Tire PSI

[Brianna]

In a related story....
I have everything inflated to 100psi.
Last summer, on a hot day, on a hot highway, the tires on the sunny side got up to 135psi.
I know it's pretty anal to be constantly checking the tpms, but that pressure range was surprising to me.

The shady side went up to 112.

Does that seem reasonable/normal to you Guys?

[richard5933]

Originally Posted by Brianna

In a related story....
I have everything inflated to 100psi.
Last summer, on a hot day, on a hot highway, the tires on the sunny side got up to 135psi.
I know it's pretty anal to be constantly checking the tpms, but that pressure range was surprising to me.

The shady side went up to 112.

Does that seem reasonable/normal to you Guys?

Sometimes too much information can be as bad as too little. If it was one tire on the sunny side or even one axle I'd be concerned. If it was multiple tires on multiple axles I wouldn't be worried, unless it kept doing that even when the sun shifted.

[Kid Gloves]

Originally Posted by Brianna

In a related story....
I have everything inflated to 100psi.
Last summer, on a hot day, on a hot highway, the tires on the sunny side got up to 135psi.
I know it's pretty anal to be constantly checking the tpms, but that pressure range was surprising to me.

The shady side went up to 112.

Does that seem reasonable/normal to you Guys?

Physics tells us that we will see a 2% increase in pressure for every 10F increase in temperature. That temperature increase can be from sun exposure, driving the vehicle, or both. You saw a 35% increase in pressure, which would indicate a 175F increase from the cold/ambient temperature at which you set the pressure. If you set the pressure at 50F, the reading that you saw would indicate an operating tire temperature of 225F. If your TPMS is accurate, I would not consider 135psi a reasonable or normal condition.

Possible causes could be overloaded tires or high operating speeds. Our EEZ Tire TPMS has a default high pressure warning of 20% above the set pressure and a temperature warning of 156F. Although, I don’t have a high degree of confidence in a valve stem sensor to provide an accurate temperature reading.

What system are you using and what default or custom settings are programmed on the unit?

[Mule Skinner]

I'm sitting here with nothing to do so I'll add some more confusion lol.
For fun, I drive a road race car on the weekends. 1/2 a pound can make a difference. having said that, I have learned from some practical findings.
Setting cold pressure at 7:00 am when it's 45 degrees out side I'll wind up with to high of a hot pressure. I have learned to compensate. My goal is to have 34-35 psi hot. to get there I start at 28 front and 29 rear when it's around 70 deg outside.
If it's 45 outside I start at 25 front and 26 rear. Not always accurate but you get the idea. It's good to know your hot temp psi under normal conditions.

I think my 34' says 95 front 90 rear cold. That would be at 70-80 degree's outside temp.
If it's 45 deg. outside, I would expect to see 85-90 front 75-80 rear.
If it's 110 deg. outside, I would expect to see cold temps high, 100 front 95 rear.
Regardless of the cold temp based on ambient temps, the hot pressure should be similar.
I find that at a higher starting pressure there is less range increase. At a lower starting pressure the sidewalls flex more and that is what generates heat. The heat then causes the air to expand.

If I remember correctly when I was shopping tires the Michelin H tire was 14 ply and the Toyo H tire was 16 ply. I think the Michelin has a softer ride. Might be the sidewall that is different? by the way, I run Toyo's that's what came on the MH new.

[richard5933]

Originally Posted by Mule Skinner

I'm sitting here with nothing to do so I'll add some more confusion lol.
For fun, I drive a road race car on the weekends. 1/2 a pound can make a difference. having said that, I have learned from some practical findings.
Setting cold pressure at 7:00 am when it's 45 degrees out side I'll wind up with to high of a hot pressure. I have learned to compensate. My goal is to have 34-35 psi hot. to get there I start at 28 front and 29 rear when it's around 70 deg outside.
If it's 45 outside I start at 25 front and 26 rear. Not always accurate but you get the idea. It's good to know your hot temp psi under normal conditions.

