Tire Pressure

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Just wondering why everyone runs such high tire pressure on their Rams. When I had a gas engine and 235x15 tires the recomended tire pressure was 35lbs. Now that I have a diesel truck with 235x16 tires the recomended pressure is 50lbs plus. No wonder the ride is so stiff. Any ideas????

Gene-C

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98 12V SLT 2500 4X2 AUTO QC SB Driftwood W/color match Topper, Full alum Boards,Delux OE mud guards, Tow package, Bugflector,SS Wheel well trim, 21. 5 mpg A lot of show and enough go



[This message has been edited by Gene-C (edited 01-09-2000). ]

 

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Gene, the Cummins engine weighs a lot more than a gasser, over 900lbs I believe. Even so, I run 45psi in the front tires and 40lbs rear. I keep an eye on tire wear and haven't notice any problems so far. When hauling a heavy load, I increase the pressure accordingly.


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'98 2500,4X4,QC,SB,Auto, 4:10's,Deezee Stainless Running Boards,5th wheel hitch,CB,MTX Moulded Sub enclosure dual 10" subs, Kenwood amp,Alpine alarm.

 

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Gene-C:
I always correlated the need for psi's to the need for more stability due to the greater weight of the diesel blocks and the tendency for these trucks to experience heavy loading. I run LR E at 70 psi's. The ride is rough but then again by RAM is a '91 D250 4x... (read kidney bruising tooth chipper #ad
Regards, kad

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Stock '91 sc D250 4x4, 5sp, 3. 54's, 235/85's,250k+.

 

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Maybe you should get a softer seat and run the tire pressure higher (LOL) see ya at work

 

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Gene C:
I, for one, don't like harsh rides. I've run my tires at 32# since 1994 when I bought the truck and inflate them more only when towing requires me to do so.
I consider myself a a maintenance nerd. I keep the front end of the truck aligned and in top shape and the tires are rotated like clockwork by the tire shop. Never, not once, have they ever showed signs of underinflation at that pressure.
I have NO problem with running less air. Don't be afraid to try it. You can always go back to the stiff ride if you feel guilty.



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'94 SLT 2WD, 5 Spd. , 3. 54, Synthetics, By-Pass, TST, Gauges, Scotty K&N, Horton, 4" Exhaust, Prime-Loc, Chromed Acc's, Gutless Cat, Silenced Ring, PIAA's, 255x85Rx16's and 12v Pride.

 

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EZ94: Thanks for the info. I will try the lower pressure for a while and see how it works. I noticed with the high pressure the the footprint of the tires is quiet small. This is probably good for fuel mileage but I would think for better traction on snow or ice and wet roads that less pressure would give a larger footprint thus better grip. Gene-C

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98 12V SLT 2500 4X2 AUTO QC SB Driftwood W/color match Topper, Full alum Boards,Delux OE mud guards, Tow package, Bugflector,SS Wheel well trim, 21. 5 mpg A lot of show and enough go

 

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Low presure can cause the tires to squirm,and accelerate tire wear. My . 02 cents worth.

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97 Ram 2500 4x4 Driftwood 5spd 3:54 E-brake Isspro,boost&pyro guages 24,500 miles

 

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You don't want a wide footprint for the snow tall and skinny is the way to go. You want to cut though the snow not stay up on top of it. Wide could be argued for mud but these trucks are to heavy to have flotation in mud you are going to find the bottom of that mudhole if there is one.

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97 2500 4x4 NV4500 NV241HD 4. 10's posi CC every heavy duty option available,Reese 15k 5th wheel,turbo silencer removed



[This message has been edited by neibe (edited 01-12-2000). ]

 

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Neibe:
You want a WIDE footprint for snow and mud. If you have ever walked in deep snow you want a WIDE snow shoe right? You don't want to cut through the snow or mud you want to ride on top of it.

For the rain you want a long narrow footprint so the tire will cut through the rain and not hydroplane. This is proven by how awful Corvettes and other WIDE tired cars do in the wet, because of the foorprint is not set up to slice through water. Look at narrow tires to do a good job at water riding but you will give up some on the dry handling side.

