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-   -   speedometer off by 5 miles at 60mph (https://ecomodder.com/forum/showthread.php/speedometer-off-5-miles-60mph-19451.html)

sc2dave 11-11-2011 02:19 PM

speedometer off by 5 miles at 60mph
 
according to a gps app that shows mph, i'm doing 60,while the speedometer shows 65.if i got ,say 300 miles to a tank,what is my actual mileage?

gone-ot 11-11-2011 03:58 PM

...which do you "believe" is more correct, GPS or car speedometer? Both have intrinsic errors, the question though, is which is LEAST wrong?

...what vehicle? GM products are "known" for speedometers displaying 2 mph ABOVE their true value...but, the odometer is (supposedly) not affected by this difference.

sc2dave 11-11-2011 04:27 PM

1987 toyota truck.

gone-ot 11-11-2011 05:12 PM

...1987 will almost certainly still be using direct cable drive from the transmission to a mechanical speedometer "head"--for these, the aftermarket sells "gears" the can be put "in-line" with the cable to compensate for tires, transmissions and axles affects on the speedometer readings.

darcane 11-11-2011 05:17 PM

Can you find a nearby section of freeway with odometer calibration markings? They have several near me in Washington, not sure how common they are elsewhere. But, you can compare your odometer to a 5 mile long section of road that is marked at precise, 1 mile increments. Use that to determine what percentage your odometer is off (which may or may not reflect the error in your speedometer).

Assuming the 60 actual miles = 65 miles indicated, you would need to multiply your indicated miles by (60/65) or .92

300 x (60/65) = 277 actual.

sc2dave 11-11-2011 10:57 PM

Not where I live,near L.A

SentraSE-R 11-12-2011 12:28 AM

i used my GPS to determine odometer error. I recorded the odometer readings at 20, 40, 60, and 80 miles, v. the GPS miles. Now, when I fill a tank, I multiply the odometer reading by the % error from my testing.

GRU 11-12-2011 07:28 AM

It could also be tires. If your tires are worn down about 1/4 inch which is 1/2 inch in diameter it will show a ~2% error compaired to a new tire. Another thing is make sure you have stock size tires on if you want the speedo to be accurate

BHarvey 11-12-2011 08:35 AM

Quote:

Originally Posted by SentraSE-R (Post 269954)
i used my GPS to determine odometer error. I recorded the odometer readings at 20, 40, 60, and 80 miles, v. the GPS miles. Now, when I fill a tank, I multiply the odometer reading by the % error from my testing.


My mileage from odo to gps was 2.8% different on many tanks of over 600 miles distance.

Speedo reads 1 high though.

SentraSE-R 11-12-2011 09:04 AM

On my xB with OEM tires, the speedometer was 5% optimistic, but the odometer was 3.3% pessimistic. Now I'm running tires that are 5.31% larger diameter, and my speedometer is accurate, but my odometer is 9.9% pessimistic.


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