Tire pressures for larger off road tires?

[LazSlate]

Expys running larger tires like 295/70 or 305 or 34"s/35"s with load range E, what pressures do you run that give you the best ride and wear?
I know there is the chalk method to determine and Toyo Rep said if your are not towing or loaded then 75% of the max is recommended, but this is pretty general.

I put 305/70/17's load range E on my Timberline and trying to dial in the perfect pressure. Starting out at 50 (max is 65) to see.
I want to find the best pressure as higher pressures you can feel every bump.

 

[ExpyNole]

Used to run ~50 in some 35's with a max of 80. Still pretty stiff, but that's what you get with load range E LT tires. I didn't venture much lower than that.

 

[Meeker]

With my LTX AT/2 load range E tires I looked at the tire capacity chart from Michelin and picked the lowest pressure that supports the vehicle weight (including payload). When towing I put them up to 55 psi. BTW the load ratings below are per axle, not per tire.

I can no longer seem to find that chart on the Michelin website unfortunately. Hopefully your tires have a similar chart somewhere...

 

[Left Coast Geek]

tire pressures are dependent on tire size and load, different brand/model tires all specify he same pressures at the same size and load. An "E" tire can handle a higher pressure than a "D" tire, but at the same load, it would use the same pressure.

sadly, all the tire makers stopped publishing those tables to the public. probably a liability thing.

my 2019 Ex. Limited w/ 22's says the front GAWR is 3375 lbs (1688 per tire), and the rear GAWR is 4380 lbs (2190 per tire). So with that 275/65R18, you should be able to run less than 35 psi front and around 40 PSI rear. (near as I can tell, the numbers on that table are per axle not per tire)

 

[wakeboarder]

The website below is a good resource. You enter the information from your door jam label. Note that your door jam references metric tires, not P metric.

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

 

[Polo08816]

I would imagine when you move from P metric tires to Load Range E tires of the same size, you can run "slightly" lower pressures all else equal. The sidewalls are stiffer and would offer more support.

 

[cptbligh]

I would imagine when you move from P metric tires to Load Range E tires of the same size, you can run "slightly" lower pressures all else equal. The sidewalls are stiffer and would offer more support.

It's actually the opposite. A LT tire needs more PSI for the same load rating.

https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf

 

[Left Coast Geek]

just fyi, "P-Metric" is an obsolete size/series of tires, afaik, no longer made. they actually had a P prefix on the size, and had lower load ratings than the current metric tire sizes. You can replace a P195/65R15 with a 195/65R15, but not visa versa.

 

[Polo08816]

I would imagine when you move from P metric tires to Load Range E tires of the same size, you can run "slightly" lower pressures all else equal. The sidewalls are stiffer and would offer more support.

It's actually the opposite. A LT tire needs more PSI for the same load rating.

https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf

So that's interesting. My assumption is that you're looking at the TRA P-metric vs TRA LT inflation tables.

I would think that the higher the load index, the more it can carry at any pressure. That's consistent with the data in the ETRTO tables at the end of that PDF.

Which begs the question, is Toyo saying an LT tire needs more PSI for the same load rating because the testing parameters are different? For example, Toyo expects a LT tire to be subjected to the load rating for a longer period of time or that it would experience more heat due to friction from engine braking on just the drive axle so it is conservative in its load ratings for the LRE tires. I ask because different SAE standards are applied for HD trucks versus passenger vehicles for engine output as well.

 

[Fastcar]

Just something that hasn't been mentioned. Before buying any tire check the date of manufacture.