 

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VWTdi, sorry guy, but you are WRONG about wanting a wide tire in the snow!! Wide tires have too much flotation on snow and will not let the weight of the vehicle push the tire down, and compress the snow into the spaces of the tire. That is what gives you traction. Snowshoes are for an entirely differant purpose, they make it possible to walk on top of snow that is too deep to walk through. Having been born and raised in snow country (Cleveland OH), lived in New Hampshire, Montana, and Lake Placid NY I can guarantee, in snow wider tires are not better. Happy Rammin, Dave Hauser

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Dave Hauser, 96 3500 4x4 extended, auto 4:10 LSD, K&N, tow hooks, fog lights, custom front reciever hitch and mount for 8000 Ramsey winch, alum diamond plate box and running boards, Dodge dually mudflaps, tow 18' flatbed, 69 Vette, 89 HD FLHS

 

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I agree with Dave. You definately want a tall skinny tire for snow that way you do "cut" through the snow and get down to the pavement where there is at least some traction. Around here (Michigan) you see lots of lifted trucks that run 33x12. 5's or larger in the summer and go to a 33x9. 5 for the winter. The exception to this is if you want to go off-road in deep snow then you would want to stay on top of the snow and have a wide footprint. Ever see a picture of the trucks they use up in Greenland and places like that? They have HUGE tires - probably 25+ inches wide that they run really low air pressures on (like 2 psi I think) so they stay on top. They are also fairly light vehicles. With the weight of our trucks I doubt you could find a tire wide enough to stay on top of the snow.

The reason our tires are run at such high pressures is because of the type of tire (load range E) and the amount of weight we have. I replaced my stock tires (215's I think?) load range E with 285/75R16's load range D. The stock tires hit their maximum load rating (3055 lbs) at 85 psi, the new ones hit their max (3300 lbs) at 65 psi. The newer tires are definately softer and give a better ride than the stock ones and I run them at 55/45 unloaded. One word of caution running too low of an air pressure. When I bought my tires the guys at the tire store put them at 35 psi all the way around. I had asked them if they had a recommended pressure chart and they looked at me like I was talking russian or something. Driving the truck home I thought "Man did I make a mistake buying these tires". The truck was all over the road. I checked the pressures then figured out what I should be running (I can post this info if you'd like) and finally settled on 55/45. The truck now handles better than it did with the stock tires. So if you lower the pressures and the truck feels loose raise them back up some.

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-Steve St. Laurent
'98 QC LB (CMNSPWR), 4x4, ISB, 5sp, 4. 10 LSD, Prime-loc, boost & pyro gauges, TST Powermax, Permatech spray in liner, Grizzly ss nerf bars, front Draw-Tite receiver, BFG 285/75R16 AT KO's
Great Lakes chapter of the TDR

 

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Steve:
One of the differences Gene and I have from your truck is that we both have 4 X 2's while you and others who have responded have 4 X 4's.
I know from the experience of a close friend of mine that 4 X 4's handle differently from the 4 X 2's. That friend's '95 would wander over the road and after two years of having the dealership try and fix it, Dodge eventually had to buy it back under our State's Lemon Law because they could not fix the problem. He loved the truck so much, however, that he ordered another one. Had the '97 4 X 4 one week and had the same problem... the truck would wander when under load and the brakes were applied. Ended up with a Ford PSD.
My point is this: there is an inherent difference between 4 X 4's and 4 X 2's and the way they drive. While lower inflation pressures may affect the tracking of 4 X 4's it certainly hasn't made a difference in my 4 X 2. My Ram drives beautifully and I have never seen evidence of increased wear from running 32 lbs. of pressure. I know what those signs are and you can be sure the tire shop would be the first to comment because they are on the hook on the mileage guarantee.
On a different note regarding tire widths, it's my understanding narrow tires are easier to drive in snow than wide ones. I don't know if easier means better.
FWIW, as long as air pressure remains constant, the size of a tire's "footprint" will always be the same regardless of whether the tire is "skinny' or "fat". The SHAPE of the footprint will change, but not the size. So much for the hype that one tire "puts more rubber on the road" than another. My $. 02 worth.

