Switching from 33's to 35's= really bad mpg - Ford Powerstroke Diesel Forum
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post #1 of 16 Old 04-02-2011, 06:01 AM Thread Starter
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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?


2010 F-350 CC SRW LongBed 4X4
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post #2 of 16 Old 04-02-2011, 06:33 AM
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doubt it i get 20mpgs with toyo 35's and factory 20s

08 Black CC/SB lariat, billet grill inserts, Toyo 35X12.5R20 open country m/t, Newton lift 2.5" front with 5" blocks
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post #3 of 16 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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post #4 of 16 Old 04-02-2011, 06:39 AM Thread Starter
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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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post #5 of 16 Old 04-02-2011, 06:40 AM
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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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post #6 of 16 Old 04-02-2011, 10:03 AM
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Quote:
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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post #7 of 16 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.

'11 F250 Lariat CrewCab 2WD - Bushwacker flares, HID Projectors with Halos and color matched headlights, all led bulbs inside and out, Recon smoked Taillights, third brake light, and side turn signals. 35" on 18" XD775 wheels, 2" spacer in front and 1" block on rear. More to come.
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post #8 of 16 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.

-Mike

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post #9 of 16 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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post #10 of 16 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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