Tire pressure question - got lighter TT

[MartyW]

Hi to all,

Our TV is a 3/4 ton 9200 GVWR 4WD Burb. We had been towing a 8500 lb TT and the Burb handled it well with Load Range E tires pumped to 80 psi. With the heavy TT/tongue the Burb had a comfortable ride with the extra weight applied by the WD hitch.

We've just downsized to a TT of about half the weight (4700 lbs) with a tongue weight (350) less than half of the large TT. We drove a few hundred miles to pick up the smaller TT and as usual I pumped the Burb tires to 80 psi.

Well, with the lighter TT the Burb ride was not pleasant... There wasn't enough weight for any cushion in the ride so it was rough and not fun..

So my question is, what would be a good psi setting for the Burb Load Range E tires (Michelin LT radials) to allow for some cushion while at the same time not damaging them? The Burb is 4WD so lowering pressure in the front only isn't an option. My hunch would be 65 psi since that is a Load Range D max, but I'd really appreciate an expert opinion from folks who have investigated and done this.

Thanks to all

[jadatis]

Some remarks to considder.

You asume the weights on tires to be GVWR/4 and this is not the case.
Fully loaded or when towing there is more weight on the rear then on the front.

Then also as long as you dont weigh and so estimate, there is always a unequal loading R/L on the axles and often it is even crossed, so fi front R highest weight and rear L highest weight.
Not important for the pressure wich side is heavyest, you need the pressure for the highest weight on axle for both.

It is even better to determine the pressure with a sertain reserve, but to much gives a hard ride.
I determined that border ( so verry discussable) to be when the real weight on tire is below 80% of the weight the pressure is calculated for for 160km/99m/h that then things begin to tremble loose on trailer.
For persons comfort I state it at 85% Loadpercentage ( as I babtised it).

If you have a weighdivision R/L of 55/45% on the axle you can use 95% Load% for the heavyest side and 85% for the lightest side , so you still have maximum reserve without bumping.

Last is that the list given in post above is made with a formula that is worse then the normally in America used for LT, I wonder why Michelin , a from origin European brand, does use this formula and not the in Europe used formula for all kind of tires, wich leads to lower loadcapacity's for the pressure, or higher pressure for the same load.

The weight distribution Hich you have , transports a part of the towbarload from rear axle to the front axle of car and Trailer axle. This is good for better stearing and braking is also more on front tires.

But the lighter Trailer can possibly do without the WDH.
Then the weight division between the 3 axles is different, so you have to weigh again ( best per tire, second best per axle).

Once you have the weights in the configuration you use, and tiredata of car and Trailer, I am able to calculate a save lowest and highest pressure for maximum reserve with still acceptable commfort and gripp.

For that I need also the maximum speed you drive and wont go over for even a minute in your use when towing and not towing.

Greatings from a Dutch Pigheaded Selfdeclared tirepressure-specialist.
Peter

[MartyW]

Thanks guys for all the replies, much appreciated.

.) On the new lighter TT: 2 each 2200 lb axles + 377 lb tongue weight = 4777 Gross from Flagstaff specs. Our old TT was 8450 lbs gross with 815 lb tongue. This new lighter one is about half the weight of the big one.

.) On the Burb GVWR, I did lie (not purposefully though). It is 8600 GVWR, 1997. I was told years ago by a gm friend that it was the heaviest 3/4 ton Burb available, before the 1 ton trucks starting a few hundred pounds heavier (I think he said around 9200 but can't remember positively). That 9200 lb figure stuck in my mind, sorry for the mis-info.

.) And many thanks for the 55-65 lb advice. I know the exact weighing will be best and I will get that done before any long trips, but in the meantime, I know that I'm well within Load Range D weights with that light camper and only my wife & I and cargo, so I'll look for the inflation chart and drop them a bit for now.

Thanks again to all

Edit: I found the exact inflation chart for that Michelin LT245/75R16 E tire, and it appears to me that nickthehunter and goducks10 are spot on, Many Thanks:

Single tires on axle:
50 psi: 4410 per axle (2 tires), 8,820 for 4 tires
55 psi: 4670 per axle (2 tires), 9,340 for 4 tires
60 psi: 4960 per axle (2 tires), 9,920 for 4 tires
65 psi: 5250 per axle (2 tires), 10,500 for 4 tires
70 psi: 5530 per axle (2 tires), 11,060 for 4 tires
75 psi: 5800 per axle (2 tires), 11,600 for 4 tires
80 psi: 6084 per axle (2 tires), 12,168 for 4 tires
(3042 lbs at 80 psi per tire)

So, if I'm understanding correctly,
then 8600 GVWR Burb (including 377 tongue weight) lbs
so anything 50 psi or above would be within load spec?
I would of course add a cushion, so the 55-65 psi
recommended sounds good, Thanks Again

[Turtle_n_Peeps]

rhagfo wrote:

Turtle n Peeps wrote:
You have a TT that weighs 4,700 lbs but the tongue weight is 350. You better hope that's a typo or I see trouble in your future. :E

No, weighs 350 pounds less than the old TT! We don't get to know how much weight on the axles of anything, yet give good information.

Thanks Russ. I misread it.

[BenK]

"....4 ton 9200 GVWR 4WD Burb..." :h

Even though I ordered the F60 option ($68 buck snow plow option which begets 1 ton font springs) for my 1996 Suburban and tongue'n cheek refer to it as a K3500 Suburban, it still has a 8,600 GVWR...how did you get a 9,200 GVWR Suburban?

[goducks10]

So whats the difference of having two people weighing 250 lbs sitting in the back seat or having a TW of 500lbs? If you have E's I'd just air up to 55-60lbs and call it good.

[rhagfo]

Turtle n Peeps wrote:
You have a TT that weighs 4,700 lbs but the tongue weight is 350. You better hope that's a typo or I see trouble in your future. :E

No, weighs 350 pounds less than the old TT! We don't get to know how much weight on the axles of anything, yet give good information.

[Turtle_n_Peeps]

You have a TT that weighs 4,700 lbs but the tongue weight is 350. You better hope that's a typo or I see trouble in your future. :E

[nickthehunter]

Those tires are probably rated at somewhere around 3200 lbs at 80psi (or 12,800 lbs total for 4). At 55 psi they are probably still up around 10,000 lbs. total, which is still more than your GVWR. In any event, you should be able to get the inflation chart online for you particular tire and use that as a starting point. Weighing it would be more exact, but even if you use your GVWR plus a cushion that should be adequate. I run mine at 65 psi all day every day.

[Old-Biscuit]

You can guess

You can experiment

You can weigh and get real info


I prefer weighing so I KNOW

[Second_Chance]

You could weigh the rig with the trailer hitched up (and Suburban occupied and with full fuel) to find out what the actual load on the rear tires is. Then you would find an inflation chart (just saw one posted in another thread in the last day or two) to find the proper inflation pressure for your size and load range tires. It's what we did when we moved up to load range G tires on the fifth wheel.

Rob