New Tire size/ speedometer corrections
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Freshman User
Joined: Sep 2006
Posts: 41
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From: Grants Creek Camp
New Tire size/ speedometer corrections
I changed to 19.5 rims and H rated tires for my F350 for better stability carrying my truck camper. The tires are 1" taller than the 16's I had previously. If I remember correctly there is 4MPH difference at 70MPH, or rather the speed shows 70 but I am actually going 66.
My problem is I seem to have lost 3mpg in my fuel economy. I concistantly averaged 13+ MPG loaded 16 to 17 empty and now get 10MPG loaded and 13 empty.
I have read a little about correcting the speedometer and how the wrong tire size can effect the info being sent to the computer. where do I start?
My problem is I seem to have lost 3mpg in my fuel economy. I concistantly averaged 13+ MPG loaded 16 to 17 empty and now get 10MPG loaded and 13 empty.
I have read a little about correcting the speedometer and how the wrong tire size can effect the info being sent to the computer. where do I start?
Postmaster
Joined: Jan 2005
Posts: 4,743
Likes: 3
From: Peoria, IL
There are a few different things you can do. You can go to the dealer and ask them to reprogram your computer for the new tire size, you can buy an aftermarket tuner that will allow you to adjust the size yourself (most do this), or you can get a truespeed from superlift. There is usually a limit on how big of a tire the computer will accept (I think 600 rev/mile) below that and you will have to get a truespeed. Check your tire manufacturers site to figure out how many rev/mile your tire does.
Fleet Mechanic
Joined: Mar 2004
Posts: 1,483
Likes: 1
From: SE PA
bboone52, I recently added a Scan Gauge to my '05 Ex, and have found that my speedo reads 3 MPH faster than I am actually going.
I am going to see the dealer in the morning to get this fixed as it will mess up the odometer, trip odometer and MPG in the overhead Thirst-O-Meter.
FWIW, my GPS and the Scan Gauge agree...it's the truck odometer and speddo that are off. I also plan to grouse about warranty coverage as it will run out before it should mileage wise.
I am going to see the dealer in the morning to get this fixed as it will mess up the odometer, trip odometer and MPG in the overhead Thirst-O-Meter.
FWIW, my GPS and the Scan Gauge agree...it's the truck odometer and speddo that are off. I also plan to grouse about warranty coverage as it will run out before it should mileage wise.
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