Tire Pressure

[JonK]

I have a heavily modified 2015 GWV. Following almost all the mods I took it to a CAT scale and with 2 of us on board, full contents except some food and clothes, full fuel and no water the rear axle weight was 5280, front axle 3860.

When I look at the tire pressure charts and the rear axle weight I end up with about 35psi in the rear duals. I am planning to try 45psi to see how it feels and how tire temps run. I have a really hard time believing the pressure can be this low, but unless I'm missing something ..... And yes I'm missing the water that I need to add in depending on which tank I'm counting it in, it moves rearward as it is used. I also need to leave some reserve for side to side imbalance, hence the 45 start.

the tires are LT215/85R16

If this is the case then a softer ride is in order pending it not making the rear squirmy.

[booster]

Originally Posted by JonK

I have a heavily modified 2015 GWV. Following almost all the mods I took it to a CAT scale and with 2 of us on board, full contents except some food and clothes, full fuel and no water the rear axle weight was 5280, front axle 3860.

When I look at the tire pressure charts and the rear axle weight I end up with about 35psi in the rear duals. I am planning to try 45psi to see how it feels and how tire temps run. I have a really hard time believing the pressure can be this low, but unless I'm missing something ..... And yes I'm missing the water that I need to add in depending on which tank I'm counting it in, it moves rearward as it is used. I also need to leave some reserve for side to side imbalance, hence the 45 start.

the tires are LT215/85R16

If this is the case then a softer ride is in order pending it not making the rear squirmy.

I think most of us have found that the tire pressure charts may be technically correct as being able to support the load, but they are usually quite a bit low for the best balance of handling and ride. If I put our Chevy on the chart minimums it drives very, very, poorly.

[Davydd]

I drive with tire pressure of 61 PSF in all six of my tires. I never rotated tires on my Great West Van Sprinter dually or my ARV dually and have had even tire ware in both front and back when I needed to replace them for tread depth. I replaced OEM Continentals for both vans at around 40,000 miles with Michelins.

[avanti]

Originally Posted by Davydd

I drive with tire pressure of 61 PSF in all six of my tires. I never rotated tires on my Great West Van Sprinter dually or my ARV dually and have had even tire ware in both front and back when I needed to replace them for tread depth. I replaced OEM Continentals for both vans at around 40,000 miles with Michelins.

Yep. Sounds about right. We run the fronts a few points lighter for the sake of comfort.

Totally agree about tire rotation. It is a persistent myth, designed to get you into the tire store more often. If your tires aren't wearing properly, something is broken.

[SteveJ]

Originally Posted by avanti

Yep. Sounds about right. We run the fronts a few points lighter for the sake of comfort.

Totally agree about tire rotation. It is a persistent myth, designed to get you into the tire store more often. If your tires aren't wearing properly, something is broken.

I'm gonna disagree here, at least for my '00 Chevy 200 RT with single rear tires. I just rotated the tires at about 20k miles. The rears have quite a bit less tread than the front, running 55lbs in the front, 80 in the back. Also, in this particular instance the front tires have/had unusual wear due to a couple of panic stops on the last trip. The tires are Cooper Discoverers with a block tread pattern. The blocks were uneven due to braking forces and howled pretty loud.

I doubt that these tires will be rotated again as the wear should even out by the time I need replacements. I wear out my tires before they age out.

With the more balanced tire load when running duals, rotation would not be nearly as important or not be required, I think.

Skol.

[avanti]

Originally Posted by SteveJ

I'm gonna disagree here, at least for my '00 Chevy 200 RT with single rear tires. I just rotated the tires at about 20k miles. The rears have quite a bit less tread than the front, running 55lbs in the front, 80 in the back. Also, in this particular instance the front tires have/had unusual wear due to a couple of panic stops on the last trip. The tires are Cooper Discoverers with a block tread pattern. The blocks were uneven due to braking forces and howled pretty loud.

I doubt that these tires will be rotated again as the wear should even out by the time I need replacements. I wear out my tires before they age out.

With the more balanced tire load when running duals, rotation would not be nearly as important or not be required, I think.

