Do you Err when you Air?

[Shan-man]

I just found out I have been over-inflating my tires on the MoHo by 20-35 pounds since I took ownership in '03! The previous owner told me to inflate to 80-85 pounds, and that's what I've always done. While preparing for this trip I found a little slip of cardstock hidden in the collection of paperwork previous owners had stored. This label that used to be on the driver's door shows the weights and inflation values the manufacturer recommends: 50lbs rear and 60lbs front! Are you kidding?! That might explain why the ride is so rough and why I've had chronic blowouts! Ok, I'm sure the ride will still be rough, but still! Speaking of blowouts, I have gone through a heck of a lot of tires in those 5 years and not one of the shops that replaced them has suggested that this might be too much pressure for my load! Ugh! Now I just hope the tire sizes are right. I have a sneaking suspicion that the tires are not mfg spec but a taller profile that when inflated to 50psi the dually's will rub (a problem I've had in the past). Anyway, that's my rant for the day... and a cautionary tale for those who haven't confirmed their mfg specs!

 

[2goofycampers]

We always go by what's writtten on the tire. So far so good.

 

[Cousin Ed C]

What is on the is the tire is the maximum, which should not be exceeded, but it might be way more than you need.
My max is 110# but Winnebago says 90 front and 85 rear. If you use more than you need, but do not exceed the max your only negative should be a harsh ride.

 

[bigdisneydaddy]

The correct inflation pressure is ALWAYS the one on the drivers door jamb or inside the vehicle near the drivers seat. The calculations for correct pressure are done by the final manufacturer (motor home chassis are shipped incomplete) and are based on the vehicle final weights and tires size. The pressures are claculated based on engineering data available to the OEM from the tire maker and their final weight calculations. The pressure on the tire will only show you the maximum inflation and are rarely the same as the operating pressure.

 

[stacktester]

The correct inflation pressure is ALWAYS the one on the drivers door jamb or inside the vehicle near the drivers seat. The calculations for correct pressure are done by the final manufacturer (motor home chassis are shipped incomplete) and are based on the vehicle final weights and tires size. The pressures are claculated based on engineering data available to the OEM from the tire maker and their final weight calculations. The pressure on the tire will only show you the maximum inflation and are rarely the same as the operating pressure.

What would we do without Scott? Oh yeah that's right, there's rv.net.

 

[Shan-man]

The correct inflation pressure is ALWAYS the one on the drivers door jamb or inside the vehicle near the drivers seat. The calculations for correct pressure are done by the final manufacturer (motor home chassis are shipped incomplete) and are based on the vehicle final weights and tires size. The pressures are claculated based on engineering data available to the OEM from the tire maker and their final weight calculations. The pressure on the tire will only show you the maximum inflation and are rarely the same as the operating pressure.

If only the label were on the driver's door. Somewhere in the course of 24 years, the ol girl's label had fallen off and been stuffed into the dark recesses of a binder along with reciepts for awnings, and the flaps from oil filter boxes, and manuals for long deceased in-dash radios! I know, I could have taken the rig to the scales and gotten weights for each corner and looked up the proper inflation from the tire mfg... but I'm not an RV.net kinda guy. The previous owner told me 80-85, and he hadn't lied to me more than 8 or 9 times! LOL

Also, I agree with Cousin Ed C... my rock hard inflation should have done no more than give a rough ride, but I sure seem to have a lot of blowouts!

Finally, Donnie, don't tick off Scott! He is kind of a conduit of good info from the RV.net universe next door, but he filters the BS and attitude to make it more palatable for us DISers!

Thanks one and all for letting me percolate a little. My irritation is just about wiped away. And just in time... I leave for WDW in 62 hours!!!

