tire pressure 20-30 psi Tire Pressure Rise?

[Bob Jones]

2 minutes ago, georgecederholm said:

Sorry! I thought I noted this in a prior post. “Cold Inflation Pressure”. “Cold” meaning ambient, not driven on, not overly warmed by the sun. Actually, it’s probably stated “Max PSI” on the sidewall, which is extra misleading since that’s the minimum cold inflation pressure for the maximum rated load of the tire for the axle type (single or dual). 🤪

Maybe it’s the tire engineers and regulators who can actually make things more complicated than the RV crowd? 😂

It's official, you've now broken my mind. I'm ordering up 6 tire pyrometers, and a Nascar team, along with some NASA scientists and ultra-precise scales. I'll case those tire pressures yet!! 

Not to really stir the pot, but had a neighbor over the other day. Was a long haul trucker for a good part of his life and the manager of a truck tire store later. He started at the bottom, changing truck tires and worked his way up. I mentioned to him that I thought the 5 year rule (or whatever you call it for RV tires) was a big load of crap! He laughed and said they NEVER cared about the tire manufacture date when they recapped tires......He said as long as it wasn't from the '70's they'd cap it. And many of them recapped many times.....go figure....

Makes you wonder what a modern tire guy would say about tire age and how it relates to recapping them if asked......

[6Wheels]

8 hours ago, Bob Jones said:

It's official, you've now broken my mind. I'm ordering up 6 tire pyrometers, and a Nascar team, along with some NASA scientists and ultra-precise scales. I'll case those tire pressures yet!! 

Not to really stir the pot, but had a neighbor over the other day. Was a long haul trucker for a good part of his life and the manager of a truck tire store later. He started at the bottom, changing truck tires and worked his way up. I mentioned to him that I thought the 5 year rule (or whatever you call it for RV tires) was a big load of crap! He laughed and said they NEVER cared about the tire manufacture date when they recapped tires......He said as long as it wasn't from the '70's they'd cap it. And many of them recapped many times.....go figure....

Makes you wonder what a modern tire guy would say about tire age and how it relates to recapping them if asked......

That applies to trailer tires, but I bet the steer tires and at least one drive axle had newer tires.  

[Ivylog]

9 hours ago, Bob Jones said:

It is funny the way it works sometimes. I tried different pressures on mine and, in the end, it turned out the best ones to use were on the tires placard behind the driver's seat the entire time. Go figure 🙂 I'm pretty Monaco sat down, did the homework, took into account typical tank levels and weights to come up with their recommended number. 

NO, the psi on the placard equals the max rating of the axle. Sounds like you’re weights are near the max rating of your 2 axles.

Take the placard 90 psi for my 12K tag… guess how muck a single 295 with 90 psi in it can carry…12,200lbs. Same with my 23K drive…100 psi equals 23,500 lbs. Not as obvious on the front axle psi as the axle’s weight is close to its max.

Edited March 3, 2022 by Ivylog

[wamcneil]

10 hours ago, georgecederholm said:

Sorry! I thought I noted this in a prior post. “Cold Inflation Pressure”. “Cold” meaning ambient, not driven on, not overly warmed by the sun. Actually, it’s probably stated “Max PSI” on the sidewall, which is extra misleading since that’s the minimum cold inflation pressure for the maximum rated load of the tire for the axle type (single or dual). 🤪

Maybe it’s the tire engineers and regulators who can actually make things more complicated than the RV crowd? 😂

I'm pretty sure that every tire made in the last 50+ years has a max inflation figure imprinted into it, lawnmower, bicycle, heavy equipment, passenger cars, whatever...

In all those cases, max inflation number on the tire has nothing to do with the pressure we need to be inflating them to... Doesn't matter if it's a riding mower or a semi truck, there's a specified inflation pressure and it's not based on what's printed on the sidewall...

Cheers,

Walter

[saflyer]

On 2/11/2022 at 7:55 PM, cbr046 said:

Start with your coach's recommended pressures, or better yet weigh each corner and set pressures according to the tire manufacturer's load vs psi rating + a safety margin.  Personally I go 5-10 psi over.  Pressures are meant to be set cold and left alone. 

When the tire heats up that's normal.  If the tire is overloaded (too much weight or too little pressure) it will heat more. 

- bob

My understanding is yes, best practice is to get weights on each corner. But don’t set pressures different at each corner. Rather, take the highest weight on each end of each axle and set the pressure for the tires on both ends of that axle the same. That pressure should be based on the tire manufacturers tables.

Now, I’d like to know where this “safety margin” came from. I know the tire guru who writes for one of the online RV newsletters uses it but never justifies the concept. He also believes you shouldn’t correct the tire manufacturers tables to account for the difference between the “cold” inflation temperature and the 75° the tables are based on. I believe you should.

Ed         
‘05 Holiday Rambler Ambassador

Edited March 3, 2022 by saflyer

[Ivylog]

My +5 psi “safety margin” is because I’ll still travel with a 25+ mph cross wind. Even with that extra 5 psi the temps and pressures on the downwind side will go up more than normal.

Some do it because they only have axle weights. Fortunately my rig is within 200 lbs of each side once I stopped trying to get the rear at exactly 9”.

[cbr046]

Ant then there's the accuracy of gauges issue.  I'm sure all our gauges are calibrated periodically against NIST standards.  Or did you pick yours out of a jar at the counter, measure 5 of them and take the mean? 

Just because it's digital doesn't make it accurate. 

THAT'S where the +5 psi safety margin comes from!

(and probably a half dozen more reasons)

- bob

[wamcneil]

18 minutes ago, cbr046 said:

Just because it's digital doesn't make it accurate. 

