General Tire Pressure / Rotation Question

[mjlyn]

I have a couple questions....

I have a 2003 Toyota Tacoma which is wearing the center of the tread more than the sides. The sticker inside the drivers door recommends 26 psi, which is what i have been running. I assume that i need to lower the pressure to even out the wear but how low is too low? Don't want to risk a blowout due to increased heat from underinflation.

Also how come tire pressure recommendations vary so much? For example my girlfriends 2005 Ford Explorer recommends 35 psi front and rear. The tire size and weight of the vehicle is similar to my Tacoma.....what determines the recommended psi?

And why does every place that i get my oil changed automatically put 35psi in the tires....has anyone else noticed that?

Lastly with all the tire and tramlining problems with the M has anyone determined which tire rotation pattern is the best. I had mine rotated last week at my local Toyota dealer and they rotated with the normal FWD pattern. They moved the fronts straight to the back then crossed the rears to the front.

Thanks for the comments.

[szh]

I have a 2003 Toyota Tacoma which is wearing the center of the tread more than the sides. The sticker inside the drivers door recommends 26 psi, which is what i have been running. I assume that i need to lower the pressure to even out the wear but how low is too low? Don't want to risk a blowout due to increased heat from underinflation.

It is tough to answer this question!

I'd look at a lot of things before going lower than recommended. Are the tires the same brand/model that the manufacturer recommends? What is their load index rating? Do you have any headroom that if the tire pressure becomes too low, you will not have a blowout? Have you checked the pressure with a good gauge - is your current gauge accurate? What is the difference in tread depth between the center and outside (halfway or a little more out from the center - not all the way to the edge)? Etc., etc., etc.!

If the pressure reading is accurate, and the load index of the tire is higher than required for the vehicle, then I might consider going down 1 psi to 25psi, but no more than that, and then check the pressure quite often ... Frankly, even this is something I would not do without thinking per se. It may indeed be better perhaps to let the tire wear out, if you got enough good miles out of them, and try a different brand of tire.

Also how come tire pressure recommendations vary so much? For example my girlfriends 2005 Ford Explorer recommends 35 psi front and rear. The tire size and weight of the vehicle is similar to my Tacoma.....what determines the recommended psi?

The brand/model and thus the load index of the tire plays a major role. If the tire was designed with higher load index capacity, then the pressure can be reduced somewhat ... for example, to provide a less harsh and softer ride in some vehicles.

Most car manufacturers test tires (to destruction) to ensure that the design goals of the vehicle are properly met, and then they correct for the variations expected accordingly. It is also possible that they want a higher margin of error (less risk), so they recommend a higher pressure, knowing that people will be sloppy about checking ... that is what caused the Ford-Firestone debacle some years ago.

And why does every place that i get my oil changed automatically put 35psi in the tires....has anyone else noticed that?

No idea.

Tires are often quite different in sidewall strengths and what may work for one tire brand/model/size may not work for another. For example, with Goodyear Eagle F1 GS-D3 245/45-18 100W tires on my M, I used and recommend 36 psi since it gave even wear, good load index values, and excellent handling. With my current Michelin Pilot Sport A/S 245/45-18 96Y tires at 36 psi, I found much increased center wear, so I am now running at 34 psi - don't want to go lower to try and even the wear, since I would be risking sidewall heating problems from too much flex.

As a side note, tire load index ratings are specified measured at 36 psi, so that is a good place to start, I suppose. After checking the tread wear, then you adjust accordingly ... up or down (only a few psi in the downward direction!)

Lastly with all the tire and tramlining problems with the M has anyone determined which tire rotation pattern is the best. I had mine rotated last week at my local Toyota dealer and they rotated with the normal FWD pattern. They moved the fronts straight to the back then crossed the rears to the front.

If the tire is one-direction rotational only, then front to back is the best way to go to get the best results for some things like water dispersal (in rain, etc.) since the rotation direction remains the same. If the tire rotation direction is not important, then a cross pattern is best for more even wear. Note that some tests that rotated directional tire the wrong way didn't necessarily show that it was a bad thing to do for performance or wear - however, the wet weather handling characteristics may be worse. Check out some of the papers at Tire Rack (www.tirerack.com) for more info.

The M tramlining appears to be more of a brand/model issue. Changing the tire model from the Goodyear Eagle RS-A pretty much cures it for most people! By the way, goes to show that it is often not a brand issue, but a model issue. For example, I think that the Eagle RS-A is a poor to mediocre tire (except for quietness and longevity), but the Eagle F1 GS-D3 is an outstanding wet weather and overall handling tire.

Z

[mjlyn]

szhosain...

Thanks for the reply...i will check the load rating when i get home. I have not measured the tread depth difference...but it is very noticeable. With regard to the accuracy of the my gauge....I'm not sure...but i have 3 different gauges and they are all within 1 psi of each other. Unless they are all bad off....i should be pretty close

On the rotation issue.....I have the RSA's on my M and they do suck. Bought it about a month ago with 51k miles on it. I assume this is the second set of RSA's on the car so the previous owner must not have minded. They are loud and rough. The tramlining is better since i rotated them. Most of the time it does not bother me but every once in a while you'd think someone grabbed the steering wheel.

I know most reviews of the M's point out the high level of road noise. Road/ Track Car and Driver Consumer Reports etc all note the noise level. It's a given that the RSA sucks but how much of the road noise is the RSA.....or is it just the car.

[mjlyn]

Checked the tires.....load rating is 111s. Same as specified on the sticker inside the driver door. Tires are BF Goodrich Long Trail TA.

I'll try lowering the psi a pound or two and monitor. I need to buy a depth gauge. I dont drive this vehicle on the interstate that much so usually i am going 60 or less. That should minimize heat related problems from lower psi.

I should also note that when i pull a trailer with my atvs or put an atv in the bed for a trip more than a few miles i do air the tires up to about 30psi just to be safe.