OK? to lower tire pressure for smoother ride?

[Ann-Marie]

Our Greyhawk 30 from the dealer came with all tires 10 psi lower than the Ford settings.
I brought them all up to recommended pressure and now the ride is stiffer.
Is it OK to run with pressures down 10 psi?
I assume fuel mpg would be better at higher pressure - - less flexing of rubber.
They should run a little cooler with less flexing.
What is the effect on tire life?

[Grumpy]

Originally Posted by Ann-Marie

Our Greyhawk 30 from the dealer came with all tires 10 psi lower than the Ford settings.
I brought them all up to recommended pressure and now the ride is stiffer.
Is it OK to run with pressures down 10 psi?
I assume fuel mpg would be better at higher pressure - - less flexing of rubber.
They should run a little cooler with less flexing.
What is the effect on tire life?

Go to a Cat scale and weigh it, then adjust the pressures accordingly...

https://www.rvsafety.com/images/pdf/...ionrvtruck.pdf

I was always able to lower the pressures after I weighed the MH's.

[jadatis]

If you base your tirepressure on weighing and speed used, and take a reserve, it is safe to lower pressure(if weight an speed calculates that lower pressure). Yust lowering it for comfort has a risk of going to low, wich can give overheating of one or more tires. This may only happen ZERO times in tires use, and can sometimes give only after 3 years a blowing tire.

I am able to calculate a highest pressure for you with still acceptable comfort and gripp, but need those weights and tire-specifications for that.

Motorhomes have airodinamics of a shoebox on wheels, so rolling resistance of tires make smaller part of total fuelconsumption, so my calculated pressure wont give that much more.

With my calculated pressure with acurate determined data, your tires still can make the 10 years to preventive renewal. OK, also cover for sunlight when standing, and dont store in spaces where electrical instruments are working, that produce peroxides like Ozon., and let them be checked by a specialist every year also on aging sighns.

[Jerry713]

Most blow outs occur due to low tire pressure. Blow outs obviously can be devastating to an RV. Is it worth the risk for a little smoother ride?

[Onyrlef]

Originally Posted by Jerry713

Most blow outs occur due to low tire pressure. Blow outs obviously can be devastating to an RV. Is it worth the risk for a little smoother ride?

I think most RV owners, thinking more is better, run at higher TP's than necessary. The Michelin tables may surprise some when they actually use the table with their actual Cat Scale axle weights. Most I suspect will find they're actually overinflated. Michelin warns against both over and under inflation.

[SloPoke]

Originally Posted by Onyrlef

I think most RV owners, thinking more is better, run at higher TP's than necessary. The Michelin tables may surprise some when they actually use the table with their actual Cat Scale axle weights. Most I suspect will find they're actually overinflated. Michelin warns against both over and under inflation.

I think most RV owners, thinking more is better, run at higher TP's than necessary have never seen a CAT Scale...

And they don't know what each tire is carrying on the scale and assumes that the Maximum pressure listed on the sidewall of the tire is going to work if they are rolling at maximum weight. As you mention, the Michelin tables should be the guide for inflation pressures at specific loads.

[bucko]

I have always used the door sticker for stock sized tire inflation, or what is embossed on the tire itself for tire inflation. I did not buy a camper for the smoothness of its ride....I expect it to be not like a car or average pick-up.

I'd think you'd have a tough time trying to obtain a warrantee replacement on a tire that failed due to it being under inflated.

[Jerry713]

Originally Posted by Onyrlef

I think most RV owners, thinking more is better, run at higher TP's than necessary. The Michelin tables may surprise some when they actually use the table with their actual Cat Scale axle weights. Most I suspect will find they're actually overinflated. Michelin warns against both over and under inflation.

Maybe so. I've always heard truckers say an underinflated tire will blow faster than an overinflated tire. Tires can handle a lot more pressure than some think. Another issue is RV's is manufactures put the smallest size axle with a weight rating barely enough to cover the trailer weight. Some fifth wheels don't even have heavy enough trailer axles to support the entire weight of the trailer banking on a portion of the trailer being on the truck. When a trailer is a little overloaded it puts more weight on the tires than necessary. That and the amount of bouncing that occurs on the tires wears them out.

[Onyrlef]

Originally Posted by Jerry713

Maybe so. I've always heard truckers say an underinflated tire will blow faster than an overinflated tire. Tires can handle a lot more pressure than some think. Another issue is RV's is manufactures put the smallest size axle with a weight rating barely enough to cover the trailer weight. Some fifth wheels don't even have heavy enough trailer axles to support the entire weight of the trailer banking on a portion of the trailer being on the truck. When a trailer is a little overloaded it puts more weight on the tires than necessary. That and the amount of bouncing that occurs on the tires wears them out.