- bob

WHAT!?!?? But my digital pressure gauge measures to 1/10 psi resolution, so it MUST be right! 🤪

Off topic anecdote... I had a digital scale and needed to step on it 3-4 times to get a stable reading. So I bought one that claimed to be far more accurate and not vary from one reading to the next. It didn't take long to figure out is was really no more accurate than any other cheap bathroom scale... except that after the first reading, if the weight didn't vary by more than .5 lb it would just display the original number. 

[moxy1962]

On 3/1/2022 at 7:41 AM, Ivylog said:

You are worried about the starting cold psi difference but won’t spend the $15 to weigh your axles at a truck stop to know where to start from?
You posted you had a 20-30 psi increase in a rear tire which tells me it was under inflated to start with… 15% increase is normal but not 25+%. Go weigh your rig!

Good advise 

21 hours ago, wamcneil said:

I'm pretty sure that every tire made in the last 50+ years has a max inflation figure imprinted into it, lawnmower, bicycle, heavy equipment, passenger cars, whatever...

In all those cases, max inflation number on the tire has nothing to do with the pressure we need to be inflating them to... Doesn't matter if it's a riding mower or a semi truck, there's a specified inflation pressure and it's not based on what's printed on the sidewall...

Cheers,

Walter

Agreed

[moxy1962]

When you have been at this long enough which a few of us have, you start to get an idea of what works. I’ve been at it for more than 25 years, most of those years at the helm of a pusher, 10 years with a tag. When I started out I read a lot and asked questions, always tried to err on the side of safety. 
 

Here’s what I know, a few times my TPMS has saved me, couple of slow leaks, few foreign objects getting in my tires and couple leaking valve stems. The TPMS actually picked up a bad trailer bearing and prevented significantly more damage and time spent on the side of the road. So i am a believer in TPMS. I also carry an infrared thermometer, if any tire seems to be higher than surrounding tires it’s usually heat, could be tire, could be bearings, excessive speed or brakes, with thermometer you can narrow it down quickly. Ive weight coach several times and set pressures to highest weight on any axle. Never drive over 65 - 67 mph to keep coach and trailer tires in their window of operation. 
 

You look after your tires, use them as they are meant to be used and take proper precautions they will look after you and your trips will be far less stressful. 
 

To those new to these incredibly complex machines, there is a wealth of information on this site, there is also some hot air, but all in all, mostly sound advise

Education is key

 

[jimc99999]

On 3/3/2022 at 8:21 AM, Ivylog said:

NO, the psi on the placard equals the max rating of the axle. Sounds like you’re weights are near the max rating of your 2 axles.

Take the placard 90 psi for my 12K tag… guess how muck a single 295 with 90 psi in it can carry…12,200lbs. Same with my 23K drive…100 psi equals 23,500 lbs. Not as obvious on the front axle psi as the axle’s weight is close to its max.

Are you sure that's not axle weight limit? Individual weight limit for single 295/75/22.5 is generally around 6600 lbs @ 120psi. Which 295 do you have that's double that weight limit with 30psi less?

https://www.herculestirescommercial.com/media/1367/new_ht_h_series_brochure_1_18f1-1.pdf

[Paul J A]

I really wish some of the ego's would diminish. 

 

[moxy1962]

4 minutes ago, Paul A. said:

I really wish some of the ego's would diminish. 

 

True that, 

[Ivylog]

2 hours ago, jimc99999 said:

Are you sure that's not axle weight limit? Individual weight limit for single 295/75/22.5 is generally around 6600 lbs @ 120psi. Which 295 do you have that's double that weight limit with 30psi less?

https://www.herculestirescommercial.com/media/1367/new_ht_h_series_brochure_1_18f1-1.pdf

Most tag axle rigs run 295/80/22.5

[Bob Jones]

On 3/3/2022 at 4:57 AM, 6Wheels said:

That applies to trailer tires, but I bet the steer tires and at least one drive axle had newer tires.  

That would make sense, to a degree. I found this from Michelin. It seems they have a service manual for their X1 tires directed at shops that do the retreading. Here's an excerpt or two which I found enlightening;

RETREAD LIMITS

• Line haul = greater than 150,000 miles per tread life: 1 retread (so, 300,000 miles total on the casing)
• Regional and P&D = 75,000 to 150,000 miles per tread life: 2 retreads (so 150,000 miles to 300,000 miles on the casing)
• Severe Service, On/Off Road, Urban, Refuse = less than 75,000 miles per tread life: multiple retreads (however many miles you like!) 🙂

CASING AGE LIMITS

Customer or tire manufacturer specifications may have more stringent (shorter life) requirements that must also be met.

• For Line Haul 7 years
• For Pickup & Delivery 10 years
• For Severe Use no age restriction

If you read between the lines it looks like what Michelin is looking at for casing age limits is not actually age, but mileage.

Michelin Retread & Repair Guidelines for the X-One Tire

Of course, it's a personal preference but I have a unit that had brand new Michelin's put on it right before I got it. As such, the tires are new. According to the general consensus of the RV owners, they have certainly aged out and must be replaced. I think they may be 7 years old? In due course the unit will be back on the road but there is no way that I would replace what are effectively new tires because of age. 

Now if they have bulges, signs of weather-checking, broken belts, flat spots that do not 'self-repair' over mileage etc, then I would do something about them. But this idea that all tires that are 'old' must be replaced regardless of condition, it's a crock. And given Michelin's guide above, it does appear that they are NOT looking at age as the decider but mileage. 

From my research, Michelin has the strictest guidelines on the matter. All of the other manufacturers appear to be much more relaxed and don't appear to consider age of importance.