RV TIRE PRESSURE CONFUSION

[dianegannon]

I am a newbie to RV world and will soon embark on first adventure from Ohio to Florida in 2016 Newmar Mountain Aire. I was lucky to get each axle weighed by the Ohio state patrol.

Front axle 9000 lbs/97000...Mid/tag/dual  9100 lbs/8600 ...rear 6600 lbs/6300.  Front tires Michelin 365/70r 22.5, tag and rear 315/80r 22.  

The current cold  tire pressure in front tires is 110 psi. The tag axle cold tire pressure  is 80 psi, and rear at 110psi.  The tire pressure manufacturer tag/label  behind driver seat advises 125 to 130 psi in the tires. 

Michelin chart for tires advises as I evaluate the chart tells me front ok at 110-115 psi. Based on axle weight rear at 85-90 psi.  What should tag and rear pressures be ? What say you for correct tire pressure. I thank you in advance for your help.

315/80R22.5 L X® LINE ENERGY Z COACH X® MULTIWAY 3D XZE®
PSI		85	90	95	100	105	110	115	120	125	130	Maximum load & pressure on sidewall
kPa		590	620	660	690	720	760	790	830	860	900
LBS	Single	6415	6670	6940	7190	7440	7610	7920	8270	8690	9090	S	9090 LBS at 130 PSI
	Dual	11680	12140	12790	13090	13540	13880	14420	15220	15820	16540	D	8270 LBS at 130 PSI
KG	Single	2910	3030	3150	3260	3370	3450	3590	3750	3940	4125	S	4125 KG at 900 kPa
	Dual	5300	5500	5800	5940	6140	6300	6540	6900	7180	7500	D	3750 KG at 900 kPa

365/70R22.5 L XZA®
PSI		80	85	90	95	100	105	110	115	120	125	Maximum load & pressure on sidewall
kPa		550	590	620	660	690	720	760	790	830	860
LBS	Single	7350	7710	8070	8430	8780	9130	9480	9820	10200	10500	S	N/A
	Dual	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	D	N/A
KG	Single	3320	3510	3660	3840	3980	4120	4300	4440	4620	4750	S	N/A
	Dual	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	D	N/A

KG

[wildebill308]

21 hours ago, DianeGannon said:

I am a newbie to RV world and will soon embark on first adventure from Ohio to Florida in 2016 Newmar Mountain Aire.

Congratulations on starting your adventure. As you have the weights and the charts you are good to go. I recommend a cushion over what the chart says. Something like 10% or I just use 10 lbs as it is easier. Remember the pressure in the chart is the MINIMUM to carry the weight safely.

Bill

[manholt]

Welcome.

I have a AC Tradition 45', run BF Goodrich 315/80/22.5, at 115 psi & that includes an extra 10 psi for my weight.  Every 2 years, I remove everything out of bays, then put back those items that we have used during the past 2 years. The items that stays out, we weigh and subtract from coach weight.  Same with all can goods & clothing in coach!  We still have 3 houses between us, so we are not full time.

[ispjs]

It looks to me like you would be fine with 115 in steer axle and 90-95 in the other six, unless you are pulling a large trailer with a lot of tongue weight on your hitch.  Is you coach equipped with some type of TPMS?

[rayin]

13 hours ago, WILDEBILL308 said:

Congratulations on starting your adventure. As you have the weights and the charts you are good to go. I recommend a cushion over what the chart says. Something like 10% or I just use 10 lbs as it is easier. Remember the pressure in the chart is the MINIMUM to carry the weight safely.

Bill

👍 When tires are running at their minimum air pressure for the load, they are running at their maximum/100%capacity.

[dianegannon]

I am going to flat tow a Ford explorer . So 115 in front and should tag and rear be at same pressure? Currently rear at 110 and tag at 80. Where do you get tires inflated?

 

[manholt]

Since we tow different weights, we find it easier to carry same PSI all the way around.  It covers the difference between a Ford Expedition EL and a Jeep 2 door Wrangler.  If you want less weight on 6, go with 90+10 for safety.

I carry a pot air compressor in my bay, 150 psi set at 115 psi.  Seldom have to use it...we fill up at the ranch, using a 225 psi compressor.  Overkill for tires, but great for power washing all the buildings and equipment.  Most any Truck Stops will have air.

[rossboyer]

I don’t understand why the towed vehicle would make a difference to need to adjust air pressure in the tires on the motor home. Surely the tongue weight would not be that much difference between towed vehicles.  The weight of the towed vehicle does need to be considered in gross vehicle weight and the weight you are licensed. 

[wolfe10]

12 minutes ago, rossboyer said:

I don’t understand why the towed vehicle would make a difference to need to adjust air pressure in the tires on the motor home. Surely the tongue weight would not be that much difference between towed vehicles.  The weight of the towed vehicle does need to be considered in gross vehicle weight and the weight you are licensed. 

Absolutely true.

[txtiger]

I just keep all the tires, front, dully and tags at 110 PSI. As you drive and the tires heat up the psi goes up too, and will vary between each individual tire.  Also as you add fuel, water, food etc and as you use up fuel, dump, and eat the food your weight is constantly changing so you do not need to be to precise on each individual tire. 

