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Old 01-06-2013, 03:55 AM   #29
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Quote:
Originally Posted by Tireman9 View Post
What is the actual loaded weight on each of the 4 tires? It is normal for their to be an imbalance axle to axle and even side to side.

Many incorrectly assume that if you get a total loaded weight and divide by 4 you know the tire loads but there is data to suggest that 45/55 axle to axle and 45/55 side to side imbalance is not unheard of. The data of thousands of measurements confirms the majority of units have one or more components overloaded.

Inflation Tandem axle trailers significantly overload the tires is side shear whenever doing any cornering. Engineering analysis indicates as high as 124% of what a similar tire would see even if carrying the same vertical load but on something like a P/U or motorhome with the tires at the corners.
My sand rail is a mid-engine Corvette powered V8, that sits with the mass of the engine over the rear trailer wheels, but there are support tools, workbench, gas parts, etc in the front of the trailer.

I don't "balance" the load every trip before I leave and come home. I use ~25 gal of gas every trip in my rail alone. Am I supposed to adjust my tire pressure for that and the gas and propane I use in my MH?

Quote:
Originally Posted by Tireman9 View Post
I believe your tire placard indicates an inflation that is the same as what is molded on the tire.
I believe you are wrong. My placard is for 205/75-15, LR C tires at 50 PSI. I had and still have 225/75-15, LR E tires and the sidewall says 80 PSI. I guess I could change it back to LR C, but I don't see what I would gain by doing that. If you will read post #1, you will see that if have ~1500 lbs/tire reserve capacity.

Quote:
Originally Posted by Tireman9 View Post
RE valve bending and leaking. Rubber snap in passenger type valves are cheaper than bolt-in type but the rubber are rated 65psi max cold inflation so any application higher than 60 cold should be running bolt in stems.
I now have the high pressure bolt in type. The tire "experts" (DT) who installed the "China Bombs", didn't even ask if I wanted the bolt in type. Even the bolt in type can leak with time. They replaced them with Carlisle ST tires and assured me that the new Carlisle's were better than the Towmasters and previous Carlisle ST tires.

Quote:
Originally Posted by Tireman9 View Post
Pressure gauge. Do you use a digital gauge? Have you checked it against a calibrated gauge? When I check gauges a high % are off by more then 5%. TPM systems are not a substitute for checking tire inflation with an accurate gauge. Very few TPMS are accurate or even consistent one to the other.
I have both types and calibrated the analog ones for the tire pressure range I am using. My digital and "certified" analog ones agree with the ones I calibrated with the Army training your tax dollars paid for. If you will read post #12 & #14, you will see that I use a certified gauge to set my tire pressure at home before each trip and that my TPMS reads within ąPSI. Is ~5 lbs going to make that big a difference with my reserve capacity?
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Old 01-06-2013, 11:55 AM   #30
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Hey Tireman!

Please don't give up... Do bear in mind that we were warned that this was to be a "rant"...

Nevertheless: I for one am learning a lot!

I found the following highlighted statement most interesting, for example- it's never occurred to me that the placement of the wheels themselves could make such a difference.

Can you further elaborate on that?

Quote:
Originally Posted by Tireman9 View Post

Inflation Tandem axle trailers significantly overload the tires is side shear whenever doing any cornering. Engineering analysis indicates as high as 124% of what a similar tire would see even if carrying the same vertical load but on something like a P/U or motorhome with the tires at the corners.
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Old 01-07-2013, 10:07 AM   #31
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Dunner said
"I don't "balance" the load every trip before I leave and come home. I use ~25 gal of gas every trip in my rail alone. Am I supposed to adjust my tire pressure for that and the gas and propane I use in my MH?"

You do not have to adjust your inflation every trip. What is needed is some assurance that when fully loaded you are not exceeding the capacity of any individual tire. Usually that means that owners should get the unit on scales and use one of the worksheets to calculate the individual loads. Cold inflation minimums would be established based on the heavy tire on each axle. All tires on the same axle should be inflated to the same level.

Quote:
Originally Posted by Tireman9
I believe your tire placard indicates an inflation that is the same as what is molded on the tire.

I believe you are wrong. My placard is for 205/75-15, LR C tires at 50 PSI. I had and still have 225/75-15, LR E tires and the sidewall says 80 PSI. I guess I could change it back to LR C, but I don't see what I would gain by doing that. If you will read post #1, you will see that if have ~1500 lbs/tire reserve capacity.

I missed your original load statement and where you said you had changed tires from the OE 205 size and Load Range C to a 225 section LR-e. My bad. My statement stands for those that have not up sized or up rated their tires as you have. Your reserve capacity sounds good.

