Tire Opinions (with data)

[EdandShelley]

I can't tell from that photo if the tires are at 90, 100, or 250 psi, but I CAN tell that is a sweet looking rig! Get those tires set to whatever pressure provides the best ride for you and your wife ("Happy Wife - Happy Life") and then go enjoy it!
In skimming through the thread, it seems like all the recommendations are within roughly 8-10% of each other, so as long as the "perfect ride" pressure is somewhere in that range, go for it. You're supposed to be thinking about what you're looking at through the windshield and enjoying the journey, not whether your tires are 92 PSI or 96 PSI!

Couldn't agree more! It's getting a few electrical mods done this week (Autoformer and build in surge protection) then we are heading to south Texas for a visit.

Really appreciate all the advice from the forum...
Believe I will go with 90 on the front and 95 on the rear. Plenty of error factor room.

THANKS EVERYONE!

 

[RV Randy]

Couldn't agree more! It's getting a few electrical mods done this week (Autoformer and build in surge protection) then we are heading to south Texas for a visit.

Really appreciate all the advice from the forum...
Believe I will go with 90 on the front and 95 on the rear. Plenty of error factor room.

THANKS EVERYONE!

That should be a good setting to go with and will improve the ride noticeably. Also, what PSI Crossfire device did you get? It will still work if these new PSI settings are lower than the device you ordered, but you will see the yellow indicator showing the tire is below the target pressure PSI.

 

[jadatis]

Front needs higher pressure then rear, that is a fact, and I hope Tireman9 finds this topic to comfirm.

But I calculated the pressure for your axle-end weights with the needed reserve, for 75 mph speed, wich you wont go over for even a minute.
Then it gave 96psi front and 87psi rear.
Axle weights filled in gave 1 psi lower.

Then assumed these are the weights with everything aboard, so all the water , fuel , persons , etc. The 10% reserve in case of only axleweight, is also to cover a little more real weight , but also inacuracy in weight and pressure reading.

Can be that I calculated with all the reserves, but by all this, you only yust have enaugh to give no overheating of tire . This must not happen even only once in the livetime of the tires. Once the structure is damaged, mechanical forces, damage the tire further in time, until after mayby only 3 years that far that it blows or treath-seperation.

 

[Tireman9]

OK folks Tireman9 here. Sorry I did not jump in earlier but I was out of the country.


Lets see if I can summarize: First there are a number of things to consider such as type of vehicle and if tires are same size & type as OE. Lets stick with the tires being same as OE. If you don't understand a term please go to my blog where I have a lot more space to cover items in detail.

Motorhomes and other vehicles that can be driven. The tires on these vehicles rotate around a centerline that points to the center of a turn radius. (See Ackerman).
All Radial tires do have Interply Shear. but it's the level of this force that is significantly different for vehicles that do not have steering Ackerman i.e. trailers.

The Interply Shear that tires in trailer application can be 24% higher than identical tires on a motorvehicle with active steering.
Increased inflation (lower load) is something the driver can do that would lower this 24% but not to 0%.


So what inflation should motorvehicles run? As a minimum they should run the same inflation on all tires on an axle. This is done to keep steering or turning response similar when turning right vs left. They also should run at least the inflation necessary to support the load on the heavier end of the axle.


The 4 corner weight is a method used to learn the actual load on each end of each axle. This measurement should be made when the vehicle is loaded to the heaviest ever expected.


So knowing the heavy tire you use the charts to learn the MINIMUM inflation for tires on that axle.


I do recommend a minimum of +10% inflation over that minimum to address day to day pressure variation due to weather (temperature and barometer) changes. I have covered this in my blog with my personal experiences of driving my Class-C across country a couple times.


Well I hope I clarified my position. If not you can email me (email is posted on my blog under my picture.

 

[EdandShelley]

OK folks Tireman9 here. Sorry I did not jump in earlier but I was out of the country.