[rossboyer]

We just made a trip from central Indiana to the Phoenix area. Temps were as low as 23 at night and as high as 83 daytime. We started with 107# in all 6 tires. Starting out in the morning the TPMS indicated as low as 96#. During the day the highest was 122#. Sunny side would about 4 to 6# higher than shady side. 

[ispjs]

16 hours ago, rossboyer said:

I don’t understand why the towed vehicle would make a difference to need to adjust air pressure in the tires on the motor home. Surely the tongue weight would not be that much difference between towed vehicles.  The weight of the towed vehicle does need to be considered in gross vehicle weight and the weight you are licensed. 

For towing 4 down you are probably  correct.  My toad adds over 3000 pounds to my tag as I would suspect it does to about anyone pulling a larger enclosed trailer.  So my toad does effect what psi goes in my tag and drive axle tires.

[wildebill308]

11 hours ago, ISPJS said:

My toad adds over 3000 pounds to my tag

That sounds like excessive tongue weight to me.

Bill

[wolfe10]

It may be that this because of a "larger enclosed trailer".

Agree, a toad that is towed 4 down only adds a few pounds to coach weight (the weight of the hitch that actually rests on the coach).

[wildebill308]

A little research confirmed my suspicions. Acceptable tongue weight for any trailer is somewhere between 9 to 15 percent of the gross trailer weight (GTW). Therefore, if you are towing a 5000 lbs trailer, the tongue weight should be measured at approximately 500 lbs.

So 3000 lbs would  be grossly overweight. 

Bill

[wolfe10]

Trailer YES-- tongue weight must be taken into account and will apply well more than its actual weight to the rear axle and subtract some from the front axle. 

Toad pulled 4 wheels down NO effect on coach weight (other than weight of tow bar).

[manholt]

It's always a pleasure to learn something new!  Ashamed to say, I have been wrong for almost 40 years! 

[rayin]

On 11/4/2019 at 11:35 AM, DianeGannon said:

I am going to flat tow a Ford explorer . So 115 in front and should tag and rear be at same pressure? Currently rear at 110 and tag at 80. Where do you get tires inflated?

 

If you do not have a 150# compressor, any truck stop  has the equipment to inflate truck and MH tires, you must specify the amount of tire pressure. You do not need higher inflation to flat-tow a vehicle vs not towing anything.

Increasing or reducing tag-axle tire pressure is one way to add or remove weight from the front axle, I would remain at  Federal Tire Placard stated tire pressures, until you have your MH weighed at each tire position.

[rayin]

20 hours ago, wolfe10 said:

Trailer YES-- tongue weight must be taken into account and will apply well more than its actual weight to the rear axle and subtract some from the front axle. 

Toad pulled 4 wheels down NO effect on coach weight (other than weight of tow bar).

"well more than it's actual weight to the rear axle"; What do you mean by that?

Wildbill308 is correct, a trailer should place no more than 15% (10% is ideal) of total trailer weight on the hitch. Trailer axles are placed at the ratio of 60/40, 60% of trailer frame is in front of center of tandem axles-unless the trailer is a gooseneck or 5th wheel pin, those can be considerably more depending upon axle placement.

[wolfe10]

2 hours ago, RayIN said:

"well more than it's actual weight to the rear axle"; What do you mean by that?

 

Weight applied well behind the rear axle DOES by leverage put more weight on the rear axle and remove weight from the front.

[rayin]

13 minutes ago, wolfe10 said:

Weight applied well behind the rear axle DOES by leverage put more weight on the rear axle and remove weight from the front.

👍 We agree,  however that does not apply to a WDH when properly adjusted, as the hitch weight is distributed equally on rear and front axle.

[ispjs]

On 11/5/2019 at 9:47 PM, WILDEBILL308 said:

A little research confirmed my suspicions. Acceptable tongue weight for any trailer is somewhere between 9 to 15 percent of the gross trailer weight (GTW). Therefore, if you are towing a 5000 lbs trailer, the tongue weight should be measured at approximately 500 lbs.

So 3000 lbs would  be grossly overweight. 

Bill

My loaded 24' enclosed trailer comes in just over 10,000 pounds.  My 1,200 pound Harley sits all the way up in the tongue.  

[wildebill308]

11 hours ago, ISPJS said:

My loaded 24' enclosed trailer comes in just over 10,000 pounds.  My 1,200 pound Harley sits all the way up in the tongue.  

Just so you know Newmar rates the hitch for 15,000 lbs towing, flat or trailer. However it is only rated for 1,500 lbs max tongue weight. 

Bill

[richard5933]

14 hours ago, ISPJS said:

My loaded 24' enclosed trailer comes in just over 10,000 pounds.  My 1,200 pound Harley sits all the way up in the tongue.  

Any way that you can re-arrange things to bring your tongue weight down?

[wolfe10]

On 11/4/2019 at 10:35 AM, DianeGannon said:

I am going to flat tow a Ford explorer . So 115 in front and should tag and rear be at same pressure? Currently rear at 110 and tag at 80. Where do you get tires inflated?

 

While the discussion of trailer towing and the trailer tongue weight is interesting, let's remember, the OP is FLAT TOWING, so no tongue weight (other than the few pounds that the tow bar weights) to consider.