I didn't mean to imply that one should NEVER rotate your tires. Front/rear differential in tire wear certainly is a real phenomenon. It is routine "every XXX miles" rotation that is nonsense.

On four-tire vehicles, I typically just replace in pairs, sometimes doing a rear-to-front rotation when I do so.

[RossWilliams]

We just replaced the tires on our used Roadtrek dually sprinter with the same Continentals. It was at 60 psi on all six tires when we got it. The front tires were badly and unevenly worn and should have been replaced sooner. We had an alignment done and hopefully that will prevent a repeat. We are now using the factory recommended pressures on the door - front:55 psi rear:61 psi. I have wondered whether 1 psi really makes any difference.

[SteveJ]

Originally Posted by RossWilliams

We just replaced the tires on our used Roadtrek dually sprinter with the same Continentals. It was at 60 psi on all six tires when we got it. The front tires were badly and unevenly worn and should have been replaced sooner. We had an alignment done and hopefully that will prevent a repeat. We are now using the factory recommended pressures on the door - front:55 psi rear:61 psi. I have wondered whether 1 psi really makes any difference.

I've found that for every change of 7 degrees F the tire pressure would change by 1 lb. This has been my experience. So 1 lb shouldn't be that big of a deal, anticipated temps on a forthcoming trip or usage should come into play. A fifty degree spread will move it by seven lbs, something to plan for this time of year when there seems to be more north/south travel.

In the summer when I leave FL and cross the southern plains states I do make sure to check the tire pressures once I get out west into the elevations and cooler weather. This is in addition to the normal walk around inspection virtually every time before getting under way while traveling.

[booster]

Originally Posted by SteveJ

I've found that for every change of 7 degrees F the tire pressure would change by 1 lb. This has been my experience. So 1 lb shouldn't be that big of a deal, anticipated temps on a forthcoming trip or usage should come into play. A fifty degree spread will move it by seven lbs, something to plan for this time of year when there seems to be more north/south travel.

In the summer when I leave FL and cross the southern plains states I do make sure to check the tire pressures once I get out west into the elevations and cooler weather. This is in addition to the normal walk around inspection virtually every time before getting under way while traveling.

I roughly use 1.5 psi/10* for the 65# tires and 2.0 psi for the 80# tires. Seems to be within reason, as we also adjust to where we are headed most of the time, although sometimes can be hard to get numbers that work out all the way.


Be aware that tire pressure changes as you go up in elevation, may or may not real depending on how you measure the pressure because most gauges are atmospherically referenced so elevation pressure change also gets seen.

[SteveJ]

Originally Posted by booster

I roughly use 1.5 psi/10* for the 65# tires and 2.0 psi for the 80# tires. Seems to be within reason, as we also adjust to where we are headed most of the time, although sometimes can be hard to get numbers that work out all the way.


Be aware that tire pressure changes as you go up in elevation, may or may not real depending on how you measure the pressure because most gauges are atmospherically referenced so elevation pressure change also gets seen.

IIRC, it's not exactly matching but sort of close, the altitude increase in pressure does go in tandem with the temp decrease in pressure.

[RossWilliams]

Tire pressures are always measured cold because the pressure increases as tires warm up as you drive. I am not clear how much difference the ambient temperature makes in how hot they will eventually get and the ultimate limit on how much the pressure will increase. Probably not much.

[booster]

Originally Posted by SteveJ

IIRC, it's not exactly matching but sort of close, the altitude increase in pressure does go in tandem with the temp decrease in pressure.

It can and can't, plus a lot depends on the pressures you start with. ATV tires at 5 psi that show 3.5psi higher on the gauge would have the same 3.5 psi change as on an 80 psi tire at the same altitude, so the altitude part is a fixed amount of change for all pressures.


Pressure change from temp is a percent change for the most part, so higher pressures see a different psi change at the same temp than low pressure tires.


Where I have heard about the most trouble is with folks that leave the cool coast at 50* and sea level in the morning and then go to the high desert at 7000+ feet and over 100* with their low pressure off road tires at 5-10 psi under those conditions, both the heat and the gauge issues increase the reading, but only the temp increase is really in the tire itself.



