Heavy load and high speed tire pressure

Just thought I’d nerd out on tire pressure for a bit.

What’s the best way to determine appropriate tire pressure based on the variable conditions a given tire model will be used under?

For example, my 255/85/16 Discoverer ST tires which have a D load range and a max psi of 65. How would I adjust pressures for a full load vs empty? Would I ideally adjust again for say driving 85 mph through Phoenix in July vs same speed through N Dakota in January? Full vs empty?

Can someone elaborate on the info on the sidewall in the attached pic?

 

what is high speed

what is high speed tire pressure

 

Why is this thread in the Armor forum?

 

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=196

 

I must have accidentally selected it. I did this on my phone.

 

No worries, just thought it would get a lot more attention in the Wheel and Tire forum.

 

The max load rating is established based on the max cold tire pressure and most tire manufacturers have a chart or graph for each tire showing a decreasing load capacity... as pressure decreases and load capacity conversely increases with increased pressure.

 

http://onlinepubs.trb.org/Onlinepubs/sr/sr73/73-008.pdf
Pretty sure since 1943 this has been established. See pages 144 and 145. Not the example I was looking for....but still an example.

 

Doesn’t the driver’s door placard show the recommended inflation based on full load? I’m pretty sure it’s full load, since it’s a safety thing...

 

Yes, Stock vehicle, stock tires. Most folks install after market and non spec tires though. Mine came with 28" or 30" tires I think? I put E rated 33"tires and different leaf springs and suspension on it within the first 30 days of owning the truck so the factory tire sticker and psi recommended ratings don't apply.

The tire data placard is one thing, the GRVW,GAVW,Curb Weights, etc. may be a separate sticker with the vin# too. One could argue that those as well are set up for a completely stock vehicle.

The OP was asking about tire loading or load vs tire pressure. Most manufacturers of Off Road tires, any on road tires really, publishes the info for each tire and it usually can be found on the tire manufacturers web site. The D rated tires have a lower max load than an E rated tire, a p vs a q tire will have a slightly lower speed rating too.

The single load vs dual ratings are the manufacturers rating for dual tires on like a 1 ton dualie for instance. The individual tire on each side of a dual tire rear end will be rated for a slightly lower load , as seen in the pic, but the combined weight rating for both tires on each side of a dual tire rear end will typically be much higher than a single rear tire or non dual set up. That's what's shown on the pic.

The D rated tires usually have a 65 psi cold max pressure rating as opposed to the E rated tires which usually have an 80 psi rating....and a heavier max load.

 

All true and good information. I honestly missed that the OP wasn’t running stock.

My OR came with 265/70/16 Goodyear Wrangler Adventure Kevlars, and the door placard shows 30psi as the recommended pressure. I moved to 265/75/16 Bridgestone Dueler AT Revo 3 (65psi max). Tried to find a load chart for the Wranglers showing load capacity at 30psi, but no luck. Filled the Bridgestones to 37 as a swag.

 

For my load range E tires, I generally use:
20-22 psi for dirt/stone logging road
34-36 psi for daily driving

I don't think I've ever added more air to tow something, but I don't tow anything more than 2,000 lbs

 

Here's some good info too:
SL = Standard Load, XL = Extra Load, RD = Reinforced, XT = Xtreme, TD = Tuff Duty, BSW = Black Sidewall, OWL = Outline White Lettering.
Speed rating M = 81 mph, N = 87 mph, P = 93 mph, Q = 99 mph, R = 106 mph, S = 112 mph, T = 118 mph, H = 130 mph, V = 149 mph, W = 168 mph, Y = 186 mph, (Y) = 195 mph.
LT tires with: “C” load range have a 6-ply rating, “D” have a 8-ply rating, “E” have a 10-ply rating, "F" have a 12-ply rating.

Helps interpret tire charts.

If you can see the detail in this crappy pic, there are some WIDE differences regarding Max psi and Max load rated weights even within the same designation like 265/70R/17.... and this can vary greatly depending upon the manufacturer.

 

Depending upon the size of your e rated tires, I'd bet on pavement and at normal highway speeds above 45 and especially at higher speeds, you're wearing the sidewalls pretty hard, causing additional heat and reducing the life of your tires as well as sacrificing some additional gas mileage. Sometimes there's even an inverse contact pattern on pavement if your sidewalls are really strong, they pouch out above the tread so much so that the middle of the tire contact patch lifts a little. If the max pressure stated on the sidewall is 80 psi, you may want to do a chalk and temp test at the dd pressure you mentioned. It's all relative though. If you drive slow mostly, on dirt or crappy roads mostly, then the low pressures your using may not make much difference. I run around 60-65 in front and 65-70 in the rears on my E's but I've got a lot of weight and run highways at or above 60 for a lot of my driving. I'm down around 25-35 off road all around with no problems. probably not as soft a ride as you or others who run lower pressures but I'm compensating a bit for the heavy pay load. I'd be interested to see if you get any mpg gains at higher pressures.

 

Bob, you may be right. OP may be running stock! I may have ass- -me-d differently. u got it right. If your set up is stock, definitely should follow the suggested air pressures on the sticker!

Air pressure will affect load carrying ability, mpg, even the speed you can go safely, every tire is different.
To add to the info, here's another chart some might find helpful. I always wondered what those LI numbers were.

 

No, you called it. OP is running pizza cutters. I read that a great way to determine tire pressure for a tire size other than stock is the following:
- Find the load rating chart for the stock tire, then look up the load capacity at the vehicle placard pressure. This would indicate the weight Toyota was trying to manage at their recommended pressure.
- Find the load rating chart for the new tire, then look up the tire pressure associated with the load capacity from above. This would indicate the pressure required to manage the same load weight as the OEM tire.

Problem is finding the load rating chart. I couldn't find one for my OEM tire, so I gave up. May need to do a chalk test.

 

Excellent methodology.

 

Catastrofe, there is some interesting info here on Goodyear tires but it’s not exactly what I was looking for.

https://www.goodyeartrucktires.com/pdf/resources/publications/2010_loadinflation.pdf#page=6

 

Here’s some more good year data:

http://download1476.mediafire.com/v...vnt/Goodyear_Tire_Inflation___Load_Charts.pdf