Dropping tire pressure for better ride

[PS56]

Originally Posted by cherv

Currently run 80psi on dually rear tires and 75 on front on our 2019 jayco class c 25 foot. I am thinking of dropping psi by 5 psi all around.

One cause of blowouts is underinflated tires. The sidewalls flex too much, build up heat and blow.

[jjrbus]

Weight+load and inflation tables. Weight+load and inflation tables. Weight+Load and inflation tables.

https://www.youtube.com/watch?v=d-gP...NuIa1o&index=1

https://www.youtube.com/watch?v=M7qj...NuIa1o&index=2

[Ron Dittmer]

Hi cherv,

As others mentioned, to optimize the quality of your ride, you really need to weigh your rig during a trip. Truck stops have weigh scales that are very convenient to drive on and pay $10 or so to get the numbers. You want to weigh the front axle separate from the rear axle, and also the entire rig of which the scale operators are very accommodating.

With the "actual" weight on each axle, you can then safely optimize your tire pressure accordingly.

I think you will learn that you have been over-inflating your tires by a lot. Just 5 psi extra is noticeable in the quality of the ride. Based on what I know with our loaded E350 rig, you might be as much as 15 psi over which makes for a very rough ride which is very hard on the house and contents.

Contrary to what you might think, more PSI is not safer. Putting 75 or 80 PSI in a tire that requires 65 PSI is over-kill, and if you run over something that causes a blow-out, that 75 PSI will be a much bigger bomb, damaging a lot more than would at 65 PSI.

If you are adding extra for the sake of improved fuel economy, you will learn that the difference is nearly unmeasurable.

When adding air, use a digital tire gauge. The mechanical ones vary too much as I learned with all my tire gauges at home. You can read about my evaluation by CLICKING HERE.

[jjrbus]

Over inflating tires to improve mpg is commonly posted. All institutions that have studied this agree that it will provide better mpg, not 10 or 20%, more like 0.04%, which comes at a danger of longer stopping distances, hydroplaning and tire damage.


I have not seen one credible study claiming over inflating tires is a good idea.


I use a non digital Harbor Freight inflator. However I upgraded the gauge to an oil filled precision gauge, works for me and is spot on. I like the body of the HF and the ability to release air at the touch of a button.

[Roland J]

load inflation table?

I can't seem to find the "load inflation table". What should i search for?

My tires are Multi Mile Radial XRT III Wild country tires.

I think they are made by Cooper tires. I haven't weight my MH yet but when i checked the pressure the front was 65PSI and the rears were 55PSI. The door jam suggested the rear be 80 PSI

[Kid Gloves]

I may have missed it. Has anyone mentioned getting the coach weighed? These rigs don’t have a tremendous amount of CCC, so it wouldn’t be that unusual for it to be near GVWR, or over, despite the owners age. This would make the recommended pressures on the placard a good starting point.

Has the OP given us the model, GVWR or tire size and load range? No. Yet we have recommendations for correct tire pressure based on having virtually no information.

The OP has proposed lowering air pressure for a better ride and we have no information on what ride qualities he would like to improve. Tire pressure is the easy part. Get that correct first, then figure out what other modifications might be necessary to improve the ride.

[THenne1713]

Reducing rear duallies by 10-PSI drops AXLE CAPACITY by +/-1000#, if you ever overload, which can be the GOOD tire when OTHER tire goes LOW, internal damage results= zipper rupture= blowout of 2nd tire 50-100-miles after replacing first blown tire; suspect also more likely to bottom out on rim= tire damage at pothole, but (I would) 1) LOOK at driver door label and the WEIGH AXLES AND TIRES WHILE FULLY LOADED, THEN decide? LOW is much more dangerous than 5# too high.

[move on]

The tire manufacturer gives us a minimum pressure in his load chart and a maximum pressure as stamped on the tire sidewall. We have to stay within that range or risk tire damage. But within that range there are tradeoffs to be decided upon. We want a smooth ride but we also want safety and what's good for one is not necessarily good for the other. One of the most important aspects of safety is how the vehicle handles in an emergency maneuver. Is it going to oversteer, swerve and roll over? What happens during a front tire blowout and what happens during a rear tire blowout? Lots of questions that can't be answered without extensive testing. The vehicle manufacturer is in a position to perform these tests and recommend what's best for the general public in the most common situations and he puts his final determination on the door sticker and in his operators manual. We can tweek these numbers but we'll never know if doing so will make us better off.

