(Yet another) tire inflation thread!

[Chateau_Nomad]

Originally Posted by txc2936@yahoo.com

I dont know why it took so long to buy one of these. Filling tires, checking with a stick gauge... Now, just point and shoot...

Fill 1/2 lb over desired pressure, for me 82.5 psi, press the little button to release air to the correct pressure, put on the TPMS sensor.

The neighbors, saying,,, there he goes again... checking and fillin those tires again..

I'm still using an old Radio Shack digital gauge that at least 20 years old! Original battery! I use it because it's VERY accurate. But.. I'm looking for a quality replacement. The problem is... many of these combo fill/pressure gauges have a head the size of a cow's head!! I want something to fit into tight spaces.

[MJC62]

I don't know how my dad did it. He put 5 kids in a mid 60's station wagon, hooked up an 18-foot travel trailer that my mother loaded with everything but the kitchen sink and without TPMS or GPS headed over the Rocky Mountains. I'm pretty sure the Pontiac tires had 32 PSI and whatever the sidewall said on the trailer tires.
Two weeks later we'd be home planning the next trip

[bry899]

Originally Posted by MJC62

I don't know how my dad did it. He put 5 kids in a mid 60's station wagon, hooked up an 18-foot travel trailer that my mother loaded with everything but the kitchen sink and without TPMS or GPS headed over the Rocky Mountains. I'm pretty sure the Pontiac tires had 32 PSI and whatever the sidewall said on the trailer tires.
Two weeks later we'd be home planning the next trip

What are bias ply tires good for?
Because there are a uniform number of plies to support the weight of a vehicle in both the tread face and the sidewall, bias ply tires are generally better when hauling heavy loads. This is why trailer tires, tractor tires, and heavy equipment tires are often bias ply; they can better support heavy loads.

[Chateau_Nomad]

In 1962 my dad drove the family from the Midwest to Florida and back for vacation in a relatively new 1961 Ford Falcon station wagon. I remember that trip very well.

He was driving to work his first day back, when the left front wheel fell off the axle. Fortunately he was just down the street from our house.

I remember him turning white as a sheet thinking about that Florida drive...

Things happen...

[Jimbo56]

Originally Posted by widdershins

Overinflating can lead to uneven wear and compromised traction. Running max PSI seems like a bad idea IMO, unless you know for a fact that the tire requires that pressure to support the actual coach weight.

Uneven wear? No!
Compromised traction? No!
If he runs 80 psi he’d be fine. Harsh ride in a truck chassis. Cmon.

[lwmcguir]

Originally Posted by widdershins

Overinflating can lead to uneven wear and compromised traction. Running max PSI seems like a bad idea IMO, unless you know for a fact that the tire requires that pressure to support the actual coach weight.

Overinflating a commercial or truck tire is inflating above the cold psig on the sidewall

Do you think trucks change their psig when they offload?

[16ACE27]

Originally Posted by Jimbo56

Uneven wear? No!
Compromised traction? No!
If he runs 80 psi he’d be fine. Harsh ride in a truck chassis. Cmon.

I thought it was common knowledge - maybe not.

[Chateau_Nomad]

So that I understand...

Both underinflation and overinflation may cause uneven wear due to compromising the "contact patch".

The chassis manufacturer (Ford) specifies Gross Axle Weight Ratings (GAWR) for both front and rear axles. For each axle based on it's GAWR, and using the specified tire, Ford specifies a specific COLD PSI. (Front = 75, Rear = 65).

The tire sidewall specifies a MAX COLD PSI of 80. Also, a MAX LOAD SINGLE, and a MAX LOAD DUAL.

What I'm getting from this is:

Ford supplied an incomplete chassis to Thor with specific tire inflation based on GAWR for both front and rear, then applied a sticker with those specs.

Then, Thor built a motorhome "box" on the chassis, including all the appliances, etc. Thor used the exact same specs that Ford supplied - essentially duplicating the GAWR and tire inflations on Thor's own sticker (see my posted pics).

My takeaway:

IF you are NOT EXCEEDING the GAWR specified on those stickers, BOTH Ford and Thor recommend 65 PSI COLD in the rear duals, and 75 PSI COLD in the fronts.