Lets see if I can summarize: First there are a number of things to consider such as type of vehicle and if tires are same size & type as OE. Lets stick with the tires being same as OE. If you don't understand a term please go to my blog where I have a lot more space to cover items in detail.

Motorhomes and other vehicles that can be driven. The tires on these vehicles rotate around a centerline that points to the center of a turn radius. (See Ackerman).
All Radial tires do have Interply Shear. but it's the level of this force that is significantly different for vehicles that do not have steering Ackerman i.e. trailers.

The Interply Shear that tires in trailer application can be 24% higher than identical tires on a motorvehicle with active steering.
Increased inflation (lower load) is something the driver can do that would lower this 24% but not to 0%.


So what inflation should motorvehicles run? As a minimum they should run the same inflation on all tires on an axle. This is done to keep steering or turning response similar when turning right vs left. They also should run at least the inflation necessary to support the load on the heavier end of the axle.


The 4 corner weight is a method used to learn the actual load on each end of each axle. This measurement should be made when the vehicle is loaded to the heaviest ever expected.


So knowing the heavy tire you use the charts to learn the MINIMUM inflation for tires on that axle.


I do recommend a minimum of +10% inflation over that minimum to address day to day pressure variation due to weather (temperature and barometer) changes. I have covered this in my blog with my personal experiences of driving my Class-C across country a couple times.


Well I hope I clarified my position. If not you can email me (email is posted on my blog under my picture.

Thank you so much Tireman9. Clear and easy to understand.
I’m settling on 90 up front and 95 in the rear.
Ed and Shelley

 

[Slow Moon]

Question for Tireman9--TRAILER TIRES

Mr. Tireman9,

You are my go-to expert on tires, and I really appreciate the information you provide here and on your blog. Based largely on what I have learned from you, I posted the following in response to a trailer tire question above:

A few might disagree, but I think the consensus by pretty much all who understand TRAILER tires agree that you always inflate them to the max cold sidewall pressure.***I will say if you do have a trailer and use TRAILER tires, you really can't go wrong with using the sidewall specified max cold pressure.
***

The following was posted in response:

BTW, the consensus is far from maxing out the PSI in trailer tires. In fact Tireman9, the expert in the group, specifically says you don't.
***

I understand "always" may be too strong but you still GENERALLY opine that tandem trailer tires should be inflated to the max sidewall-molded PSI, and you really can't go wrong doing that.

My research did not find any support for a post that Tireman9 specifically says don't do that.

Can you tell us if you really specifically say don't do that?

I understand in very rare extreme cases--such as where stock tires are replaced by enormously higher load rated tires--one might run a little less pressure to gain a little tread wear. I'd think that would very rarely, if ever, apply to heavy TTs or large 5ers. In any case, tread-wear seems a minimal concern compared to "blowouts," so it's generally not wrong to run max sidewall PSI even if you think your tires have 20% more capacity than required.

I would certainly appreciate your comments, especially if I'm wrong and need to lower the pressure in my 5er.

I apologize to any MH guys that don't want to read trailer riff-raff in their MH thread. I did include a title to enable you to skip this post.

 

[bradbill-FRF]

Since we are talking about trailers again...I follow Tireman's advice from the post that was mentioned earlier in this thread. For my tandem trailer, I went up from 205/75/14 load range C(OEM size) to 205/75/14 load range D to get some safety margin. I took my load and divided by 0.85 for the margin that Tireman9 suggested. I used that number to look at the inflation table, again as suggested by Tireman9 and inflate to 55PSI. Almost exactly the example that he stated in that other thread. Gives me the margin that I need.

 

[jadatis]

@ Tireman9

Can you react on this specific situation in this topic of lower pressure in front then rear for a dual axle rear axle. That is my contradicting advice , to give yust higher on front. The numbers are given in this topic.

 

[jadatis]

In addition to post above, see post #35 and # 36.
Also see my edit at post # 34.

