Speedometer reading off a little
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Senior User
Joined: Apr 2006
Posts: 154
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From: Southwestern Ohio
Speedometer reading off a little
Has anybody else with the new 6.7 ('11 or '12) Super Duty noticed the speedometer is off a little? When my speedo registers 70 mph, my GPS indicates 67 or 68. BTW, everything on my truck is stock.
Laughing Gas
Joined: May 2005
Posts: 1,082
Likes: 1
From: Illinois
Mine shows the same thing. Any vehicle I have done this comparison too is similar. In fact, I have seen different variances as you go through different speed ranges. When I am in the 0 to 30 MPH range my GPS and truck speedo are the same. They start diverting above 30 MPH in my scenario.
Mountain Pass
Joined: Feb 2003
Posts: 188
Likes: 12
From: Tennessee
My speedometer is off by around 3mph consistently when compared to my Garmin. It reads high. I was concerned about the odometer and checked it on round trip from Knoxville, TN to Charlotte, NC (around 500 miles). The odometer and the Garmin agreed within a few tenths of a mile! Therefore it appears the truck knows how fast it is really moving and purposely displays a lower value.
Senior User
Joined: Oct 2010
Posts: 266
Likes: 1
From: Sunshine Coast, BC
Mine is 2% off as determined by me via careful observation with GPS.
When odometer says I have gone 100 miles, I have in fact gone 102 miles.
When I hit 100,000 miles, I will have 2,000 free warranty miles on the engine.
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Senior User
Joined: Apr 2006
Posts: 154
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From: Southwestern Ohio
Thanks for the verifications/observations guys. I'm sure the manufacturers have a motive for this because I'm also sure they could get it right if they really wanted to. But in the end, I guess it's really no big deal.
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Laughing Gas
Joined: May 2005
Posts: 1,082
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From: Illinois
That is a very good point, I have never thought of that aspect before. I'll have to measure that, although I am not sure how accurate my measurements would be.
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Senior User
Joined: Sep 2010
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From: League City, TX
I read a similar thread last year and someone (maybe it was Epic) posted that the government required the speedometer variance. There was a document attached, but I don't remember if it was regulated by the State or Federal government. I thought that it had something to do with speeding tickets.
I think that all vehicles have this "variance" built in to some degree. Then again, I have slept since then and that thread may have been a dream.
I think that all vehicles have this "variance" built in to some degree. Then again, I have slept since then and that thread may have been a dream.
Lead Driver
Joined: Jan 2010
Posts: 6,600
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The odometer should be correct because the truck actually knows how fast it's going, it just reports it 2-3 mph faster to you on the gauge.
If you put your truck in engineering mode and scroll until you find the speed screen, you'll find it's very close to a good GPS within the tenths decimal place.
If you put your truck in engineering mode and scroll until you find the speed screen, you'll find it's very close to a good GPS within the tenths decimal place.
Senior User
Joined: Jan 2012
Posts: 193
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From: Cedar Rapids, IA
It is the mechanical speedometer that reads fast. The truck knows how fast it's actually going as indicated in engineering mode. That's why the odometer is relatively accuarate as well. Yes, said it's a law that the speedometer can never be "slow" or the manufacturer will face a fine.
With that being said, is there a way to tweak the mechanical speedometer to display the correct speed? I swear mine reads at least 10% fast.
With that being said, is there a way to tweak the mechanical speedometer to display the correct speed? I swear mine reads at least 10% fast.
Senior User
Joined: Sep 2011
Posts: 305
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From: Colorado
It's the other way around. If your speedometer is reading high (says you are going faster than you really are), your odometer is reading low (says you are going fewer miles than you really are).
Mine is 2% off as determined by me via careful observation with GPS.
When odometer says I have gone 100 miles, I have in fact gone 102 miles.
When I hit 100,000 miles, I will have 2,000 free warranty miles on the engine.
Mine is 2% off as determined by me via careful observation with GPS.
When odometer says I have gone 100 miles, I have in fact gone 102 miles.
When I hit 100,000 miles, I will have 2,000 free warranty miles on the engine.
The more your tires wear, the faster your speedometer will indicate for a given speed. Additionally, those tires will spin more revolutions per mile due to the decreased circumference so more "ticks" per mile will accumulate, hence the odometer will become faster with the speedometer. If you put oversize tires on the vehicle without recalibrating the speedometer for those oversize tires, both the speedometer and odometer will be "slow".
If you're checking your odometer using a GPS device over the course of 100 miles, a GPS will overstate the distance traveled due to the sampling nature of the device. The sampling and inherent accuracy causes the straight line path you've actually traveled to be a slight "sawtooth". The cumulative distance of this sawtooth (think roughly 15 meters) causes the device to slightly overstate straight line distances.
