Tires: where do I even start?!

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JudyJB

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Jul 6, 2010
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You have the same size tires as I do: 225/75/R16

The reason I mention tire pressure is that I have had to argue with several RV service places about pressure. The Fleetwood sticker inside my motorhome says 75 in front and 80 in rear, but I had a guy in a very small RV repair place try to tell me that his friend who worked in a bigger dealership told him that the correct pressure in a motorhome tire was 65 pounds! That is ridiculous for a lot of reasons, the biggest of which is that motorhomes are NOT all the same size or weight or use the same tires.

I have also had a couple of instances where the mechanic I was asking to check the pressure in my tires would run around looking for the sticker on my driver's side door for the correct Ford manufacturer's tire pressure. I told him that any sticker there was put on by Ford BEFORE Fleetwood installed a motorhome on top of the bare chassis, and that the correct pressure was on the inside sticker. I went as far as taking a photo of the Fleetwood sticker because this guy thought he was arguing with a stupid woman, and i was losing patience. I was about to walk out and get air put in elsewhere!

My point is to find the correct pressure and don't let someone assume you don't know anything.

I now own a TPM (tire pressure monitor) device which tells me the pressure and temperature of each of my tires while I am driving.
 

jadatis

Active member
Joined
Jul 26, 2008
Posts
39
Used the info you gave in several posts, and filled in in my made calculator.

For GAWR'S with maximum reserve with still acceptable comfort and grip, front 67psi reardrive 80 psi.

But better is to weigh per axle-end , second best axle, fully loaded as going on trip, also the persons.
 
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jadatis

Active member
Joined
Jul 26, 2008
Posts
39
Used the info you gave in several posts, and filled in in my made calculator.

For GAWR'S with maximum reserve with still acceptable comfort and grip, front 67psi reardrive 80 psi.

But better is to weigh per axle-end , second best axle, fully loaded as going on trip, also the persons
 

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3CMomma

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Joined
Nov 30, 2021
Posts
13
Location
East Texas
You have the same size tires as I do: 225/75/R16

The reason I mention tire pressure is that I have had to argue with several RV service places about pressure. The Fleetwood sticker inside my motorhome says 75 in front and 80 in rear, but I had a guy in a very small RV repair place try to tell me that his friend who worked in a bigger dealership told him that the correct pressure in a motorhome tire was 65 pounds! That is ridiculous for a lot of reasons, the biggest of which is that motorhomes are NOT all the same size or weight or use the same tires.

I have also had a couple of instances where the mechanic I was asking to check the pressure in my tires would run around looking for the sticker on my driver's side door for the correct Ford manufacturer's tire pressure. I told him that any sticker there was put on by Ford BEFORE Fleetwood installed a motorhome on top of the bare chassis, and that the correct pressure was on the inside sticker. I went as far as taking a photo of the Fleetwood sticker because this guy thought he was arguing with a stupid woman, and i was losing patience. I was about to walk out and get air put in elsewhere!

My point is to find the correct pressure and don't let someone assume you don't know anything.

I now own a TPM (tire pressure monitor) device which tells me the pressure and temperature of each of my tires while I am driving.
🙌🏻👍🏻Great advice!!
 

3CMomma

Member
Joined
Nov 30, 2021
Posts
13
Location
East Texas
Used the info you gave in several posts, and filled in in my made calculator.

For GAWR'S with maximum reserve with still acceptable comfort and grip, front 67psi reardrive 80 psi.

But better is to weigh per axle-end , second best axle, fully loaded as going on trip, also the persons
This looks so impressive!!! I need a lecture on what it all means 🙌🏻
 

Mark_K5LXP

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Nov 17, 2018
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1,803
Location
Albuquerque, NM
Used the info you gave in several posts, and filled in in my made calculator.
NOT a criticism but a question, given the limited information on the screenshot. Are manufacturer tire parameters somehow entered, or is this more of a general calculation based on load range and weights? Same for "comfort and grip", what's "acceptable"?

Mark B.
Albuquerque, NM
 

jadatis

Active member
Joined
Jul 26, 2008
Posts
39
If you click on the screenshot, you get the full picture, wich you can enlarge .

I myself determined by reactions about bumping, that if the pressure is calculated for a deflection belonging to 160kmph/99mph and using 90% of the loadcapacity belonging to the calculated pressure, that then comfort and gripp is still acceptable.

In fact 85%, but I calculate for average of 90, so unequall load R/L is covered

For instance R 85% L 95% used then R yust no bumping and L still some reserve.

And because your max speed is most likely only 75mph, it gives some extra reserve.

For traveltrailers with no persons in it, I dare to go as low as 80% used of the loadcapacity belonging to the pressure, before screws turn loose from the woodwork or rivets.
Or doors open after the ride.