I think my 34' says 95 front 90 rear cold. That would be at 70-80 degree's outside temp.
If it's 45 deg. outside, I would expect to see 85-90 front 75-80 rear.
If it's 110 deg. outside, I would expect to see cold temps high, 100 front 95 rear.
Regardless of the cold temp based on ambient temps, the hot pressure should be similar.
I find that at a higher starting pressure there is less range increase. At a lower starting pressure the sidewalls flex more and that is what generates heat. The heat then causes the air to expand.

If I remember correctly when I was shopping tires the Michelin H tire was 14 ply and the Toyo H tire was 16 ply. I think the Michelin has a softer ride. Might be the sidewall that is different? by the way, I run Toyo's that's what came on the MH new.

Do you have any information from any RV tire manufacturers which show what the recommended hot tire pressures are?

I ask this knowing that they don't generally publish this information, and that the generally accepted practice is to set all the pressures based on cold temps before beginning the day's drive.

I get it that for things like your road race situation you have specific needs, but I don't think that the practice translates directly to the RV world.

[Kid Gloves]

Put simply, if the recommended tire pressure for a rig is 95psi Front and 90psi Rear, and you check them in the morning, at any temperature, and they read 94psi Front and 89psi Rear, the tires are underinflated. If you plan to drive the rig that day, put some air in the tires.

[Tom and Patty]

Originally Posted by PitMan51

At an FMCA rally a few years ago, we had the coach (09 40 MDTS) weighed (4corners). They recommend 95 rears and 90 for the fronts and suggested 95 all around. We are full timers, so fairly loaded.

Bill & Sonia
09 40MDTS

I'm not saying that is wrong, but usually more pressure is required up front.
I ran 95 in the fronts of our 2000 and your 2009 is heavier. Unless you have 295/80r22.5 I would give the 90 psi a second look.

[Alpine03]

I had my coach weighed at the desert rally a couple years ago. Front weight 9,750lbs Rear weight 16,725lbs. My tires are Michelin 275/80R/22.5. They recommended 95psi in the front and 80 psi in the rear. I have a 2003
34FDDS. I Usually run the back at 85psi.

[Theturboman]

I have always been a fan of ride over fuel mileage/wear as long as I fit within the weight requirements of the tire. My Monaco Sig 45 ft I chose to run 95 psi all around as I dont ever wear out tires they always go bad do to age not to miles. ( I hope to change that) The ride quality was so much better at 95 then 110 I didnt care about wear. My new to me Alpine I will start to experiment soon

[Ernieo]

I ran my Goodyear 295 80/22.5’s in front at 110 and on this last trip developed cupping on both sides of the tires. One guy said they were underinflated, while another one said it could be an issue with shocks, kingpin or tow bar. I am taking it in on Monday for a suspension inspection and will report back.

[Dave Fernandez]

WRV installed Toyo tires on all of the Alpine coaches until the eventually changed to Goodyear. The Toyo’s were known for the same problem they were good tires but not the top of the line Toyo’s. It was the design of the tire not the Coach. Looking at your photos, I would say it is probably the tire design and not the Alpine. Tires made without a tread near the side of the do not wear like your tires unless there is a problem with the front end or tire pressure. When I replaced the tires, I upgraded to a better Toyo Tire and the problem went away and has never returned. I now use Michelins Tires and do not have a problem.

[rrthor]

Originally Posted by Ernieo

I ran my Goodyear 295 80/22.5’s in front at 110 and on this last trip developed cupping on both sides of the tires. One guy said they were underinflated, while another one said it could be an issue with shocks, kingpin or tow bar. I am taking it in on Monday for a suspension inspection and will report back.

Have them check front wheel bearing adjustment.

[sctalbott]

I weigh my Coach, front and rear axles. I have 305R70-22.5 in front 295R80-22.5 rear. Looked a manufacturer specs. I run 80 lbs all around. I get a much nicer ride and it doesn’t shake my Coach apart as much. Plan on replacing rear tires with 295R75-22.5 soon. I’m not saying 80 lbs is for everyone but it works for me. As they heat up they get to 95 psi anyway.

[wolfe10]

Originally Posted by sctalbott

I’m not saying 80 lbs is for everyone but it works for me.

Right.


Basing YOUR tire pressure on what is correct for THEIRS is not a reasonable concept.