for those of you running 35's with spartan tuning... - Ford Powerstroke Diesel Forum
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Old 06-28-2010, 02:36 PM
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Question for those of you running 35's with spartan tuning...

i recently upgraded my stock tires to some toyo open county mt's 35X12.5R20. they're on the stock 20" wheel. im currently and have been running the first production 310 tune. i've notcied a siginifigant drop in mileage ever since i slapped these bad boys on. with the exact same type of driving i used to get about 330 miles on a full tank. now i get about 270! is this normal? are you those of you runing 35's experiencing this as well?

i was planning on putting a lift on the truck and running some 37's but am a little weary now. if mileage has gone down this much form going to 35's, i dont even want to think about what might happen if i slap on some 37's!
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Old 06-28-2010, 02:44 PM
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Are you compensating for the difference in size on the mileage? I know its not much of a difference compared to stock tire height, but the difference in size will throw the miles off.
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Old 06-28-2010, 02:46 PM
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What type of truck I have truck in sig. I put on 35.5 x 12 20 nit to trail grappler mt mileage went down down about two mpg but down pipe and intake cured that I am also getting tunes redone for correct tire size as my speedo was off about 5.5 at 70 with two different gps units at the same time. Your new tires are heavier than stock tires but I would not think you get much loss from going to 37" except the lift will add more air drag. I have 3.73 reared
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Old 06-28-2010, 03:37 PM
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you'll see a significant drop between the 35s and 37s. But yes your mileage drop is normal
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Old 06-28-2010, 04:02 PM
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Quote:
Originally Posted by O2ShootTheJ View Post
you'll see a significant drop between the 35s and 37s. But yes your mileage drop is normal
but is this drop in mileage between stock and 35's normal? ive lost about 60 miles to the tank. thats losing 2mgs from goin up 2 inches in size!
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Old 06-28-2010, 04:14 PM
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Quote:
Originally Posted by OC Stroker View Post
but is this drop in mileage between stock and 35's normal? ive lost about 60 miles to the tank. thats losing 2mgs from goin up 2 inches in size!
Once again.....are you compensating for the mileage being lost with the tires?....and when I say mileage I mean the actual miles you are losing now that your speedo is off. When your speedo is off, it throws your odometer off as well. All of this together will throw your fuel mileage off when you hand calculate it. Just a thought because I did lose some city mileage with 35's, but definitely not 60 miles total. Highway mileage didn't suffer from them though.
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Old 06-28-2010, 04:46 PM
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330 to full tank with 310 tune?
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Old 06-29-2010, 03:49 AM
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Now you got me worried I'm getting ready to put 35s on. I thougt the stock tire on factory 20s were like 34" sounds crazy such a small increase would effect MPG that much.
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Old 06-29-2010, 06:18 AM
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I have an s&b intake, 4in flo pro exhaust running the spartan 250 tune. Also im running 18" Xd wheels on 35" nitto trail grapplers which i think are almost the same as the toyo MTs. On my last trip which was about 450 miles I avg 12.5 mpg which was about 95% highway driving around 70-75mph taking it easy and this was pulling a 2 place atv trailer with 2 450 sport quads which together with the trailer are probably barely over 1,000lbs. Is this normal to see such bad gas mileage with the spartan tune and supporting mods?
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Old 06-29-2010, 06:41 AM
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I am running the 275 tune and I get about 330 miles to a tank with Toyo MT 35x12.5x20's.

That's without correction for tire size increase. To correct odometer for tire size increase:

All you have to do is take your new tire size (35") and divide by your old tire size (34") to get your correction factor. So 35/34=1.029=correction factor.
Take your correction factor and multiply by the mileage reading. so my 330 miles on the odometer becomes 339.7 miles.
So when you say 270 you are actually going 278 miles.

Not much of an increase but it makes you feel a little better.

Last edited by HoosierHick; 06-29-2010 at 06:50 AM.
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