Centrewear probably happens below 65% used of loadcapacity.
And overheating driving constant speed of 99mph, above 100%.

Can be that you calculate for highest pressure with still comfort, but by all the inacuracies you end up with only yust enaugh to prevent overheating at least one tire driving your maximum speed.

That overheating is only alowed ZERO times in the use of tire.

So its wise to change the tires , you dont know the history of it , and you saw already cracks.

But once you have the new tires, use high enaugh pressure, and cover them ( when standing still) for sunlight, and dont store motorhome near electrical instruments that produce peroxides like Ozon .

Then tires can last 10 years.
2 years profesional storing after production date ( DOT) can be sold as new.

Michelin advices to preventively renew the tires after 10 years of use, and have them checked by a profesional every year after 6 years of use, especially on agingsighns. Can sometimes mean after 12 years after DOT date preventive renewal.
 

jadatis

Active member
Joined
Jul 26, 2008
Posts
39
NOT a criticism but a question, given the limited information on the screenshot. Are manufacturer tire parameters somehow entered, or is this more of a general calculation based on load range and weights? Same for "comfort and grip", what's "acceptable"?

Mark B.
Albuquerque, NM
Forgot about the tires.

The tiremaker calculates the maxload ( here 2680lbs belonging to Load-index 115) for maxspeed of tire ( belonging to speedcode).
Above 160kmph/99mph, so speedcode R ,S,T,H,V, the maxload is for 99mph calculated, and gives that on sidewall , Service descriptions its called ( Here 115/112R , have to look back the picture) . In theory you can drive with the reference- pressure in tire ( 80psi for E-load), and maxload on tire, the reference-speed ( mostly 160kmph/99mph) constantly, without overheating any part of tire.

So this is minimum pressure needed if everything is 100% acurate determined, wich is never possible.

But you can go higher in pressure, but if to high, comfort gets bad, and that is per tire if below 85% of loadcapacity is used, as explained in former post.
So I add 10% or 11% to given load ( here GAWR 4300lbs front,I used 5% extra because frontaxle seldom overloaded, but real weghed loads I add 10% for motorhomes, wich makes 91% used of loadcapacity belonging to the pressure I calculate.
Rear I used here 15% because rear axle often close to or over GAWR.
In my made traveltrailer-calculator, I add 11% to make that average 90% used of loadcapacity, and mayby I will change that to 11% in the motorhome-calculator too.
So I use the service descriptions wich the tiremakers determined for the tire , so loadindex and speedcode, and pressure behind AT wich is in America fixed for the loadrange, in Europe there are exeptions.

C-load /LRC AT 50 psi
D-Load/ LRD AT 65 psi
E- Load/LRE AT 80psi
F-Load/ LRF AT 95psi

But the sise LT225/75R16 is in Europe E-load is called 10 plyrated C(omercial) tyre and there are 2 .
1. 118R AT 5.25bar/77psi. and 121R AT 5.75bar/83psi. So bith higher maxload then LT 115R AT 80psi.
To laws of nature they should have the same service descriptions
 

3CMomma

Member
Joined
Nov 30, 2021
Posts
13
Location
East Texas
Forgot about the tires.

The tiremaker calculates the maxload ( here 2680lbs belonging to Load-index 115) for maxspeed of tire ( belonging to speedcode).
Above 160kmph/99mph, so speedcode R ,S,T,H,V, the maxload is for 99mph calculated, and gives that on sidewall , Service descriptions its called ( Here 115/112R , have to look back the picture) . In theory you can drive with the reference- pressure in tire ( 80psi for E-load), and maxload on tire, the reference-speed ( mostly 160kmph/99mph) constantly, without overheating any part of tire.

So this is minimum pressure needed if everything is 100% acurate determined, wich is never possible.

But you can go higher in pressure, but if to high, comfort gets bad, and that is per tire if below 85% of loadcapacity is used, as explained in former post.
So I add 10% or 11% to given load ( here GAWR 4300lbs front,I used 5% extra because frontaxle seldom overloaded, but real weghed loads I add 10% for motorhomes, wich makes 91% used of loadcapacity belonging to the pressure I calculate.
Rear I used here 15% because rear axle often close to or over GAWR.
In my made traveltrailer-calculator, I add 11% to make that average 90% used of loadcapacity, and mayby I will change that to 11% in the motorhome-calculator too.
So I use the service descriptions wich the tiremakers determined for the tire , so loadindex and speedcode, and pressure behind AT wich is in America fixed for the loadrange, in Europe there are exeptions.

