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Old 04-08-2016, 04:53 PM   #1
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Ride vs tire pressure

The past couple of years we went to Florida and I-65 in both the Montgomery and Birmingham, Al areas were like driving on a washboard. It just beats you to death and almost rattles your teeth. I usually have tire pressure at 90 PSI cold, front and rear. My tires are 255/80R/22.5 and my 378 is on a 24,000 lb chassis. Tow dolly tongue weight almost nil. Based on numerous FROG forum input, my front axle will be real close to 7700 LBS and about 15200 on the rear, ready to roll. I have been thinking of lowering the pressure per the Michelin Tire specs to 75 or 80 on the front and 80 on the rear. I know that lower tire pressure causes faster wear to some degree, but don't know the effect if I am with in the tire specs. Wondering if this may help the harsh, beat you to death ride on rough roads. Does anyone have any input as to ride vs pressure vs wear? Thanks.
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Old 04-08-2016, 05:01 PM   #2
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You have no idea what your actual loads are on your tires unless you get on a scale. Corner weights are what you really need to know but lacking that you should assume a 55/45 side to side split in load for each axle. Using the load/inflation tables you then can learn the MINIMUM inflation needed. You should then add 10% margin so you don't drop below the minimum inflation needed when temperature drop or the tires loose air through normal air permeation.
Also if you are going to cut it close you need to have your air pressure gauge checked against a know accurate gauge. Running a TPMS is also very good insurance and can easily pay for itself with the first low pressure warning.

However I doubt you will feel much improvement in ride by lowering pressure 5 or 10 psi.

Tire durability (life) is also reduced when you run lower pressure not just tread wear.


Note the above inflation pressure info applies to motorized RVs not to trailers.
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Old 04-08-2016, 10:55 PM   #3
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That five or ten pounds will make a big difference. I figured mine the same way as you were trying to do and it worked out perfect I'm running a 22000 pound chassis and I run 80 pounds front and rear. Made a big difference in handling and ride but it still wasn't good so I added some sumos to the unit and that is what made the big difference and now it rides great.
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Old 04-08-2016, 11:07 PM   #4
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Ride vs tire pressure

Tireman9, in a previous post a 378 loaded ready to go was 7716 lbs front axle and 15200 lbs rear axle, and my 378 would be extremely close to the same weight. Although I usually do not run with much water. I am comfortable using that weight. I do have A TPMS system and my tire pressure gauge is within 2psi. I don't have corner weights, but even if I did you can not run different pressures on the same axle. You have to go with the higher of the two. I was simply looking for information as to trying to help with the harsh, bone rattling highways, but do not want to run a low pressure and cause premature tire wear.

Jergeod thanks for the info. I may drop the pressures and give it a try.
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Old 04-09-2016, 12:57 AM   #5
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It will help. How much is debatable and only you can be the judge.

If you want to find exactly what tire pressure each axle likes, you need a tire crayon available at any parts store, a flat parking lot, and an afternoon.

Fill your tires to their max pressure as indicated on the sidewall. Don't worry about recommendations for now and no disaster will befall you.

Go to your flat parking lot, then use the crayon to draw a three inch wide stripe all the way side to side across the tread block. Do this on all the tires. Then hop in, and drive forward about 20 feet. You want the tires to turn at least twice. Try to watch the valve stem and stop with it at the same place you started so you can see your marks.

Then look at your crayon marks. Chances are the center will be gone, but not the sides. The high pressure causes the center to bulge slightly. Drop the pressure five psi, fill in where the crayon was rubbed off, and drive forward again. Check, color the block back in, and repeat dropping the pressure each time. As you get close you can drop less pressure at a time.

Once the crayon block is evenly rubbed off, that is your pressure the tire likes under that load. Don't drop below minimum recommended pressure.

What this does is establish even pressure across the tread block, which is what the inflation charts do if you know your actual weights.

The next morning when the tires are cold check the pressures, but it shouldn't vary much since odds are they won't be too hot driving to then playing in a parking lot. Reset the pressure to your new number established in the parking lot, and give it a try.
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Old 04-09-2016, 09:14 AM   #6
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Mickeystamper, just be sure you are using the pressures recommended by the tires you have and their chart.
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Old 04-09-2016, 09:57 AM   #7
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Ride vs tire pressure

Jergeod

I do have specs page, thanks
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Old 04-09-2016, 01:17 PM   #8
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I've driven on and off road all my life. Motorcycles, 4WD, passenger cars, RVs. I've always run the recommended air pressure in all my tires. Not only will you get better tire wear, but you have improved handling and control while cornering and braking. Plus lower inflation pressure too much can cause the tire to spin on the rim or come off during a hard corner. (Not that I think dropping from 90 to 80 lbs would cause this).
But as far as improving handling I have ALWAYS had my best results with suspension "mods" and upgrades. (Shocks, Steering Stabilizers, Springs). On my 360, I've added Sumo Springs, and a Steering Stabilizer. The difference in handling is "Night and Day"!!
And of course I drive per road conditions. If I need to slow a bit, I do! Nothing is that critical that I have to be there at a particular time. I can always call ahead and update the folks at our next stop.
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Old 04-09-2016, 01:44 PM   #9
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What are sumo's? We are looking at making our ride more comfortable, but have been quoted over $2k for a stablizer kit. Any other suggestions would be welcome.
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Old 04-09-2016, 02:30 PM   #10
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If you search the internet you will find Sumo, they mount between your frame and leaf spring for better ride and sway control. I have been thinking about getting them as all I have read and heard are good things.
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