TV Tire Pressure

[Pat Cassity]

I just returned from a 1000 mile trip through parts of Texas and Arkansas towing a 27' International. Before I started out, I increased my Denali's tires to a cold pressure of 38lbs. According to the TPMS the pressure increased to approximately 40 to 41 lbs after being on the road for a while. The problem is that the vehicle road extremely rough throughout the entire trip. Is it absolutely necessary to increase the tire pressure above the vehicle recommendations while towing?

[ghaynes755]

Pat what is the recommended tire pressure on the door sticker on your Denali? That pressure should be good for the max allowable GVW for your Denali. Need more information to really give you an answer. Sticker info, same tires as OEM, weight of tow vehicle with TT attached (CAT scale info).

[Pat Cassity]

The recommended tire pressure on the door is 32 psi for all 4 tires. The front axel gvwr is 3200, rear 4300. Although I have not yet weighed the current setup, the total weight from a previous weigh was approximately 13200 lbs. I do plan weigh again soon but from my 'rough' calculations, my denali loaded for camping weighs approximately 7234 lbs ( including the tongue weight). The trailer, loaded, with water tanks containing about 125 lbs in the fresh water and black water tanks weighs approximately 5900 lbs. Based on the way the unit is handling, I am assuming that my WD hitch is setup correctly which means that approximately 20% of the TV weight ( 1450lbs ) is being transferred to the trailer axel. This would leave the truck weighing approximately 5784 lbs. Again, assuming that the WD is set up correctly, this put less than the maximum weight on each axel. Your thoughts?

[AnnArborBob]

Pat, the weight distributing hitch should NOT be distributing the TV's weight BACK to the TT. It's purpose in life is to distribute some of the TT's hitch weight from the rear axle of the TV to the TV's front axle. Please reassess the information in your previous post and modify and re-post as needed so we can properly advise you. On the other hand, if your hitch really is sending some of your TV's weight back to the TT, then please find a professional in your local area to work with you before you tow anywhere!!!

[Pat Cassity]

Thanks Bob. It's apparent that I need to find a scale before my next trip.

[jadatis]

The WD hich transports some load to front axle of TV and axle of trailer axle, but not all of it . Would not be right if it did.
I think you can compare the weight distribution to an European trailer wich has only about 5% on the towbar, instead of the American trailer wich has 10 to 15% on towbar of the trailer total weight.

But then still when towing less weight on front axle of TV and more weight on rear axle of TV then when not towing.

This means that your front tires of TV do not need higher pressure , only the rear of TV. and ofcource the Trailer tires need high enaugh pressure , higher then when no WD hich is used.

If you ever weigh, then do it loaded as you want to drive, preferably per wheel( pair, and with the WD hich working, so you have the actual loads on the wheels in your use.

A trich to measure per wheel( pair) is first to ride over the schale normally and then again whith only one side of combination, depending on wich side there is space to do it.
then yust substact that one side from the axle to get the other side.
Do as much possible weighings in one drive over.
Dont be surprised if you notice crossed weightdifferences R/L between the axles.

As much possible measurements is for instance this.
Whole combination 3 axles , schale long enaugh for 2 axles.
then
1 : Axle 1
2: axle 1+2 |substact axle 1 to get 2
3: axle 2+3 | substract outcome mesurement 2 from mes 3 to get axle3 weight.
4: axle 3 |can substract it from measurement 3 to check weight axle 2.

Then drive over with only left wheels for instance ( then right on the space besides de schale wich is free of obstacles.

1: axle1 left substract this from axle 1 of first drive over to get Right wheelweight
2: axle 1+2 left | can do several calculations to get the weigt of Right.
3: axle 2+3 left | first the same as first series and after that substract
4: axle 3 left. | left from axle per axle .

If you have those weights , give them here with maximum load and needed pressure for that of tires ( on sidewall given) and I will calculate with my Motorhome and Travel-trailer calculator the needed pressure , wich leaves some reserve for things like pressureloss in time misreadings of weight and pressure schales , but still acceptable comfort and gripp.

[ghaynes755]

jadatis there is a large number of threads on how to setup and weigh an AS. In the US the suggestion is to go to a commercial truck scale like those from CAT. Take a look in the forums for some of these posts. Complete list of steps and even a spreadsheet to load the data into.

[jadatis]

Pat is writing in post 3 that 1450 so 20% of trailer weight is lowered from TV and going to Trailer axle(s).
But I think only that 15% tonge weight is distributed to front wheels of TV and axles of Trailer and then even not totally .
Cant find it but read once that 60% of tonge-weight is distributed from rear axle of Tv to front of Tv and Trailer.
Can be wrong about that , but this would mean the , lets make it 20 % of trailer tonge weight of 5900x20%= 1180 lbs and then 60% of that is distributed.
So about 700 devided over front wheels of TV and axles of trailer so still rear of TV about 500lbs heaviër , and front and trailer 350 each more weight on wheels.

Stil googling further for the exact info.

[AnnArborBob]

I'm hoping that when Pat said that his weight distributing hitch was transferring weight FROM HIS TOW VEHICLE TO HIS TRAILER that he was simply misspeaking (or mis-writing?) As we all know, the weight distributing hitch is supposed to take some of the trailer's hitch weight from the rear axle of the tow vehicle and send it to the front axle of the tow vehicle.

