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Old 07-04-2017, 08:18 PM   #1
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Tire pressure F-350 SRW

I usually run 55-60 lbs empty in all 4, we will be towing for the first time this week. The trailer has a hitch weight of 655 lbs and weighs 6403 dry. We will be packed fairly lightly with only 2 adults. I am estimating about 1,000 lbs of stuff not counting us. I don't have time to get it weighed, this will be a trial run in a rented SOB to see how we like trailer camping. The side wall on the 285's reads 3750 LBS Max load at 80 PSI. The fuel door placard reads 55 front/80 rear for the OEM 265's.

So I am thinking I should be at 80 PSI in the rears but not sure what to do on the fronts. I have the diesel engine which weighs 920 LBS dry and the truck is a crew cab 4X4 long bed SRW with topper (300 lbs). Will the load equalizing hitch setup add some weight to the front tires?

Any of you with similar rigs I would sure appreciate some advice.
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Old 07-04-2017, 09:49 PM   #2
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You have time to buy fuel then you have time to use CAT Scale. Nationwide. Phone app.

Estimates are meaningless.

Always inside vehicle manufacturer values. Not over or under.

Trailer tires need to be taken to max sidewall pressure anyway. A grand goal of an hour or less at a Flying J or Pilot or Loves or Petro will do the whole thing.

Because it's new or unfamiliar shouldn't be an excuse. Truckstops have great corporate websites.

Call the one on your route. Ask where air hose is located. Where is fuel desk to get paper copy of scale ticket if you want it.

Etc.
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Old 07-05-2017, 04:26 AM   #3
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This is our second Super Duty, same type tires on both, Michelins. We run max stamped air pressure in all four tires 24/7.

Our Michelin trailer tires have same max pressure as the truck - 80#. But, we run those at 75#, makes for a little smoother ride in the trailer.
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Old 07-05-2017, 04:27 AM   #4
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Weight on towbar , gives even more weight on rear tires of towing vehicle, and lifts up the front a little.
So your 655 lbs hitch weight, gives about 800 lbs more weight on rear tires, and lifts up the front by 145 lbs, is my carefull estimation, so in real mayby even more.

This means that you dont have to highen up the front pressure, because weight on front axle wont get more then when not towing.

Even when a weight distribution hitch ( WDH) is used, as you indicate, a part of weight on hitch is transported from rear to front of car and trailer tires.
So this means that front is lifted up a bit less , but still lifted up a bit, so still does not need higher pressure.
Stuff you put in car extra, is positioned mostly on rear axle or even behind it.
So this also does not need higher front pressure.
So as you write, that WDH used add up weight to front, is in a way true, but better would state that it substracts lesser weight from front then when not used.

Once you weighed , I can calculate a save pressure for car and trailer.
But my quess is that still rear dont need the 80 psi.
That prescribing "maximum"pressure is done for responcibilty reasons, so that even if you overload and the pressure is in real lower, because of inacuracy , the tires stil wont damage, and you cant sew the car-maker for the accident it cources.

In America often E-load tires ( with that AT 80 psi ) are supplied , because Americans think that bigger is better.
In Europe the tyres are often yust Standard load normal car tyres ( compare P-tires) or XL/reinforced/Extraload. And law is that both tires on the axle must carry the axle load, mostly those also have a reserve still.
And a comfortable reserve is adviced, to cover a little overloading, and R/L unbalance per axle, wich can prove crossed between the axles once weighed.

The 3750 lbs maximum load of your tires, could cover a GAWR ( gross axle weight rating, that maximum allowed on axle to law) of 7500 lbs.
On the same plate of pressure advices, mostly the GAWR's are given, and in earlyer days , the yust calculated the advice pressure in America, for that weight with no reserve, and up to maximum technical car speed.
Yes , also speed is a factor in pressure-advice.
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Old 07-05-2017, 06:53 AM   #5
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Quote:
Originally Posted by slowmover View Post
You have time to buy fuel then you have time to use CAT Scale. Nationwide. Phone app.

Estimates are meaningless.

Always inside vehicle manufacturer values. Not over or under.

Trailer tires need to be taken to max sidewall pressure anyway. A grand goal of an hour or less at a Flying J or Pilot or Loves or Petro will do the whole thing.

Because it's new or unfamiliar shouldn't be an excuse. Truckstops have great corporate websites.

Call the one on your route. Ask where air hose is located. Where is fuel desk to get paper copy of scale ticket if you want it.

Etc.