Since the tire is sitting on the ground, the atmospheric pressure has very little to do with supporting that area, which is what counts the most and I think you would need to look at absolute pressure anyway. This would also mean that if you had a bit temp swing going to altitude the reduction from temp would change the support the tire is doing, but the altitude increase wouldn't much.

[JonK]

This type of discussion is why this site is so valuable to me. I appreciate all the input.

The sense I'm making of the situation now is that the tire pressure charts are correct for carrying the load and SHOULD, but maybe don't provide the correct tire contact patch with the pavement. The nice thing is that according to the pressure chart I'm won't damage the tires due to low pressure and I'll just work my way up in pressure to achieve good drive-ability. The ride quality will be what it ends up being, it's not a prime concern for me.

With my big heavy class A I carried a IR temperature gun and would check temperatures across treads for the tires I could reach and a comparable single spot on the inside dual to see if it was wonky overall. I noticed a couple things. Sunny side tires were frequently 10 degrees hotter than the shady side, that freaked me out until I figured out what was going on. I noticed that after driving for awhile the tires warmed 5-25 degrees over ambient depending on speed. I also noticed that when I played with the tire pressures I would see an alteration in the temperatures pattern across the tread. I didn't use a TPMS, no good reason for that lack.

So, I plan to track tire tread temperatures and build a history that will help me know what is going on. For instance, it seems many are using pressures higher than the chart calls for and not getting uneven wear, I'm not saying those folks are wrong, it is their experience, but I can't explain how that works. Maybe the temperature measurements will be informative. Maybe not.

[BillsPaseo]

I'm currently running about 63 in the fronts and 58 in the rears on our dually Transit. I am running up-sized tires (Yokohama Geolander A/T G015 215/85R16) which have about a 20% higher load rating than the stock tires did, so that is about 4 pounds lower than what I was running with the stock tires.

I started out at 67 when I got the new tires, but at that pressure they wanted to wander all over the road. Huge improvement in tracking by dropping a few pounds of air.

[BillsPaseo]

Originally Posted by booster

Where I have heard about the most trouble is with folks that leave the cool coast at 50* and sea level in the morning and then go to the high desert at 7000+ feet and over 100* with their low pressure off road tires at 5-10 psi under those conditions, both the heat and the gauge issues increase the reading, but only the temp increase is really in the tire itself.

We run into this all the time with our dual sport motorcycles. I run about 15 PSI in the tires for all around best handling for dirt, gravel and pavement combined. We'll leave the house early on a chilly morning, maybe 48 degrees and at sea level. Head up to the top of Stevens Pass (4000 ft) where we leave the pavement and hit the dirt roads after a gas and breakfast stop. By now it is 80 degrees and climbing, and we're climbing in altitude. Tires start to feel super hard and handling is suffering. Stop to check pressure, and they are reading 25 PSI. Let air out, ride all day, then stop to add air before heading home...

[MobileCabin]

Just in case people have missed it, a retired tire engineer has a site on rv tire safety. The link to his posts on temperature impact on tires is:

http://www.rvtiresafety.net/search/label/Temperature

[RossWilliams]

Key quote from above link:

"We all need to remember that not every change or difference that is measurable is meaningful"

[jadatis]

Googled your tires as 115/112 E-load.
Trew it trough my made calculator and gave front 63 psi and rear if singleload 88 psi and duall load 46psi. This makes me suspect you have dualload axle behind.
In this I used an extra safe formula and added first 10% to your given axleloads.
So max reserve with still acceptable comfort and gripp.

[Thevon]

I’ve noticed that 3 tire pressure gauges I have show a different pressure, all within a few pounds of each other. Has anyone found a gauge they believe is the correct tire pressure?

Greg
2006 190P

[jadatis]

That is the reason why I give the maximum pressure ,with max reserve, .
Can be that you calculate this max, but by all the inacuracies, like pressuredevice giving to high, and even weighed load being a bit to low, and possible pressuredrop in time, etc, that you yust have enaugh to prevent overheating at higher speed.