Just thought I'd add one more point to the curve. I put my 2WD, auto tran, truck across the CAT Scales today. Nothing in the cab, bed completely empty, but with full tank of fuel.
Front axle - 3300#
Rear axle - 2320#
Total 5620#.

Still running Firestone Steeltex tires 235 85 R16, so naively I thought, hey! I'll call them up and ask what tire pressures I should be using. Wrong!

I guess the SUV roll-overs have them jittery. They refused to recommend a tire pressure for a particular load. They said they would not recommend anything less than 80% of the full rating that Dodge gave the tires, which was 80psi. So they wouldn't recommend anything less than 60 psi. I asked them how many people ran 60 psi with their trucks empty, and they replied that if I thought that was too hard, it was my risk to lower the pressures.

I did get out of them that according to the industry published tire pressure loading chart, the 235 E rated tires would support the front axle with 35 psi. Which when I went to look, is exactly what Dodge recommended in the owner's manual, for a lightly loaded condition. They recommended 35 psi front and 35 psi rear.

I've since backed my pressures down to 38 psi. to see what it feels like (couldn't force myself to run 35 psi). Is anyone else out there running such low pressures?

John

 

The tire dealer I got my tires from recommended 50# empty and the max, 80#, when I put my 3,000+# cabover camper on. The tag on the truck says to run 55# empty not 35#.

 

Took an old garage door to the dump, on the way out the truck plus me weighed 6,340 and I'm 235, so that's roughly 6,100 pounds. If I took all the tools out of the bed box I could probably get down to an even 3 tons. I run 45 psi all around. They look too poochy to me at 35. When I got new rears, the tire store sent me out at 80 psi! Rode worse and felt "nervous" at high speed.

 

I always run 80#, really helps the fuel mileage. Rides a little rough but not too bad. If I want a smoother ride I drive my big Olds wagon (Just like a boat, it floats along!!!)

 

Bnrealfast0 - - If you run at 80# all the time what kind of wear are you getting? Seems like you'd be riding only on the center of the tires. May get good milage but are you paying for it at the other end?

 

i run 5 over what tires say

 

The last time I had my truck on the scale it weighed in at 7000 right on the nose. That's with a canopy, tool boxes, and a 45 gallon aux tank full. I run my tires at 60 with the rears at 65 when towing. My last run up to Piers Dyno Mania 2003 and back to Portland OR - including 5 days around town and another 250 mile trip showed 21.45 mpg. See my sig for mods.
Bob

 

sounds like the scales were a little light, my 85 Chevy 4x4 weighs 5200 lbs empty, that Cummins gotta weigh more than the difference there it would seem. I run Michelin XTH, I think thats what it is, 35 in the front and 40 in rear when empty. then adjust per the load. I got about 30k out of them so far and there getting down pretty good. I drive 25 miles of winding country roads every day probably pushing harder than I should. What else is good for wear and ride quality?.
Thanks, Apache

 

I think his numbers agree with mine pretty well. He's about 400 pounds lighter, but I'm carrying 2 extra wheels and that cast iron 5 speed. Remember he's in a 2wd truck, 4x4 adds another 400 pounds of iron. Knock that Chevy back 400 pounds to make it a 2wd and he's 800 pounds ahead. Seems reasonable to me.

 

Last time I weighed mine it was 3940 fornt, 2500 rear with me and a full tank. I weigh 180 so truck is 6260 empty. I have 265 BFGs and I run 30 rear and 45 front empty. (bad back) On vacation this year I crossed the scales once at 8700 and once at 9200. Rides good at those weights. Thats with an 8 ft cabover.

 

There is a mathmatical formula that will get you into the ball park for tire pressures.

Take the weight of the axel divide by 2 divided by the max wt your tire will carry times max pressure cold.

wt of front axel = 3300lbs.
max weight tire will carry = 3042lbs.
max pressure cold = 80psi.

3300 / 2 = (1650 / 3042) x 80psi = 43.4psi for each tire.

It works for me when running empty, when carring a 2800lb cab over camper, I air the rears to 75lbs and the fronts to 70 and get on down the road. This is only a suggestion, to each his own.

Jim

 

I run my fronts at 80#, rears at 43#. Dust marks on tread looks even edge to edge, checked them in a dirt lot they looked even, wear looks good. See signature for add-ons, plus 400lbs loads weekly. Patrick

 

[quote author=Bob Beauchaine link=board=9;threadid=20839;start=0#msg195676 date=1065899434]
The last time I had my truck on the scale it weighed in at 7000 right on the nose. That's with a canopy, tool boxes, and a 45 gallon aux tank full. I run my tires at 60 with the rears at 65 when towing. My last run up to Piers Dyno Mania 2003 and back to Portland OR - including 5 days around town and another 250 mile trip showed 21.45 mpg. See my sig for mods.
Bob
[/quote]

After I posted that message, I took off for Mississippi. Drove 960 miles in 16 hours. The truck rode positively comfortable. I've never felt it so smooth. I checked the mileage on the way down. Cruising at speed limit +5, about 70-75 mph, I got 21.8 mpg. Cruising at 60-65, I got 26.5 mpg.

I also checked the tires, and don't see any obvious wear at the edges as yet. I probably don't have enough miles on the tires yet, to really know whether I will get excessive wear.

I can't imagine driving with an empty truck with 80 psi. in the tires. I wouldn't have any fillings left in my teeth. I have always run at 45 psi. before this, but if I don't get any bad tire wear, I am going to continue at 38 psi. Maybe even drop further to 35 psi. ;D

John

 

To finalize this, I came out tonight, just as the sun was going down, the sun was at the right angle, and it highlighted the tread on the tires. I could see the fronts were starting to cup on both inner and outer edges, but the rears were fine. I guess 38 psi under that heavy engine was too low (regardless of what Dodge said in the manual). I have now put the fronts back to 45 psi. I'll leave the rears at 38 psi for the trip home, and check to see if they still look OK when I get home.

John

 

I got home tonight and checked the rear tires. After 2514 miles, 38 psi on the rears was starting to cup the edges, ever so slightly. They'll be back up to 45 psi tomorrow along with the fronts. I guess this aught to teach me not to mess with things.

Oh by the way, over that many miles, cruising at 65-75 mph (typically 6-7 mph over the speed limit), I got 21.4 mpg. This is the first time I've driven so many miles without towing something, but I never thought I'd get anything like that.

John