Tires, Gas Tank Capacity and Air Pressure

[SwiftRunner]

Looking at my owner's manual ('94 4Runner), I see that they list two types of tires and corresponding fuel tank sizes as buying options. My car door label gives stats for the P225 and not the 31X10.5. However, when I bought it used it had the 31X10.5 tires on it. I assume they were added later. Now, these tires are marked Load Range C, Max load 2270lbs@50 P.S.I. First of all what should I inflate them to? Right now, I have started inflating them to 35 PSI. I drive on a rough seriously pot-holed dirt road as well as pavement, but rarely on Hiway. I figure the Max load is in addition to the weight of the vehicle i.e. near the GVWR listed on the door label i.e. 5400 lbs. How can the tire mfg.'er figure that without knowing the vehicle type? Finally, if I do a long trip on the interstate should I alter the pressure?

 

[nevada]

35 is about right.

unless you're loaded heavy.

i sometimes pump mine up a bit more if on a road trip. it does help with fuel economy a little bit. but it will also stiffen up the ride some.

 

[BucknutBob]

First off, 35-40 is a good range for all-around driving without making you feel every little pebble. Your tire label isn't assuming anything (like the weight of your vehicle)--that's simply the max. weight for that one tire to carry (not all four). I wouldn't alter the pressure for highway driving. Remember, the pressure is going to increase on the highway as the tire heats up, so you don't want to go with any higher cool pressure.

 

[fourwd1]

The pressure on the doorjamb plate is the correct pressure (plus or minus a few PSI for fine tuning to your specific vehicle), tire size has nothing to do with it, it's pressure, not volume.

The max press rating on the tire is just that, the max pressure the tire can handle, not necessarily what you should inflate it to (unless maybe your driving a F350 Superduty towing a 5th wheel).

 

[SwiftRunner]

First of all I appreciate the comments. Second, the door jamb plate is a piece of paper, not a plate. When it specifies a kind of tire, I would expect it to be the tire on the vehicle. However, in that it was built by humans, and we all make mistakes, I wonder if the wrong piece of paper was glued to the door jamb. Since the tire I found on my vehicle was not the tire specified on the door jamb, I really can't guide my maintenance on it. Finally, keeping the tire pressure between 35 and 40 seems reasonable to me. As to the tank capacity, I really don't want to drive to empty and find out what it is. I don't trust the guage, either.

 

[85toy4runner]

on my 85 4runners plate I think it says but not sure , 28 psi front and 26 psi rear . I thought that was a miss print cause I thought that was low , do you think I should go back to that ? I run 35 to 40 psi now , with 225/75/15 stock tire size

 

[KidVermicious]

Second, the door jamb plate is a piece of paper, not a plate.

Well hell, that just changes everything, doesn't it?

:redbrick:

 

[fourwd1]

Well hell, that just changes everything, doesn't it?

:redbrick:

For sure.

And again, The pressure reccomended on the tag is the place to start.
It's the manufacturers spec for the best wear/ride/handling for that vehicle.
Tire size has nothing to do with inflation pressure, although construction (like # of plys, etc) may have an overall effect.

 

[Sunfire3rdGen]

I keep mine at 35psi. I feel like 30 is kinda low for the 4Runner.

 

[89FourRunner]

I keep mine at 35psi. I feel like 30 is kinda low for the 4Runner.

You just replied to a 4 year old thread.

The correct pressure is on the door jam. The tire manufacturer has no idea what vehicle the tire is going on. Toyota has already done the math. The tire maufacturer puts the max psi (therefore the max load capacity) the tire can handle on the side wall. This way if a vehicles door jam says "44psi" and the tire sidewall says "max 35psi" the tire installer can say "oh sh*t, I need a stronger tire for this vehicle". This is because when the tire is at its max 35psi, its max load capacity is still lower than the weight per tire on each axle thst is requires to safely support the vehicle.

If the door jam sticker says 26psi for front tires, it is 26 psi for a 31" or 225/75 tire.

This provides the best handling, balances out cornering, and creates the smoothest ride. The OP states his max tire pressure rating is 50psi, and that provides 2200lbs of weight per tire. This vehicles weighs no where near 8000lbs. The truck will ride awful.

This is one of the most misunderstood things in the auto world lol. Many consumers think their tire looks low because of sidewall buldge, but modern day tires are supposed to have a different buldge at the bottom compared to the topm. It is the contact patch that matters. One could fill a tire to its max psi ans it still may look low. It is supposed to.