SPEEDO IS OFF ??
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Senior User
Joined: Jul 2011
Posts: 242
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From: Oklahoma
SPEEDO IS OFF ??
put gps in the truck today and noticed the gps showed me 3mph slower than speedo..it has the 265/75 on it...why would she be off...
w that being said does than mean my odo is showing more miles i have driven or less miles(as far as checking fuel mileage)
w that being said does than mean my odo is showing more miles i have driven or less miles(as far as checking fuel mileage)
Logistics Pro
Joined: May 2004
Posts: 3,607
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Anything larger than a stock tire (not sure what that is) will affect the speedometer. Superlift has a speedo correction which I dont think is worth the money. Just be cognizant of the change. As for fuel mileage....not sure how to help you on that one
Hotshot
Joined: Dec 2003
Posts: 15,368
Likes: 121
From: Stuttgart, Ar
You'll find that the speedo needle is off compared to reading the vehicle speed sensor digitally by about 3 mph but that the odometer is actually VERY close. Mine has been like that since new and mine came with 265-75-16's also.
Lead Driver
Joined: Sep 2007
Posts: 8,180
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From: Scio, OR
LT265/75R16 is one of the stock tire options on his 2003.
If your GPS will read miles driven, use it to check the odometer. There is a decent chance the odometer is right.
As I understand it, the Fed requirement is that speedo's can read a little high but not a little low, so automakers err on the side of high. Even if it is effecting the odometer, it's probably not enough to really notice.
If your GPS will read miles driven, use it to check the odometer. There is a decent chance the odometer is right.
As I understand it, the Fed requirement is that speedo's can read a little high but not a little low, so automakers err on the side of high. Even if it is effecting the odometer, it's probably not enough to really notice.
Lead Driver
Joined: Feb 2011
Posts: 8,241
Likes: 155
From: L.A. (Lower Alabama)
The error will increase with speed since both devices agree at "0". If GPS is correct and speed o is off, you are not traveling as far/fast as speedo displays. So odo shows more miles than actual.
If ur 3mph off at 60mph, error is .05 ( not significant)
GPS can have errors also.
If ur 3mph off at 60mph, error is .05 ( not significant)
GPS can have errors also.
Lead Driver
Joined: Oct 2010
Posts: 5,420
Likes: 16
From: Ouray, CO
On my Ex with stock-size tires 265.75.16 I have
the same thing.
Lots of threads that 285.75.16 tires make the
speedo "dead on" but they also cause lowered MPG.
Well, if you change tire size all the computer
calculations are effected so everything will be
different - "real" MPG might actually be the SAME, but
now the computer thinks you didn't go as far thus
less miles/gallon would not be surpising, but did you
really drive less miles??? Even hand calculating,
if the odometer is wrong your by hand math won't be accurate either.
Amazingly, when I fill-up (40-44 GAL) my SGII is within 1 or 2 TENTHS of a
gallon @ how much fuel I actually take. I'd trust the SGII vs. dash.
the same thing.
Lots of threads that 285.75.16 tires make the
speedo "dead on" but they also cause lowered MPG.
Well, if you change tire size all the computer
calculations are effected so everything will be
different - "real" MPG might actually be the SAME, but
now the computer thinks you didn't go as far thus
less miles/gallon would not be surpising, but did you
really drive less miles??? Even hand calculating,
if the odometer is wrong your by hand math won't be accurate either.
Amazingly, when I fill-up (40-44 GAL) my SGII is within 1 or 2 TENTHS of a
gallon @ how much fuel I actually take. I'd trust the SGII vs. dash.
Hotshot
Joined: Dec 2003
Posts: 15,368
Likes: 121
From: Stuttgart, Ar
The error will increase with speed since both devices agree at "0". If GPS is correct and speed o is off, you are not traveling as far/fast as speedo displays. So odo shows more miles than actual.
If ur 3mph off at 60mph, error is .05 ( not significant)
GPS can have errors also.
If ur 3mph off at 60mph, error is .05 ( not significant)
GPS can have errors also.
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