 

[bigdisneydaddy]

If only the label were on the driver's door. Somewhere in the course of 24 years, the ol girl's label had fallen off and been stuffed into the dark recesses of a binder along with reciepts for awnings, and the flaps from oil filter boxes, and manuals for long deceased in-dash radios! I know, I could have taken the rig to the scales and gotten weights for each corner and looked up the proper inflation from the tire mfg... but I'm not an RV.net kinda guy. The previous owner told me 80-85, and he hadn't lied to me more than 8 or 9 times! LOL

Also, I agree with Cousin Ed C... my rock hard inflation should have done no more than give a rough ride, but I sure seem to have a lot of blowouts!

Finally, Donnie, don't tick off Scott! He is kind of a conduit of good info from the RV.net universe next door, but he filters the BS and attitude to make it more palatable for us DISers!

Thanks one and all for letting me percolate a little. My irritation is just about wiped away. And just in time... I leave for WDW in 62 hours!!!

We will, of course, expect some of that good holiday Karma to come our way from FW while you are there...

 

[Shan-man]

I will have my aircard and expect to give daily updates... but don't expect TCD-quality script-writing and cinematography! I will be a sad replacement for cable! But yes, I will share my enthusiasm as best I can whilst in the Fort!

 

[LarryJ]

I'll make a few comments here since this is something I always pay particular attention to.

1. For ST trailer tires (e.g. GY) they are generally limited to about 60 mph for the pressures on the tire sidewalls. For sustained speeds up to about 65 or a bit more GY says to increase the cold pressure by about 5 to 10 lbs. These figures are close but not exact and one needs to confirm if you want to tow faster than about 60mph. 60 is my tow speed so I use what is on the sidewall.

2. This door jamb sticker can be very tricky. For passenger cars it's fine, but for trucks, vans that tow those pressures are for the max load on the axle for the OEM tire size. The only way to properly inflate a tow vehicle tires is to go by the manufacturer's load rating specs and go to a set of scales loaded up and on the road to determine the proper pressure. Let me give you an example for my E-350. The door jamb pressures say 80psi in the rear and something like 55psi in the front and for the GY OEM E-rated tires and that equates to around 6084 on the rear and 4600 on the front axles which are the RAWR and FAWR on the same door jamb sticker. However, when not towing and loaded for bear, my Van only weighs 7700lbs for 3850 on each axle as measured by the scales at the local dump. The GY tire inflation tables show that I should be running around 40 to 50 psi. If I drove my Van unloaded and not towing with the pressures on the door jamb I would need a kidney transplant every couple of years. My first fuel stop which is always a truck stop, I take the few extra minutes and for 7 or 8 bucks get this current towing combo weighed so I know exactly where I'm at as far as axle loads and tire capacity.

When we left for WDW in Oct for this trip I weighed at the Carmel Church FJ and I had the following:

TV Front Axle 3820 for a 4600 rated axle
TV Rear Axle 5820 for a 6084 rated axle
TT Axles 6800 for a pair of 3500lb axles with tires rated at around 3560 per axle.

Typically I know within a few hundred pounds what I will weigh on every axle since I do this all the time and start out with the max TV rear of 80psi, TV front of 55psi (good for around 4000), and 50psi on the trailer good for the 7,000 combined axle weight rating on the trailer.

BTW I've been doing this for over 25 years and have never had a blow out with just a few flats from road hazards like nails, etc. IMHO a lot of tire failures are from either overloaded tires on the TT/5er and screaming down the interstate at 70mph on ST type tires.

ON EDIT Seems some of these posts are for the larger MH G-rated or higher tires and those I have no idea what the rules are there.

Larry

 

[John VN]

As mentioned above, the ONLY way to know what the tire inflation pressure should be is to WEIGH the vehicle in question and THEN consult the tire manufacture inflation charts.

 

[des1954]

No one had addressed the REAL question....
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What's a "henway"?