 

[Tireman9]

OK lets talk about tandem axle trailers (The word dual does mean two but usually is reserved to two tires mounted next to each other on one end of an axle as seen in the rear of many Motorhomes)


Tandem or triple axle trailers mean the tires are fighting each other when the trailer is pulled around any turn or corner. You can see the result in the video in my blog post of September 7, 2018 on InterPly Shear. This tire distortion is the result of a tire being forced around a turn rather than steering around a corner.
The result of this distortion is the primary cause of the significant increase in Interply Shear.


If you discover that different axles on a trailer have significantly different loads then I would recommend to first learn why this is the case. Given that most RV trailers have the axles supporting the frame through suspension components that are suppose to equalize the load between axles something is out of wack. Hitch too high or low, worn or binding shackle or other component causing binding?


While I have no hard data I would think that axles should have measured loads within 5% or less of each other. ( If any owners of multi-axle trailers have hard data maybe they can post axle to axle GAW numbers)


In general I would think it desirable to try and have the tire loading, and inflation of all tires on a trailer to be as close as possible to the same level. But in NO case should any tire run even 1 psi below the pressure needed to support the actual static load and the goal should be a MINIMUM of 15% load capacity margin on the worst case tire.

 

[jadatis]

Correction, I meanth Dual-load axle, so 4 tires on one axle . Mostly then front axles tires need higher pressure then behind, sometimes the same, but never lower pressure then behind.

For a single- load rearaxle , behind higher pressure then front, so the other way around.

 

[Slow Moon]

TIREMAN 9—¿DO or DO NOT: Inflate TANDEM TRAILER Tires to Max Sidewall PSI?

Dear Tireman9,

Except to solve ride problems, Goodyear recommends inflating RV trailer tires to max sidewall PSI:

"Unless trying to resolve poor ride quality problems with an RV trailer,
it is recommended that trailer tires be inflated to the pressure indicated
on the sidewall of the tire. Trailer tires experience significant lateral
(side-to-side) loads due to vehicle sway from uneven roads or passing
vehicles. Using the inflation pressure engraved on the sidewall will
provide optimum load carrying capacity and minimize heat build-up."
https://www.goodyearrvtires.com/weighing-your-rv.aspx

As traceable in my post #21, above, I rely on your statements:

“Towables . . . should run the tire sidewall inflation to lower the tire Slip Angle. Lower slip angle yields lower Interply Shear.” (Post #87), and

“Trailers inflate to pressure on the tire sidewall.” (Post #91)
https://www.forestriverforums.com/for...-198414-5.html

Based on your post #50, above, reading your blog and Goodyear's booklet, I do what I THINK you and Goodyear say: Inflate tandem 5er tires to max sidewall PSI. Post #50 is not clear on this point. Am I doing the wrong thing?

 

[Tireman9]

Dear Tireman9,

Except to solve ride problems, Goodyear recommends inflating RV trailer tires to max sidewall PSI:

"Unless trying to resolve poor ride quality problems with an RV trailer,
it is recommended that trailer tires be inflated to the pressure indicated
on the sidewall of the tire. Trailer tires experience significant lateral
(side-to-side) loads due to vehicle sway from uneven roads or passing
vehicles. Using the inflation pressure engraved on the sidewall will
provide optimum load carrying capacity and minimize heat build-up."
https://www.goodyearrvtires.com/weighing-your-rv.aspx

As traceable in my post #21, above, I rely on your statements:

“Towables . . . should run the tire sidewall inflation to lower the tire Slip Angle. Lower slip angle yields lower Interply Shear.” (Post #87), and

“Trailers inflate to pressure on the tire sidewall.” (Post #91)
https://www.forestriverforums.com/for...-198414-5.html

Based on your post #50, above, reading your blog and Goodyear's booklet, I do what I THINK you and Goodyear say: Inflate tandem 5er tires to max sidewall PSI. Post #50 is not clear on this point. Am I doing the wrong thing?

