Tire pressure and fuel economy RESULTS

[wyatt]

A different type of test you could try with the accelerometer would echo the test that Metro did. You could measure your acceleration from a dead stop down a hill. You would probably need a very accurate accelerometer to get any accurate results, but it wouldn't ware out your tires. Also, if you got a good constant slope hill, you could see your acceleration decrease as you picked up speed due to aero-forces.

[cfg83]

bikin' Ed -

Originally Posted by bikin' Ed

I was considered a tire expert in a former life. I got tours and info that others did not. Here are a few bits for you...

...

5)Plastic valve caps are only dust covers and the shrader valve is only supposed to be a temporary seal. Use a metal cap with a seal for higher pressures. For best results, use a metal valve stem with a sealing cap.

Man, I remember having these back in the 1970's. I have plastic right now. I'm gonna get metal sealed ones like you said.

CarloSW2

[CapriRacer]

Originally Posted by wyatt

A different type of test you could try with the accelerometer would echo the test that Metro did. You could measure your acceleration from a dead stop down a hill. You would probably need a very accurate accelerometer to get any accurate results, but it wouldn't ware out your tires. Also, if you got a good constant slope hill, you could see your acceleration decrease as you picked up speed due to aero-forces.

If the point is to measure the MAX traction of tires at various inflation pressures, you have to be spinning the tires if you are accellerating, or have the brakes locked (or near locked) if you are braking, or cornering hard if you are doing lateral grip. Any of those will severely wear the tires. Any test that doesn't severely wear the tires is testing something less than the MAX.

[MazdaMatt]

Here is an example of tire pressure tuning for max grip

Autocross is an excellent example of "real world" because many people use street tires, the speeds are typically under 60mph and the tires don't get to "track temperatures". The turns are often quite similar to what you would be doing in an emergency situation - slam brakes, sharp turn.

Note that they don't say anything about "max sidewall pressure" because it is FAR out of the range of "max grip". Point being, bigger ain't better and further from optimal is less than optimal (gee). Safety first kids.

[wyatt]

Originally Posted by CapriRacer

If the point is to measure the MAX traction of tires at various inflation pressures, you have to be spinning the tires if you are accellerating, or have the brakes locked (or near locked) if you are braking, or cornering hard if you are doing lateral grip. Any of those will severely wear the tires. Any test that doesn't severely wear the tires is testing something less than the MAX.

Sorry, I was not exactly clear on what I was saying. I wasn't talking about max traction, I was talking about measuring the rolling resistance, but using an accelerometer to do so.

[MazdaMatt]

RR is better measured with a coast-down test and GPS log. accelerometers are for fine movements or g forces. RR is very low force.

[Tony Raine]

all i have to add are my own experiences.

2001 ford explorer sport, 2 sets of 31x10.5 generic mud tires

1st set:
-don't remember how many miles i got out of them, but it was quite a bit for mud tires. maybe 35,000 or so
-tire pressure kept at ford specs religiously (35 front, 30 rear)
-tires rotated every other oil change (every 10,000 miles)
-the tires in the front cupped pretty badly, thought it was an alignment problem.
-lots of body roll and bounce getting on the highway.

2nd set:
-10 to 15,000 miles so far, very little wear
-about to do first rotation (im due to change my oil)
-45 psi all 4 corners for most of those miles
-tire cupping is non-existent (and i never got an alignment)
-handling is very noticeably improved (its still a lifted suv, but its much better than even bone stock)

[MazdaMatt]

Bet you lost traction in the mud where they were designed to be used.

I always hated the term "handling". Does that mean response, feedback, wander or ultimate traction? Seems everyone with a pickup says it "handles great". Meh. My cousins mudder handles like the mud its made to drive on

[tasdrouille]

Originally Posted by 07b2300

So I'm wondering how much tire pressures are helping anyone else because if the effect is negligable I'm going to put it back to help keep my coffee off my lap!

To answer the OP's question, in “The Effects of Tire Inflation Pressure on Passenger Car Fuel Consumption”, SAE paper 810069, the authors argue that the effect of inflation pressure on passenger car tires will affect overall fuel consumption by 0.33 percent/psi.

[Tony Raine]

Originally Posted by MazdaMatt

Bet you lost traction in the mud where they were designed to be used.

nope. i carry a small, 12v portable air compressor with me. freedom of psi choice in different terrain

Originally Posted by MazdaMatt

I always hated the term "handling". Does that mean response, feedback, wander or ultimate traction? Seems everyone with a pickup says it "handles great". Meh. My cousins mudder handles like the mud its made to drive on

Originally Posted by Tony Raine

-handling is very noticeably improved (its still a lifted suv, but its much better than even bone stock)

when i take a turn onto an onramp and accelerate, it doesn't bounce all over the place.



i've owned 2 lifted SUV's and 1 lifted pickup in my life. one is a Bronco II that would make "consumer reports" **** a brick sideways. none of them handled great. in fact, they handle like crap compared to just about any car. but i prefer the "feel". i like ground clearance, better visibility, and a stiffer ride. i have never been in a situation where a car would have handled an evasive maneuver any better. i've been run off the road, airborne, drove in dallas during rush hour, the mountains of northern new york in the dead of winter, and have had little brats run out in front of me. i just drive my vehicles within their limits. i learned a long time ago that being in a big hurry just makes life go by faster.