 

[bigdisneydaddy]

The original question was about a vehicle that I assumed was not being used for towing. As larry says, on a vehicle being used to tow with the game changes, I agree with his comments 100%. As an example, I run an "E" rated tire on my truck, unloaded I run about 40-45 psi for everyday. With the trailer I run them at about 75 psi ( IIRC the max is 80 )
The amount of pressure change in a tire is dramatic sometimes. My TT tires will gain an easy 5 PSI at 60 MPH during the summer. When I leave MI in the winter my tires will be at 60 PSI cold, when I arrive in FL they will be around 65 cold just due to the rise in ambient air temp.

 

[big kahuna1]

My door sticker gives both the unloaded and loaded inflation recs. It also give the tire size installed by the mfg. It is still not a bad idea to know you weight and inflate accordingly.

 

[jugman]

You had better weigh first before you start letting air out. What's on the door could be alright as long as your not overweight. What they put on the door is the carrying capacity for the vehicle, if you have more weight, then the door sticker will not be right. Example my tires are rated for more weight than the trucks capacity, so I could run what is on the door for a better ride and probably be alright, but if I had a little more weight then the air pressure would need to be upped. As for the duals rubbing at 50 psi, my question is do they rub at 80 psi. At 50 psi they may be squatting due to the fact of low air pressure and the amount of weight on them, but if they rub at 80 psi then you will need to go to a smaller size to stop the rubbing. It is not normal to keep having blow-outs for no reason.

You also might see if you have a tire that is defective. You see I found out on rv.net that I had tires that I could get replaced because they were defective.

 

[stacktester]

I'll make a few comments here since this is something I always pay particular attention to.

1. For ST trailer tires (e.g. GY) they are generally limited to about 60 mph for the pressures on the tire sidewalls. For sustained speeds up to about 65 or a bit more GY says to increase the cold pressure by about 5 to 10 lbs. These figures are close but not exact and one needs to confirm if you want to tow faster than about 60mph. 60 is my tow speed so I use what is on the sidewall.

2. This door jamb sticker can be very tricky. For passenger cars it's fine, but for trucks, vans that tow those pressures are for the max load on the axle for the OEM tire size. The only way to properly inflate a tow vehicle tires is to go by the manufacturer's load rating specs and go to a set of scales loaded up and on the road to determine the proper pressure. Let me give you an example for my E-350. The door jamb pressures say 80psi in the rear and something like 55psi in the front and for the GY OEM E-rated tires and that equates to around 6084 on the rear and 4600 on the front axles which are the RAWR and FAWR on the same door jamb sticker. However, when not towing and loaded for bear, my Van only weighs 7700lbs for 3850 on each axle as measured by the scales at the local dump. The GY tire inflation tables show that I should be running around 40 to 50 psi. If I drove my Van unloaded and not towing with the pressures on the door jamb I would need a kidney transplant every couple of years. My first fuel stop which is always a truck stop, I take the few extra minutes and for 7 or 8 bucks get this current towing combo weighed so I know exactly where I'm at as far as axle loads and tire capacity.

When we left for WDW in Oct for this trip I weighed at the Carmel Church FJ and I had the following:

TV Front Axle 3820 for a 4600 rated axle
TV Rear Axle 5820 for a 6084 rated axle
TT Axles 6800 for a pair of 3500lb axles with tires rated at around 3560 per axle.

Typically I know within a few hundred pounds what I will weigh on every axle since I do this all the time and start out with the max TV rear of 80psi, TV front of 55psi (good for around 4000), and 50psi on the trailer good for the 7,000 combined axle weight rating on the trailer.

BTW I've been doing this for over 25 years and have never had a blow out with just a few flats from road hazards like nails, etc. IMHO a lot of tire failures are from either overloaded tires on the TT/5er and screaming down the interstate at 70mph on ST type tires.

ON EDIT Seems some of these posts are for the larger MH G-rated or higher tires and those I have no idea what the rules are there.

Larry

I got lost, can you repeat this one more time.

 

[BRDof3]

I followed it perfectly, right up to "1."

 

[LarryJ]

I got lost, can you repeat this one more time.