Quote:
Originally Posted by Tireman9
RE valve bending and leaking. Rubber snap in passenger type valves are cheaper than bolt-in type but the rubber are rated 65psi max cold inflation so any application higher than 60 cold should be running bolt in stems.

I now have the high pressure bolt in type. The tire "experts" (DT) who installed the "China Bombs", didn't even ask if I wanted the bolt in type. Even the bolt in type can leak with time. They replaced them with Carlisle ST tires and assured me that the new Carlisle's were better than the Towmasters and previous Carlisle ST tires.

Again my statement stands and again you are ahead of me. Bolt in valves have rubber "O" rings or gaskets and these rubber pieces should be replaced every time you replace tires as these rubber parts age just as the tires age if not faster. They obviously need to be installed correctly. You do realize that many of the tire techs are the new hires with the least experience and that few tire dealers have any serious tire technical training beyond the minimum needed to make a sale.


Quote:
Originally Posted by Tireman9
Pressure gauge. Do you use a digital gauge? Have you checked it against a calibrated gauge? When I check gauges a high % are off by more then 5%. TPM systems are not a substitute for checking tire inflation with an accurate gauge. Very few TPMS are accurate or even consistent one to the other.

I have both types and calibrated the analog ones for the tire pressure range I am using. My digital and "certified" analog ones agree with the ones I calibrated with the Army training your tax dollars paid for. If you will read post #12 & #14, you will see that I use a certified gauge to set my tire pressure at home before each trip and that my TPMS reads within ąPSI. Is ~5 lbs going to make that big a difference with my reserve capacity?

Again you are doing more than 95- 98% of the rest of the RV community having checked and calibrated your gauges. Since you know the real inflation as shown with the good gauges you also know what is "normal" reading from the TPMS. Sounds like you covered all the bases other than the reason for the loss of signal and erroneous reading you observed with your TPM. The repeater should improve signal strength as it travels through bodywork of MH & trailer.
FYI I have OE type TPMS on my Class-C and occasionally had one sender that droped its signal for 30 seconds to a few minutes every once in a while. I discovered that a wireless back-up camera was inter feering with the signal as when I removed the camera I stopped having problems with the TPM. Took me a year to discover that conflict as nothing the literature suggested possible signal interferance.
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Old 01-07-2013, 10:32 AM   #32
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Quote:
Originally Posted by Francesca View Post
Hey Tireman!

Please don't give up... Do bear in mind that we were warned that this was to be a "rant"...

Nevertheless: I for one am learning a lot!

I found the following highlighted statement most interesting, for example- it's never occurred to me that the placement of the wheels themselves could make such a difference.

Can you further elaborate on that?
Warning this gets technical.
I observed a tandem axle trailer making a tight turn on a campground roadway that happened to have a fresh topping of fine gravel. I noticed that some of the tires turned and left a relatively normal mark in the gravel. Other tires slid and did not leave a smooth track.

I happened to stumble across an interesting video. If you watch 0:48 to 1:09 you will see the serious deformation seen in tandem axle service.

With this in mind I had a friend (still working at tire company who has access to the $$$ software program) to run an engineering Finite Element Analysis of the internal tire structure loads for a tandem axle trailer application and compare it to the structural loads seen in a tire with identical vertical loading but has axle spacing as seen in regular vehicles such as cars, trucks and motorhomes.
The bottom line was that internal shear forces in the tandem axle trailer application were 24% higher than those observed in normal vehicles.

Tire durability testing is almost never done on tandem axle trailers so there is no reason for the tire industry to think of this given that their volume market is 99+% normal vehicles.

This lead to my position that the load tables for tires used in tandem application should use the "dual" load as the max as this is an established calculation and would result in a about a 12% reduction in stress. I also recommend running the inflation shown on the tire as this is equal or higher than placard or calculated load based on scale weight. Again this will decrease the slip angle and also the lateral shear force that is trying to tear the belts off the tire.

I will be doing a post on this force stuff on my blog in the future.
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Old 01-07-2013, 01:26 PM   #33
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I always set trailer tires to the to the sidewall pressure and make any U turns on dirt, if possible. Of course I can't do that at home, but I try to maximize my turns and do it at a crawl speed.

Not sure about other tire companies, but I would think that new hires at DT would start on the floor, before going to the front desk.

I have an OE back-up camera and have installed a gas pump camera, with commercial grade video cable, before the start of my season and my TPMS has worked fine for 4 trips and on the way home this trip. Before I put the gas pump camera on, it would occasionally lose the signal from a MH or trailer tire, but would see them fine after I re-boot the monitor. The repeater from TST should prevent this from happening again, if it was a weak signal from the sensors. The sensor low battery light has blinked/flashed at home, but never on the road.
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