 

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The difference between 4x2 and 4x4 could very well be my wandering problem with lower pressures. Plus with a 4x4 your gonna have to run higher pressures anyways cause it's heavier (especially in the front). However, I have to greatly disagree with you that a tire's footprint doesn't change with width. Let's say that 6 inches of the length of the tire contacts going from front to rear and you have an 8 inch wide tire (tread is really the only thing that matters). Then you have 48 square inches of contact patch or footprint. Now take that exact diameter tire but make it 12 inches wide. You now have 72 square inches of contact patch. What I think you may have been thinking of is if you put the same size tire on a narrow or wide rim. Then you will have the same contact patch but your sidewalls may be bulging.

-Steve

 

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Steve,
Thanks for the response. When I first learned the concept about size of the footprint remaining constant, it seemed to go against the grain of everything that made sense to me. I'n not an engineer so it took a little time for it to sink in.
If the tires patch on a given vehicle measures 8" wide by 8" long you have a total of 64 sq. inches of footprint. If you're running 32 lbs. of air pressure (32 lbs. per square inch) that tire with that patch will carry 2,048 lbs. of weight. Now, using the same vehicle and changing the design of the tire so that its footprint changes to only 4" wide you will find that to support the same weight, the length of the footprint will have to lengthen to 16". The one item that must remain constant throughout all of this is the air pressure. If it remains the same then the area of the footprint will remain the same. Play with the air pressure and you can play with the footprint all you want.
Now comes the disclaimer. I wasn't a physics major in college and there's a good chance I may have misunderstood this concept. But this discussion left such an impression on me when I first heard it that I've never forgotten it and I hope I remembered it correctly.
D'ya think we should ask one of the members with an engineering or physics background for their input (Joe D. ?). If I'm wrong, I sure need to know it.
Anyway, that's why these discussions are so much fun.

 

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Gentleman: Let me jump back in and relate an experience that I have had. In about 1975 I bought a Dautson pickup. It was an import with very narrow small tires from the factory. Someone had replaced the rear tires with much larger american made snow tires. I thought that when it snowed that I would be in deep do' do'. Mutch to my surprise that little truck not weighing more than maybe 2600lb went thru the snow like a four wheeler. The narrow tires in front cut thru like sled runners and the big wide snow tires with the larger footprint pushed the little truck in snow up to the bumper. Speaking of footprints in relation to tire pressure. We have all had flat tires. The footprint gets pretty big when the air press goes down to 0 lbs. In that respect it should get bigger if we lower the press a few lbs. Gene-C

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98 12V SLT 2500 4X2 AUTO QC SB Driftwood W/color match Topper, Full alum Boards,Delux OE mud guards, Tow package, Bugflector,SS Wheel well trim, 21. 5 mpg A lot of show and enough go

 

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On my '98 12V 4x4, I ran 55 PSI in front and 40 PSI in the rear. In 50K miles on those tires, I had slight over-inflation wear. But the truck ran about stable as could be expected. The owner's manual says what the pressure should be. The few times I loaded the bed (with railroad ties or horse manure), I ran the pressure up to 65 PSI front and 80 rear. When I hauled the ties from IL to VA, the tires never got hot; I don't think they got more than warm.

The one thing you *don't* want to do is underinflate. Tires with low pressure have a lot more flex when rolling. This flex causes heat, and excess heat will surely cause rapid failure.

If you have the tires inflated to DC's specs and the truck still wanders, there are likely two reasons. First, the track bar could be worn. After I installed the new 19'5" Yokohamas and had the FE aligned, the track bar was found to be worn out. THe shop that did the front end always has a supply of replacements on hand, as they are *known* to fail (the one ball-n-socket joint fails). Unfortunately, only DC makes the track bar, so the problem is solved only for a short-ish while. [The track bar is what keeps the front axle from moving side-to-side during operation. ] My truck wandered a little on rough roads, but now it's fairly solid.