I would like to weigh it but I guess I don't know how. I did not know there were scales available for use at truck stops, how long of a cooling period before checking pressures? I do have on board air on my TV so I can easily adjust as needed.


edit: I just Googled "CAT scales near me" and we have a Pilot just 7 miles into the trip, I had no idea you could weigh there. Will call them today, thanks for the advice.

Where can I go to study up on what to do once I have the numbers?
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Old 07-05-2017, 07:43 AM   #6
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For weighing its not important to have cold tires, its only to weigh.
Then later at home , when tires are cooled down, you can fill the right pressures. Before the tires are cooled down so tire inside air = tire outside/AmbiŽnt can take even several hours.

Weighing can be done per axle by driving first the front wheels on plate, and read weight, then drive rear on plate so both axles on plate for total weight.
Then you have enaugh, but you can also drive on until front is off the plate to weigh the rear axle.

If there is space besides the plate, you can drive with only one side over the plate , for instance Right side and Left wheels beside the plate.

By substracting R from axleweight, you then get the Left weight.
The same you can do with total weigh minus frontaxle to get the rear weight.

When you have more axles, and you cant get them seperate on the plate, you can also do the substracting trick.

For instance a TAG axle or rear Drive axle, can only be on the plate together with the trailer axle(s) , becouse the plate is that long that the front wont get off the plate without getting the tag or trailer tires on the plate at the behind.
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Old 07-05-2017, 07:56 AM   #7
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On my 3500 SRW I used max front...55 pounds according to placard, and 75 in rear because I never was close to max weight. At max weight it would have been 80 in rear. My payload as 3500'pounds so max in rear would never be reached. The was no dif on the placard between max load and normal load on front....55 pounds. Rear was 65 light load to 80 heavy load. So loaded and hooked up I ran 75, knowing I was not even close to the 3500 max payload.
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Old 07-05-2017, 11:30 AM   #8
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As the sticker says

I've been running on my 2006 f350, diesel, manual, 4x4, srw as spec'd on the drivers door sticker for almost 300k miles (towing both our 1999 safari and 2007 classic): Front:55 psi, Rear:80 psi

Just my $0.02
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Old 07-05-2017, 01:08 PM   #9
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Truck door says 65 front, 80 rear. I set them at 65 & 75, respectively, & the trailer tires (E-rated) at 65.
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Old 07-05-2017, 01:59 PM   #10
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Quote:
Originally Posted by paiceman View Post
This is our second Super Duty, same type tires on both, Michelins. We run max stamped air pressure in all four tires 24/7.

Our Michelin trailer tires have same max pressure as the truck - 80#. But, we run those at 75#, makes for a little smoother ride in the trailer.
I have the same rig except '16 for the TV and '15 for the AS. I also run max air pressure on the TV, but also on the AS with the theory that the tires end up at around 90 degrees and 84-86 lbs. after running for an hour at 60MPH on a 70 degree day. If you start out with less air in the tires wouldn't they heat up faster and end up at the same pressure?
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Old 07-05-2017, 06:12 PM   #11
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Dealer sets them per the door sticker when I change oil. Never had to touch 'em between changes. Recently put on 3000 miles in two weeks! Great truck.
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Old 07-05-2017, 07:13 PM   #12
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I called the Pilot today, sounds pretty easy. But still unsure what to do when I get the numbers. Just take the max numbers and create an equation to figure out how much pressure for a given weight? Is there an app for that
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Old 07-06-2017, 06:07 AM   #13
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I would like to weigh it but I guess I don't know how. I did not know there were scales available for use at truck stops, how long of a cooling period before checking pressures? I do have on board air on my TV so I can easily adjust as needed.


edit: I just Googled "CAT scales near me" and we have a Pilot just 7 miles into the trip, I had no idea you could weigh there. Will call them today, thanks for the advice.

Where can I go to study up on what to do once I have the numbers?
Check pressures cold at home. After sitting overnight. Record the value.

For interim, trailer tires at sidewall maximum. For truck, inside truck manufacturer limits.

Get a copy of a Load & Pressure Table for your size/spec truck tire. It's pretty much universal. I'd take the pickup over to the scale solo. Full fuel with driver. Get those weights and adjust pressure for best solo. First.

Once hitched and across scale, adjust hot reading to cold value. If table calls for another five psi from your solo, add five despite what hot value shows. Or more.

Next morning, adjust down to prescribed value.

It's a minimum. Another five on E tires wont hurt. But best to work from Table for a time.
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Old 09-07-2017, 05:56 PM   #14
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