Mine are Michelin XZE's on a 32' MH. Cat Scale drive axle weight is 11,580, Steer Axle 5,260. The Michelin table for a 245/70R19.5 LRH XZE allows 3390 lbs. on the axle end for a sgl. @ 75lbs. 6420 on each axle end dual also at 75lbs. 75lbs. is the minimum psi which can be run on this tire.
In a perfect world, after the first weigh, I'd have weighed either the driver or passenger side axles and determined individual axle end weights but Cat Scale policy doesn't allow that. Had I however, my TP for each axle would have been determined by the heavier axle end weight. Michelin is emphatic that all tires on an axle must run within 3 lbs or so of one another.
The data plate for my unit lists a psi for each tire of 82lbs. GAWR front -7k, rear-12k
I'm going to default to the data plate which gives me some wiggle room on my actual axle end weights since I wasn't able to get that second weigh.


Point being however, those tables and the data plate tire psi guidelines are not opinions and proper tire inflation shouldn't be conflated with under inflation.

[ependydad]

Originally Posted by Grumpy

Go to a Cat scale and weigh it, then adjust the pressures accordingly...

https://www.rvsafety.com/images/pdf/...ionrvtruck.pdf

I was always able to lower the pressures after I weighed the MH's.

100% agreed that this is the way/weigh .

[Tireman9]

Originally Posted by Onyrlef

I think most RV owners, thinking more is better, run at higher TP's than necessary. The Michelin tables may surprise some when they actually use the table with their actual Cat Scale axle weights. Most I suspect will find they're actually overinflated. Michelin warns against both over and under inflation.

People seem to forget that the pressure in the tables is the absolute minimum pressure needed by the tire to support the measured load.

Most cars and trucks you see on the road run with a +25 to +30% "Reserve Load". Based on thousands of checks we know that a MAJORITY of RV have a tire and or axle in overload ( a negative Reserve Load) yet people have difficulty in understanding why tire life in RV application is significantly worse than seen on cars and non-RVs.

As a tire Design and Forensic Engineer I recommend a minimum of15% Reserve Load with being closer to 25% being better. I run + 20% to + 28% in my RV.

Just running 10% low will probably not result in an immediate tire failure as tires are very resilient. BUT you are consuming the life of your tires with every mile you drive and running low will consume more than is you run with a good level of Reserve Load.

Tire "Blowouts" are the result of crack growth in the internal structure of your tires. Cracks start at the molecular level and will grow with every mile driven. Tires can not and do not "repair" themselves The cracks can only grow and eventually can end with you on the side of the road with a shreded tire.

You will read posts from non-engineers offering the idea that you might be able to get a couple years life out of your tires even with pressure a little low for a better ride. That might be true. BUT are you planning on changing your tires every 24 months?
You mentioned "Ford Inflation" Is that the inflation shown on your RV Certification label? That is the MINIMUM inflation needed to support the GAWR based on guidelines from RVIA.
Have you been on a truck scale with the RV fully loaded to the heaviest you ever expect when traveling? There are blogs and even FB pages monitored by actual tire design engineers giving facts based on their professional Engineering experience. or you can listen to people who think all you need to do to be an "expert" is to have bought a bunch of tires over a few decades of RV life.


Your choice.

[craigav]

Tireman has always provide good information. (Thanks). A point to note though on many of our Class C's is that the Ford sticker for the minimum (or recommended) rear tire pressure is the same pressure as the max pressure is as listed on the tire (80 psi). In other words, I wouldn't (don't) run anything other than 80psi. I think the front tire recommendation is 65 (need to check) however, as Tireman suggested, I run them a little higher, not quite 20% but close (~15%) at ~75 psi. ~CA


One other thought to share, with the colder temps the pressures will drop and it is that time of the year for many locations.

[Tireman9]

Originally Posted by craigav

Tireman has always provide good information. (Thanks). A point to note though on many of our Class C's is that the Ford sticker for the minimum (or recommended) rear tire pressure is the same pressure as the max pressure is as listed on the tire (80 psi). In other words, I wouldn't (don't) run anything other than 80psi. I think the front tire recommendation is 65 (need to check) however, as Tireman suggested, I run them a little higher, not quite 20% but close (~15%) at ~75 psi. ~CA


One other thought to share, with the colder temps the pressures will drop and it is that time of the year for many locations.

Yes the pressure will drop but people should not plan on the drop or increase. Example For a number of years I have headed from Akron OH to Perry GA to the large FMCA Convention. A couple times it has been at or below freezing when I start in Ohio and can be a nice 75 when I leave GA. In both cases My tire pressures are set to the same level. Based on my 4 corner weight + my Reserve load I set the PSI to 70 in F and 80 in Rear on morning of travel day on my Coachmen 24QB. BUT I am not going on an extended vacation and only carry 5 gal of water (in jugs) and minimal food as I plan on eating the "junk food" at the GA fair grounds so I am close to the minimum weight of the RV.