Switching from 33's to 35's= really bad mpg - Ford Powerstroke Diesel Forum
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Old 04-02-2011, 06:01 AM
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Switching from 33's to 35's= really bad mpg

So I had 18 inch wheels with goodyear duratrac 33 inch tires. I was avg around 19-20 mpg per fill up. I mostly do highway driving. But now I got some 20" factory wheels with goodyear duratrac 325-60-20 which comes out to be a little bit bigger then a 35" tire. Well I've had this 35's on the truck now for two weeks and I am avg about 15-17 mpg per fill. Will switching tires make that big of a difference in my mpg? I knew it would drop some but nothing like I am seeing or do I have other issues I need to be looking for?
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Old 04-02-2011, 06:33 AM
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doubt it i get 20mpgs with toyo 35's and factory 20s
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Old 04-02-2011, 06:35 AM
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Is that hand-calculated WITH your speedometer AND odometer adjusted to make up for the difference in tire side? (Rim size only changes ride quality)
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Old 04-02-2011, 06:39 AM
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Quote:
Originally Posted by ToMang07 View Post
Is that hand-calculated WITH your speedometer AND odometer adjusted to make up for the difference in tire side? (Rim size only changes ride quality)
Yeah that's hand calculated. But I do need to adjust the speedometer and all. I guess I need to go spend a 100 bucks at spartan.
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Old 04-02-2011, 06:40 AM
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Quote:
Stock Tire - 33x12.50R18 >Search Tires Tire 1 - 35x12.50R20

Rim Diameter: 18 in - Rim Diameter: 20 in

Overall Diameter: 33.02 in - Overall Diameter: 35.02 in

Radius: 16.51 in - Radius: 17.51 in

Circumference: 103.7 in - Circumference: 110.0 in

Revs per Mile: 629.9 - Revs per Mile: 593.9

Actual Speed: 60 mph - Speedometer1: 56.5 mph

Speedometer Difference: 6.061% too slow

Diameter Difference: - Diameter Difference: 5.72%

This is a quick conversion chart I pulled up, going from 33-35" tires.

http://www.1010tires.com/TireSizeCal...?action=submit
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Old 04-02-2011, 10:03 AM
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Originally Posted by ToMang07 View Post
This is a quick conversion chart I pulled up, going from 33-35" tires.

Tire Size Calculator - tire & wheel plus sizing
love that site, use it all the time
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Old 04-03-2011, 09:09 PM
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I was getting around 20-21 MPG (hand calculated) before suspension and tires. I went from a 32" tire to a 35", lifted the front end 2.5" and the rear 1" and went to about 17 MPG. Sometimes I think about going back.
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Old 04-04-2011, 02:02 PM
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wow, thats pretty surprising. i knew it would effect it, but i didnt know it would change that much. i'm about to change from a 8.5" lift with 37s, to stock height and tires. i'm hoping my mpg will jump a lot.
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Old 04-04-2011, 02:23 PM
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ok so idk how to "hand" calculate it. now i kind of want to know what my mpgs are.
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Old 04-04-2011, 02:41 PM
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Quote:
Originally Posted by landyacht27 View Post
ok so idk how to "hand" calculate it. now i kind of want to know what my mpgs are.
Use the tire size calculator above to calculate how far off your speedo is. Say it's 5% off, and you go 200 miles according to your odometer. Your actual mileage is 210 miles. (200miles x 1.05)/Gallons used = MPG.
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