Ah .... OH never mind

Larry

 

[Just Beachy]

What's a "henway"?

3 or 4 lbs?

 

[2goofycampers]

3 or 4 lbs?

 

[LarryJ]

You had better weigh first before you start letting air out. What's on the door could be alright as long as your not overweight. What they put on the door is the carrying capacity for the vehicle, if you have more weight, then the door sticker will not be right. Example my tires are rated for more weight than the trucks capacity, so I could run what is on the door for a better ride and probably be alright, but if I had a little more weight then the air pressure would need to be upped. As for the duals rubbing at 50 psi, my question is do they rub at 80 psi. At 50 psi they may be squatting due to the fact of low air pressure and the amount of weight on them, but if they rub at 80 psi then you will need to go to a smaller size to stop the rubbing. It is not normal to keep having blow-outs for no reason.

You also might see if you have a tire that is defective. You see I found out on rv.net that I had tires that I could get replaced because they were defective.

Here you have to be careful because your actual capacity for that axle might not be tire limited and this is true especially like for dually pickups or pickups in general where the rear might be tire limited and they put the same rated tires on the front. Most Ford pickups including my Van have E-rated tires (3042@80psi for 245s and something like 3405 for the 265s found on a lot of pickups). However my front axle is only rated for 4600 so I can't put 80 psi in the front and increase it's carrying capacity more than the 4600 on the door jamb sticker. This is even more of an issue with the Ford PUs both SRW and DRW with the 265s since most Ford front axles are only rated for around 5200 to maybe 5600.

Boiled down is that if the sticker load number is less than the tire capacity at max inflation you are axle limited and if the tire capacity equals the sticker number then you are tire limited.

The DRW vehicles are a special case because potential rubbing issues with a full rated load on the axle. That's why a lot of DRW rears even with 265s (3405 each tire capacity at 80 psi) can only be inflated to a number less than 80. You can't just put 80 in them and think you have 4x3405=13,620lbs of load carrying capacity) I'm not all that familiar with the Ford DRW, but I think they use the Dana 80 which has like a 10,000+ lb actual axle rating, but because of the the tires used with the specific offsets and suspension used ends up being able to actually carry less than what the actual axle is capable of.

When I say axle limited that includes the axle itself and the springs/coils in the suspension for that axle.

My Van comes stock with a 4400 lb front axle capacity, but when I ordered it there was an option for a "one up front WR" which increased by front axle load capacity by 200lbs and the coil springs were what changed based on actually comparing numbers with similiar Vans w/o the "one up front WR". So the each front axle is capable of more than 2200lbs each, but is limited by the coils used to support that axle.

Some vehicles might have an unloaded and loaded number on the door jamb, but again I would think that the unloaded would be for a base vehicle so if you have added say 500lbs of tool boxes and a 100gal aux tank you will be somewhere between the unloaded pressure and loaded pressure and the only way then is to weigh your vehicle and use the manufacturer's load inflation tables. My base Van is a cargo Van which probably only weighs around 6,000 lbs as shipped by the factory, but no body runs around with a cargo van completely empty.

I know some of this might sound complicated, but one has to really understand how things work or they can get into serious trouble in a hurry. Every time I see a TT or 5er go screaming past me at what is probably 70 to 75 mph, I just shake my head and say I hope he/she is not running the OEM ST tires since at some point he/she could be facing a blowout because of his speed and if you have ever talked to someone that has had a blowout on a trailer or if you have yourself experienced one it can get real expensive since the tire fragments normally do a lot of damage to the trailer it's self. Some years ago, maybe 10, I was following a large 5er maybe 1/2 mile behind him when I saw this giant puff of white from the road side of the 5er and he immediately pulled onto the shoulder and I slowed down and as I passed him I could see he had a blowout and could see the wheel fender destroyed along with a lot of damage above the wheel in the aluminum siding about 2 to 3 feet up onto the side of the trailer.

Larry