Ted in Toronto

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?

marakbai

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

PoaMike

...Mile markers? Just an idea im kinda confused and tipsy... and tired... night all. Now to walk up my flight of stairs.


-Mike

Savage c-300

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

rb23lb

very interesting

however, I have passed many speed checks on the side of the road, and they all agree with my speedometer on my c350

rb23lb

drive by a speed check radar that cops set up... or their are a few built in ones around so cal

jrct9454

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.

Carzzz

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...

sagar350z

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.

C300Sport

I have three radar signs that I pass occasionally. When I am driving about 45,the sign reads from 43-44.

amdeutsch

1 mile = 1.6 kilometer. Same?

sagar350z

Actually now that i think of it... yeah that didnt make sense.. anyways thanks for the correction.

keith100

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.