What is NOT clear to me... why the MAX COLD 80 PSI on the sidewall? Possibly because this tire might be used in a different application?? The (possibly flawed) math I'm doing shows all tires on the unloaded coach within 300# of the specified MAX load rating. Is there a situation where I would want to use UP TO 80# per tire instead of the 75#/65#?

Finally an OPINION:

To me, tire inflation is about safety and using the tires as a load bearing medium as they are intended. Adjusting tire inflation to achieve aesthetics like a softer ride is dangerous - IF those inflations are outside of those specified by the tire OR chassis manufacturer.

[happy]

The maker of our tires has an online chart that shows the CORRECT tire pressure to run. It is based purely on vehicle weight. Beginning at 70 psi and going to 110 psi you have to match your psi by the weight of your vehicle. Joe may need to put in 105 psi and Larry may need 72 psi and each of them using the very same identical tire.



Thor had no idea I would ever use this particular tire and I pay zero attention to the decal Thor put on my vehicle. That sticker is for the factory tire. I pay strict attention to the maker of the tire I have mount on my vehicle.

[Jimbo56]

Originally Posted by 16ACE27

I thought it was common knowledge - maybe not.

I thought we were talking about 80 psi.

[Travelin' Texans]

Originally Posted by lwmcguir

Overinflating a commercial or truck tire is inflating above the cold psig on the sidewall

Do you think trucks change their psig when they offload?

I'd agree about the over inflation & those truck tires are supporting 80k lbs.
As for the tire profiles shown for under inflation, on all my towable rvs most all the tires wore similar to that, although not quite that severe, not due to under inflation but rather due to scrubbing while making tight turns. The fronts on motorhomes will most likely wear similar also due to turning.
I never had one wear like the over inflation shown when inflated to the max cold pressures on rvs, trucks or other vehicles.
If you inflate by weight then every time you travel with full fresh water you'll need to inflate, empty fresh water, deflate. DW adds a couple pairs of shoes, inflate. Drink the case of beer you loaded in the fridge, deflate.
Yes I'm being ridiculous, but if you use either the rv manufacturers pressures or the sidewall pressures you inflate once & done, no worries about over/under inflation, heat build up or squirmy/squishy ride, it might be a bit stiff but it's a truck.
I've never looked up the inflation charts for weight carrying but I'd suspect it would take several hundred pounds +/- to affect the tire pressures a pound or two, that pound or two won't make any noticeable difference in ride or tire wear. Wouldn't be worth the effort to me to have 6 tires inflated to different pressures due a few extra pounds here or there.
Weighing is a good idea to know where you stand as far as GVWR, but not to constantly have to adjust tire pressures.

[16ACE27]

Originally Posted by Jimbo56

I thought we were talking about 80 psi.

80 PSI is overinflated on a tire that just requires 75 PSI or even 65 PSI.

[Beau388]

Originally Posted by Chateau_Nomad

S


[snip]



What is NOT clear to me... why the MAX COLD 80 PSI on the sidewall? Possibly because this tire might be used in a different application?? The (possibly flawed) math I'm doing shows all tires on the unloaded coach within 300# of the specified MAX load rating. Is there a situation where I would want to use UP TO 80# per tire instead of the 75#/65#?

Finally an OPINION:

To me, tire inflation is about safety and using the tires as a load bearing medium as they are intended. Adjusting tire inflation to achieve aesthetics like a softer ride is dangerous - IF those inflations are outside of those specified by the tire OR chassis manufacturer.

Tire manufacturers seldom make a single tire for a single application. An exception like Corvette summer tires. I use Sumitomo tires (ST719 SE) made for a cross-country box truck. The side wall shows 110 lbs max cold pressure. Thor door sticker for Goodyear RV tires of the same size shows 82 lbs. A little arithmetic shows that the recommended 82 psi cold comes from the rear axle being loaded to exactly.12,000 lbs. The tire chart shows if the front axle is loaded to 6,000 lbs (max allowable weight for the coach is 18,000 lbs) the recommended tire pressure is 74 psi for the front. Goodyear recommends 80 psi as the minimum for the tire rim combination.
Starting out with the pressure set on 72 degree morning, the fronts will gain 12 psi when the black pavement hits 120 degrees. (Yes, I have a infrared heat gun), the inside rears 22 degrees and the outside rears 18 degrees. I ended putting the rears to 88 psi which gives a tire pressure gain of 18 psi on the inside and 16 on the outside.
It is the flexing of the tire that generates the heat. The less the pressure the more heat the tire generates and the more fuel the coach uses.