No you are doing nothing wrong.
The confusion comes when talking MINIMUM inflation for towables vs DESIRABLE inflation.


Minimum would be load based.
Desirable woule be based on lower Interply shear which I cover extensively in my blog where I say trailers should inflate to tire sidewall. This creates a problem when some up-size or up-rate their tires by a couple Load Range (LR-C to LR-D or LR-E) Now I have to start warning about exceeding the wheel rating.


There NEVER is a simple answer that will cover ALL possible situations. That's why I have written over 412 posts on my blog. I have tried to answer the simple basic questions and to provide examples for the complicated unusual cases.


I could even make the case that GY is wrong when they say inflate to sidewall pressure, without offering the warning about special cases. A review of their Endurance line will show that there are a number of sizes where the only option is to go up a Load Range but they make no mention of possible exceeding the wheel inflation rating.

 

[Tireman9]

Correction, I meanth Dual-load axle, so 4 tires on one axle . Mostly then front axles tires need higher pressure then behind, sometimes the same, but never lower pressure then behind.

For a single- load rearaxle , behind higher pressure then front, so the other way around.

Motorhome Front vs rear Single vs Dual. You have to look at each case. You can not make simple statements that would cover all vehicles or all trailers in 100% of the cases. This is why all you folks are paying me the big bucks to provide answers.


Oh wait... You aren't paying me. Oh darn.

 

[Slow Moon]

Thanks tireman9--you are the best!

Maybe we should be paying you.

I do at least read the blog and click the ads.

Thanks again for all your info, help and patience with us.

You are a great resource.

 

[jadatis]

Motorhome Front vs rear Single vs Dual. You have to look at each case. You can not make simple statements that would cover all vehicles or all trailers in 100% of the cases. This is why all you folks are paying me the big bucks to provide answers.


Oh wait... You aren't paying me. Oh darn.

You still did not look into this specific case .
Here even axle-end weights given fully loaded ( exept water) . So what would you have calculated .
Your using highest axle-end x 2 and adding 10% to the searched back pressure in list, comes to practically the same pressure as my adding 10% to axle-load and searching back pressure for that.

 

[Tireman9]

You still did not look into this specific case .
Here even axle-end weights given fully loaded ( exept water) . So what would you have calculated .
Your using highest axle-end x 2 and adding 10% to the searched back pressure in list, comes to practically the same pressure as my adding 10% to axle-load and searching back pressure for that.

If each end is 50% of total then 2x one end = the total. Basic math the same.


The note I got with a Pm gave different scale readings. I do not know what numbers you are working with.

 

[jadatis]

I used the data given in this topic, also the same as given by PM to me, again see post #34,#35,#36. Or do you also dont see the pictures, as I did in the beginning?

 

[RV Randy]

I used the data given in this topic, also the same as given by PM to me, again see post #34,#35,#36. Or do you also dont see the pictures, as I did in the beginning?

Not sure why you keep insisting front tire psi should always be higher than rears? When my rig was weighed fully loaded with fuel, water, all equipment and a 1200 lb trailer tongue weight, the 90 front-95 rear was exactly what the mfgs chart recommended. I could actually go 85 in the front but if I don't have the 1200 lb tongue weight when not towing, it shifts a little more weight to the front axle.

 

[jadatis]

Adviced is to keep at least 30% of total weight on front axle. If so the rear dual load axle needs higher pressure then front. But then you should ask yourselfes if it is better to shift some weight to the front.

So yes , it happens front lower then rear.

But the case in this topic is, that front calculates higher pressure, whatever way you calculate it, my system, or that of Tireman 9.

Or it must be that topicstarter gave totally different axleweights in his PM to Tireman9.

And then there is the watertank , not filled, as I read between the lines.

Where is it placed and howmanny gallons can it hold?

And was there more not in the motorhome when you weighed ( persons)?