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Old 05-30-2017, 10:01 AM   #43
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My owners manual goes a different direction:
Quote:
Tire Industry Changes
The tire industry, as a whole, has changed its traditional stance on adjusting cold tire inflation pressure for RV tires installed on recreational vehicles and busses. Previously, tire manufacturers supported a policy where tire inflation could be adjusted according to the actual loaded weight of the vehicle. Now, the major tire manufacturers recommend that medium duty truck tires be maintained at the pressure that corresponds to the Gross Axle Weight Rating for the axle to which they are mounted. To make this recommendation uniform across the industry, tire manufacturers strongly urge the consumer to keep all tires inflated to the pressures recorded on the Federal Tire Label.

Tire Inflation
Country Coach recommends that the cold tire inflation pressures should at all times be maintained at the inflation pressure(s) recorded on the Federal Tire Label. There are no acceptable circumstances where tire inflation pressure(s) should be reduced below that pressure recorded on the Federal Tire Label.
And the Les Schwab where I had the new tires and SmarTire TPMS sensors replaced goes by the same "rule" My tires run very cool as a result. I'm not concerned about having to reweigh every year either. I probably should get a good scale readout though. I've gone into a few closed weigh stations and have found that my front axle is way below the 20,000# rating at 17,700 although my fuel tank wasn't full either.
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Old 05-31-2017, 03:48 AM   #44
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If you have an adjustable tag axle, you could lower the suspension-pressure ( so not the tirepressure) a bit so for instance only 7000 lbs on Tag so 1500 lbs lesser weight on Tag.
This would give about 1200 lbs lesser weigt on Front and 1800 more weight on Drive axle , wich would stay then yust below GAWR of 20000 lbs.
But then you would have to weigh again and use other tirepressures , because the weights have chanched.
Would solve your overloaded front, even when your wife is in the motorhome.

Some Tag axles cant be adjusted, some can even be adjusted from within the cabine, others by some tubesystem with a valve on wich you can put a normal tirepressure-gauge. then if for instance it gives 60 psi on that system, lower it to for instance 50 psi.
i dont know if you are someone that crawls under the motorhome , but if so , search for such a tube system, or mayby you now find out what that swich is for somewhere in the cabine.

Quote:
Originally Posted by RMD3819 View Post
OK....starting over I did a weigh without the toad and with the axles on separate platforms:

Steer 14140
Drive 17640
Tag 8520
Gross 40300

The only glitch is my wife was not in the coach at the time-she was spotting me on the scale. I assume just add her weight to the front axle. The 14140 is 140# over the axle limit so that will just make that number worse.

I don't know of a way to adjust the tag axle as you have mentioned to help compensate for this.

Following your formula of 53% of the weight plus 10% I come up with the following:

Front 8243 which is overweight I know but 120psi cold
Rear 10285 85psi cold
Tag 4966 75psi cold

Tires are Michelin 305 70 22.5
Axle ratings:
Front 14000
Rear 20000
Tag 10000
GVWR 44000

Is this correct?
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Old 05-31-2017, 09:04 AM   #45
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Quote:
Originally Posted by RMD3819 View Post
OK....starting over I did a weigh without the toad and with the axles on separate platforms:

Steer 14140
Drive 17640
Tag 8520
Gross 40300

The only glitch is my wife was not in the coach at the time-she was spotting me on the scale. I assume just add her weight to the front axle. The 14140 is 140# over the axle limit so that will just make that number worse.

I don't know of a way to adjust the tag axle as you have mentioned to help compensate for this.

Following your formula of 53% of the weight plus 10% I come up with the following:

Front 8243 which is overweight I know but 120psi cold
Rear 10285 85psi cold
Tag 4966 75psi cold

Tires are Michelin 305 70 22.5
Axle ratings:
Front 14000
Rear 20000
Tag 10000
GVWR 44000

Is this correct?
Most Tag axles loads can be adjusted so I suggest you contact the chassis manufacturer if your RV dealer can't answer the question.

Second you should have some margin as side loading from wind, road curves shift weight around

The 53% is a conservative estimate. with your numbers it shows that you really need to find a way of confirming individual tire positions (6 in your case) need to be confirmed. You may be lucky and have one end of front only at 51%. Still overloaded but not so much.

You also need to learn the max inflation (cold) the wheels are rated for. Again Dealer or chassis mfg. should be able to provide that info.
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Old 05-31-2017, 09:12 AM   #46
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[QUOTE=jadatis;3624196]If you have an adjustable tag axle, you could lower the suspension-pressure ( so not the tirepressure) a bit so for instance only 7000 lbs on Tag so 1500 lbs lesser weight on Tag.
This would give about 1200 lbs lesser weigt on Front and 1800 more weight on Drive axle , wich would stay then yust below GAWR of 20000 lbs.
But then you would have to weigh again and use other tirepressures , because the weights have chanched.
Would solve your overloaded front, even when your wife is in the motorhome. [Quote]

Your weight shift from lowering the tag suspension is wrong. You show a total of 2700# being removed from the front and tag axles, but only 1800# added to the drive. That's 900# unaccounted for. If the OP's wheelbase is similar to mine, which it should be close, then every 7# removed from the tag will lower the front by 1# and all 8#'s will go to the drive. It's a 7 to 1 ratio on his wheelbase. So removing 1500# from the tag will lower the front by 215#'s and 1715#'s will be added to the drive.

