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Old 09-24-2021, 02:17 PM   #1
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2014 Lexington 265DS - Weight Distribution, Tire Pressure, Air Bag Pressure

2014 Lexington 265DS - Weight Distribution, Tire Pressure, Air Bag Pressure

I recently joined IRV2 to take advantage of the 5-Star Tuner discount. Here is my first post to IRV2 so hopefully I post it to the right area. This post will give you the tire and air bag inflation pressures I have decided on after weighing and reviewing the tire inflation pressures charts and the RV weight capacities for our fully loaded 2014 Forest River Lexington 265DS Class B+, built on a 2013 Ford E450 V10 5 speed.

SUMMARY:
The manufacturer recommended tire inflations are 75 psi front and 80 psi rear. I have set my tire inflations to 65 psi front and 80 psi rear.
I have set my air bag pressures to 60 psi on the drivers side and 50 psi on the passenger side (I may have gone with a higher air bag pressure without my upgraded shocks and sway bars - see my notes below).

WEIGHT DISTRIBUTION:
This motorhome is light in the front and heavy in the back. The 265DS is particularly heavy on the back driverís side due to the extra weight of the two slides and the 3500 watt generator, all located on the driverís side. The unit is light in the front given no overhead bunk and some lightening effect from the weight of the rear overhang, where the water, waste and fuel tanks are all located, all behind the rear wheels. The RV remained within its weight ratings at full load, however it was approaching its maximum capacity on the rear axle at full load, so when fully loaded I will have any additional weight or passengers ahead of the rear tires to transfer some of that weight towards the light front end. Cargo weight can also be added to a towed vehicle.

INFLATION PRESSURES:
Tire placard recommended inflations: 75 psi front, 80 psi rear.
Weighing RV and using inflation charts: 65 psi front, 80 psi rear.
Air bags:
60 psi driverís side, 50 psi passenger side.
I will consider an additional 5 psi per air bag for extra load / passengers / towing.

WEIGHTS AND RATINGS:
The RV was weighed with a full load including full freshwater, full fuel, full propane, empty waste tanks, fully loaded for travel, and with two passengers.

Front Axle 3770 lbs (5000 lbs GVAW)
Rear Axle 9281 lbs (9600 lbs GVAW)
Total weight 13,051 lbs (Dry weight 11,200; 14,500 GVWR)
Front drivers side 1852 lbs (inflation chart 48 psi)
Front passenger side 2178 lbs (inflation chart 60 psi)
Rear drivers side 4708 lbs (inflation chart 76 psi)
Rear passenger side 4378 lbs (inflation chart 68 psi)

CHOOSING TIRE INFLATION PRESSURES:
My goal was to reduce the tire inflations if possible for a better ride and better tire to road contact, but stay within safe limits on all four tires, with some additional buffer above the full load condition.

65 psi was chosen for the front tires, allowing for an additional 155 lbs capacity above the fully loaded heavier front passenger tire. I felt 65 psi was safe since this would require 620 pounds to be added at the RV mid point, over and above the full load, just to reach the capacity on the heavy side at 65 psi. It also allows room for some extra weight on the front as lower fuel and water levels reduce the front lifting effect from having that weight behind the rear wheels.

As much as I wanted to reduce the rear tire inflation for an improved ride, I chose the full 80 psi for the rear tire inflations. This maintained a small buffer (222 lbs) above the heavy drivers side 76 psi inflation chart pressure at full load. I have since redistributed heavy items from the drivers side to the passenger side so the buffer is closer 350 lbs now. This buffer would be needed if the RV was ever fully loaded for travel, plus full fuel, plus full fresh water, plus full black water (unlikely to ever happen, but still safe).

Of course, both tires on an axle must be the same pressure so the weights on the light side tires are much lower than their weight capacities at these inflation pressures.

CHOOSING AIR BAG PRESSURES:
It was difficult to find specific info on air bag pressures, with people using various pressures from 40 to 70 psi. I found 40 psi too low to adequately support the rear on big bumps at highway speed but still wanted to keep the pressure as low as possible for ride comfort so I settled on 60 psi on the drivers side and 50 psi on the passenger side. I am still testing this and may increase this by 5 psi per side, especially with extra load, passengers or towing.

The rear drivers side is 330 lbs heavier than the rear passenger side at full load, with full fuel and water. The rear drivers side was heavier even with the 337 lbs of water in the rear passenger side tank, so the weight difference between sides will increase as the fresh water on the passenger side decreases and the black water on the drivers side increases. I set the drivers side air bag 10 psi higher than the passenger side based on the air bags supporting about 40 lbs per psi (an extra 400 lbs support for the heavy drivers side). This seemed to work well on a recent 400 km (250 mile) road trip which included both highway driving and secondary roads.

If you are referencing my information to help determine your air bag inflation pressures, bear in mind that I have Bilstein RV shocks and Hellwig sway bars. If you have the lighter original equipment shocks and sway bars you may choose additional air bag pressure at full load to help support and counteract the extra movement in the rear of your RV. Also, I set my air bag pressures after the RV is loaded and off the jacks as air bag pressures can change with load.

TOWING:
The RV was not weighed with our Honda Fit towed vehicle, however there would be minimal additional weight on the RV wheels as the Fit is towed on all four wheels. Weight such as bikes can also be carried in the Fit (max 850 lbs) to avoid adding weight to the RV or to redistribute heavy items from the RV. The tow capacity of the RV is 5000 lbs and the Fit dry weight is 2550 lbs, so we are well within the towing capacity.
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Old 09-26-2021, 05:04 AM   #2
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You seemed to have done very well with your homework. The only thing I wonder about is having different tire pressure for tires on the same axle. I always thought that was a no-no. If one rear corner requires more air than the other, bring the other up to that same pressure. But maybe that applies only to the front axle. I am surely no expert.

Like your rig, our 2007 E350 chassis is tail-heavy and front-light. Our rear axle is at the rated limit and our front axle has a lot of extra weight margin. Like you did, I used the weight numbers to determine the proper tire pressure with our new set of 6 Michelins. In our case, I put 60 PSI in all rear tires. I was not comfortable running with only 40 PSI in our new front tires so I ran with 50 this past trip. I am considering 45 PSI on our next trip.

To further soften the ride up front, I took advantage of the lightly weighted front and changed the front coil springs to the next lower-rated ones. You can read about and review pictures of the process by CLICKING HERE. Between having the right tire pressure that is lower than we practiced before, along with softer front coil springs, our ride is noticeably more comfortable without a sacrifice to handling. We do have aftermarket heavy duty stabilizer bars, shocks, steering stabilizer, and rear trac bar.
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Old 09-26-2021, 03:48 PM   #3
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Thanks for the reply - I will check out your suspension mods.
Yes - you are correct about the same tire inflation for the tires on the same axle. I showed the different inflation chart pressures required for the different loads on each tire, but went with the higher pressure for all the tires on that axle - for me that was 65 psi for front axle tires and and 80 psi rear for the rear axle tires.
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Old 09-26-2021, 08:54 PM   #4
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Read your post on the suspension mods - excellent post and great idea to change out the front springs. My new shocks, sway bars and reduced tire pressure help my handling and overall ride but but still leaves me with pretty harsh banging over the small sharp bumps, especially in the back, which I hate. I can imagine your softer springs help with that and probably help reduce wear and tear.
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