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Sedans Ford Crown Victoria/Mercury Grand Marquis Ford Crown Victoria/Mercury Grand Marquis General Maintenance
102 messages, Last post on Oct 10, 2009 at 5:59 PM
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Replying to: fscarano (May 05, 2006 9:37 am) 
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Replying to: euphonium (May 05, 2006 12:36 pm) |
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Replying to: fscarano (May 05, 2006 9:37 am) I'd say that MPG isn't too bad, though, for a 6 year old car.
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Replying to: turbo301 (May 06, 2006 10:41 am) Why 37psi for more fuel economy?
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Replying to: fscarano (May 07, 2006 12:28 pm) It also mitigates in favor of wearing out the rear tires at their centers. So you had better be sure you are saving more on gas than it is costing you extra for tires.
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Replying to: g45 (May 08, 2006 7:14 pm) That would mean that you could put on larger tires and get better mpg?? I believe the reason for better mpg with increasing tire pressure is that it reduces friction. Just like if you were driving with tires more narrow. Just don't keep the pressure that high if it's snowing, because then you'll want more traction.
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Replying to: bobw3 (May 09, 2006 6:34 am) Excellent analysis. I wish I'd thought of that! First, though, re your tire diameter remark: Yes, of course larger tires will result in better gas mileage because, once again, rolling diameter is increased. This is equivalent to changing to a higher rear-end ratio. Done within the transmission this is called "overdrive". All three approaches yield more forward travel of the vehicle per engine revolution. But your idea is cooler, more subtle, and I agree with it. One can ask, for a fixed final drive ratio, including tire diameter: With which tires will I get better mileage, those absorbing energy through added flex or those flexing less and running "harder"? I agree with you that absorbtion of energy by the softer tires, even when rolling diameters are meticulously held constant, will result in a larger throttle opening at the same vehicle velocity. It's because that lost energy, quite literally, has to come from somewhere. It WILL come from the engine and reduce mileage, just as you pointed out. So it isn't just the rolling diameter which contributes to better mileage, but the reduction in rolling resistance as well, when the tires are run at greater pressure.
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Replying to: g45 (May 09, 2006 3:32 pm) 
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Replying to: g45 (May 09, 2006 3:32 pm) Here's a quote: http://autos.msn.com/Advice/Article.aspx?contentid=4018909 "Even larger tires can have an effect. A tire with a larger "footprint" on the road that doesn't have a special rubber compound designed to improve fuel economy has more rolling resistance than a comparable smaller tire, and this can lower fuel economy"
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Replying to: bobw3 (May 10, 2006 8:35 am) A larger tire diameter effectively translates the rotation of the hub to a higher velocity at the outside. Just look at a record or CD as it's turning: the hub is fairly slow, but the circumference is moving very quickly. v = r*w, where "v" is the linear velocity (tangential to the circumference), "r" is the radius of the circle, and "w" is the angular velocity. Thus, the bigger the radius, the larger the linear velocity, which translates into a faster-moving car. Or, you could look at it from the other way: the less fast the hub has to turn in order to maintain a given speed, and thus the less fast the engine has to turn, thereby saving fuel. That's my theory, anyway
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