Hey,

I do adhere to manufacturers recommendation, but this number has always seemed quite low to me. The swiss truck even has a lower rec of 24 PSI for street and 26 for highway.
The rear is supposed to be at 35 PSI.

I tend to put 2.2 bar, or 32 PSI all around, as my "bed" is always empty. I feel the 24/26 is just too soft for the front. It even hurts steering input snappyness. I don't see any benefit under braking wet conditions, it sucks (jumps and locks even with new shocks) under all tire pressures pretty much the same, marginally better with recommended pressure.

Has anyone weighed a stock 4Runner 1 gen (Manual 22re) and knows how it's weight distribution is?

 

Well, back in the 80's, before fuel economy got to be such a hot issue, a lot of manufacturers recommended 24-26 psi for their p-rated radials, strictly for ride comfort. The P-rated tires with their soft sidewalls will handle those low pressures. On the other hand, if you put LT tires on, you need to raise the pressure, or you risk overheating those stiff sidewalls with too much flexing. (Sidewall flexing is determined by air pressure and load, NOT by sidewall stiffness. Heat build up, on the other hand, gets worse with increasing sidewall stiffness and flexing.)

As economy and safety became more important, vehicle mfgs raised their recommended pressures, trading off some comfort for better fuel economy and better handling.

 

So what pressures should I run?

 

What tires do you have, and what loads do you haul?

For a stock truck with minimal cargo, and p-rated tires, 32-34 psi is a good starting point. If you have C-rated LT tires, 38-40 is good. With E-rated LT tires you might be up to 44-46. Heavier loads need more pressure, wider tires need less.

You can do a chalk test to check for uniformity of tread contact across the tire. (google "chalk test for tires" for how to do this and how to interpret the results.)

 

They're a BF Goodrich AT LT235/75/R15. I used to haul my bike back and forth to track days. But not so much anymore. I have noticed that it wears on the inside and outside too much. These tires are 13 years old with 30k miles at 26/29 for the most part. I just recently changed the rear to 35. I'll probably do the same for the front and see how it rides.

 

If the edges of the tread are wearing faster than the center, you are indeed under inflated.

Also, no tire company will tell you that 13 year-old tires are safe, especially not at highway speeds. You need to think about replacing them sooner rather than later, regardless of tread wear. Then you can talk to your tire shop about proper inflation for whatever tires you buy. Any good tire shop will have up-to-date recommendations for your particular vehicle/tire combo.

 

I always kinda thought there is one single tire pressure that is correct for a certain weight. The chalk test sounds pretty great, I will do that and report back.

 

I thought the same thing when I noticed the tire wear. I plan on experimenting with the pressures and ride quality to see what works best. But I ride dirt roads and I already have a "firm" ride with these race seats I regret installing. I'm wishing I had my old bench seat back. I was stupid to throw it away in the first place.

 

There are a lot of variables that go into "correct" tire pressure, some of them conflicting. In general
Higher pressure improves::
- sidewall heating
- Load carrying capability
- fuel economy
- traction on hard snow*
Moderate pressure improves
- uniform tread wear
- handling
- wet road traction*
Low tire pressure improves
- soft snow traction*
- comfort
- offroad performance

*traction vs pressure is highly variable - these are only generalizations.

Some of these conflict, others are complementary. Bottom line, you can't optimize all of them at the same time, so you pick the compromises that work for you. The vehicle and tire manufacturers' recommendations are compromises as well, based on their expertise and estimate of the average use model of the vehicle.