Speedometer Error
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Junior Member
Joined: Oct 2007
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C300 4matic
Speedometer Error
My C300 4matic reads 105 km per hour when I am travelling at exactly 100 km per hour, as displayed on my Garmin GPS - a 5% error. At a true 60 km per hr, the speedometer reads 63 km per hr - 5% again; and at an indicated 130 km per hr, I am only going a true 124 km per hour. My last car - '04 Volvo XC70 - had no discrepency vs. the Garmin, and I have checked the Garmin against my SLK and wife's Odyssey - both were within 1 to 2% error.
I'm assuming this means my odometer is racking up km's 5% higher than actual (I'll hit the warranty mileage limit at 95% of true mileage) and my gas mileage is also being reported 5% on the optimistic side.
Has anyone else checked their speedometer for accuracy?
I'm assuming this means my odometer is racking up km's 5% higher than actual (I'll hit the warranty mileage limit at 95% of true mileage) and my gas mileage is also being reported 5% on the optimistic side.
Has anyone else checked their speedometer for accuracy?
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Joined: Sep 2007
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From: Toronto, On
2008 MB C300; 2007 Acura RDX
Interesting ... I wonder how a non Garmin owner can measure this ... I'm at 4000K's already, granted I drive from Newmarket to Toronto daily, but would love to know if it's accurate
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From: Irvine, CA
C300 Sport, MM, P1
do you have larger wheels or anything to that effect? i know that could cause the speedometer to be off. i have a garmin too, maybe i should try your theory out. ill update when i do
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LOADED 08' C350 & 14' GLK-350 Diamond White (P1, MM, AMG Pkg, Ln Trkng, Htd Sts, Keylss Go)
My C300 4matic reads 105 km per hour when I am travelling at exactly 100 km per hour, as displayed on my Garmin GPS - a 5% error. At a true 60 km per hr, the speedometer reads 63 km per hr - 5% again; and at an indicated 130 km per hr, I am only going a true 124 km per hour. My last car - '04 Volvo XC70 - had no discrepency vs. the Garmin, and I have checked the Garmin against my SLK and wife's Odyssey - both were within 1 to 2% error.
I'm assuming this means my odometer is racking up km's 5% higher than actual (I'll hit the warranty mileage limit at 95% of true mileage) and my gas mileage is also being reported 5% on the optimistic side.
Has anyone else checked their speedometer for accuracy?
I'm assuming this means my odometer is racking up km's 5% higher than actual (I'll hit the warranty mileage limit at 95% of true mileage) and my gas mileage is also being reported 5% on the optimistic side.
Has anyone else checked their speedometer for accuracy?
however, I have passed many speed checks on the side of the road, and they all agree with my speedometer on my c350
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LOADED 08' C350 & 14' GLK-350 Diamond White (P1, MM, AMG Pkg, Ln Trkng, Htd Sts, Keylss Go)
drive by a speed check radar that cops set up... or their are a few built in ones around so cal
Super Member
Joined: Jul 2002
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From: Vancouver WA
'14 GLK250 Diesel
Speedometer error and odometer error are not synonymous - the odo, I suspect you'll find if you check it against a measured distance marker, will be within 1% or less.
We once had a '96 Acura RL [aka Legend] which had a ridiculous 7% speedometer error, but whose odometer was absolutely spot on
Don't assume you're accumulating KMs 5% faster because the speedo is that far off - check the odometer for yourself.
And, incidentally, our C300 Lux has speedo readings that are within 1-2% of measured markings and radar readouts.
We once had a '96 Acura RL [aka Legend] which had a ridiculous 7% speedometer error, but whose odometer was absolutely spot on
Don't assume you're accumulating KMs 5% faster because the speedo is that far off - check the odometer for yourself.
And, incidentally, our C300 Lux has speedo readings that are within 1-2% of measured markings and radar readouts.
Last edited by jrct9454; Jan 11, 2008 at 05:52 PM.
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C250 4M Sport
My speedometer is overstated the speed by 3% with the "plus-sized" (205/60R16 instead of 205/55R16) winter tires... This is comparing with the GPS (Garmin) and radar display in my neighbourhood. When the speedomoter indicating the car is going at 103km/hr, actually it is going at 100km/hr
I would imagine my OEM all season will be at least 5% off, also...
I would imagine my OEM all season will be at least 5% off, also...
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Member
Joined: Nov 2010
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From: NJ
2012 C350 coupe
I currently have OE tires and wheels and with a garmin nuvi navigation i get 1mph less on the nav. I hardly see a 2mph difference. I have not checked the kph difference, but i would think it would be the same.
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From: Atlanta, GA
2008 C300 Sport 6 Speed Manual, 1953 Chevy Bel-Air, 2015 Audi allroad, 1963 Chevy Apache
I have three radar signs that I pass occasionally. When I am driving about 45,the sign reads from 43-44.
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From: www.Traben-Trarbach.de
MPG+ ROLFCOPTER
Actually now that i think of it... yeah that didnt make sense.. anyways thanks for the correction. 
Senior Member
Joined: Feb 2008
Posts: 300
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From: Toronto
2008 c300
I get about 4-5 kph optimistic reading on my 204, at 100kph, versus a Tomtom.
I understand most speedos are optimistic, to reduce the likely hood of drivers trying to blame the manufacturer for marginal speeding offenses. I don't there is any similar effect on the the odometer.
I understand most speedos are optimistic, to reduce the likely hood of drivers trying to blame the manufacturer for marginal speeding offenses. I don't there is any similar effect on the the odometer.