I have done this. I lowered my tag from 9000# down to 5,000# which lowered the steer from 15,300 to 14,700# and increased the drive from 14,700 up to 19,400#. All tags can be adjusted, however, some would need to have the proportioning valves replaced with different ratios or manual regulator valves, which is what I did. It's not rocket science, but is beyond the understanding of many.

FWIW: My axle ratings are
Steer.........15,680
Drive.........22,000
Tag............13,000
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Old 05-31-2017, 02:35 PM   #47
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reaction to above:

Your right, i was dreaming for a while
total must be zero .
so new 1500 of tag will give that 1800 on drive but lifts the front axle only 300 .
Now corrected , it is yust an average , its different if the wheelbase is different, and it depends also on distance between Drive and tag axle.

So for RMD's motorhome this would mean that lowering the tag by 1500 gives yust enaugh to lower the overloading and the weight of Wife ( Ooh dangerous that estimating wifes weight).
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Old 05-31-2017, 02:39 PM   #48
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Quote:
Originally Posted by jadatis View Post
reaction to above:

Your right, i was dreaming for a while
total must be zero .
so new 1500 of tag will give that 1800 on drive but lifts the front axle only 300 .
Now corrected , it is yust an average , its different if the wheelbase is different, and it depends also on distance between Drive and tag axle.

So for RMD's motorhome this would mean that lowering the tag by 1500 gives yust enaugh to lower the overloading and the weight of Wife ( Ooh dangerous that estimating wifes weight).
In the meantime, while waiting to get corner weights and the tag axle adjusted, are my calculations for psi good for now?

Front 8243 which is overweight I know but 120psi cold
Rear 10285 85psi cold
Tag 4966 75psi cold
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Old 05-31-2017, 02:47 PM   #49
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The 7 to 1 weight shift ratio would be good for most 42-45' tag coaches or at least close enough. I did a lot of experimenting and weighing because I had to deal with a trailer with 1500# of tongue weight and also with no trailer at all.Finally, when I thought I had it close, I had the WI State Patrol come to my home with their six scales. After two weighs, I had it right where I wanted it. I sent my results to Tiffin and they followed up and changed the way they deal with their tag coaches.

No charge from the State Patrol and now I can keep the steer axle 1000# below it's max load. A side benefit is that the coach handles better with a much better balance between axles
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Old 05-31-2017, 03:02 PM   #50
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RMD3819. After you get individual weights, if the front weights have more than 300# difference, have the ride height adjustments checked as that can shift weight from corner to corner. Then if you can take 2000# off of the tag, it will remove 300# from the steer and the drive will be at it's rated capacity. Check with Newmar. They had a front axle problem with the Dutch Stars and upgraded or replaced the front axles to get out of the overload they had.
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Old 06-02-2017, 04:03 PM   #51
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Quote:
Originally Posted by RMD3819 View Post
In the meantime, while waiting to get corner weights and the tag axle adjusted, are my calculations for psi good for now?

Front 8243 which is overweight I know but 120psi cold
Rear 10285 85psi cold
Tag 4966 75psi cold
First read all your posts to get the data right, but saw the Drive and TAg on one weighing so this does not count
Your last post with the seperate weighing I used, not the one of this quote because you yourselfes already added the 10%, what I automatically do in my spreadsheet.
Front 14140 lbs highened up for Wife to 14300.
So Front 14300+10% needs 120.5 psi
Rear/Drive 17640lbs + 10% needs 82 psi
Tag 8520 lbs + 10% needs 70 psi.


This would cover if everything 100% acurate ( forget it!!!) a 55%/45% weigtdivision per axle. used the LI 152/148 Loadindex as I found before for your tires. and asume max speed of tires to be 75m/120km/h wich is L-speedrated.
so this means that you can drive with these pressures , again if everything 100% accurate, up to 75m/h , with all axles 55/45 weightdivision,without overheating any part of the tires, so no damage to structure of tires.

Also calculated as if the tires where set in the market for 160km/99m/h, wich I determined to be giving with this 10% reserve still acceptable comfort and gripp, for wich I lowered the single loadindex of all tires by 4 steps, so dual stays the same, so to 148LI.

This would give more reserve and still acceptable gripp and comfort, and as extra some fuel saving.

Gave for the same weights , F 137psi , R/D 82psi, T 79 psi.
So for front see how high you dare to go above the 120psi the tiremaker gives, already wrote about it in earlyer post, in earlyer days also American tiremakers allowed 10 psi extra for LT tires and 20 psi for trucktires , wich in fact your tires are. for LT most tiremakers dont allow this 10 psi extra above the cold AT-pressure anymore, but mayby the 20 for trucktires they still allow. Mother nature would like the 137 psi in front for the least chanche on damage to your tires .

The Loadindex for RD so dual was given 4 lower then for single load, and thats what is used in America, In Europe its mostly only 2 steps lower, wich would give for your Rear/Drive axle a needed pressure for 75m/h of 77 psi.

Als read that your Toad was a 4 wheeled trailer wich puts almoast no weight on the "towbar", so these pressures would be alright for when the toad behind too.

So using the last given highest pressures would give the most reserve, but if dropped in time to the lowest of F120 RD 77 , T70 psi you probably still be save and chanche you damaged your tires is minimal.

Forgive me if I use some wrong words, In Holland we dont have these heavy motorhomes, so not familiair with all the terms, and sertainly not when in English. So if I drew a wrong conclusion ( about toad for instance) correct me .
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