I just leave them at 65. I have a TPMS on the tires now so I only adjust when needed.

 

[prestinb]

My initial question is more about trying to understand the calculations or theory behind tire pressure.

Here is the load and inflation chart that I was referencing. It is the most recent publication from Tire and Rim Association (TRA).

---------------------35psi 40psi 45psi 50psi 55psi 60psi 65psi 70psi 75psi 80psi

LT235/80R17 Single 1725 1895 2055 2270 2405 2545 2680 2815 2950 3085
LT235/80R17 Dual --1570 1725 1870 2040 2190 2315 2470 2560 2685 2835

My door placard states 65 Front / 40 Rear for Light Load and 65 Front / 65 Rear for Max Load.

With this stated and using the chart above, that would suggest the tire could support up to (2x2680) 5360lbs on the front axle and (4x1725) 6900lbs on the rear axle when running empty (Light Load 65/40).

I had my truck weighed at the scale and it was 7580lbs (4548lbs Front Axle / 3032lbs Rear Axle). The front pressure at 65psi is about right but it would seem that the rear tires are significantly overinflated at 40psi even though that is what is recommended while running empty.

I going to run the 70 Front / 65 Rear combo that was suggested because that is from real-world experience. I am just trying to figure out what is going on since it just doesn't really add up.

prestinb

 

[SWC]

Just to add my 2 cents to this discussion. I have a 01. 5 3500 quad cab with a deck. It is heavier then a conventional dually. I do have the weights but not with me now.

I have run 58 lbs on the front and 44 to 52 on the rear depending on the load.

I hauled RV's for 1 year 02 - 03 and during that time I watched the tire tread wear closely. The first set of tires I ran higher pressures and wore the center tread faster.

I recently bought 2 new tires which I mounted on the front. The guy mounting the tires recommended 65 for the front. I disagreed but he asked me to try 65. I said okay (not wanting a p***ing match), knowing where I would put the pressure when I left the shop.

I settled on those numbers but others experience may differ.

Stan

 

[Skydiver]

First thing, never run anything but "E" range tires or heavier.
I run 32 psi in my rears when carrying less than 2000 lbs load. They wear even and drive ok around town. If I'm headed out on the interstate I will run them up to 40 psi. If I'm loaded heavy I will run my Goodyear G-90 up to 75-80 psi. Yes it's a pain to match air pressure to the trip load, but I seldom buy tires. They last.
I always keep my front Goodyear street rated tires above 75psi.

 

[HBarlow]

My initial question is more about trying to understand the calculations or theory behind tire pressure.

Here is the load and inflation chart that I was referencing. It is the most recent publication from Tire and Rim Association (TRA).

---------------------35psi 40psi 45psi 50psi 55psi 60psi 65psi 70psi 75psi 80psi

LT235/80R17 Single 1725 1895 2055 2270 2405 2545 2680 2815 2950 3085
LT235/80R17 Dual --1570 1725 1870 2040 2190 2315 2470 2560 2685 2835

My door placard states 65 Front / 40 Rear for Light Load and 65 Front / 65 Rear for Max Load.

With this stated and using the chart above, that would suggest the tire could support up to (2x2680) 5360lbs on the front axle and (4x1725) 6900lbs on the rear axle when running empty (Light Load 65/40).

I had my truck weighed at the scale and it was 7580lbs (4548lbs Front Axle / 3032lbs Rear Axle). The front pressure at 65psi is about right but it would seem that the rear tires are significantly overinflated at 40psi even though that is what is recommended while running empty.

I going to run the 70 Front / 65 Rear combo that was suggested because that is from real-world experience. I am just trying to figure out what is going on since it just doesn't really add up.

prestinb

Modern and high quality radial tires seem to be less sensitive to tire pressures than old and poorly made bias ply tires were.

What I mean by that statement is I don't think you are going to see noticeable wear on the tread centers with a little extra inflation pressure unless you routinely accelerate hard and keep the rears slipping slightly.

I suspect a tire engineer would lecture us about always adjusting pressure to the load but I have never bothered with my duallies. Too much trouble to get down on my hands and knees to inflate and later deflate the inside rears every time I tow a heavy trailer.

I've used many sets of Michelins and always get approximately 110,000 miles of service from each set of six.

 

[macdaddy]

I run 80 psig in front and check them regularly (quarterly). The rears I also run 80. The rears I check every 10K miles. Ive tried running 65 psi and cant tell any noticeable difference in ride quality when empty.



