What tire pressure do you run when not towing or loaded? I only tow and haul anything heavy 4-6 times a year. I have load E rated tires on my 1970 F250. I ran the pressure at 75 lbs for a long time and man it was rough. I lowered the pressure to 65 lbs and made a huge improvement in ride and handling. I was thinking of trying 55 lbs but didn't want to hurt the tires. This is my first 3/4 ton truck and first set of load rated tires.

 

I can calculate a lowest save pressure for you, with even better formula then the American tire makers use and even saver then the European Tyre makers use.
Once got hold of that formula and went running with it.

Need for that the specifications of tire ( maximum load and needed pressure for that =AT pressure yours E-load 80 psi, and the speedcode of tire.

From car best is seperate weighed wheelpair loads , second best axle weighing, in the load you drive normaly.
But in lack of that GAWR's GVWR ( Gross Axle/Vehicle Weight Rating) ,Emty weight and the way you load it normally ( persons and load and about where).

If then calculated for normal use, and when towing once in a while, you probably can use a lower speed , so still save for the tires.

Greatings from a Dutch Pigheadedd Self declared tire-pressure specialist

 

As you stated the max press is 80 psi. The speed rating is "R".
I know the truck with me, the kids & half tank of gas weigh 5380. That's pretty typical day in, day out.
The trucks GVWR is 7500 lbs.

Is that everything?

Thanks for your help.

 

Saw your reaction for me yesterday at about 22.00 h ( because of the time difference, Holland Europe ).
But now tried to google your car for the tires and GAWR's. The weights you gave can give an idea of the loading , so those I can use.

So cant calculate still because need the GAWR's and tire specifications ( only maximum load needed, but sises can do , will google again then).

 

I have stock type LT235/85R16's on my 96 F250 4X4. They are rated for 80psi max. Truck is used mostly for hauling, towing and plowing snow. I only put about 2k miles on per year.

When I am running empty or light hauling I drop tire pressure down to 45-50psi for a much better ride. I only tow medium weight trailer 4000-7000lb so dpending on the load I bring fronts and rears to 60-75psi. With snow plow on (about 650lb) and winter ballast in the bed (about 700lb) I keep 50-55lb rear and 65-70psi front.

Drop them all to 25-30psi for dirt drags in the summer.

Todd

 

My tires are Michelin M/S2 in size 265/75R16 .
Ford didn't give a GAWR for my truck in 1970 just the GVWR which is 7500 lbs.

 

Thanks for the input.
I think I'm going to drop the rears to 55 lbs and the front to 50 lbs until I tow the camper again.

 

I calculated with front GAWR of half of the GVWR of 7500 lbs,so 3750 lbs front.
Rear I add 10% so 1.1*3750= 4125 lbs .
I think this is pretty close to the truth .
This is the maximum weight you are allowed to put on the axles.
then I add 18% to that and calculate the pressure for that .
This will give the absolute highest pressure needed with some reserve for unequall loading.
Higher is not needed . this is front 50 and rear 56 psi , and then fully loaded and when towing, and even a reserve for little overloading, unequal loading R/L ,pressure loss in time etc. So completely save for the tires in all situations.

Front can even use lower , because you are not putting a snowplough or motorrack on the front bumper.
I expect the weight on front to be even lower then normal because of the leaver working when towing , the weight on the towbar ( minimum 10% of trailerweight in America) lifts up the front. Once decided the Motorhome standard and that is fully loaded GAWR front= GVWR -/- GAWR rear and that would be here 7500-4125=3375 lbs weight on front wich needs with 10% reserve added about 42 psi advice.

Once
Made picture of the filled in motorhome tirepressure calculator and this advice is for up to 160km/99m/h and for the highest weight on wheels you are allowed. Your tires are R speedrated so for 170km/106m/h but I suspect the tire makers to have calculated the maximum load still for 160/99 .
But because your maximum speed will be below 99m/h not important.


Here the picture of it,but I will give the pressure for your given total normal weight of 5380 lbs wich I think is low estimated, with also 18% reserve, how did you determine that. For those weights Front and rear ( 2700 lbs) 35 psi .

So the pressures CTC01 is using are probably OK
Also he uses front higher when snowplough on it wich makes the weight on front axle higher as exeption to the rule.
Normally front does not get higher so you only have to highen up the pressure for rear when towing.

Here the picture but if you can produce reliable new weights or info I will recalculate.

 

That's really cool. My 5380 lbs truck weight was on some truck scales. That was me in it and a half tank of gas.

I'm getting a little crazy. I forgot the factory brochure list the axle weights based on your GVWR. For my truck the front axle capacity is 3000 lbs and the rear axle is 5200 lbs.

Thanks again for your help. That is a really cool tool.

 

When I had my 89 f250, empty I ran about 60 rear 55 front. Also had air bags installed and kept them at about 10-15psi. When towing or loaded would run up to about 65 rear and 60 or so in fronts. Never had any wear issues. On my 04 F350 still run in the same general area with no issues.

 

I drove to work today with 55 psi front and rear. Rides & drives much better. I think I'll try the front at 50 psi next.

Thanks for everyone's input. I'm new to load rated tires.

 

Knowing this I made a new picture and made the rear weight that high so it gave 50 psi as you want to try in your next post.
used front 2900 lbs ( 100 below max allowed) and rear 4000 lbs.
Together this makes 6900 lbs so slightly below the GVWR of 7500.
To my estimation for your situation save .
Even used 10% reserve to those axle loads.
But be ware that devices for pressure measurement arent always that acurate, 5 to 10% to high given pressure can easyly happen.
But extra reserve is created by not driving to fast when fully loaded.
The pressure advice is for up to 160km/99m/h wich you probably never make.
If you fully loaded keep maximum speed of 75m/h you dont need to highen the pressure , at that pressure the tires maximum load can be highened by <>10% so this would give that extra savety for the tires.
Front can even go as low as 40 psi when the GAWR's are right now.
Think I have to adjust my idea about weight division for american cars.
For european cars often the GAWR rear is reached or overloaded.
Also the heavyer weight on tow bar ( 10 to 15% by law) in America versus Europe (1% to 10%) needs more GAWR rear to carry that towbar load.

 

That is a really neat tool.

Thank you for sharing.

 

You can find it in next map in my public map of One-drive that belongs to my hotmail.com adress with same username as in this forum ( so jadatis , combine yourselfes , spamm machines cant this way)

https://onedrive.live.com/?cid=A526E...E092E6DC%21793

Best is to first download it by rightclicking and choosing download.
But hotmail is getting better , I think it will even work now in the browser so leftclicking. So if you have Excell or Open office CALC , you can play with the Loads yourselfes.
In the examples map you will find PDF and PNG picture of it with your name.

That its for motorhomes originally is not the problem, I even use it for sport-cars , but then I have to adjust the reference-pressure/AT/maxloadpr my self.

 

Thanks. I was able to download V1.9 and open it in Excel. This is very useful.