Tire Pressure - Highway

[Steve_382]

Yes, there are many discussion here about tire pressure.




This information is from Toyo Tires and was using their Open Country A/T as an example. My tires are rated at 3195 pounds with 80 PSI, so if I load them to 2,000 I could really run 40 PSI if I wanted to. I usually run about 50 though. I am trying to attach the file also.

Table 9. TRA Light Truck Load Inflation Table.

Tire Size Inflation Pressure (PSI)
Tire Size -------- 35 PSI -40 PSI -45 PSI -50 PSI -55 PSI -60 PSI -65 PSI -70 PSI -75 PSI -80 PSI
LT265/70R17 --- 1890 -- 2075 --2255 --2470 --2595 -- 2760 --2910 -- 3005 --3100 -- 3195 [E]

[my3kids]

To clarify Steve_382's choice of 55psi and ANZAC's caution of air-ing down too much here's how the numbers stack up using Steve_382's 55psi on his LT265/70-17E tires:

According to the chart he's got 5190 lbs load capacity per axle. If he went the full 80psi he would have 6390 lbs load capacity per axle.

Without looking at his vehicle's placard and using Steve_382's weight of ~7800 lbs it sounds like he's in the money .. although I have no idea about the front/rear weight distribution.

Of course if you have smaller tires such as the common LT245/75-16E and you run 55psi you only have 4670 lbs load capacity per axle. (At 55psi its only 4120 lbs load capacity per axle if you have the original LT225/75/16E commonly found on E250 cargo vans and E350 passenger vans.) If you pork up your van up to 9500+ lbs total weight then you may have some problems. You'll have to up the psi and depending on weight distribution will exceed the ~5400 lb axle rating of the common dana 60 semi-float. (I think the full floaters rate at ~6400 lbs.)

That's all,
Ray
06 E350 RB
06 E350 Quigley V10

[geoffff]

Originally Posted by Steve_382

This information is from Toyo Tires and was using their Open Country A/T as an example. My tires are rated at 3195 pounds with 80 PSI, so if I load them to 2,000 I could really run 40 PSI if I wanted to. I usually run about 50 though. I am trying to attach the file also.

Table 9. TRA Light Truck Load Inflation Table.

Tire Size Inflation Pressure (PSI)
Tire Size -------- 35 PSI -40 PSI -45 PSI -50 PSI -55 PSI -60 PSI -65 PSI -70 PSI -75 PSI -80 PSI
LT265/70R17 --- 1890 -- 2075 --2255 --2470 --2595 -- 2760 --2910 -- 3005 --3100 -- 3195 [E]

[attachment]

Wow, the thing that really surprised me is that the load ratings are the same regardless of brand, style, etc. All LT tires of a given size and pressure have the same load rating.

Sure enough, when I check for my LT tires (BFG TA KO 285/75R16), the load ratings listed in the Toyo document you attached match my data, as well as the values in the TRA tables (attached below).

-- Geoff

[ANZAC]

Originally Posted by my3kids

To clarify Steve_382's choice of 55psi and ANZAC's caution of air-ing down too much here's how the numbers stack up using Steve_382's 55psi on his LT265/70-17E tires:

According to the chart he's got 5190 lbs load capacity per axle. If he went the full 80psi he would have 6390 lbs load capacity per axle.

Without looking at his vehicle's placard and using Steve_382's weight of ~7800 lbs it sounds like he's in the money .. although I have no idea about the front/rear weight distribution.

Don't worry about the actual weight. As long as the actual weight per axle is within the tire capacity, you are fine. You don't set the pressure to match the actual weight.

You're heading in the right direction, but you do need to start with the placard. My van actually has a Quigley placard which replaces the Ford. (makes sense because they replaced an axle and changed tire size)

All the E350's are the same though I think, for tire pressure on stock tires. So you can start with mine, just as an example exercise....

if his tire placard reads:
60 PSI cold front
80 PSI cold rear
and the OE tire size is 245/75 16.

Looking that tire size up in the Toyo copy of the RTA inflation tables gives (per tire):
2480 lb front load carrying capacity
3042 lb rear load carrying capacity

With a new tire size of 265/70-17 single axle, the tire pressures that correspond to >= those load carrying capacities are:
55 PSI cold front (2595lb load carrying capacity)
75 PSI cold rear (3100lb load carrying capacity)

You could probably run the front at 50PSI, which is 2470lb....

[ANZAC]

Originally Posted by geoffff

Wow, the thing that really surprised me is that the load ratings are the same regardless of brand, style, etc. All LT tires of a given size and pressure have the same load rating.

I swear I heard that somewhere.....

And it isn't a load rating, it is a load carrying capacity for a given pressure. The rating is the maximum capacity. You will see some blank cells where other tires from a different manufacturer list a pressure whereas the first brand it was beyond the rating for that tire. or you'll see a D, E whatever. (ie only for that rating tire)

[Pschitt]

Originally Posted by ANZAC

I swear I heard that somewhere.....

It's not exactly the case. It also depends of tire build structure. But most important factors are tire size and load, so approximate with such load/pressure index isn't that bad.

[geoffff]

Originally Posted by ANZAC

It's not exactly te case. It also depends of tire build structure. But most important factors are tire size and load, so approximate with such load/pressure index isn't that bad.

I imagine it should depend on other factors. However, these same Tire and Rim Association tire load limits seem to be what various (all?) manufacturers list for their tires.

-- Geoff

[rob_gendreau]

I've never been able to find a tire inflation table for my BFG AT K/Os, but I assume it's similar. Doing a linear calculation gets you close to the table's pressures, but their aren't linear. Eyeballing between weights works pretty well.

And although the guides are designed for the maximum load of your vehicle, as noted, some of us do adjust for weight. But that means keeping on top of it. Although I suspect a surprising number are

always at the max weight

[Steve_382]

Rob, I haven't found a table for BFG either, but I did talk to tech support at BFG a few years ago and they said we were on the right track. In my example, he said that with a load of 2,200 pounds per wheel, 45psi should be fine. I am only at 2,000, so could probably run 40psi, but I run 50 normally. The sidewalls kind of start to squish a little at 45 and it makes me nervous. My tires are rated at just under 3,200 at 80 psi max.

[ANZAC]

Originally Posted by rob_gendreau

I've never been able to find a tire inflation table for my BFG AT K/Os, but I assume it's similar. Doing a linear calculation gets you close to the table's pressures, but their aren't linear. Eyeballing between weights works pretty well.

From what I can see it is the same as the ones from the TRA, so they're all the same except that they will stop listing pressures beyond what they think the load limit is.

So use the Toyo or Michelin one.