By maintaining them at 80 psig at each rotation they usually "bleed" off to between 65-70 psi (rears) between each rotation 10K. The sticker in the door jam by the way states that all thats required for max GVWR is in fact 65 psig. This way the only time removing the rear liners and caps are required is when I do a tire rotation.



Mac

 

[WestTN]

Remember that the manufacturer's inflation pressure is the minimum pressure required to carry the maximum load. You can add additional air to at least the maximum tire pressure rating and will then have a safety margin as well as longer tire life.

 

[Skydiver]

A simple question. How much weight is on each of the 4 tires of an empty dually?
Empty not loaded.
Thanks

 

[HBarlow]

Probably 1200 to 1500 lbs. per tire. The tires could probably survive if only inflated to 30 psi. but I wouldn't want to run them that way.

 

[Skydiver]

I weighed my 96 extended cab empty. It was 6400 lbs. I did read on TDR that these 2x4 trucks average 65/35 % front rear. Might have been 70/30%, can't remember. Using 65/35 places 560 lbs. on each of my 4 rear tires. That's why I can let them down to 30 psi and the side walls do not bulge.
I do know if I get on soft soil my front tires sink and the rears are almost useless. Finally went with a wider front and a very agressive, hard to find Goodyear G-90 rears which helped a lot. I still get stuck during hunting season. I often have to call my wife with her Ridgeline to pull me out. She loves it when I get stuck and tells everybody. I just grin. LOL

 

[Newt]

09 Dodge 3500 Laramie Quad Cab Long Bed 4X4 Dually

The truck was weighed with over 3/4 tank of fuel, both of us in the cab, tool box, hitch, generators and all the stuff we expect to carry on the road.

Front 4820#
Rear 3960#
both 8780#

That leaves a cushion of 380# for the front, 5390# for the rear and 3420# for the GVW.

Newt

 

[MAshley]

Well my experiance with the stock factory tires running at about 55lb all around was about 55K miles, Mind you I did tow a trailer "Bumper Pull" at about 14,000 lbs the entire time, Next I install what Les Shwab recomend for tires, They at first want to put 80 PSI in all 6 tires, Told them 55 please. . so that went on for awhile Did normal rotations and still pulling the trailer. Had an employee air up the trailer tires and not knowing it they also air up the truck tires to 80 PSI. . At the time for the next 50 miles it was ok seeing as there was a pallet of Salt in the rear. . well about 5-10K mile latter basically empty towing I had them air back down to 55 PSI... . Now at 92,0000 mile or 37,000 mile on the tires The centers are worn bad with the outside edges still with plenty of tread... slight cupping on the front tires but maybe 3-4 thousand differance. Deffenatly need new tires for fall.



This leads me to believe at least with these les Shawb tires, I should really pay attention to tire PSI per the load on the truck. Truck sees about 1500 lbs from the trailer and another 100 to 1000 lbs from the 100 gallon fuel tank. No big 5ver, camper or GN yet.

Or maybe tires just naturaly wear the centers faster I don't know





David

06 CTD 3500 Dully, 4x4, Quad, LB

 

[MAshley]

I've used many sets of Michelins and always get approximately 110,000 miles of service from each set of six.

Harvey



Please share whch tires you are running, and how you drive to get 100K + miles out of a set of tires... My second and first set barley get the truck to 100,000 miles



David

06 CTD 3500 Dully, 4x4, Quad, LB

 

[HBarlow]

David,

I used ordinary Michelins purchased from SAM's Club. The first couple of sets were LT235/85 16s on a 2001 and a couple more sets on an '06 with 17s. I"ve used nothing but Michelin tires for more than ten years begining before I was a transporter.

An old friend who is retired federal civil service and lives in Pahrump, NV has been transporting for 10 or 12 years now. He put just under a million miles on a '95 Ram 2500 4wd and probably now has more than 500k on an '04. It was him who first told me he used Michelins and got over 100k out of each set.

I had the same experience. I was actually getting about 120k miles out of a set of six but always pulled them off at around 110k as winter approached for obvious reasons.

The truth is I did nothing except have a free rotate and balance done whenever I was home and had time. Rotate and balance intervals varied from somewhere around 8k to as much as 15k. I am careful to avoid road hazards and broken pavement as much as possible but I didn't baby either truck. The '06 had a full DTT built 48RE and would spin the tires off line and on the 1-2 shift (unloaded of course) if I put my foot in it and I did occasionally. I ran fast when empty and pulled heavy loads all the time.

Anyone using Michelins giving the tires the basic minimum care will see similar results.

I should add, my driving was highway driving on pavement and I tend to back off early and allow the truck to begin slowing rather than braking hard at a stop.