The other reason for wander could be the 'links':
the bars that keep the axle from moving forward and backward during operation. The factory uses rubber bushing which may allow too much motion. There are after-market links that use polyurethane bushing which are much stiffer. Disclaimer: I haven't replaced mine as yet; I've only read about a couple folks who have replaced theirs and have marvelled as the enhanced control afterward.

Back to tire pressure, remember that the Cummins engine weighs about 500 pounds more than a gas engine; the front tires *need* more pressure to maintain proper tire 'formation'. The rear pressure can be reduced because there's much less weight on that axle (unladen). With the new 19'5" tires, I run 65 PSI in the front and 55 in the rear. I might be able to get away with a little less pressure, but the radial 'bulge' looks about right and the ride is good enough on less-than-rough roads, and wonderful on smooth roads.

If you have stock tires, use the pressures recommended in the owner's manual; they may cause
slight over-inflation wear over the life of the tires, but the tires will run nice and cool.

Fest3er

 

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Good information all,

I'vee always thought that a 'flexing' tire would generate more heat and possible failure under heavy loading.

What puzzles me is the information contained in the inflation guide that came with my 2k 3500 from Goodyear... .

50 front / 40 rear when empty
65 front / 50 rear at capacity

NOTE: stated on sidewall of each tire, "maximum pressure 80 psi".


50 pounds in the front tires on the Cummins look like 'flat' tires... too much sidewall curve... 60/70 looks and handles much better.

Also, 50 in the rear under load (3400 pound camper) also look 'flat', with the sidewalls between the rear tires almost touching.

So, I've been running 65 front and 70 rear under load. On our recent 5300 mile trip, I checked pressure daily (cold and hot) and the pressure never got higher than 75... . (ambient air temperature was in the 40s). I haven't noticed any irregular wear other than the outsides of the front tires (probably normal).

Tire heat is a killer here in Texas so I'm going to watch my pressures REAL careful this summer.

Charlie

 

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wcharlie, You didn't mention weather you have the 215s or the 235s. My 96 3500 has 215s and to keep from "eating the edges" of the front tires I run 80 psi at all times, and run 50 psi rear. This works well for me towing or not. I gross 14000 towing the Vette and with the Harley in the back of the truck. If your front edges are wearing you are not running enough pressure for your weight/driving style. The tread should wear even accross, YES you will give up some of the soft ride but you will gain HANDLEING and milage. I would recomend going up 5 psi at a time and observe, presure shouldn't go up more than 2-4 lb. after driving. Yes heat is a killer, and sidewall flex = heat. I have 45000 miles on the OEM Goodyears and will be changing by the end of this summer (about 50000). Hope this helps. Dave Hauser

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Dave Hauser, 96 3500 4x4 extended, auto 4:10 LSD, K&N, tow hooks, fog lights, custom front reciever hitch and mount for 8000 Ramsey winch, alum diamond plate box and running boards, Dodge dually mudflaps, tow 18' flatbed, 69 Vette, 89 HD FLHS

 

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A way to confirm this pressure vs footprint would be: ( i will let my Quality Experience help here) but am not going to do the work.

raise up one wheel, apply a light coat of soap, oil, or whateer to the tire. set the pressure, lower the tire onto cardboard, repeat this process thru several pressures on different spots on the cardboard, measure the impressions, results could then be quantified.

if you want the effect of different size tires just find a friend with the other tire size.

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95-2500-ExtCab-LB-4x4-Auto-AMSoil Air Filter, Bypass Oil Filter by others, AMSOIL and Mobil Synthetics, TST 255HP and TransGO Shift kit .

 

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I recently purchased 285's by Goodrich formy 98 4x4 at the recommendation of a friend that has a Ford diesel. I started them out at 40 and have now dropped to 36 on all 4 and it rides like a car. He ran his Ford at 32 all around and it was a 4x4, has 50,000 on them and no signs of underinflation. I guess whatever works for you. What a difference in the ride from the 245 to 285 tire.