If you worry about tire wear you an chalk the surface of the tire (not the full tire but a good size patch across the tire, then drive about 20 revolutions in a straight line. Where the tire is scrubbing will wear the chalk off.
For you info, Ford in 2015 put the same rim and tire on the 27 ft 16,000 lb stripped F-53 chassis; 29 /31 ft 18,000 lbs chassis and the 34/35 foot 20,500lb chassis.

[Jimbo56]

Originally Posted by 16ACE27

80 PSI is overinflated on a tire that just requires 75 PSI or even 65 PSI.

Excuse me. But it is not.

[Hooligan2]

Your Class C RV weight range is limited and the recommended (sticker) tire pressures are based on the full GAWR. Your normal loading will be fairly close. The small difference between your required tire pressure and max allowed won't have a great effect.
Your weight limit for your tires, changes by 100-120 lbs for a 5 psi change in air pressure.

FWIW Tire pressure charts for the same tire size and load rating are identical. Chart pressures are the MINIMUM pressure required to support that weight.



My previous Class A motorhome had 22.5 inch tires with a sidewall limit of 120psi. My actual weight was well (5500 lbs) below max GVWR. Minimum required pressure was 85 front and 90 rear, ride and handling were noticeably affected by over-inflating to the sticker GAWR limits.

[happy]

This is one makers chart showing how tire pressure is dependent on the weight of your vehicle....not the max PSI of the tires. And not the sticker the vehicle maker put on as a general guide.

[dkoldman]

Originally Posted by happy

This is one makers chart showing how tire pressure is dependent on the weight of your vehicle....not the max PSI of the tires. And not the sticker the vehicle maker put on as a general guide.

I don't think one excludes one or the other. Nothing is absolute, may be why this topic will never die.

In my honest assessment of reading a lot of the views/opinions; I concluded axle weight is mostly like only going to be relevant if you are
#1. Hauling a Towed
#2. Have different tire than what was OEM specified.
#3. Knowing you are loading your RV a lot more than normal, like exceeding passengers and/or luggage, or using the RV as to save money versus renting a U-Haul truck or trailer to haul some heavy stuff like Gold bars .

Case in point, weight is NEVER going to be factor for me. Why?

Because I have the Goodyear OEM tires and based on Goodyear Mfg specifications, my tires MUST be at least 80 PSI, at the same time based on the same Goodyear chart; 85 PSI coincides with the Maximum weight rating permissible on my Ford Chassis based on RV Manufacturer Specifications. So the Engineering works out in between to 82 PSI; which is what my Yellow sticker says. So my Yellow sticker is 100% correct, and I am also following the weight guidelines of Tire Mfg. So when I check my air pressure, if lower than 80 psi, I add to 82 psi. If higher than 85 psi; I lower to 82. I have never had a weigh, may get one one day, but in my use case, I do not need a weight to figure out what pressure to inflate my tires too.

[dkoldman]

Originally Posted by Chateau_Nomad

I put 75# in the fronts an 65# in the rear duallies. A trip in October takes us past a Cat scale... where I'll get an accurate weight (fully loaded and with toad in tow). That should give me everything I need to know.

I pass Cat Scales all the time, NEVER had to worry about pressure being too high, but when I need pressure, I set my gauge to 82 and let the Makita do the work. I guess I need to take pictures of my tires because after 26,000 miles; treads are nice & smooth with even wear. Maybe at year 4 or 5; I may rotate two of the front tires as they get the bulk of work from turning, especially when I park on my RV Port, I can see spots of rubber.

[happy]

You have a plan that is working. That speaks a lot.

Nice compressor!