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how far off am i?


tsanderson7

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i just put 32 inch tires on my 89 ranger. I think stock it had 27s on it. and now i am trying to figure out what kindve gas mileage i am getting. And from what i hear theres a ratio or equation i can use to find out how far off my trip meter is. ie: it says 180, how far have i really gone? anybody got an idea??
 


martin

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I made an exel spreadsheet to calculate those kind of things many years ago when I got fed up with sitting there with a calculator every time I filled up. If you went from to 27 to 32 you will have a discrepency of approximately 18% so you actually went 212.
 

tsanderson7

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okay well i do that and it says im getting around 14.5 miles to the gallon. which sounds ridiculous because with stock tires i was getting only 12. and these tires are a whole hell of a lot bigger. so wouldnt my mpgs go down rather than up?? i dunno what to make of it?
 

martin

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fuel mileage is dependent on so many variables, anything can happen.
 

strvger

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larger diameter tires has the effect of "lowering" the gear ratio in your axle. go to the tech library and check the calculators to see what i mean. sorta like 3.73 axles with original 28 inch tires dropping to 3.27 gears with 30 inch tires. this is just an example and not accurate, but you get what i'm trying to say.
my original tires were 26.5 inches tall. current tires are 31 inches tall. i re-geared from 3.45 to 4.56. my current highway gas mileage is 21 mpg. engine rpm's are lower because of the increased diameter of the tires, but speed stays at about 63-65 mph which is fine with me getting that kind of mileage. any faster and my 27 year old drive train wouldn't last as long as i need it to i don't think.
 

kimcrwbr1

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follow someone and find the difference in mph figure the percentage add that percentage to your trip meter and divide it with gallons. Or get a spedo gear set and clock it with different gears till you get close.
 

tsanderson7

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so the 14 miles to the gallon is wrong or would it be correct? im still a little bit confused. like i understand all the logic but its pretty confusing. haha basically what i wanna know is if the 14 mpgs is correct or incorrect?
 

06RangerXLT

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so the 14 miles to the gallon is wrong or would it be correct? im still a little bit confused. like i understand all the logic but its pretty confusing. haha basically what i wanna know is if the 14 mpgs is correct or incorrect?
its correct. basically your engine turns less times per mile and your wheels turn less per mile because they have a larger diameter. hence a fuel savings. but dam if i was getting 14 mpg id be looking for something wrong with my rig. the worst ive ever gotten was 18 mpg.

so your 27 inch tire has say, 800 rotations per mile. ( just a # not actual) your 32's will only have a # like 680 rotations per mile. so your saving fuel by having to work less, and the engine is now at a lower rpm at the speeds you drove before.

If your worried about fuel economy, let me know. i have done far too much research and can give you some great ideas to save gas. ( tailgate down makes MPG worse btw)

Let me know.
:icon_cheers::icon_thumby:
 
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tsanderson7

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thats what ive heard before. my gas mileage has always been bad. i am a teenager so i am on it a little bit but i stay off it for the most part. what do you think could be wrong. and what reccomendations do you have on how to increase it?
 

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