Tire pressure-Which is it?

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I have Goodyear Wrangler-SRA tire which are 245/65 17inch.The door jam states that cold tire pressure should be 33lbs each tire(front/rear.I just had my tires rotated and the pressure hot is 38lbs and I know it's more than 33lbs each when they are cold.Would it pay to increase cold tire pressure to 35lbs for each.The tire states that a maximum tire pressure cannot exceed 44lbs.Thanks Joe
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Recommended door-jamb sticker pressure and max tire inflation is universally when the tire is cold.

If it says MAX PRESSURE 51 PSI on the side of the tire - that means when cold. The manufacturer accounts for the pressure increase when the tires warm up.
 
Increasing your tire pressure over the recommended (what's printed on the inside of the door) may increase your gas mileage and improve steering response (stiffer sidewalls). However, the downside is that your ride will be a bit harsher. On the extreme, overfilling a tire will lead to uneven wear (center of tread will wear out quicker).

As a general rule of thumb, you should never have less pressure than what is recommended (on the door) or more pressure than what the max listed for the tire. It's all a trade-off between comfort and gas mileage... whichever is your preference.
 
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chalk test
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As in what autocrossers used to do to determine their "right" pressures?? (i.e.; Put chalk or liquid white shoe polish on their sidewalls near the shoulder to see how far the tread is "rolling over" due to pressure.)
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My door jam pressure calls for 30 in the front and 35 in the rear for a 02 explorer. When set to that, the truck handles like a sluggish mushy boat. In the winter I set them 38 front and 35 back. For long driving in the summer I adjust the tire pressure after 10 minutes of driving or so to maintain my 38/35 pressure. If not the ride will get very harsh as the tire really heats up.
 
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I keep my Explorer Sport Track at 36 all around...it helps with the mushy handling.




Does your sport track have the same specs for 30/35?

I wonder why my vehicle had such a low pressure specd for front. Maybe to keep the front wheels spinning slightly faster than the rear, so it stays out of 4x4 mode
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Yeah, we probably have the same placard. I tried it at those pressures for a while and find that turn-in response is more to my liking at 36.
 
Same thing was on my old Ranger (30/35 F/R). They recommend this because if you load the back up, they want you to have 35 psi in the rear tires. This way the average Joe can haul stuff without having to adjust tire pressure.

At least that is what my manual said.
 
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Quote:


chalk test
wink.gif





As in what autocrossers used to do to determine their "right" pressures?? (i.e.; Put chalk or liquid white shoe polish on their sidewalls near the shoulder to see how far the tread is "rolling over" due to pressure.)
dunno.gif






well actually draw a straight line across the tread area and then drive the vehicle a few yards and then look at the line to see where its worn off, you can keep drawing a line and then add or decrease air pressure to get an even footprint.
 
Played around one day on my nose heavy subaru. Noticed how much more bulge to the front tire than the rear with the factory equal psi. Assume they took into account rear seat passengers and cargo. Found that lowering the rear psi made it handle better. For the heck of it I measured from the ground to the edge of each rim, then aired the tires do they were the same. Front was at tire max 44psi, rear at 28 to set the rim heights the same. Sounds goofy eh? test drive was the best the car had ever handled and the twitchy feeling I had felt for years vanished. Not sying this is a good idea but it worked on this car.
 
WileyE,

What you experienced is common for most cars - trucks as well. Decreasing understeer makes a car feel more nimble and responsive. You can accomplish this by increasing the inflation pressure in the front or by decreasing the inflation pressure in the rear - or both, like you did.

Unfortunately, when you add cargo in the back, instead of having a tiny bit of understeer, you have oversteer, and that is not only difficult for the average driver to cope with, it is also more dangerous.

One word of caution for everyone reading this thread:

Tires are much more prone to failure the less pressure you use. Be cautious if any of the methods you try result in an inflation pressure below what is listed on the placard - and the further away you get, the more cautious you should be.
 
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WileyE,

What you experienced is common for most cars - trucks as well. Decreasing understeer makes a car feel more nimble and responsive. You can accomplish this by increasing the inflation pressure in the front or by decreasing the inflation pressure in the rear - or both, like you did.




But isn't this also; drive axle (or torque split for AWD), weight distribution, power on/off during cornering dependent, as well??
 
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But isn't this also; drive axle (or torque split for AWD), weight distribution, power on/off during cornering dependent, as well??




If you are asking if those things you mentioned affect understeer/oversteer - yes they do. But they are a characteristic of the vehicle, and unless you change something, what you have is what you have. However, changing the tire pressure more or less changes the overall affect.

So if you have a vehicle that has a lot of understeer, you can dial a lot out by changing tire pressure. This is a common practice for folks who race cars where you are not allowed to change the stock springs, and sway bars. You can change a car that pushes like a pig into a fairly nimble pig.
 
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