[jjrbus]

Originally Posted by Roland J

load inflation table?

I can't seem to find the "load inflation table". What should i search for?

My tires are Multi Mile Radial XRT III Wild country tires.

I think they are made by Cooper tires. I haven't weight my MH yet but when i checked the pressure the front was 65PSI and the rears were 55PSI. The door jam suggested the rear be 80 PSI

Check where you bought your tires from.

[Roland J]

Originally Posted by jjrbus

Check where you bought your tires from.

I just bought the MH 10 days ago, no idea where the tires came from.
I found a chart for my rear tires

[Roland J]

I found a chart for my rear tires.

If I understand this right, my rear tires should never need more than 65PSI in them, yet the door suggest 80 psi. Strange.
I haven't weighted it yet but i suspect 55-60PSI may have been the right pressure.

Based on a rear GAWR of 9450lbs / 4 = 2350lbs per tire. The tire chart says 2350lbs should have 65PSI.
This stuff is good to know.

[Kid Gloves]

Originally Posted by Roland J

I found a chart for my rear tires.

If I understand this right, my rear tires should never need more than 65PSI in them, yet the door suggest 80 psi. Strange.
I haven't weighted it yet but i suspect 55-60PSI may have been the right pressure.

Based on a rear GAWR of 9450lbs / 4 = 2350lbs per tire. The tire chart says 2350lbs should have 65PSI.
This stuff is good to know.

At GAWR, your rears would need a MINIMUM of 65psi, based on your chart. Many would probably run them at ~70psi. The tires would be under inflated at 55-60psi.

[Roland J]

Originally Posted by Kid Gloves

At GAWR, your rears would need a MINIMUM of 65psi, based on your chart. Many would probably run them at ~70psi. The tires would be under inflated at 55-60psi.

Thanks for looking at my statement. As I'm trying to sort this out I did catch a mistake I made. I was looking for a single wheel load weight, I should have been looking at the dual tire load, which says 75PSI (not 65).

But if I understand correctly GAWR means the Maximum weight that the Axle should ever have on it. So the 80 PSI door sticker makes sense now.

[Ron Dittmer]

Originally Posted by Roland J

But if I understand correctly GAWR means the Maximum weight that the Axle should ever have on it. So the 80 PSI door sticker makes sense now.

Our small rig HERE is built on a 2007 E350 SuperDuty DRW chassis with V10 engine, with GAWR numbers as follows.

GAWR front - 4600 pounds
GAWR rear - 7800 pounds

Our rig empty weighs as follows (nobody inside, full gas & propane, no water's)
front - 3160
rear - 6760

On our heaviest trip (with us in the front seats)
front - 3260
rear - 8220 (exceeded GAWR by 420 pounds)

Our 4 LTX M/S Michelin tires combined at 80psi are capable of 9880 pounds (2470/tire)
So in our case, the rear axle rating is the weakest link, not the tires.

A long time ago, I read somewhere that the ratings are not necessarily limited to the weight placed on the axle alone, but in combination with the balance of the chassis. Our E350 chassis is a 2007 model year which had NO rear stabilizer bar of any kind. Ford never installed one. Adding a heavy duty rear bar and changing the front bar to a heavy duty, likely increases the GAWR for each axle by "some" amount. The heavy duty Bilstein shocks and rear trac bar also installed could further increase GAWR.

I initially brushed off what I read, but then I compared the specs of my 2007 to a 2008 which was the first year Ford installed a rear stabilizer bar. The rear axle GAWR increased from 7800 to 8500 pounds. I assume Ford also added one more leaf spring to an otherwise unchanged rear suspension. If I am over by a little on my rear axle once in a great while, I still rest well. My rear leaf springs might be a bit over-loaded now and then, but we appreciate a more comfortable ride.

If you review my numbers, you will see that our rig suffers from the teeter-totter effect. My wife and I weigh 300 pounds together, yet we added only 100 pounds on the front axle during that extra heavy trip. What does that tell you? Here is my weight distribution.


For reference, here is our tire weight/psi chart.