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## Re: [Tigers] Gas milage with different tires?

 To: drmayf@mayfco.com, tigers@autox.team.net Re: [Tigers] Gas milage with different tires? David T Johnson Mon, 5 Jul 2010 08:23:13 -0700 (PDT)
 ```Why not do what they do in Kentucky. Put 13 in wheels on the front and 15 in on the back. This way you are always driving downhill. Then get one of those secret 200 mpg carbs that Detroit is hiding. Dave 90degrees on July 4th..Damn Global warming! ________________________________ From: drmayf To: tigers@autox.team.net Sent: Mon, July 5, 2010 1:10:14 AM Subject: Re: [Tigers] Gas milage with different tires? Resent...list owner said too long mayf Duke, all.... The issue of better fuel mileage seems to periodically pop up, which is not a bad thing. The Sunbeam's drag coefficient is published at 0.45, which amounts to it being a rolling brick. At a generally constant speed, drag, which directly translates to hp and tq needed to move the car down the road, you can generally estimate the power needs based on the summation of the drag forces. At least to the point where you can convince yourselves that a change in driving habits is needed for better mileage, lol. In this case, we'll run some numbers assuming that getting to speed is done in a gentle fashion and not in some screaming kamakazi banzai manner. We'll start here: frontal area is approximately 17.9 sq ft Cd is 0.45 We won't use the mechanical or rolling resistance losses since they will be fairly constant is the range of highway speeds we'll look at Drag = 1/2 * rho * V * V * A * Cd rho = air density, in slugs.. and we will use a STP value of 0.0023718 V = car speed in ft/sec for th etwo cases, we will use 78 mph = 114.4 ft/sec and 70 mph = 102.7 ft /sec. Plugging in Drag (78) = 0.5 * 0.0023718 * 114.4 * 114.4 * 17.9 * 0.45 = 125.02 lbs Drag (70) = 0.5 * 0.0023718 * 102.7 * 102.7 * 17.9 * 0.45 = 100.8 lbs HP(78) = Drag (78) * 114.4 / 550 = 26.004 hp HP(78) = Drag (70) * 102.7 / 550 = 18.8 hp As mentioed, mechanical losses and rolling resistance adds to the power required. As can bee seen, the power difference is significant. And that power requires fuel in direct proportion. It all points to the old adage of "Speed costs, how fast do you want to go?" The best fuel mileage can be had by simply going slower. In this case a drop from 78 mph to 70 will increase your mileage quite a bit. But, it also depends on the other two facors as well. If you have happy feet then it is going to get worse mileage, happy feet being the ones that are constantly twiddling with the gas pedal: everytime you do that, it pumps raw fuel into the carb through the accelerator pump. So, my suggestions? First, slow down Second, get larger skinnier tires as fat ones have a lot more rolling resistance. In fact maybe some old bias belted tires that can be pumped up hard. High tire pressures reduce rolling resistance in those tires. Also get skinnier tires on the front and keep them pumped up. Third, get an AFR meter, not even a fancy wideband. Just one of those that have led lights and show rich or lean. Then tune the car for as lean or as close to stoic as you can. Then drive it with the AFR meter lean side led lit. Fourth, maybe get a old timey vacuum meter and put it on the dash as well. A high vacuum means best economy. Fifth, keep it tuned. Get an electronic dizzy or innerds like Pertronic. I hope this may help. But, as in all things, your milage may vary.. mayf _______________________________________________ Tigers@autox.team.net Donate: http://www.team.net/donate.html Archive: http://www.team.net/archive Forums: http://www.team.net/forums Unsubscribe/Manage: http://autox.team.net/mailman/options/tigers/djoh797014@yahoo.com _______________________________________________ Tigers@autox.team.net Donate: http://www.team.net/donate.html Archive: http://www.team.net/archive Forums: http://www.team.net/forums ```
 Current Thread Re: [Tigers] Gas milage with different tires?, (continued) Re: [Tigers] Gas milage with different tires?, michael king Re: [Tigers] Gas milage with different tires?, Dave Munroe Re: [Tigers] Gas milage with different tires?, e.coiner Re: [Tigers] Gas milage with different tires?, Tom Parker Re: [Tigers] Gas milage with different tires?, Thomas Witt Re: [Tigers] Gas milage with different tires?, Ron Fraser Re: [Tigers] Gas milage with different tires?, Jim Re: [Tigers] Gas milage with different tires?, drmayf Re: [Tigers] Gas milage with different tires?, drmayf Re: [Tigers] Gas milage with different tires?, Ron Fraser Re: [Tigers] Gas milage with different tires?, David T Johnson <= Re: [Tigers] Gas milage with different tires?, Thomas Witt Re: [Tigers] Gas milage with different tires?, CoolVT