C-load /LRC AT 50 psi
D-Load/ LRD AT 65 psi
E- Load/LRE AT 80psi
F-Load/ LRF AT 95psi

But the sise LT225/75R16 is in Europe E-load is called 10 plyrated C(omercial) tyre and there are 2 .
1. 118R AT 5.25bar/77psi. and 121R AT 5.75bar/83psi. So bith higher maxload then LT 115R AT 80psi.
To laws of nature they should have the same service descriptions
I would to toss out here what I THINK I understand from everything everyone has shared ☺️
•225/75R16 is the tire for my rig-commercial is a good way to go if we have $$ to spend; make sure it has E rating
•Brand depends on $$ and usage(less than 5k miles per year)can be stored up to 2 years post production date and still be sold as new tires
•Making sure they are at correct pressure is VERY important for wear pattern and need to check before heading out each time!
•Front axle and rear axle are different psi due to load carried at each axle
•I should probably hit a scale fully loaded at some point just to know what I am working with in real life
 

jadatis

Active member
Joined
Jul 26, 2008
Posts
39
About next.

•Making sure they are at correct pressure is VERY important for wear pattern and need to check before heading out each time!

Even a bit to low pressure still gives even wear for radial tires, and only much to high gives centrewear ( my estimation that 65% load%).

So correct pressure is for savety, so you wont have a blowing tire, or treath seperation.
 

Larry N.

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Joined
May 26, 2010
Posts
8,559
Location
Westminster, Colorado
Making sure they are at correct pressure is VERY important for wear pattern and need to check before heading out each time!
As jadatis says, it's not nearly so much for wear pattern as it is for safety. Tires even a little low for the weight can sustain damage surprisingly quickly, and blowouts soon become a concern, while pressure being a little high isn't a problem, and gives a cushion as conditions change.

But on the high side, pressure that is a LOT too high can cause handling problems. On one rig I had pressure too high caused certain road bumps to almost throw the rig out of control, while another rig with pressure too high had tires following grooves in highway, causing a lot of sideways wiggle going down the road at highway speeds.

So for safety, go with weighing and setting pressure per the tire manufacturer's tables.
 

jadatis

Active member
Joined
Jul 26, 2008
Posts
39
About hat last about setting pressure per the tire manufacturer's tables, I also have a remark.

American pressure/loadcapacity-lists, are made wirh a formula that leads to higher loadcapacity then the European official formula. So leads to lower pressure, and in my spreadsheets I set the formula that tight, that it leads to even lower loadcapacity for the pressure, or the other way around, leads to higher pressure for the same load.

Now the maximum load of LT is set lower then European C-tyres in your sise,( US 115/112 at 80psi, EUR 118/115 at 77psi and 121/118 at 83 psi),as I already wrote before, so this compensates the US calculation .

So use the US lists, but important is also that you add first enaugh reserve, before looking in the list, whatever list you use.
Or, when you weighed with also the kids in it, give it here and I will recalculate.

And wear on only one side is an alignment thing, whatever you do with the pressure wont solve it. Mayby low pressure will make it wear a little faster, but you can only solve it by letting the allignment be fixed.
 
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jadatis

Active member
Joined
Jul 26, 2008
Posts
39
About hat last about setting pressure per the tire manufacturer's tables, I also have a remark.

American pressure/loadcapacity-lists, are made with a formula that leads to higher loadcapacity then the European official formula. So leads to lower pressure, and in my spreadsheets I set the formula that tight, that it leads to even lower loadcapacity for the pressure, or the other way around, leads to higher pressure for the same load.

Now the maximum load of LT is set lower then European C-tyres US 115/112, EUR 118 at 77psi and 121 at 83 psi), so this compensates the US calculation .

So use the US lists, but important is also that you add first enaugh reserve, before looking in the list, whatever list you use.
Or, when you weighed with also the kids in it, give it here and I will recalcul
 

Gary RV_Wizard

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At my Silver Springs FL home
I think jadatis's estimator is way over the top for any RV. This isn't rocket science and "close enough" does just fine.

If possible get real weights. If not practical, use axle GAWRs are assume they are fully loaded. Then use the psi from the tire manufacturer's table. As a last resort, use the vehiclemakers recommended psi, which will almost surely be for a max-loaded vehicle. That maybe a bit more than needed, but it's probably safe.
 

jadatis

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Joined
Jul 26, 2008
Posts
39
See you are in the site team. Are you also a moderator then.

By several editings, mostly for writing errors, 2 post got double.
So if you can , will you remove post # 22 and #33 for me?
After that you can remove up to this sentence.

A little rocket science is not that bad for RV tires, on fora you read a lot about tire-failure often by using to low pressure.
But also hard ride, wich belongs mostly to to high pressure.
 
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