But, on the off chance that he was not misspeaking, then I have to conclude that his hitch setup is way off and he needs professional help before towing anywhere.

[jadatis]

Found one topic on Forestriver forum with weights when Hich used and not used.
Its a bit of a puzzle but confirms my suspicion .
Weight Stats - Forest River Forums

but whatever the effect is , if you weigh with hich used and fully loaded as in trip, those weight count for determining needed tire pressure wich is original question of topic starter.

Weighing is still the best way to be shure, otherwise you keep estimating and practice proves that those estimations are almost always that much off, that one of the axles has substantial more weight on it so determined pressure to low and so tire damage and missery that goes with it.

But topic starter probably can do with lower pressure , wich is better for comfort and gripp. He already experiënced the hard ride.

[Pat Cassity]

Folks, I was mis-speaking and mis-writing. Thanks for the clarification. Of course, a portion of the tongue weight is being transferred to the front axel but as I understand it some of the weight is transferred to the trailer axel, as well? Correct? Although, I have yet to weigh my current setup, I feel comfortable that I am within the TV and TT weight limitations. My original concern was the necessity to increase my TV tire pressure while towing. Thanks to all for setting me straight!

[AnnArborBob]

Pat, good! You had me worried there for a moment.

To your original question which you clarified above,

1) download the tire manufacturer's tire pressure/load table from their website,

2) weigh your TV/TT combination at a CAT scale. Make sure you get the weight per axle of the TV with the TT hitched and make sure both vehicles are loaded as you would for a trip (water, fuel, gear passengers, etc...)

3) divide the weight on the TV's rear axle the by 2 and that will give you the weight on each of the TV's rear tires. You can do the same with the TV's front tires and the TT's tires too.

4) look up the manufacturer's recommended pressure based on this weight and there you go....

[CapriRacer]

A couple of thoughts:

First, there is side to side variation in tire loading in vehicles. So unless you weigh each corner, you'll have to figure out a way to account for this. I have seen as much as a 10% variation, so do NOT assume each side is the same.

Second, tire load tables are MINIMUMS (or maximums depending on which direction you come from). They are NOT recommendations. I recommend that you use a 15% reserve when using the tire load tables.

Vehicle manufacturers test their vehicles with the inflation pressures they specify - and they select springs, sway bars and shock setting based on those tests. So if you use a pressure different than what they specify you might be creating a handling problem - and unless you do the testing needed, you will never know until it is too late. I urge caution here.

[AnnArborBob]

CapriRacer makes a good point about side to side weight differentials with respect to trailer loading. My suggestion for simply dividing the weight of the rear axle by two to arrive at the per tire load was for the tow vehicle only. In general unless you really load the tow vehicle with a lot of very heavy stuff and do so poorly, the biggest added weight is the hitch weight which is evenly distributed from side to side so dividing the rear axle weight by half works pretty well.

If you are going to try to minimize the trailer's tire pressure based on the tire manufacturer's tables, it is best to measure the weight carried by all the tires of the trailer separately. In fact, you should measure the weight carried by each of the trailer tires regardless of what your plans are for tire pressure management just to make sure you do not have any serious imbalances. Even if you run the trailer tires at the recommended pressures for a fully loaded trailer (on the sticker) an unbalanced trailer will be more difficult to handle and you might need to do some load balancing to maximize the safety of your tow.

There are several threads in this forum which you can search if you want to see how to get the weight of each of the trailer's tires at a CAT scale.

[Pat Cassity]

Thanks. I'm really not too concerned about the TT air pressure. I only have food and clothes and about 50 lbs in the storage compartment. My issue was with the TV tire pressure. Other than the hitch, I have calculated that I have no more than 100lbs loaded into the rear of the Denali. I feel that your suggestion to weigh the vehicle and the divide axel weights in half to determine the weight on each wheel is the way to go.

[xrvr]

Go with the pressure on the door panel that should be for max load. This is figured for the oem tires installed on your vehicle. Jim

[CapriRacer]

Originally Posted by AnnArborBob

CapriRacer makes a good point about side to side weight differentials with respect to trailer loading. My suggestion for simply dividing the weight of the rear axle by two to arrive at the per tire load was for the tow vehicle only. In general unless you really load the tow vehicle with a lot of very heavy stuff and do so poorly, the biggest added weight is the hitch weight which is evenly distributed from side to side so dividing the rear axle weight by half works pretty well.....

The principle applies to tow vehicles as well. I have seen the same sorts of side to side variation in tow vehicles.

Again: Do NOT assume there is no side variation - and if your weights are by axle and not individual corner weights, account for the variation in some way.

Originally Posted by AnnArborBob

.....If you are going to try to minimize the trailer's tire pressure based on the tire manufacturer's tables, it is best to measure the weight carried by all the tires of the trailer separately. In fact, you should measure the weight carried by each of the trailer tires regardless of what your plans are for tire pressure management just to make sure you do not have any serious imbalances. Even if you run the trailer tires at the recommended pressures for a fully loaded trailer (on the sticker) an unbalanced trailer will be more difficult to handle and you might need to do some load balancing to maximize the safety of your tow.

There are several threads in this forum which you can search if you want to see how to get the weight of each of the trailer's tires at a CAT scale.

Yes, search for the ways to get individual tire weights. That way you will know.