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Old 05-18-2012, 09:30 PM
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Tire Revs Per Mile

Maybe I'm stupid but I've never set my revs per mile on my SCT. I have 37" tires. Does this just make adjustments for shift points? Will it help MPG's?
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Old 05-18-2012, 09:45 PM
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Yes, it changes shift points.

No (probably not), you won't see an increase in fuel efficiency*.




*Hwy driving you won't see any change. City driving, stop and go, you may see a slight increase, but I'd doubt it would be much at all.
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Old 05-18-2012, 09:54 PM
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Looking at the fuelly report in your sig.... 10.7avg MPG

What is your typical driving? City/hwy. Do you tow often? How do you drive the truck? Heavy footed vs babying it. A lot of idleing?

I've been tracking on fuelly for the last 32K+ miles (78 fuel-ups). 17.1MPG average, best MPG for a tank is 21.9. I drive "conservatively" most of the time, about 50/50 hwy/city with a few pretty decent hwy road trip thrown in there.
I am slightly lowered on 33" tires for about half of that, stock height on 34's for the first half.
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Old 05-19-2012, 05:54 AM
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I drive about 50/50. I only use my truck to get to work and back, about 30 miles per day. I also drive very conservatively. Really light on the skinny pedal.

I'm not sure why my mileage is so low? I always just thought it was the big tires.


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Old 05-20-2012, 09:54 AM
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imo it is the tires like you suspect. but do you have a custom sct tune or canned? also ficm tuning will really help.
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Old 05-20-2012, 10:16 AM
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Depends on how your tunes were written, if you told your tuner about the 37" tires, that calculation should be in the programing already.

I haven't started messing with the features on the hand-held, I rely on the program from my tuner.

Also, did you have everything recalibrated for the larger tires?
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Old 05-20-2012, 12:23 PM
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How big are your tires? Are you adjusting for that when you calculate your mileage? If you're not correcting for the error that you tires put into your speedo, your mileage will be at least 9% low if you're on 35s.

34.6/31.5=1.09 (9%) so 287 miles observed on the odometer is really 312.83 traveled. If you took on 24 gallons, that makes your mileage 13.03 NOT 11.95.

BTW, I have messed with the gear/tire settings on my X3 and it shifts at the same points it does in stock mode, on two different transmissions. Converter locks at 45 mph indicated on the speedo (49 mph on the GPS), light throttle pressure unless I have the writer change that setting.

Although, adjusting the shift pressure in % DOES change the shifts.

Last edited by Karls03; 05-20-2012 at 12:34 PM.
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Old 05-20-2012, 09:55 PM
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I'm really not even sure if the speedo has been adjusted by Ford. Bought the truck used about four months ago. If I run a GPS and the mileage is the same would that tell me if it's been adjusted? I didn't even think of this stuff...


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Old 05-20-2012, 09:56 PM
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Also I running the canned tunes still. Sometimes street and sometimes performance.


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Old 05-21-2012, 06:33 AM
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If you have a smart phone, you can download a GPS, I use UlyssesSpeed (probably spelled that wrong). That would be the perfect place to start. Or take it out on the highway, if the tach says 2000 rpm and the speedo is at 70 mph, it has not been recalibrated for taller tires.

What year is your rig? 2005 and up can get the speedo corrections via SCT programs.
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